{"id":7641,"date":"2024-12-05T16:17:25","date_gmt":"2024-12-05T21:17:25","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/pathology\/chapter\/the-central-nervous-system-copied-but-not-cloned-from-gj-betts\/"},"modified":"2025-08-23T13:28:17","modified_gmt":"2025-08-23T17:28:17","slug":"the-central-nervous-system-copied-but-not-cloned-from-gj-betts","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/pathology\/chapter\/the-central-nervous-system-copied-but-not-cloned-from-gj-betts\/","title":{"raw":"The Central Nervous System","rendered":"The Central Nervous System"},"content":{"raw":"<div id=\"1\" class=\"ui-has-child-title\" data-type=\"abstract\"><section>\r\n<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\">Learning Objectives<\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<p id=\"para-00001\">By the end of this section, you will be able to:<\/p>\r\n\r\n<ul id=\"list-00001\">\r\n \t<li>Name the major regions of the adult brain.<\/li>\r\n \t<li>Describe the connections between the cerebrum and brain stem through the diencephalon, and from those regions into the spinal cord.<\/li>\r\n \t<li>Recognize the complex connections within the subcortical structures of the basal nuclei.<\/li>\r\n \t<li>Explain the arrangement of gray and white matter in the spinal cord.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<\/section><\/div>\r\n<p id=\"fs-id1518907\">The central nervous system (CNS) consists of the brain and the spinal cord, which are the main organs of the nervous system. The spinal cord is a single structure, whereas the adult brain is described in terms of four major regions: the cerebrum, the diencephalon, the brain stem, and the cerebellum. Neural activity in the brain and spinal cord governs many diverse and important functions in the body, for example a person\u2019s conscious experiences, the regulation of homeostasis, the coordination of reflexes, and many more.<\/p>\r\n\r\n<h2>Divisions of the CNS<\/h2>\r\n<section id=\"fs-id1488700\" data-depth=\"1\">\r\n\r\n[caption id=\"attachment_6229\" align=\"aligncenter\" width=\"726\"]<img class=\"wp-image-6229 \" title=\"https:\/\/commons.wikimedia.org\/wiki\/File:Diagram_showing_the_brain_stem_which_includes_the_medulla_oblongata,_the_pons_and_the_midbrain_(2)_CRUK_294.svg\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/brain-diagram-1024x860.png\" alt=\"This illustration shows a midsection of the human brain cut in the sagittal plane. Highlighted are the main divisions of the brain, brainstem, and spinal cord. This includes the Forebrain, cerebrum, midbrain, pons, medulla, hindbrain, cerebellum, and spinal cord.\" width=\"726\" height=\"610\" \/> <strong>Divisions of the Central Nervous System<\/strong> - Diagram showing the brain_stem which includes the medulla oblongata, the pons and the midbrain on Wikimedia Commons is used under a CC BY-SA 4.0[\/caption]\r\n<h3 data-type=\"title\">The Forebrain: Cerebral Cortex and Diencephalon<\/h3>\r\n<h4 data-type=\"title\">The Cerebrum<\/h4>\r\n<p id=\"fs-id1476424\">The most outwardly visible gray-coloured tissue of the human brain is the <a href=\"#cerebrum\"><span id=\"term-00001\" data-type=\"term\">cerebrum<\/span><\/a>. Many of the higher neurological functions, such as memory, emotion, and consciousness, are the result of neural activity in the cerebrum.\u00a0The folded portion of the tissue on the outermost surface of the cerebrum is the <span id=\"term-00002\" data-type=\"term\">cerebral cortex<\/span>, and the rest of the structure is beneath that outer covering. There is a distinct separation between the two sides of the cerebrum called the <span id=\"term-00003\" data-type=\"term\">longitudinal fissure<\/span>. It separates the cerebrum into two distinct halves, a right and left\u00a0<span id=\"term-00004\" data-type=\"term\">cerebral hemisphere<\/span>. Deep within the cerebrum, the white matter of the\u00a0<span id=\"term-00005\" data-type=\"term\">corpus callosum<\/span>\u00a0provides the major pathway for communication between the two hemispheres of the cerebral cortex.<a id=\"cerebrum\"><\/a><\/p>\r\n\r\n\r\n[caption id=\"attachment_9264\" align=\"aligncenter\" width=\"1024\"]<img class=\"wp-image-9264 size-large\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebrum-1024x477.jpeg\" alt=\"This figure shows the lateral view on the left panel and anterior view on the right panel of the brain. The major parts including the cerebrum are labeled.\" width=\"1024\" height=\"477\" \/> <strong>The Cerebrum<\/strong> - The cerebrum is a large component of the CNS in humans, and the most obvious aspect of it is the folded surface called the cerebral cortex.[\/caption]\r\n<p id=\"fs-id2081500\"><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.42425em;font-style: italic\">Cerebral Cortex<\/span><\/p>\r\n\r\n<section id=\"fs-id1318756\" data-depth=\"2\">\r\n<p id=\"fs-id1298164\">The cerebrum is covered by a continuous layer of folded gray matter that wraps around its surface\u2014the cerebral cortex. This thin, extensive region of gray matter is responsible for the higher functions of the nervous system. A <span id=\"term-00010\" data-type=\"term\">gyrus<\/span> (plural = gyri) is the topmost ridge of one of those folds, and a <span id=\"term-00011\" data-type=\"term\">sulcus<\/span> (plural = sulci) is the furrow between two gyri. The pattern of these folds of tissue indicates specific regions of the cerebral cortex.<\/p>\r\n<p id=\"fs-id1300741\">The head is limited by the size of the birth canal, and the brain must fit inside the cranial cavity of the skull. Extensive folding in the cerebral cortex enables more gray matter to fit into this limited space. If the gray matter of the cortex were peeled off of the cerebrum and laid out flat, its surface area would be roughly equal to one square meter.<\/p>\r\n<p id=\"fs-id1137638\">During embryonic development, as the telencephalon expands within the skull, the brain goes through a regular course of growth that results in everyone\u2019s brain having a similar pattern of folds. The surface of the brain can be mapped on the basis of the locations of large gyri and sulci. Using these landmarks, the <a href=\"#cerebralcortexlobes\">cortex<\/a> can be separated into four major regions, or lobes: the frontal, parietal, occipital, and temporal lobes. The\u00a0<span id=\"term-00012\" data-type=\"term\">lateral sulcus<\/span>\u00a0that separates the\u00a0<span id=\"term-00013\" data-type=\"term\">temporal lobe<\/span>\u00a0from the other regions is one such landmark. Superior to the lateral sulcus are the\u00a0<span id=\"term-00014\" data-type=\"term\">parietal lobe<\/span>\u00a0and\u00a0<span id=\"term-00015\" data-type=\"term\">frontal lobe<\/span>, which are separated from each other by the\u00a0<span id=\"term-00016\" data-type=\"term\">central sulcus<\/span>. The posterior region of the cortex is the\u00a0<span id=\"term-00017\" data-type=\"term\">occipital lobe<\/span>, which has no obvious anatomical border between it and the parietal or temporal lobes on the lateral surface of the brain. From the medial surface, an obvious landmark separating the parietal and occipital lobes is called the\u00a0<span id=\"term-00018\" data-type=\"term\">parieto-occipital sulcus<\/span>. The fact that there is no obvious anatomical border between these lobes is consistent with the functions of these regions being interrelated.<a id=\"cerebralcortexlobes\"><\/a><\/p>\r\n\r\n<div id=\"fig-ch13_02_02\" class=\"os-figure\">\r\n<figure data-id=\"fig-ch13_02_02\">\r\n\r\n[caption id=\"attachment_9265\" align=\"aligncenter\" width=\"521\"]<img class=\" wp-image-9265\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Lobes-of-the-Cerebral-Cortex.jpeg\" alt=\"This figure shows the lateral view of the brain and the major lobes are labeled.\" width=\"521\" height=\"441\" \/> <strong>Lobes of the Cerebral Cortex<\/strong> - The cerebral cortex is divided into four lobes. Extensive folding increases the surface area available for cerebral functions.[\/caption]<\/figure>\r\n<\/div>\r\n<p id=\"fs-id1163314\">Different locations of the cerebral cortex are associated with particular functions, a concept known as localization. In the early 1900s, a German neuroscientist named Korbinian Brodmann performed an extensive study of the microscopic anatomy\u2014the cytoarchitecture\u2014of the cerebral cortex and divided the cortex into 52 separate regions on the basis of the histology of the cortex. His work resulted in a system of classification known as <a href=\"#Brodmannareas\"><span id=\"term-00019\" data-type=\"term\">Brodmann\u2019s areas<\/span><\/a>, which is still used today to describe the anatomical distinctions within the cortex. The results from Brodmann\u2019s work on the anatomy align very well with the functional differences within the cortex. Areas 17 and 18 in the occipital lobe are responsible for primary visual perception. That visual information is complex, so it is processed in the temporal and parietal lobes as well.<\/p>\r\n<p id=\"fs-id2055928\">The temporal lobe is associated with primary auditory sensation, known as Brodmann\u2019s areas 41 and 42 in the superior temporal lobe.\u00a0 The main sensation associated with the parietal lobe is\u00a0<span id=\"term-00020\" data-type=\"term\">somatosensation<\/span>, meaning the general sensations associated with the body. Posterior to the central sulcus is Brodmann's areas 1, 2, and 3, collectively called <span id=\"term-00021\" data-type=\"term\">postcentral gyrus or<\/span> the primary somatosensory cortex. All of the tactile senses are processed in this area, including touch, pressure, tickle, pain, itch, and vibration, as well as more general senses of the body such as <span id=\"term-00022\" data-type=\"term\">proprioception<\/span>\u00a0and\u00a0<span id=\"term-00023\" data-type=\"term\">kinesthesia<\/span>, which are the senses of body position and movement, respectively.<\/p>\r\n<p id=\"fs-id1119780\">Anterior to the central sulcus is the frontal lobe, which is primarily associated with motor functions. The\u00a0<span id=\"term-00024\" data-type=\"term\">precentral gyrus<\/span> is the primary motor cortex. Cells from this region of the cerebral cortex are the upper motor neurons that instruct lower motor neurons in the spinal cord to trigger contraction and relaxation of muscles. Anterior to this region are a few areas that are associated with planned movements. The <span id=\"term-00025\" data-type=\"term\">premotor area<\/span>\u00a0is responsible for thinking of a movement to be made. The\u00a0<span id=\"term-00026\" data-type=\"term\">frontal eye fields<\/span>\u00a0are important in eliciting eye movements and in attending to visual stimuli.\u00a0<span id=\"term-00027\" data-type=\"term\">Broca\u2019s area<\/span>\u00a0is responsible for the production of language, or controlling movements responsible for speech; in the vast majority of people, it is located only on the left side. Anterior to these regions is the\u00a0<span id=\"term-00028\" data-type=\"term\">prefrontal lobe<\/span>, which serves cognitive functions that can be the basis of personality, short-term memory, and consciousness. The prefrontal lobotomy is an outdated mode of treatment for personality disorders (psychiatric conditions) that profoundly affected the personality of the patient.<\/p>\r\n<span style=\"color: #000000\">The fascinating case of a man named Phineas Gage highlights the important functions of the prefrontal lobe . In the autumn of 1948, Mr. Gage was part of a work group blasting rock for the construction of a railroad south of Cavendish, Vermont. Unfortunately, a blast resulted in an iron rod piercing his cheek, passing behind his left eye, through his prefrontal lobe and exiting his skull. Amazingly, within a few months Mr. Gage regained normal motor and speech function, but his personality was drastically changed. Friends and family of Mr. Gage described him as unreliable, disrespectful, and impulsive; he was \"no longer Gage\" as they had once known him.<a id=\"Brodmannareas\"><\/a><\/span>\r\n<div id=\"fig-ch13_02_03\" class=\"os-figure\">\r\n<figure data-id=\"fig-ch13_02_03\">\r\n\r\n[caption id=\"attachment_9267\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-9267\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-1024x603.jpeg\" alt=\"In this figure, the Brodmann areas, identifying the functional regions of the brain, are mapped. The left panel shows the lateral surface of the brain and the right panel shows the medial surface.