{"id":239,"date":"2018-08-27T14:34:37","date_gmt":"2018-08-27T18:34:37","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/thescienceofhumanpotential\/?post_type=chapter&p=239"},"modified":"2021-02-18T15:10:27","modified_gmt":"2021-02-18T20:10:27","slug":"the-nervous-system-connecting-sensation-and-movement","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/thescienceofhumanpotential\/chapter\/the-nervous-system-connecting-sensation-and-movement\/","title":{"raw":"The Nervous and Endocrine Systems","rendered":"The Nervous and Endocrine Systems"},"content":{"raw":"

The Nervous System: Connecting Sensation and Movement<\/strong><\/h2>\r\nAs we consider the human genotype, we will start by providing an overview of the [pb_glossary id=\"2843\"]nervous system[\/pb_glossary] (see Figure 2.7), those structures which transmit information regarding external and internal stimulation and coordinate behavior.\r\n\r\n \r\n\r\n\"Datoteka:NSdiagram.svg\"\r\n

Figure 2.7\u00a0 Overview of human nervous system<\/em><\/p>\r\n \r\n\r\nhttps:\/\/www.youtube.com\/watch?v=R0X-cFdUv3o\r\n\r\nThe [pb_glossary id=\"3366\"] central nervous system [\/pb_glossary], consisting of the brain and spinal cord, organizes and interprets information received from the peripheral nervous system and initiates responding. The [pb_glossary id=\"2844\"]somatic division of the peripheral nervous system[\/pb_glossary] responds to sensory information originating outside the body and stimulates the skin, joints, and skeletal muscles. This type of behavior is often considered voluntary. The [pb_glossary id=\"2845\"]autonomic nervous system[\/pb_glossary] governs the activity of the smooth muscles and glands internal to the body involved in circulation, respiration, and digestion (see Figure 2.8). This type of activity is often considered involuntary. The [pb_glossary id=\"2846\"] sympathetic [\/pb_glossary] division results in arousal under stressful or dangerous conditions as the body is prepared for \u201cfight or flight.\u201d The [pb_glossary id=\"2847\"] parasympathetic [\/pb_glossary] division calms the body upon removal of the stress or danger.\r\n\r\n \r\n\r\n\"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/archive\/c\/c5\/20160307081502%21The_Autonomic_Nervous_System.jpg\"\r\n

Figure 2.8\u00a0 The autonomic nervous system<\/em><\/p>\r\n\r\n

Making the Physical Connections: The Neuron<\/h3>\r\nEven very simple animals require some way of connecting environmental input with behavioral output. Specialized nerve cells called [pb_glossary id=\"2848\"]neurons [\/pb_glossary]are required to respond to external and internal stimulation (i.e., sensory neurons) and carry information to parts of the body capable of responding (i.e., motor neurons). A third type of cell referred to as an [pb_glossary id=\"2849\"] interneuron [\/pb_glossary] connects nerve cells to each other. Nervous systems consist of these types of specialized neurons and range in size from a few hundred nerve cells in worms to approximately 100 billion nerve cells in humans. Neurons are capable of transmitting information electrically and chemically. Figure 2.9 portrays the major parts of a neuron. [pb_glossary id=\"2850\"]Dendrites [\/pb_glossary]are small branches which can connect to nearby neurons. A single [pb_glossary id=\"2851\"]axon[\/pb_glossary] can extend in length up to about a meter in humans and connect to the dendrites of more distant neurons. For example, a neuron could connect the spinal cord to a foot.\r\n\r\n\"\"\r\n

Figure 2.9\u00a0 The neuron<\/em><\/p>\r\n \r\n\r\nhttps:\/\/www.youtube.com\/watch?v=1bC0FG6a0W0\r\n\r\nNerve cells \u201cfire\u201d (i.e., achieve their electrical [pb_glossary id=\"2853\"]action potential[\/pb_glossary]) according to an [pb_glossary id=\"2854\"]all-or-none principle[\/pb_glossary]. That is, either the cell is totally activated or not at all. Increasing the intensity of stimulation does not increase the likelihood of a nerve responding. Rather, it increases the nerve\u2019s rate of firing (i.e., frequency over time). For example, as a lamp becomes brighter, this does not increase the likelihood of a receptor cell in your eye firing. Rather, it increases the frequency with which the receptor cell fires. Nerves can fire at rates as high as a thousand times per second.\r\n

Making Chemical Connections: Neurotransmitters<\/h3>\r\nThe chemical exchange between neurons occurs at [pb_glossary id=\"2855\"]synapses[\/pb_glossary], the small spaces separating the dendrites and axon endings (see Figure 2.10).\r\n\r\n\"\"\r\n

Figure 2.10\u00a0 The synapse<\/em><\/p>\r\n \r\n\r\nThe first nerve cell releases chemical [pb_glossary id=\"2856\"]neurotransmitters[\/pb_glossary] that can bind with receptors in the second neuron. The exchange can result in [pb_glossary id=\"2857\"]excitation[\/pb_glossary] or [pb_glossary id=\"2858\"]inhibition[\/pb_glossary], depending upon the type of receptor activated. Figure 2.11 lists the major neurotransmitters along with their roles in the body.\r\n\r\n\"File:DopamineNorepinephrineSerotoninVennDiagram.png\"\r\n