\" width=\"1024\" height=\"603\" \/> <strong>Brodmann's Areas of the Cerebral Cortex<\/strong> - Brodmann mapping of functionally distinct regions of the cortex was based on its cytoarchitecture at a microscopic level.[\/caption]<\/figure>\r\n<\/div>\r\n<\/section><section id=\"fs-id1087946\" data-depth=\"2\">\r\n<h4 data-type=\"title\">Subcortical structures<\/h4>\r\n<p id=\"fs-id793857\">Beneath the cerebral cortex are clusters of neuron cell bodies called <span id=\"term-00029\" data-type=\"term\">subcortical nuclei<\/span> which are responsible for various important neural functions. These include:<\/p>\r\n\r\n<ul>\r\n \t<li><strong>The basal forebrain:\u00a0<\/strong>this group of subcortical nuclei serve as the primary location for acetylcholine production, which is a neurotransmitter that modulates the overall activity of the cortex, possibly leading to greater attention to sensory stimuli. Alzheimer\u2019s disease is associated with a loss of neurons in the basal forebrain.<\/li>\r\n \t<li><strong>The h<span id=\"term-00030\" data-type=\"term\">ippocampus<\/span>\u00a0and\u00a0<span id=\"term-00031\" data-type=\"term\">amygdala: <\/span><\/strong><span id=\"term-00031\" data-type=\"term\">these<\/span> are medial structures that, along with the adjacent cortex, are involved in long-term memory formation and emotional responses.<\/li>\r\n \t<li><strong>The caudate, putamen, and globus pallidus:<\/strong> These are a group of major nuclei in the cerebrum called the basal ganglia\u00a0 responsible for fine-tuning voluntary movements. The caudate is a long nucleus that follows the basic C-shape of the cerebrum from the frontal lobe, through the parietal and occipital lobes, into the temporal lobe. The putamen is mostly deep in the anterior regions of the frontal and parietal lobes. Together, the caudate and putamen are called the <span id=\"term-00035\" style=\"text-align: initial;font-size: 1em\" data-type=\"term\">striatum<\/span><span style=\"text-align: initial;font-size: 1em\">. The globus pallidus is a layered nucleus that lies just medial to the putamen; they are called the lenticular nuclei because they look like curved pieces fitting together like lenses. The globus pallidus has two subdivisions, the external and internal segments, which are lateral and medial, respectively. These nuclei are depicted in a frontal section of the brain in\u00a0<\/span>the figure below<span style=\"text-align: initial;font-size: 1em\">.<\/span><\/li>\r\n<\/ul>\r\n<div id=\"fig-ch13_02_04\" class=\"os-figure\">\r\n<figure data-id=\"fig-ch13_02_04\">\r\n\r\n[caption id=\"attachment_9269\" align=\"aligncenter\" width=\"684\"]<img class=\"size-full wp-image-9269\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Frontal-Section-of-Cerebral-Cortex-and-Basal-Nuclei.jpeg\" alt=\"This diagram shows the frontal section of the brain and identifies the major components of the basal nuclei.\" width=\"684\" height=\"535\" \/> <strong>Frontal Section of Cerebral Cortex and Basal Nuclei<\/strong> - The major components of the basal nuclei, shown in a frontal section of the brain, are the caudate (just lateral to the lateral ventricle), the putamen (inferior to the caudate and separated by the large white-matter structure called the internal capsule), and the globus pallidus (medial to the putamen).[\/caption]<\/figure>\r\n<\/div>\r\n<div id=\"fs-id1967418\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\"><section>\r\n<div class=\"os-note-body\">\r\n<div class=\"textbox shaded\">Watch this\u00a0<a href=\"http:\/\/openstax.org\/l\/basalnuclei1\" target=\"_blank\" rel=\"noopener nofollow\">video<\/a>\u00a0to learn about the basal nuclei (also known as the basal ganglia), which have two pathways that process information within the cerebrum. As shown in this video, the direct pathway is the shorter pathway through the system that results in increased activity in the cerebral cortex and increased motor activity. The direct pathway is described as resulting in \u201cdisinhibition\u201d of the thalamus. What does disinhibition mean? What are the two neurons doing individually to cause this?<\/div>\r\n<\/div>\r\n<\/section><\/div>\r\n<div id=\"fs-id1301935\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\"><section>\r\n<div class=\"os-note-body\">\r\n<div class=\"textbox shaded\">Watch this\u00a0<a href=\"http:\/\/openstax.org\/l\/basalnuclei2\" target=\"_blank\" rel=\"noopener nofollow\">video<\/a>\u00a0to learn about the basal nuclei (also known as the basal ganglia), which have two pathways that process information within the cerebrum. As shown in this video, the indirect pathway is the longer pathway through the system that results in decreased activity in the cerebral cortex, and therefore less motor activity. The indirect pathway has an extra couple of connections in it, including disinhibition of the subthalamic nucleus. What is the end result on the thalamus, and therefore on movement initiated by the cerebral cortex?<\/div>\r\n<span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.42425em;font-style: italic\">The Diencephalon<\/span>\r\n\r\n<\/div>\r\n<\/section><\/div>\r\n<\/section><\/section><section id=\"fs-id1230531\" data-depth=\"1\">\r\n<p id=\"fs-id1120163\">The diencephalon is the one region of the adult brain that retains its name from embryologic development. The etymology of the word diencephalon translates to \u201cthrough brain.\u201d It is the connection between the cerebrum and the rest of the nervous system, with one exception. The rest of the brain, the spinal cord, and the PNS all send information to the cerebrum through the diencephalon. Output from the cerebrum passes through the diencephalon. The single exception is the system associated with\u00a0<span id=\"term-00041\" data-type=\"term\">olfaction<\/span>, or the sense of smell, which connects directly with the cerebrum. In the earliest vertebrate species, the cerebrum was not much more than olfactory bulbs that received peripheral information about the chemical environment (to call it smell in these organisms is imprecise because they lived in the ocean).<\/p>\r\n<p id=\"fs-id2026939\"><a href=\"#diencephalon\">The diencephalon<\/a> is deep beneath the cerebrum and can be described as any region of the brain with \u201cthalamus\u201d in its name. The two major regions of the diencephalon are the thalamus itself and the hypothalamus.<\/p>\r\n\r\n<section id=\"fs-id1196887\" data-depth=\"2\">\r\n<h5 data-type=\"title\">Thalamus<\/h5>\r\n<p id=\"fs-id1234023\">You can think of the thalamus as a giant postal system where information is received, processed, and sent where it needs to go. The <span id=\"term-00044\" data-type=\"term\">thalamus<\/span> is a collection of nuclei that relay information between the cerebral cortex and the periphery, spinal cord, or brain stem. All sensory information, except for the sense of smell, passes through the thalamus before processing by the cortex. Axons from the peripheral sensory organs synapse in the thalamus and thalamic neurons project directly to the cerebrum. It is a requisite synapse in any sensory pathway, except for olfaction. The thalamus does not just pass the information on, it also processes that information. For example, the portion of the thalamus that receives visual information will influence what visual stimuli are important, or what receives attention.<\/p>\r\n<p id=\"fs-id1509482\">The cerebrum also sends information down to the thalamus, which usually communicates motor commands. This involves interactions with the cerebellum and other nuclei in the brain stem. The cerebrum interacts with the basal ganglia, which involves connections with the thalamus. The primary output of the basal ganglia is to the thalamus, which relays that output to the cerebral cortex. The cortex also sends information to the thalamus that will then influence the effects of the basal nuclei.<\/p>\r\n\r\n<\/section><section id=\"fs-id1076072\" data-depth=\"2\">\r\n<h5 data-type=\"title\">Hypothalamus<\/h5>\r\n<p id=\"fs-id1490316\">Inferior and slightly anterior to the thalamus is the\u00a0<span id=\"term-00045\" data-type=\"term\">hypothalamus<\/span>, the other major region of the diencephalon. The hypothalamus is a collection of nuclei that are largely involved in regulating homeostasis. The hypothalamus is the executive region in charge of the autonomic nervous system and the endocrine system through its regulation of the anterior pituitary gland. Other parts of the hypothalamus are involved in memory and emotion as part of the limbic system.<a id=\"diencephalon\"><\/a><\/p>\r\n\r\n<div id=\"fig-ch13_02_06\" class=\"os-figure\">\r\n<figure data-id=\"fig-ch13_02_06\">\r\n\r\n[caption id=\"attachment_9270\" align=\"aligncenter\" width=\"720\"]<img class=\" wp-image-9270\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Diencephalon.jpeg\" alt=\"This figure shows the location of the thalamus, hypothalamus and pituitary gland in the brain.\" width=\"720\" height=\"571\" \/> <strong>The Diencephalon<\/strong> -The diencephalon is composed primarily of the thalamus and hypothalamus. The thalami are two elongated, ovoid structures on either side of the midline that make contact in the middle. The hypothalamus is inferior and anterior to the thalamus, culminating in a sharp angle to which the pituitary gland is attached.[\/caption]<\/figure>\r\n<\/div>\r\n<\/section><\/section><section id=\"fs-id1886090\" data-depth=\"1\">\r\n<h3 data-type=\"title\">Midbrain and Hindbrain<\/h3>\r\n<h4 data-type=\"title\">Brain Stem<\/h4>\r\n<p id=\"fs-id1523364\">Parts of the midbrain and hindbrain (composed of the pons and the medulla) are collectively referred to as the <a href=\"#brainstem\">brain stem<\/a>. The structure emerges from the ventral surface of the forebrain as a tapering cone that connects the brain to the spinal cord. Attached to the brain stem, but considered a separate region of the hindbrain, is the cerebellum. The midbrain coordinates sensory representations of the visual, auditory, and somatosensory perceptual spaces. The pons is the main connection with the cerebellum. The pons and the medulla regulate several crucial functions, including the cardiovascular and respiratory systems and rates.<\/p>\r\n<p id=\"fs-id1510727\">The cranial nerves connect through the brain stem and provide the brain with the sensory input and motor output associated with the head and neck, including most of the special senses. The major ascending and descending pathways between the spinal cord and brain, specifically the cerebrum, pass through the brain stem.<a id=\"brainstem\"><\/a><\/p>\r\n\r\n\r\n[caption id=\"attachment_9271\" align=\"aligncenter\" width=\"754\"]<img class=\" wp-image-9271\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Brain-Stem.jpeg\" alt=\"This figure shows the location of the midbrain, pons and the medulla in the brain.\" width=\"754\" height=\"570\" \/> <strong>The Brain Stem<\/strong> -\u00a0The brain stem comprises three regions: the midbrain, the pons, and the medulla.[\/caption]\r\n\r\n<div id=\"fig-ch13_02_07\" class=\"os-figure\">\r\n<figure data-id=\"fig-ch13_02_07\"><\/figure>\r\n<div class=\"os-caption-container\"><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.42425em;font-style: italic\">Midbrain<\/span><\/div>\r\n<\/div>\r\n<section id=\"fs-id1284242\" data-depth=\"2\">\r\n<p id=\"fs-id890816\">One of the original regions of the embryonic brain, the midbrain is a small region between the thalamus and pons. It is separated into the\u00a0<span id=\"term-00046\" data-type=\"term\">tectum<\/span>\u00a0and\u00a0<span id=\"term-00047\" data-type=\"term\">tegmentum<\/span>, from the Latin words for roof and floor, respectively. The cerebral aqueduct passes through the center of the midbrain, such that these regions are the roof and floor of that canal.<\/p>\r\n<p id=\"fs-id1282943\">The tectum is composed of four bumps known as the colliculi (singular = colliculus), which means \u201clittle hill\u201d in Latin. The\u00a0<span id=\"term-00048\" data-type=\"term\">inferior colliculus<\/span>\u00a0is the inferior pair of these enlargements and is part of the auditory brain stem pathway. Neurons of the inferior colliculus project to the thalamus, which then sends auditory information to the cerebrum for the conscious perception of sound. The\u00a0<span id=\"term-00049\" data-type=\"term\">superior colliculus<\/span>\u00a0is the superior pair and combines sensory information about visual space, auditory space, and somatosensory space. Activity in the superior colliculus is related to orienting the eyes to a sound or touch stimulus. If you are walking along the sidewalk on campus and you hear chirping, the superior colliculus coordinates that information with your awareness of the visual location of the tree right above you. That is the correlation of auditory and visual maps. If you suddenly feel something wet fall on your head, your superior colliculus integrates that with the auditory and visual maps and you know that the chirping bird just relieved itself on you. You want to look up to see the culprit, but do not.<\/p>\r\n<p id=\"fs-id1301789\">The tegmentum is continuous with the gray matter of the rest of the brain stem. Throughout the midbrain, pons, and medulla, the tegmentum contains the nuclei that receive and send information through the cranial nerves, as well as regions that regulate important functions such as those of the cardiovascular and respiratory systems.<\/p>\r\n\r\n<\/section><section id=\"fs-id1126733\" data-depth=\"2\">\r\n<h4 data-type=\"title\">Pons<\/h4>\r\n<p id=\"fs-id1179935\">The word pons comes from the Latin word for bridge. It is visible on the anterior surface of the brain stem as the thick bundle of white matter attached to the cerebellum. The pons is the main connection between the cerebellum and the brain stem. The bridge-like white matter is only the anterior surface of the pons; the gray matter beneath that is a continuation of the tegmentum from the midbrain. Gray matter in the tegmentum region of the pons contains neurons receiving descending input from the forebrain that is sent to the cerebellum.<\/p>\r\n\r\n<\/section><section id=\"fs-id1187846\" data-depth=\"2\">\r\n<h4 data-type=\"title\">Medulla<\/h4>\r\n<p id=\"fs-id2166609\">The medulla is the region known as the myelencephalon in the embryonic brain. The initial portion of the name, \u201cmyel,\u201d refers to the significant white matter found in this region\u2014especially on its exterior, which is continuous with the white matter of the spinal cord. The tegmentum of the midbrain and pons continues into the medulla because this gray matter is responsible for processing cranial nerve information. A diffuse region of gray matter throughout the brain stem, known as the\u00a0<span id=\"term-00050\" data-type=\"term\">reticular formation<\/span>, is related to sleep and wakefulness, such as general brain activity and attention.<\/p>\r\n\r\n<\/section><\/section><section id=\"fs-id2824451\" data-depth=\"1\">\r\n<h4 data-type=\"title\">The Cerebellum<\/h4>\r\n<p id=\"fs-id1520379\">The\u00a0<a href=\"#cerebellum\"><span id=\"term-00051\" data-type=\"term\">cerebellum<\/span><\/a>, as the name suggests, is the \u201clittle brain.\u201d It is covered in gyri and sulci like the cerebrum, and looks like a miniature version of that part of the brain. The cerebellum is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord. It accounts for approximately 10 percent of the mass of the brain.<a id=\"cerebellum\"><\/a><\/p>\r\n\r\n\r\n[caption id=\"attachment_9272\" align=\"aligncenter\" width=\"830\"]<img class=\"size-large wp-image-9272\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebellum-830x1024.jpeg\" alt=\"This figure shows the location of the cerebellum in the brain. In the top panel, a lateral view labels the location of the cerebellum and the deep cerebellar white matter. In the bottom panel, a photograph of a brain, with the cerebellum in pink is shown.\" width=\"830\" height=\"1024\" \/> <strong>The Cerebellum<\/strong> - The cerebellum is situated on the posterior surface of the brain stem. Descending input from the cerebellum enters through the large white matter structure of the pons. Ascending input from the periphery and spinal cord enters through the fibers of the inferior olive. Output goes to the midbrain, which sends a descending signal to the spinal cord.[\/caption]\r\n<p id=\"fs-id1315185\">Descending fibers from the cerebrum have branches that connect to neurons in the pons. Those neurons project into the cerebellum, providing a copy of motor commands sent to the spinal cord. Sensory information from the periphery, which enters through spinal or cranial nerves, is copied to a nucleus in the medulla known as the\u00a0<span id=\"term-00052\" data-type=\"term\">inferior olive<\/span>. Fibers from this nucleus enter the cerebellum and are compared with the descending commands from the cerebrum. If the primary motor cortex of the frontal lobe sends a command down to the spinal cord to initiate walking, a copy of that instruction is sent to the cerebellum. Sensory feedback from the muscles and joints, proprioceptive information about the movements of walking, and sensations of balance are sent to the cerebellum through the inferior olive and the cerebellum compares them. If walking is not coordinated, perhaps because the ground is uneven or a strong wind is blowing, then the cerebellum sends out a corrective command to compensate for the difference between the original cortical command and the sensory feedback. The output of the cerebellum is into the midbrain, which then sends a descending input to the spinal cord to correct the messages going to skeletal muscles.<\/p>\r\n\r\n<\/section><section id=\"fs-id1518219\" data-depth=\"1\">\r\n<h2 data-type=\"title\">The Spinal Cord<\/h2>\r\n<p id=\"fs-id1523219\">The description of the CNS is concentrated on the structures of the brain, but the spinal cord is another major organ of the system. The spinal cord is a long tube-like structure which begins at the medulla oblongata in the brainstem and extends down the spine. It serves to connect the CNS with the peripheral nervous system (PNS).<\/p>\r\n\r\n<section id=\"fs-id1153084\" data-depth=\"2\">\r\n<h3 data-type=\"title\">The Spinal Cord in Cross-Section: Gray and White Matter<\/h3>\r\nA striking feature of the spinal cord when viewed in cross section is it's organization of gray and white matter. As we learned before, gray matter refers to the cell bodies of neurons while white matter signifies the myelinated axon processes of nerves. You can remember this by thinking of the lipid-rich contents of myelin, which appear white. The gray matter of the spinal cord is organized into horns, while the white matter is organized into columns<span style=\"color: #99cc00\">.\u00a0<\/span><span style=\"font-size: 1em\"> In cross-section, the gray matter of the spinal cord has the appearance of an ink-blot test, with the spread of the gray matter on one side replicated on the other\u2014a shape reminiscent of a bulbous capital \u201cH.\u201d <a id=\"crosssectionspinalcord\"><\/a><\/span>\r\n\r\n[caption id=\"attachment_9273\" align=\"aligncenter\" width=\"797\"]<img class=\" wp-image-9273\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord-893x1024.jpeg\" alt=\"This figure shows the cross section of the spinal cord. The top panel shows a diagram of the cross section and the major parts are labeled. The bottom panel shows an ultrasound image of the spinal cord cross section.\" width=\"797\" height=\"914\" \/> <strong>Cross-section of Spinal Cord<\/strong> - The cross-section of a thoracic spinal cord segment shows the posterior, anterior, and lateral horns of gray matter, as well as the posterior, anterior, and lateral columns of white matter. LM \u00d7 40. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n\r\n<section id=\"fs-id1153084\" data-depth=\"2\">\r\n<div id=\"fig-ch13_02_09\" class=\"os-figure\">\r\n<figure data-id=\"fig-ch13_02_09\"><\/figure>\r\n<div class=\"os-caption-container\"><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.42425em;font-style: italic\">Gray Horns<\/span><\/div>\r\n<\/div>\r\n<\/section>\r\n<p id=\"fs-id704969\">As shown in <a href=\"#crosssectionspinalcord\">the figure above<\/a>, the gray matter is subdivided into regions that are referred to as horns. The <span id=\"term-00061\" data-type=\"term\">posterior horn<\/span> is responsible for sensory processing, while the <span id=\"term-00062\" data-type=\"term\">anterior horn<\/span> sends out motor signals to the skeletal muscles. Note that it is common to see the terms dorsal (dorsal = \u201cback\u201d) and ventral (ventral = \u201cbelly\u201d) used interchangeably with posterior and anterior, particularly in reference to nerves and the structures of the spinal cord. You should learn to be comfortable with both. The <span id=\"term-00063\" data-type=\"term\">lateral horn<\/span>, which is only found in the thoracic, upper lumbar, and sacral regions, contains cell bodies of motor neurons of the autonomic nervous system.<\/p>\r\n<p id=\"fs-id1462544\">Some of the largest neurons of the spinal cord are the multipolar motor neurons in the anterior horn. The fibers that cause contraction of skeletal muscles are the axons of these neurons. The motor neuron that causes contraction of the big toe, for example, is located in the sacral spinal cord. The axon that has to reach all the way to the belly of that muscle may be a meter in length. The neuronal cell body that maintains that long fiber must be quite large, possibly several hundred micrometers in diameter, making it one of the largest cells in the body.<\/p>\r\n\r\n<\/section><section id=\"fs-id1862662\" data-depth=\"2\">\r\n<h4 data-type=\"title\">White Columns<\/h4>\r\n<p id=\"fs-id1173979\">Just as the gray matter is separated into horns, the white matter of the spinal cord is separated into columns.\u00a0<span id=\"term-00064\" data-type=\"term\">Ascending tracts<\/span>\u00a0of nervous system fibers in these columns carry sensory information up to the brain, whereas\u00a0<span id=\"term-00065\" data-type=\"term\">descending tracts<\/span> carry motor commands from the brain to the muscles. Looking at the spinal cord longitudinally, the columns extend along its length as continuous bands of white matter. Between the two posterior horns of gray matter are the <span id=\"term-00066\" data-type=\"term\">posterior columns<\/span>. Between the two anterior horns, and bounded by the axons of motor neurons emerging from that gray matter area, are the\u00a0<span id=\"term-00067\" data-type=\"term\">anterior columns<\/span>. The white matter on either side of the spinal cord, between the posterior horn and the axons of the anterior horn neurons, are the\u00a0<span id=\"term-00068\" data-type=\"term\">lateral columns<\/span>. The posterior columns are composed of axons of ascending tracts. The anterior and lateral columns are composed of many different groups of axons of both ascending and descending tracts\u2014the latter carrying motor commands down from the brain to the spinal cord to control output to the periphery.<\/p>\r\n\r\n<div id=\"fs-id1148241\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\"><header>\r\n<h4 class=\"os-title\" data-type=\"title\">Spinal Cord Segments<\/h4>\r\n<\/header><\/div>\r\n<\/section>\u00a0The spinal cord itself is composed of a number of segments, each of which has bundles of axons exiting and entering the cord in structures called roots. Axons enter the posterior side through the\u00a0<span id=\"term-00055\" data-type=\"term\">dorsal (posterior) nerve root<\/span>. The axons emerging from the anterior side do so through the\u00a0<span id=\"term-00057\" data-type=\"term\">ventral (anterior) nerve root<\/span>. On the whole, the posterior regions are responsible for sensory functions and the anterior regions are associated with motor functions, just like the corresponding anterior and posterior horns of gray matter. The roots then combine to form a pair of <a href=\"#spinalnerve\">spinal nerves<\/a>, one for each component of the spine.<a id=\"spinalnerve\"><\/a>\r\n\r\n[caption id=\"attachment_6247\" align=\"aligncenter\" width=\"1024\"]<img class=\"wp-image-6247 size-large\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/1200px-Spinal_nerve.svg_-1-1024x597.png\" alt=\"This illustration shows a segment of the spinal cord in cross-section. The spinal cord itself is composed of inner grey-matter in a butterfly shape surrounded by white matter. The ventral and dorsal roots contain neurons leaving the spinal cord, which combine to form a mixed spinal nerve containing both sensory and motor fibres.\" width=\"1024\" height=\"597\" \/> <strong>Spinal Nerve<\/strong> - A spinal nerve is formed from the merging of the dorsal and ventral roots. Each spinal nerve emerges from the spinal column in between vertebrae. Modified image originally by Tristanb.[\/caption]\r\n<p id=\"fs-id1942720\">The spinal cord is surrounded and protected by the bones in our back, which are called vertebrae. These are the protruding boney structures that you can feel in your neck and back.\u00a0Each of these segments of spinal cord is named according to the level at which it's spinal nerves pass through the intervertebral foramina, which is the space between two vertebrae. <span style=\"font-size: 1em\">\u00a0For example, the first pair of spinal nerves are the first cervical nerves (C1), which exits the spinal cord above the first cervical vertebrae (CI). You should take note of this nomenclature- spinal nerves are numbered with arabic numerals (1, 2, 3, 4, etc.) while vertebrae are numbered with roman numerals (I, II, III, IV, etc.)<\/span><\/p>\r\n<span style=\"text-align: initial;font-size: 1em\">The <a href=\"#spinalcordregions\">spinal cord<\/a> is also split lengthwise into five major regions. Immediately adjacent to the brain stem is the cervical region, followed by the thoracic, then the lumbar, the sacral, and finally the coccygeal region. The spinal cord is not the full length of the vertebral column because the spinal cord does not grow significantly longer after the first or second year, but the skeleton continues to grow. The nerves that emerge from the spinal cord pass through the intervertebral foramina at the respective levels. As the vertebral column grows, these nerves grow with it and result in a long bundle of nerves that resembles a horse\u2019s tail and is named the <\/span><span id=\"term-00060\" style=\"text-align: initial;font-size: 1em\" data-type=\"term\">cauda equina<\/span><span style=\"text-align: initial;font-size: 1em\">. The sacral spinal cord is at the level of the upper lumbar vertebral bones. The spinal nerves extend from their various levels to the proper level of the vertebral column.<a id=\"spinalcordregions\"><\/a><\/span>\r\n\r\n[caption id=\"attachment_6248\" align=\"aligncenter\" width=\"516\"]<img class=\"wp-image-6248 \" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/spinal-cord.png\" alt=\"This illustration demonstrates the position of the spinal cord and vertebrae within the human body and the three spinal cord areas- the cervical, thoracic, and lumbar areas (running superior to inferior as listed).\" width=\"516\" height=\"696\" \/> The different regions of the vertebrae and spinal cord. By Cancer Research UK and used under CC license.[\/caption]\r\n\r\n<section id=\"fs-id1862662\" data-depth=\"2\">\r\n<div id=\"fs-id1148241\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\"><section>\r\n<div class=\"os-note-body\">\r\n<div class=\"textbox shaded\">Watch this\u00a0<a href=\"http:\/\/openstax.org\/l\/graymatter\" target=\"_blank\" rel=\"noopener nofollow\">video<\/a>\u00a0to learn about the gray matter of the spinal cord that receives input from fibers of the dorsal (posterior) root and sends information out through the fibers of the ventral (anterior) root. As discussed in this video, these connections represent the interactions of the CNS with peripheral structures for both sensory and motor functions. The cervical and lumbar spinal cords have enlargements as a result of larger populations of neurons. What are these enlargements responsible for?<\/div>\r\n&nbsp;\r\n\r\n<\/div>\r\n<\/section><\/div>\r\n<div id=\"fs-id1070949\" class=\"anatomy disorders ui-has-child-title\" data-type=\"note\">\r\n<div class=\"textbox textbox--examples\"><header class=\"textbox__header\"><header>\r\n<h3 class=\"os-title\" data-type=\"title\"><span class=\"os-title-label\">DISORDERS OF THE <\/span>Basal Nuclei<\/h3>\r\n<\/header><\/header>\r\n<div class=\"textbox__content\"><section>\r\n<div class=\"os-note-body\">\r\n<p id=\"fs-id1467131\">Parkinson\u2019s disease is a disorder of the basal nuclei, specifically of the substantia nigra, that demonstrates the effects of the direct and indirect pathways. Parkinson\u2019s disease is the result of neurons in the substantia nigra pars compacta dying. These neurons release dopamine into the striatum. Without that modulatory influence, the basal nuclei are stuck in the indirect pathway, without the direct pathway being activated. The direct pathway is responsible for increasing cortical movement commands. The increased activity of the indirect pathway results in the hypokinetic disorder of Parkinson\u2019s disease.<\/p>\r\n<p id=\"fs-id856277\">Parkinson\u2019s disease is neurodegenerative, meaning that neurons die that cannot be replaced, so there is no cure for the disorder. Treatments for Parkinson\u2019s disease are aimed at increasing dopamine levels in the striatum. Currently, the most common way of doing that is by providing the amino acid L-DOPA, which is a precursor to the neurotransmitter dopamine and can cross the blood-brain barrier. With levels of the precursor elevated, the remaining cells of the substantia nigra pars compacta can make more neurotransmitter and have a greater effect. Unfortunately, the patient will become less responsive to L-DOPA treatment as time progresses, and it can cause increased dopamine levels elsewhere in the brain, which are associated with psychosis or schizophrenia.<\/p>\r\n\r\n<\/div>\r\n<\/section>Visit this\u00a0<a href=\"http:\/\/openstax.org\/l\/parkinsons\" target=\"_blank\" rel=\"noopener nofollow\">site<\/a> for a thorough explanation of Parkinson\u2019s disease.\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1539338\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\"><section>\r\n<div class=\"os-note-body\">\r\n<h1>Adaption<\/h1>\r\n<p style=\"text-align: start\">This chapter was adapted by Valerie Swanston from the following text:<\/p>\r\n<p style=\"text-align: start\"><a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\" target=\"_blank\" rel=\"noopener\">The Central Nervous System<\/a>\u00a0in <a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/\">Anatomy and Physiology<\/a>\u00a0by\u00a0OSCRiceUniversity\u00a0is licensed under a\u00a0<a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">Creative Commons Attribution 4.0 International License<\/a><\/p>\r\n\r\n<\/div>\r\n<\/section><\/div>\r\n<\/section><\/section>","rendered":"<div id=\"1\" class=\"ui-has-child-title\" data-type=\"abstract\">\n<section>\n<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\">Learning Objectives<\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p id=\"para-00001\">By the end of this section, you will be able to:<\/p>\n<ul id=\"list-00001\">\n<li>Name the major regions of the adult brain.<\/li>\n<li>Describe the connections between the cerebrum and brain stem through the diencephalon, and from those regions into the spinal cord.<\/li>\n<li>Recognize the complex connections within the subcortical structures of the basal nuclei.<\/li>\n<li>Explain the arrangement of gray and white matter in the spinal cord.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/section>\n<\/div>\n<p id=\"fs-id1518907\">The central nervous system (CNS) consists of the brain and the spinal cord, which are the main organs of the nervous system. The spinal cord is a single structure, whereas the adult brain is described in terms of four major regions: the cerebrum, the diencephalon, the brain stem, and the cerebellum. Neural activity in the brain and spinal cord governs many diverse and important functions in the body, for example a person\u2019s conscious experiences, the regulation of homeostasis, the coordination of reflexes, and many more.<\/p>\n<h2>Divisions of the CNS<\/h2>\n<section id=\"fs-id1488700\" data-depth=\"1\">\n<figure id=\"attachment_6229\" aria-describedby=\"caption-attachment-6229\" style=\"width: 726px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-6229\" title=\"https:\/\/commons.wikimedia.org\/wiki\/File:Diagram_showing_the_brain_stem_which_includes_the_medulla_oblongata,_the_pons_and_the_midbrain_(2)_CRUK_294.svg\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/brain-diagram-1024x860.png\" alt=\"This illustration shows a midsection of the human brain cut in the sagittal plane. Highlighted are the main divisions of the brain, brainstem, and spinal cord. This includes the Forebrain, cerebrum, midbrain, pons, medulla, hindbrain, cerebellum, and spinal cord.\" width=\"726\" height=\"610\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/brain-diagram-1024x860.png 1024w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/brain-diagram-300x252.png 300w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/brain-diagram-768x645.png 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/brain-diagram-65x55.png 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/brain-diagram-225x189.png 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/brain-diagram-350x294.png 350w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/brain-diagram.png 1219w\" sizes=\"auto, (max-width: 726px) 100vw, 726px\" \/><figcaption id=\"caption-attachment-6229\" class=\"wp-caption-text\"><strong>Divisions of the Central Nervous System<\/strong> &#8211; Diagram showing the brain_stem which includes the medulla oblongata, the pons and the midbrain on Wikimedia Commons is used under a CC BY-SA 4.0<\/figcaption><\/figure>\n<h3 data-type=\"title\">The Forebrain: Cerebral Cortex and Diencephalon<\/h3>\n<h4 data-type=\"title\">The Cerebrum<\/h4>\n<p id=\"fs-id1476424\">The most outwardly visible gray-coloured tissue of the human brain is the <a href=\"#cerebrum\"><span id=\"term-00001\" data-type=\"term\">cerebrum<\/span><\/a>. Many of the higher neurological functions, such as memory, emotion, and consciousness, are the result of neural activity in the cerebrum.\u00a0The folded portion of the tissue on the outermost surface of the cerebrum is the <span id=\"term-00002\" data-type=\"term\">cerebral cortex<\/span>, and the rest of the structure is beneath that outer covering. There is a distinct separation between the two sides of the cerebrum called the <span id=\"term-00003\" data-type=\"term\">longitudinal fissure<\/span>. It separates the cerebrum into two distinct halves, a right and left\u00a0<span id=\"term-00004\" data-type=\"term\">cerebral hemisphere<\/span>. Deep within the cerebrum, the white matter of the\u00a0<span id=\"term-00005\" data-type=\"term\">corpus callosum<\/span>\u00a0provides the major pathway for communication between the two hemispheres of the cerebral cortex.<a id=\"cerebrum\"><\/a><\/p>\n<figure id=\"attachment_9264\" aria-describedby=\"caption-attachment-9264\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-9264 size-large\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebrum-1024x477.jpeg\" alt=\"This figure shows the lateral view on the left panel and anterior view on the right panel of the brain. The major parts including the cerebrum are labeled.\" width=\"1024\" height=\"477\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebrum-1024x477.jpeg 1024w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebrum-300x140.jpeg 300w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebrum-768x358.jpeg 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebrum-65x30.jpeg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebrum-225x105.jpeg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebrum-350x163.jpeg 350w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebrum.jpeg 1119w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption id=\"caption-attachment-9264\" class=\"wp-caption-text\"><strong>The Cerebrum<\/strong> &#8211; The cerebrum is a large component of the CNS in humans, and the most obvious aspect of it is the folded surface called the cerebral cortex.<\/figcaption><\/figure>\n<p id=\"fs-id2081500\"><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.42425em;font-style: italic\">Cerebral Cortex<\/span><\/p>\n<section id=\"fs-id1318756\" data-depth=\"2\">\n<p id=\"fs-id1298164\">The cerebrum is covered by a continuous layer of folded gray matter that wraps around its surface\u2014the cerebral cortex. This thin, extensive region of gray matter is responsible for the higher functions of the nervous system. A <span id=\"term-00010\" data-type=\"term\">gyrus<\/span> (plural = gyri) is the topmost ridge of one of those folds, and a <span id=\"term-00011\" data-type=\"term\">sulcus<\/span> (plural = sulci) is the furrow between two gyri. The pattern of these folds of tissue indicates specific regions of the cerebral cortex.<\/p>\n<p id=\"fs-id1300741\">The head is limited by the size of the birth canal, and the brain must fit inside the cranial cavity of the skull. Extensive folding in the cerebral cortex enables more gray matter to fit into this limited space. If the gray matter of the cortex were peeled off of the cerebrum and laid out flat, its surface area would be roughly equal to one square meter.<\/p>\n<p id=\"fs-id1137638\">During embryonic development, as the telencephalon expands within the skull, the brain goes through a regular course of growth that results in everyone\u2019s brain having a similar pattern of folds. The surface of the brain can be mapped on the basis of the locations of large gyri and sulci. Using these landmarks, the <a href=\"#cerebralcortexlobes\">cortex<\/a> can be separated into four major regions, or lobes: the frontal, parietal, occipital, and temporal lobes. The\u00a0<span id=\"term-00012\" data-type=\"term\">lateral sulcus<\/span>\u00a0that separates the\u00a0<span id=\"term-00013\" data-type=\"term\">temporal lobe<\/span>\u00a0from the other regions is one such landmark. Superior to the lateral sulcus are the\u00a0<span id=\"term-00014\" data-type=\"term\">parietal lobe<\/span>\u00a0and\u00a0<span id=\"term-00015\" data-type=\"term\">frontal lobe<\/span>, which are separated from each other by the\u00a0<span id=\"term-00016\" data-type=\"term\">central sulcus<\/span>. The posterior region of the cortex is the\u00a0<span id=\"term-00017\" data-type=\"term\">occipital lobe<\/span>, which has no obvious anatomical border between it and the parietal or temporal lobes on the lateral surface of the brain. From the medial surface, an obvious landmark separating the parietal and occipital lobes is called the\u00a0<span id=\"term-00018\" data-type=\"term\">parieto-occipital sulcus<\/span>. The fact that there is no obvious anatomical border between these lobes is consistent with the functions of these regions being interrelated.<a id=\"cerebralcortexlobes\"><\/a><\/p>\n<div id=\"fig-ch13_02_02\" class=\"os-figure\">\n<figure data-id=\"fig-ch13_02_02\">\n<figure id=\"attachment_9265\" aria-describedby=\"caption-attachment-9265\" style=\"width: 521px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-9265\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Lobes-of-the-Cerebral-Cortex.jpeg\" alt=\"This figure shows the lateral view of the brain and the major lobes are labeled.\" width=\"521\" height=\"441\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Lobes-of-the-Cerebral-Cortex.jpeg 733w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Lobes-of-the-Cerebral-Cortex-300x254.jpeg 300w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Lobes-of-the-Cerebral-Cortex-65x55.jpeg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Lobes-of-the-Cerebral-Cortex-225x191.jpeg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Lobes-of-the-Cerebral-Cortex-350x297.jpeg 350w\" sizes=\"auto, (max-width: 521px) 100vw, 521px\" \/><figcaption id=\"caption-attachment-9265\" class=\"wp-caption-text\"><strong>Lobes of the Cerebral Cortex<\/strong> &#8211; The cerebral cortex is divided into four lobes. Extensive folding increases the surface area available for cerebral functions.<\/figcaption><\/figure>\n<\/figure>\n<\/div>\n<p id=\"fs-id1163314\">Different locations of the cerebral cortex are associated with particular functions, a concept known as localization. In the early 1900s, a German neuroscientist named Korbinian Brodmann performed an extensive study of the microscopic anatomy\u2014the cytoarchitecture\u2014of the cerebral cortex and divided the cortex into 52 separate regions on the basis of the histology of the cortex. His work resulted in a system of classification known as <a href=\"#Brodmannareas\"><span id=\"term-00019\" data-type=\"term\">Brodmann\u2019s areas<\/span><\/a>, which is still used today to describe the anatomical distinctions within the cortex. The results from Brodmann\u2019s work on the anatomy align very well with the functional differences within the cortex. Areas 17 and 18 in the occipital lobe are responsible for primary visual perception. That visual information is complex, so it is processed in the temporal and parietal lobes as well.<\/p>\n<p id=\"fs-id2055928\">The temporal lobe is associated with primary auditory sensation, known as Brodmann\u2019s areas 41 and 42 in the superior temporal lobe.\u00a0 The main sensation associated with the parietal lobe is\u00a0<span id=\"term-00020\" data-type=\"term\">somatosensation<\/span>, meaning the general sensations associated with the body. Posterior to the central sulcus is Brodmann&#8217;s areas 1, 2, and 3, collectively called <span id=\"term-00021\" data-type=\"term\">postcentral gyrus or<\/span> the primary somatosensory cortex. All of the tactile senses are processed in this area, including touch, pressure, tickle, pain, itch, and vibration, as well as more general senses of the body such as <span id=\"term-00022\" data-type=\"term\">proprioception<\/span>\u00a0and\u00a0<span id=\"term-00023\" data-type=\"term\">kinesthesia<\/span>, which are the senses of body position and movement, respectively.<\/p>\n<p id=\"fs-id1119780\">Anterior to the central sulcus is the frontal lobe, which is primarily associated with motor functions. The\u00a0<span id=\"term-00024\" data-type=\"term\">precentral gyrus<\/span> is the primary motor cortex. Cells from this region of the cerebral cortex are the upper motor neurons that instruct lower motor neurons in the spinal cord to trigger contraction and relaxation of muscles. Anterior to this region are a few areas that are associated with planned movements. The <span id=\"term-00025\" data-type=\"term\">premotor area<\/span>\u00a0is responsible for thinking of a movement to be made. The\u00a0<span id=\"term-00026\" data-type=\"term\">frontal eye fields<\/span>\u00a0are important in eliciting eye movements and in attending to visual stimuli.\u00a0<span id=\"term-00027\" data-type=\"term\">Broca\u2019s area<\/span>\u00a0is responsible for the production of language, or controlling movements responsible for speech; in the vast majority of people, it is located only on the left side. Anterior to these regions is the\u00a0<span id=\"term-00028\" data-type=\"term\">prefrontal lobe<\/span>, which serves cognitive functions that can be the basis of personality, short-term memory, and consciousness. The prefrontal lobotomy is an outdated mode of treatment for personality disorders (psychiatric conditions) that profoundly affected the personality of the patient.<\/p>\n<p><span style=\"color: #000000\">The fascinating case of a man named Phineas Gage highlights the important functions of the prefrontal lobe . In the autumn of 1948, Mr. Gage was part of a work group blasting rock for the construction of a railroad south of Cavendish, Vermont. Unfortunately, a blast resulted in an iron rod piercing his cheek, passing behind his left eye, through his prefrontal lobe and exiting his skull. Amazingly, within a few months Mr. Gage regained normal motor and speech function, but his personality was drastically changed. Friends and family of Mr. Gage described him as unreliable, disrespectful, and impulsive; he was &#8220;no longer Gage&#8221; as they had once known him.<a id=\"Brodmannareas\"><\/a><\/span><\/p>\n<div id=\"fig-ch13_02_03\" class=\"os-figure\">\n<figure data-id=\"fig-ch13_02_03\">\n<figure id=\"attachment_9267\" aria-describedby=\"caption-attachment-9267\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"size-large wp-image-9267\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-1024x603.jpeg\" alt=\"In this figure, the Brodmann areas, identifying the functional regions of the brain, are mapped. The left panel shows the lateral surface of the brain and the right panel shows the medial surface.\" width=\"1024\" height=\"603\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-1024x603.jpeg 1024w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-300x177.jpeg 300w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-768x452.jpeg 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-1536x904.jpeg 1536w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-2048x1205.jpeg 2048w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-65x38.jpeg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-225x132.jpeg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Brodmanns-Areas-of-the-Cerebral-Cortex-350x206.jpeg 350w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption id=\"caption-attachment-9267\" class=\"wp-caption-text\"><strong>Brodmann&#8217;s Areas of the Cerebral Cortex<\/strong> &#8211; Brodmann mapping of functionally distinct regions of the cortex was based on its cytoarchitecture at a microscopic level.<\/figcaption><\/figure>\n<\/figure>\n<\/div>\n<\/section>\n<section id=\"fs-id1087946\" data-depth=\"2\">\n<h4 data-type=\"title\">Subcortical structures<\/h4>\n<p id=\"fs-id793857\">Beneath the cerebral cortex are clusters of neuron cell bodies called <span id=\"term-00029\" data-type=\"term\">subcortical nuclei<\/span> which are responsible for various important neural functions. These include:<\/p>\n<ul>\n<li><strong>The basal forebrain:\u00a0<\/strong>this group of subcortical nuclei serve as the primary location for acetylcholine production, which is a neurotransmitter that modulates the overall activity of the cortex, possibly leading to greater attention to sensory stimuli. Alzheimer\u2019s disease is associated with a loss of neurons in the basal forebrain.<\/li>\n<li><strong>The h<span id=\"term-00030\" data-type=\"term\">ippocampus<\/span>\u00a0and\u00a0<span id=\"term-00031\" data-type=\"term\">amygdala: <\/span><\/strong><span id=\"term-00031\" data-type=\"term\">these<\/span> are medial structures that, along with the adjacent cortex, are involved in long-term memory formation and emotional responses.<\/li>\n<li><strong>The caudate, putamen, and globus pallidus:<\/strong> These are a group of major nuclei in the cerebrum called the basal ganglia\u00a0 responsible for fine-tuning voluntary movements. The caudate is a long nucleus that follows the basic C-shape of the cerebrum from the frontal lobe, through the parietal and occipital lobes, into the temporal lobe. The putamen is mostly deep in the anterior regions of the frontal and parietal lobes. Together, the caudate and putamen are called the <span id=\"term-00035\" style=\"text-align: initial;font-size: 1em\" data-type=\"term\">striatum<\/span><span style=\"text-align: initial;font-size: 1em\">. The globus pallidus is a layered nucleus that lies just medial to the putamen; they are called the lenticular nuclei because they look like curved pieces fitting together like lenses. The globus pallidus has two subdivisions, the external and internal segments, which are lateral and medial, respectively. These nuclei are depicted in a frontal section of the brain in\u00a0<\/span>the figure below<span style=\"text-align: initial;font-size: 1em\">.<\/span><\/li>\n<\/ul>\n<div id=\"fig-ch13_02_04\" class=\"os-figure\">\n<figure data-id=\"fig-ch13_02_04\">\n<figure id=\"attachment_9269\" aria-describedby=\"caption-attachment-9269\" style=\"width: 684px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-9269\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Frontal-Section-of-Cerebral-Cortex-and-Basal-Nuclei.jpeg\" alt=\"This diagram shows the frontal section of the brain and identifies the major components of the basal nuclei.\" width=\"684\" height=\"535\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Frontal-Section-of-Cerebral-Cortex-and-Basal-Nuclei.jpeg 684w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Frontal-Section-of-Cerebral-Cortex-and-Basal-Nuclei-300x235.jpeg 300w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Frontal-Section-of-Cerebral-Cortex-and-Basal-Nuclei-65x51.jpeg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Frontal-Section-of-Cerebral-Cortex-and-Basal-Nuclei-225x176.jpeg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Frontal-Section-of-Cerebral-Cortex-and-Basal-Nuclei-350x274.jpeg 350w\" sizes=\"auto, (max-width: 684px) 100vw, 684px\" \/><figcaption id=\"caption-attachment-9269\" class=\"wp-caption-text\"><strong>Frontal Section of Cerebral Cortex and Basal Nuclei<\/strong> &#8211; The major components of the basal nuclei, shown in a frontal section of the brain, are the caudate (just lateral to the lateral ventricle), the putamen (inferior to the caudate and separated by the large white-matter structure called the internal capsule), and the globus pallidus (medial to the putamen).<\/figcaption><\/figure>\n<\/figure>\n<\/div>\n<div id=\"fs-id1967418\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\">\n<section>\n<div class=\"os-note-body\">\n<div class=\"textbox shaded\">Watch this\u00a0<a href=\"http:\/\/openstax.org\/l\/basalnuclei1\" target=\"_blank\" rel=\"noopener nofollow\">video<\/a>\u00a0to learn about the basal nuclei (also known as the basal ganglia), which have two pathways that process information within the cerebrum. As shown in this video, the direct pathway is the shorter pathway through the system that results in increased activity in the cerebral cortex and increased motor activity. The direct pathway is described as resulting in \u201cdisinhibition\u201d of the thalamus. What does disinhibition mean? What are the two neurons doing individually to cause this?<\/div>\n<\/div>\n<\/section>\n<\/div>\n<div id=\"fs-id1301935\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\">\n<section>\n<div class=\"os-note-body\">\n<div class=\"textbox shaded\">Watch this\u00a0<a href=\"http:\/\/openstax.org\/l\/basalnuclei2\" target=\"_blank\" rel=\"noopener nofollow\">video<\/a>\u00a0to learn about the basal nuclei (also known as the basal ganglia), which have two pathways that process information within the cerebrum. As shown in this video, the indirect pathway is the longer pathway through the system that results in decreased activity in the cerebral cortex, and therefore less motor activity. The indirect pathway has an extra couple of connections in it, including disinhibition of the subthalamic nucleus. What is the end result on the thalamus, and therefore on movement initiated by the cerebral cortex?<\/div>\n<p><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.42425em;font-style: italic\">The Diencephalon<\/span><\/p>\n<\/div>\n<\/section>\n<\/div>\n<\/section>\n<\/section>\n<section id=\"fs-id1230531\" data-depth=\"1\">\n<p id=\"fs-id1120163\">The diencephalon is the one region of the adult brain that retains its name from embryologic development. The etymology of the word diencephalon translates to \u201cthrough brain.\u201d It is the connection between the cerebrum and the rest of the nervous system, with one exception. The rest of the brain, the spinal cord, and the PNS all send information to the cerebrum through the diencephalon. Output from the cerebrum passes through the diencephalon. The single exception is the system associated with\u00a0<span id=\"term-00041\" data-type=\"term\">olfaction<\/span>, or the sense of smell, which connects directly with the cerebrum. In the earliest vertebrate species, the cerebrum was not much more than olfactory bulbs that received peripheral information about the chemical environment (to call it smell in these organisms is imprecise because they lived in the ocean).<\/p>\n<p id=\"fs-id2026939\"><a href=\"#diencephalon\">The diencephalon<\/a> is deep beneath the cerebrum and can be described as any region of the brain with \u201cthalamus\u201d in its name. The two major regions of the diencephalon are the thalamus itself and the hypothalamus.<\/p>\n<section id=\"fs-id1196887\" data-depth=\"2\">\n<h5 data-type=\"title\">Thalamus<\/h5>\n<p id=\"fs-id1234023\">You can think of the thalamus as a giant postal system where information is received, processed, and sent where it needs to go. The <span id=\"term-00044\" data-type=\"term\">thalamus<\/span> is a collection of nuclei that relay information between the cerebral cortex and the periphery, spinal cord, or brain stem. All sensory information, except for the sense of smell, passes through the thalamus before processing by the cortex. Axons from the peripheral sensory organs synapse in the thalamus and thalamic neurons project directly to the cerebrum. It is a requisite synapse in any sensory pathway, except for olfaction. The thalamus does not just pass the information on, it also processes that information. For example, the portion of the thalamus that receives visual information will influence what visual stimuli are important, or what receives attention.<\/p>\n<p id=\"fs-id1509482\">The cerebrum also sends information down to the thalamus, which usually communicates motor commands. This involves interactions with the cerebellum and other nuclei in the brain stem. The cerebrum interacts with the basal ganglia, which involves connections with the thalamus. The primary output of the basal ganglia is to the thalamus, which relays that output to the cerebral cortex. The cortex also sends information to the thalamus that will then influence the effects of the basal nuclei.<\/p>\n<\/section>\n<section id=\"fs-id1076072\" data-depth=\"2\">\n<h5 data-type=\"title\">Hypothalamus<\/h5>\n<p id=\"fs-id1490316\">Inferior and slightly anterior to the thalamus is the\u00a0<span id=\"term-00045\" data-type=\"term\">hypothalamus<\/span>, the other major region of the diencephalon. The hypothalamus is a collection of nuclei that are largely involved in regulating homeostasis. The hypothalamus is the executive region in charge of the autonomic nervous system and the endocrine system through its regulation of the anterior pituitary gland. Other parts of the hypothalamus are involved in memory and emotion as part of the limbic system.<a id=\"diencephalon\"><\/a><\/p>\n<div id=\"fig-ch13_02_06\" class=\"os-figure\">\n<figure data-id=\"fig-ch13_02_06\">\n<figure id=\"attachment_9270\" aria-describedby=\"caption-attachment-9270\" style=\"width: 720px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-9270\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Diencephalon.jpeg\" alt=\"This figure shows the location of the thalamus, hypothalamus and pituitary gland in the brain.\" width=\"720\" height=\"571\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Diencephalon.jpeg 869w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Diencephalon-300x238.jpeg 300w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Diencephalon-768x609.jpeg 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Diencephalon-65x52.jpeg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Diencephalon-225x178.jpeg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Diencephalon-350x278.jpeg 350w\" sizes=\"auto, (max-width: 720px) 100vw, 720px\" \/><figcaption id=\"caption-attachment-9270\" class=\"wp-caption-text\"><strong>The Diencephalon<\/strong> -The diencephalon is composed primarily of the thalamus and hypothalamus. The thalami are two elongated, ovoid structures on either side of the midline that make contact in the middle. The hypothalamus is inferior and anterior to the thalamus, culminating in a sharp angle to which the pituitary gland is attached.<\/figcaption><\/figure>\n<\/figure>\n<\/div>\n<\/section>\n<\/section>\n<section id=\"fs-id1886090\" data-depth=\"1\">\n<h3 data-type=\"title\">Midbrain and Hindbrain<\/h3>\n<h4 data-type=\"title\">Brain Stem<\/h4>\n<p id=\"fs-id1523364\">Parts of the midbrain and hindbrain (composed of the pons and the medulla) are collectively referred to as the <a href=\"#brainstem\">brain stem<\/a>. The structure emerges from the ventral surface of the forebrain as a tapering cone that connects the brain to the spinal cord. Attached to the brain stem, but considered a separate region of the hindbrain, is the cerebellum. The midbrain coordinates sensory representations of the visual, auditory, and somatosensory perceptual spaces. The pons is the main connection with the cerebellum. The pons and the medulla regulate several crucial functions, including the cardiovascular and respiratory systems and rates.<\/p>\n<p id=\"fs-id1510727\">The cranial nerves connect through the brain stem and provide the brain with the sensory input and motor output associated with the head and neck, including most of the special senses. The major ascending and descending pathways between the spinal cord and brain, specifically the cerebrum, pass through the brain stem.<a id=\"brainstem\"><\/a><\/p>\n<figure id=\"attachment_9271\" aria-describedby=\"caption-attachment-9271\" style=\"width: 754px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-9271\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Brain-Stem.jpeg\" alt=\"This figure shows the location of the midbrain, pons and the medulla in the brain.\" width=\"754\" height=\"570\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Brain-Stem.jpeg 906w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Brain-Stem-300x227.jpeg 300w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Brain-Stem-768x581.jpeg 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Brain-Stem-65x49.jpeg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Brain-Stem-225x170.jpeg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Brain-Stem-350x265.jpeg 350w\" sizes=\"auto, (max-width: 754px) 100vw, 754px\" \/><figcaption id=\"caption-attachment-9271\" class=\"wp-caption-text\"><strong>The Brain Stem<\/strong> &#8211;\u00a0The brain stem comprises three regions: the midbrain, the pons, and the medulla.<\/figcaption><\/figure>\n<div id=\"fig-ch13_02_07\" class=\"os-figure\">\n<figure data-id=\"fig-ch13_02_07\"><\/figure>\n<div class=\"os-caption-container\"><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.42425em;font-style: italic\">Midbrain<\/span><\/div>\n<\/div>\n<section id=\"fs-id1284242\" data-depth=\"2\">\n<p id=\"fs-id890816\">One of the original regions of the embryonic brain, the midbrain is a small region between the thalamus and pons. It is separated into the\u00a0<span id=\"term-00046\" data-type=\"term\">tectum<\/span>\u00a0and\u00a0<span id=\"term-00047\" data-type=\"term\">tegmentum<\/span>, from the Latin words for roof and floor, respectively. The cerebral aqueduct passes through the center of the midbrain, such that these regions are the roof and floor of that canal.<\/p>\n<p id=\"fs-id1282943\">The tectum is composed of four bumps known as the colliculi (singular = colliculus), which means \u201clittle hill\u201d in Latin. The\u00a0<span id=\"term-00048\" data-type=\"term\">inferior colliculus<\/span>\u00a0is the inferior pair of these enlargements and is part of the auditory brain stem pathway. Neurons of the inferior colliculus project to the thalamus, which then sends auditory information to the cerebrum for the conscious perception of sound. The\u00a0<span id=\"term-00049\" data-type=\"term\">superior colliculus<\/span>\u00a0is the superior pair and combines sensory information about visual space, auditory space, and somatosensory space. Activity in the superior colliculus is related to orienting the eyes to a sound or touch stimulus. If you are walking along the sidewalk on campus and you hear chirping, the superior colliculus coordinates that information with your awareness of the visual location of the tree right above you. That is the correlation of auditory and visual maps. If you suddenly feel something wet fall on your head, your superior colliculus integrates that with the auditory and visual maps and you know that the chirping bird just relieved itself on you. You want to look up to see the culprit, but do not.<\/p>\n<p id=\"fs-id1301789\">The tegmentum is continuous with the gray matter of the rest of the brain stem. Throughout the midbrain, pons, and medulla, the tegmentum contains the nuclei that receive and send information through the cranial nerves, as well as regions that regulate important functions such as those of the cardiovascular and respiratory systems.<\/p>\n<\/section>\n<section id=\"fs-id1126733\" data-depth=\"2\">\n<h4 data-type=\"title\">Pons<\/h4>\n<p id=\"fs-id1179935\">The word pons comes from the Latin word for bridge. It is visible on the anterior surface of the brain stem as the thick bundle of white matter attached to the cerebellum. The pons is the main connection between the cerebellum and the brain stem. The bridge-like white matter is only the anterior surface of the pons; the gray matter beneath that is a continuation of the tegmentum from the midbrain. Gray matter in the tegmentum region of the pons contains neurons receiving descending input from the forebrain that is sent to the cerebellum.<\/p>\n<\/section>\n<section id=\"fs-id1187846\" data-depth=\"2\">\n<h4 data-type=\"title\">Medulla<\/h4>\n<p id=\"fs-id2166609\">The medulla is the region known as the myelencephalon in the embryonic brain. The initial portion of the name, \u201cmyel,\u201d refers to the significant white matter found in this region\u2014especially on its exterior, which is continuous with the white matter of the spinal cord. The tegmentum of the midbrain and pons continues into the medulla because this gray matter is responsible for processing cranial nerve information. A diffuse region of gray matter throughout the brain stem, known as the\u00a0<span id=\"term-00050\" data-type=\"term\">reticular formation<\/span>, is related to sleep and wakefulness, such as general brain activity and attention.<\/p>\n<\/section>\n<\/section>\n<section id=\"fs-id2824451\" data-depth=\"1\">\n<h4 data-type=\"title\">The Cerebellum<\/h4>\n<p id=\"fs-id1520379\">The\u00a0<a href=\"#cerebellum\"><span id=\"term-00051\" data-type=\"term\">cerebellum<\/span><\/a>, as the name suggests, is the \u201clittle brain.\u201d It is covered in gyri and sulci like the cerebrum, and looks like a miniature version of that part of the brain. The cerebellum is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord. It accounts for approximately 10 percent of the mass of the brain.<a id=\"cerebellum\"><\/a><\/p>\n<figure id=\"attachment_9272\" aria-describedby=\"caption-attachment-9272\" style=\"width: 830px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"size-large wp-image-9272\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebellum-830x1024.jpeg\" alt=\"This figure shows the location of the cerebellum in the brain. In the top panel, a lateral view labels the location of the cerebellum and the deep cerebellar white matter. In the bottom panel, a photograph of a brain, with the cerebellum in pink is shown.\" width=\"830\" height=\"1024\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebellum-830x1024.jpeg 830w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebellum-243x300.jpeg 243w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebellum-768x948.jpeg 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebellum-65x80.jpeg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebellum-225x278.jpeg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebellum-350x432.jpeg 350w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/The-Cerebellum.jpeg 875w\" sizes=\"auto, (max-width: 830px) 100vw, 830px\" \/><figcaption id=\"caption-attachment-9272\" class=\"wp-caption-text\"><strong>The Cerebellum<\/strong> &#8211; The cerebellum is situated on the posterior surface of the brain stem. Descending input from the cerebellum enters through the large white matter structure of the pons. Ascending input from the periphery and spinal cord enters through the fibers of the inferior olive. Output goes to the midbrain, which sends a descending signal to the spinal cord.<\/figcaption><\/figure>\n<p id=\"fs-id1315185\">Descending fibers from the cerebrum have branches that connect to neurons in the pons. Those neurons project into the cerebellum, providing a copy of motor commands sent to the spinal cord. Sensory information from the periphery, which enters through spinal or cranial nerves, is copied to a nucleus in the medulla known as the\u00a0<span id=\"term-00052\" data-type=\"term\">inferior olive<\/span>. Fibers from this nucleus enter the cerebellum and are compared with the descending commands from the cerebrum. If the primary motor cortex of the frontal lobe sends a command down to the spinal cord to initiate walking, a copy of that instruction is sent to the cerebellum. Sensory feedback from the muscles and joints, proprioceptive information about the movements of walking, and sensations of balance are sent to the cerebellum through the inferior olive and the cerebellum compares them. If walking is not coordinated, perhaps because the ground is uneven or a strong wind is blowing, then the cerebellum sends out a corrective command to compensate for the difference between the original cortical command and the sensory feedback. The output of the cerebellum is into the midbrain, which then sends a descending input to the spinal cord to correct the messages going to skeletal muscles.<\/p>\n<\/section>\n<section id=\"fs-id1518219\" data-depth=\"1\">\n<h2 data-type=\"title\">The Spinal Cord<\/h2>\n<p id=\"fs-id1523219\">The description of the CNS is concentrated on the structures of the brain, but the spinal cord is another major organ of the system. The spinal cord is a long tube-like structure which begins at the medulla oblongata in the brainstem and extends down the spine. It serves to connect the CNS with the peripheral nervous system (PNS).<\/p>\n<section id=\"fs-id1153084\" data-depth=\"2\">\n<h3 data-type=\"title\">The Spinal Cord in Cross-Section: Gray and White Matter<\/h3>\n<p>A striking feature of the spinal cord when viewed in cross section is it&#8217;s organization of gray and white matter. As we learned before, gray matter refers to the cell bodies of neurons while white matter signifies the myelinated axon processes of nerves. You can remember this by thinking of the lipid-rich contents of myelin, which appear white. The gray matter of the spinal cord is organized into horns, while the white matter is organized into columns<span style=\"color: #99cc00\">.\u00a0<\/span><span style=\"font-size: 1em\"> In cross-section, the gray matter of the spinal cord has the appearance of an ink-blot test, with the spread of the gray matter on one side replicated on the other\u2014a shape reminiscent of a bulbous capital \u201cH.\u201d <a id=\"crosssectionspinalcord\"><\/a><\/span><\/p>\n<figure id=\"attachment_9273\" aria-describedby=\"caption-attachment-9273\" style=\"width: 797px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-9273\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord-893x1024.jpeg\" alt=\"This figure shows the cross section of the spinal cord. The top panel shows a diagram of the cross section and the major parts are labeled. The bottom panel shows an ultrasound image of the spinal cord cross section.\" width=\"797\" height=\"914\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord-893x1024.jpeg 893w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord-262x300.jpeg 262w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord-768x881.jpeg 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord-1339x1536.jpeg 1339w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord-65x75.jpeg 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord-225x258.jpeg 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord-350x401.jpeg 350w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2025\/08\/Cross-section-of-Spinal-Cord.jpeg 1642w\" sizes=\"auto, (max-width: 797px) 100vw, 797px\" \/><figcaption id=\"caption-attachment-9273\" class=\"wp-caption-text\"><strong>Cross-section of Spinal Cord<\/strong> &#8211; The cross-section of a thoracic spinal cord segment shows the posterior, anterior, and lateral horns of gray matter, as well as the posterior, anterior, and lateral columns of white matter. LM \u00d7 40. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<section id=\"fs-id1153084\" data-depth=\"2\">\n<div id=\"fig-ch13_02_09\" class=\"os-figure\">\n<figure data-id=\"fig-ch13_02_09\"><\/figure>\n<div class=\"os-caption-container\"><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1.42425em;font-style: italic\">Gray Horns<\/span><\/div>\n<\/div>\n<\/section>\n<p id=\"fs-id704969\">As shown in <a href=\"#crosssectionspinalcord\">the figure above<\/a>, the gray matter is subdivided into regions that are referred to as horns. The <span id=\"term-00061\" data-type=\"term\">posterior horn<\/span> is responsible for sensory processing, while the <span id=\"term-00062\" data-type=\"term\">anterior horn<\/span> sends out motor signals to the skeletal muscles. Note that it is common to see the terms dorsal (dorsal = \u201cback\u201d) and ventral (ventral = \u201cbelly\u201d) used interchangeably with posterior and anterior, particularly in reference to nerves and the structures of the spinal cord. You should learn to be comfortable with both. The <span id=\"term-00063\" data-type=\"term\">lateral horn<\/span>, which is only found in the thoracic, upper lumbar, and sacral regions, contains cell bodies of motor neurons of the autonomic nervous system.<\/p>\n<p id=\"fs-id1462544\">Some of the largest neurons of the spinal cord are the multipolar motor neurons in the anterior horn. The fibers that cause contraction of skeletal muscles are the axons of these neurons. The motor neuron that causes contraction of the big toe, for example, is located in the sacral spinal cord. The axon that has to reach all the way to the belly of that muscle may be a meter in length. The neuronal cell body that maintains that long fiber must be quite large, possibly several hundred micrometers in diameter, making it one of the largest cells in the body.<\/p>\n<\/section>\n<section id=\"fs-id1862662\" data-depth=\"2\">\n<h4 data-type=\"title\">White Columns<\/h4>\n<p id=\"fs-id1173979\">Just as the gray matter is separated into horns, the white matter of the spinal cord is separated into columns.\u00a0<span id=\"term-00064\" data-type=\"term\">Ascending tracts<\/span>\u00a0of nervous system fibers in these columns carry sensory information up to the brain, whereas\u00a0<span id=\"term-00065\" data-type=\"term\">descending tracts<\/span> carry motor commands from the brain to the muscles. Looking at the spinal cord longitudinally, the columns extend along its length as continuous bands of white matter. Between the two posterior horns of gray matter are the <span id=\"term-00066\" data-type=\"term\">posterior columns<\/span>. Between the two anterior horns, and bounded by the axons of motor neurons emerging from that gray matter area, are the\u00a0<span id=\"term-00067\" data-type=\"term\">anterior columns<\/span>. The white matter on either side of the spinal cord, between the posterior horn and the axons of the anterior horn neurons, are the\u00a0<span id=\"term-00068\" data-type=\"term\">lateral columns<\/span>. The posterior columns are composed of axons of ascending tracts. The anterior and lateral columns are composed of many different groups of axons of both ascending and descending tracts\u2014the latter carrying motor commands down from the brain to the spinal cord to control output to the periphery.<\/p>\n<div id=\"fs-id1148241\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\">\n<header>\n<h4 class=\"os-title\" data-type=\"title\">Spinal Cord Segments<\/h4>\n<\/header>\n<\/div>\n<\/section>\n<p>\u00a0The spinal cord itself is composed of a number of segments, each of which has bundles of axons exiting and entering the cord in structures called roots. Axons enter the posterior side through the\u00a0<span id=\"term-00055\" data-type=\"term\">dorsal (posterior) nerve root<\/span>. The axons emerging from the anterior side do so through the\u00a0<span id=\"term-00057\" data-type=\"term\">ventral (anterior) nerve root<\/span>. On the whole, the posterior regions are responsible for sensory functions and the anterior regions are associated with motor functions, just like the corresponding anterior and posterior horns of gray matter. The roots then combine to form a pair of <a href=\"#spinalnerve\">spinal nerves<\/a>, one for each component of the spine.<a id=\"spinalnerve\"><\/a><\/p>\n<figure id=\"attachment_6247\" aria-describedby=\"caption-attachment-6247\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-6247 size-large\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/1200px-Spinal_nerve.svg_-1-1024x597.png\" alt=\"This illustration shows a segment of the spinal cord in cross-section. The spinal cord itself is composed of inner grey-matter in a butterfly shape surrounded by white matter. The ventral and dorsal roots contain neurons leaving the spinal cord, which combine to form a mixed spinal nerve containing both sensory and motor fibres.\" width=\"1024\" height=\"597\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/1200px-Spinal_nerve.svg_-1-1024x597.png 1024w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/1200px-Spinal_nerve.svg_-1-300x175.png 300w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/1200px-Spinal_nerve.svg_-1-768x448.png 768w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/1200px-Spinal_nerve.svg_-1-65x38.png 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/1200px-Spinal_nerve.svg_-1-225x131.png 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/1200px-Spinal_nerve.svg_-1-350x204.png 350w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/1200px-Spinal_nerve.svg_-1.png 1200w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption id=\"caption-attachment-6247\" class=\"wp-caption-text\"><strong>Spinal Nerve<\/strong> &#8211; A spinal nerve is formed from the merging of the dorsal and ventral roots. Each spinal nerve emerges from the spinal column in between vertebrae. Modified image originally by Tristanb.<\/figcaption><\/figure>\n<p id=\"fs-id1942720\">The spinal cord is surrounded and protected by the bones in our back, which are called vertebrae. These are the protruding boney structures that you can feel in your neck and back.\u00a0Each of these segments of spinal cord is named according to the level at which it&#8217;s spinal nerves pass through the intervertebral foramina, which is the space between two vertebrae. <span style=\"font-size: 1em\">\u00a0For example, the first pair of spinal nerves are the first cervical nerves (C1), which exits the spinal cord above the first cervical vertebrae (CI). You should take note of this nomenclature- spinal nerves are numbered with arabic numerals (1, 2, 3, 4, etc.) while vertebrae are numbered with roman numerals (I, II, III, IV, etc.)<\/span><\/p>\n<p><span style=\"text-align: initial;font-size: 1em\">The <a href=\"#spinalcordregions\">spinal cord<\/a> is also split lengthwise into five major regions. Immediately adjacent to the brain stem is the cervical region, followed by the thoracic, then the lumbar, the sacral, and finally the coccygeal region. The spinal cord is not the full length of the vertebral column because the spinal cord does not grow significantly longer after the first or second year, but the skeleton continues to grow. The nerves that emerge from the spinal cord pass through the intervertebral foramina at the respective levels. As the vertebral column grows, these nerves grow with it and result in a long bundle of nerves that resembles a horse\u2019s tail and is named the <\/span><span id=\"term-00060\" style=\"text-align: initial;font-size: 1em\" data-type=\"term\">cauda equina<\/span><span style=\"text-align: initial;font-size: 1em\">. The sacral spinal cord is at the level of the upper lumbar vertebral bones. The spinal nerves extend from their various levels to the proper level of the vertebral column.<a id=\"spinalcordregions\"><\/a><\/span><\/p>\n<figure id=\"attachment_6248\" aria-describedby=\"caption-attachment-6248\" style=\"width: 516px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-6248\" src=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/spinal-cord.png\" alt=\"This illustration demonstrates the position of the spinal cord and vertebrae within the human body and the three spinal cord areas- the cervical, thoracic, and lumbar areas (running superior to inferior as listed).\" width=\"516\" height=\"696\" srcset=\"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/spinal-cord.png 603w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/spinal-cord-223x300.png 223w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/spinal-cord-65x88.png 65w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/spinal-cord-225x303.png 225w, https:\/\/pressbooks.bccampus.ca\/pathology\/wp-content\/uploads\/sites\/1260\/2022\/12\/spinal-cord-350x472.png 350w\" sizes=\"auto, (max-width: 516px) 100vw, 516px\" \/><figcaption id=\"caption-attachment-6248\" class=\"wp-caption-text\">The different regions of the vertebrae and spinal cord. By Cancer Research UK and used under CC license.<\/figcaption><\/figure>\n<section id=\"fs-id1862662\" data-depth=\"2\">\n<div id=\"fs-id1148241\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\">\n<section>\n<div class=\"os-note-body\">\n<div class=\"textbox shaded\">Watch this\u00a0<a href=\"http:\/\/openstax.org\/l\/graymatter\" target=\"_blank\" rel=\"noopener nofollow\">video<\/a>\u00a0to learn about the gray matter of the spinal cord that receives input from fibers of the dorsal (posterior) root and sends information out through the fibers of the ventral (anterior) root. As discussed in this video, these connections represent the interactions of the CNS with peripheral structures for both sensory and motor functions. The cervical and lumbar spinal cords have enlargements as a result of larger populations of neurons. What are these enlargements responsible for?<\/div>\n<p>&nbsp;<\/p>\n<\/div>\n<\/section>\n<\/div>\n<div id=\"fs-id1070949\" class=\"anatomy disorders ui-has-child-title\" data-type=\"note\">\n<div class=\"textbox textbox--examples\">\n<header class=\"textbox__header\"><\/header>\n<header>\n<h3 class=\"os-title\" data-type=\"title\"><span class=\"os-title-label\">DISORDERS OF THE <\/span>Basal Nuclei<\/h3>\n<\/header>\n<div class=\"textbox__content\">\n<section>\n<div class=\"os-note-body\">\n<p id=\"fs-id1467131\">Parkinson\u2019s disease is a disorder of the basal nuclei, specifically of the substantia nigra, that demonstrates the effects of the direct and indirect pathways. Parkinson\u2019s disease is the result of neurons in the substantia nigra pars compacta dying. These neurons release dopamine into the striatum. Without that modulatory influence, the basal nuclei are stuck in the indirect pathway, without the direct pathway being activated. The direct pathway is responsible for increasing cortical movement commands. The increased activity of the indirect pathway results in the hypokinetic disorder of Parkinson\u2019s disease.<\/p>\n<p id=\"fs-id856277\">Parkinson\u2019s disease is neurodegenerative, meaning that neurons die that cannot be replaced, so there is no cure for the disorder. Treatments for Parkinson\u2019s disease are aimed at increasing dopamine levels in the striatum. Currently, the most common way of doing that is by providing the amino acid L-DOPA, which is a precursor to the neurotransmitter dopamine and can cross the blood-brain barrier. With levels of the precursor elevated, the remaining cells of the substantia nigra pars compacta can make more neurotransmitter and have a greater effect. Unfortunately, the patient will become less responsive to L-DOPA treatment as time progresses, and it can cause increased dopamine levels elsewhere in the brain, which are associated with psychosis or schizophrenia.<\/p>\n<\/div>\n<\/section>\n<p>Visit this\u00a0<a href=\"http:\/\/openstax.org\/l\/parkinsons\" target=\"_blank\" rel=\"noopener nofollow\">site<\/a> for a thorough explanation of Parkinson\u2019s disease.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1539338\" class=\"anatomy interactive ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\">\n<section>\n<div class=\"os-note-body\">\n<h1>Adaption<\/h1>\n<p style=\"text-align: start\">This chapter was adapted by Valerie Swanston from the following text:<\/p>\n<p style=\"text-align: start\"><a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\" target=\"_blank\" rel=\"noopener\">The Central Nervous System<\/a>\u00a0in <a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/\">Anatomy and Physiology<\/a>\u00a0by\u00a0OSCRiceUniversity\u00a0is licensed under a\u00a0<a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">Creative Commons Attribution 4.0 International License<\/a><\/p>\n<\/div>\n<\/section>\n<\/div>\n<\/section>\n<\/section>\n<div class=\"media-attributions clear\" prefix:cc=\"http:\/\/creativecommons.org\/ns#\" prefix:dc=\"http:\/\/purl.org\/dc\/terms\/\"><h2>Media Attributions<\/h2><ul><li about=\"https:\/\/commons.wikimedia.org\/wiki\/File:Diagram_showing_the_brain_stem_which_includes_the_medulla_oblongata,_the_pons_and_the_midbrain_(2)_CRUK_294.svg\"><a rel=\"cc:attributionURL\" href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Diagram_showing_the_brain_stem_which_includes_the_medulla_oblongata,_the_pons_and_the_midbrain_(2)_CRUK_294.svg\" property=\"dc:title\">brain diagram<\/a>  &copy;  Cancer Research UK    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\">CC BY-SA (Attribution ShareAlike)<\/a> license<\/li><li about=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\"><a rel=\"cc:attributionURL\" href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\" property=\"dc:title\">The Cerebrum<\/a>  &copy;  OSCRiceUniversity    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><li about=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\"><a rel=\"cc:attributionURL\" href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\" property=\"dc:title\">Lobes of the Cerebral Cortex<\/a>  &copy;  OSCRiceUniversity    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><li about=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\"><a rel=\"cc:attributionURL\" href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\" property=\"dc:title\">Brodmann&#8217;s Areas of the Cerebral Cortex<\/a>  &copy;  OSCRiceUniversity    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><li about=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\"><a rel=\"cc:attributionURL\" href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\" property=\"dc:title\">Frontal Section of Cerebral Cortex and Basal Nuclei<\/a>  &copy;  OSCRiceUniversity    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><li about=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\"><a rel=\"cc:attributionURL\" href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\" property=\"dc:title\">The Diencephalon<\/a>  &copy;  OSCRiceUniversity    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY (Attribution)<\/a> license<\/li><li about=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\"><a rel=\"cc:attributionURL\" href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/13-2-the-central-nervous-system\" property=\"dc:title\">The Brain Stem<\/a>  &copy; 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 Mysid (original by Tristanb)    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\">CC BY-SA (Attribution ShareAlike)<\/a> license<\/li><li about=\"https:\/\/commons.wikimedia.org\/wiki\/File:Diagram_of_the_spinal_cord_CRUK_046.svg\"><a rel=\"cc:attributionURL\" href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Diagram_of_the_spinal_cord_CRUK_046.svg\" property=\"dc:title\">spinal cord<\/a>  &copy;  Cancer Research UK    is licensed under a  <a rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\">CC BY-SA (Attribution ShareAlike)<\/a> license<\/li><\/ul><\/div>","protected":false},"author":1076,"menu_order":5,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["j-gordon-betts-xxp6oozdgm","kelly-a-young-b1bjkh8ncy-yutl7dqqjv","james-a-wise-oouiyvzss6-eyteble7py","eddie-johnson-sztuysjpin-8bz8zd3gz0","brandon-poe-fjzinvjayf-j8fjw2ni6s","dean-h-kruse-3a9nnuhaym","oksana-korol-1jgnlzwovs-cs2f0d5oko","jody-e-johnson-gmyqec8nhu-y4rakvwrep","mark-womble-oqasblbzan-mgykbeyoow","peter-desaix-cgobjrlxm6-gyduxmdxxe"],"pb_section_license":""},"chapter-type":[],"contributor":[260,278,290,317,339,355,371,401,447,464],"license":[],"class_list":["post-7641","chapter","type-chapter","status-publish","hentry","contributor-brandon-poe-fjzinvjayf-j8fjw2ni6s","contributor-dean-h-kruse-3a9nnuhaym","contributor-eddie-johnson-sztuysjpin-8bz8zd3gz0","contributor-j-gordon-betts-xxp6oozdgm","contributor-james-a-wise-oouiyvzss6-eyteble7py","contributor-jody-e-johnson-gmyqec8nhu-y4rakvwrep","contributor-kelly-a-young-b1bjkh8ncy-yutl7dqqjv","contributor-mark-womble-oqasblbzan-mgykbeyoow","contributor-oksana-korol-1jgnlzwovs-cs2f0d5oko","contributor-peter-desaix-cgobjrlxm6-gyduxmdxxe"],"part":7631,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters\/7641","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/users\/1076"}],"version-history":[{"count":8,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters\/7641\/revisions"}],"predecessor-version":[{"id":9484,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters\/7641\/revisions\/9484"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/parts\/7631"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapters\/7641\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/media?parent=7641"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/pressbooks\/v2\/chapter-type?post=7641"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/contributor?post=7641"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathology\/wp-json\/wp\/v2\/license?post=7641"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}