Figure 2.11\u00a0 The major neurotransmitters<\/em><\/p>\r\n\u00a0<\/span>\r\n\r\n[pb_glossary id=\"2859\"]Psychoactive drugs[\/pb_glossary] can affect mood, thought, and behavior. Most achieve these effects by impacting upon neurotransmitters and synaptic connections. In Chapter 11 (Maladaptive Behavior), we will consider the use of psychoactive drugs in the treatment of depression and schizophrenia.\r\n

The Brain<\/strong><\/h2>\r\nFor literal and figurative reasons, it is tempting to refer to the human brain as evolution\u2019s crowning achievement. After all, the brain sits atop our nervous system and enables our most complex overt and covert behaviors. Your thoughts, your feelings, all the complex things you do, would not be possible without this organ housed inside your skull on top of your head.\r\n\r\nThe human brain is similar in construction to the brains of other mammals but much larger in comparison to the size of our bodies. Without the increase in brain size occurring during human evolution it would not matter if we inherited the physical structures necessary to speak and create tools. This potential would never be realized. Manhattan would still look the same as it did 400 years ago. We are now using our remarkable brain to study itself. The United States government declared the 1990s as the \u201cDecade of the Brain\u201d and much progress has been made in understanding how the brain operates. President Barack Obama of the United States declared \u201cThe BRAIN (Brain Research through Advancing Innovative Neurotechnologies) Initiative\u201d in 2013, hoping to advance this knowledge.\r\n\r\nThere are many ways of describing the brain in terms of its structure (i.e., anatomy) or function (i.e., parts operating together in producing a specific effect). Figure 2.12 shows the major parts of the human brain.\u00a0 The [pb_glossary id=\"2860\"]prefrontal cortex[\/pb_glossary] is involved in the higher human cognitive functions including attention, perception, thinking, memory, language and consciousness.\r\n\r\n \r\n\r\n\"Human\r\n

Figure 2.12\u00a0 Human brain<\/em><\/p>\r\n \r\n\r\nThe brain is an adaptive organ connecting sensation with movement. Besides the primary somatosensory area in the [pb_glossary id=\"2863\"]parietal lobe[\/pb_glossary], sensory areas include the [pb_glossary id=\"2861\"]occipital lobe[\/pb_glossary] for vision and [pb_glossary id=\"2862\"]temporal lobe[\/pb_glossary] for hearing. Besides the primary motor area at the rear of the [pb_glossary id=\"2865\"]frontal lobe[\/pb_glossary], motor areas include the brain stem and spinal cord. The rest of the cortex is referred to as association areas and is dedicated to perception and cognition. It is the size and structure of this area which expanded enormously as humans evolved and enabled us to not only survive but to transform the human condition.\r\n\r\nA human brain weighs about three pounds and feels \u201csquishy\u201d (something like gelatin). The cerebral cortex covers most of the brain and is comprised of nerve fibers folded in such a manner (called [pb_glossary id=\"3370\"] convolutions [\/pb_glossary]) to increase the amount of surface area in the total space. There are two symmetrical halves often referred to as the left brain (or hemisphere) and right brain (or hemisphere). The two halves are connected by the [pb_glossary id=\"2864\"]corpus callosum[\/pb_glossary], a thick network of nerve fibers enabling the two sides to communicate. The left side of the brain connects to the right side of the body and vice versa. Certain activities appear more characteristic of one side than the other (see Figure 2.13). These distinctions are referred to as [pb_glossary id=\"3372\"] lateralization [\/pb_glossary]. Despite the different emphases, both sides usually act in concert in carrying out these activities (Toga & Thompson, 2003).\r\n\r\n \r\n\r\n\"File:Brain\r\n

Figure 2.13\u00a0 Brain lateralization<\/em><\/p>\r\n \r\n\r\nMost of the expansion in the size of the human brain occurred in the frontal lobe. This part of the brain is involved in self-control, described in Chapter 1, and in abstract thought and problem-solving, described in Chapter 7. The small occipital lobe is dedicated to vision, described in Chapter 3. At the borders of the frontal and parietal lobes is a deep fissure (the [pb_glossary id=\"3374\"] central sulcus [\/pb_glossary]) where large strips of neural tissue dedicated to sensation (the primary somatosensory cortex) and movement (the primary motor cortex) meet. The temporal lobe is primarily involved with memory and language, described in Chapter 6. The parietal lobe is involved with sensation originating in the skin, muscles, and joints.\r\n\r\n \r\n\r\nhttps:\/\/www.youtube.com\/watch?v=9UukcdU258A\r\n

The Endocrine System: Hormonal Regulation<\/strong><\/h2>\r\nThe [pb_glossary id=\"2866\"]endocrine system[\/pb_glossary] consists of ductless glands that secrete [pb_glossary id=\"2868\"]hormone[\/pb_glossary]s (chemical messengers) into the blood stream to maintain homeostasis. It exists in all animals having a nervous system. Like the nervous system, the endocrine system enables communication between different parts of the body.\r\n\r\nThe endocrine system maintains homeostasis through a series of feedback loops, the most important of which are controlled by the [pb_glossary id=\"3377\"] hypothalamus [\/pb_glossary] interacting with the[pb_glossary id=\"2867\"] pituitary gland[\/pb_glossary]. Often, the hypothalamus stimulates the pituitary gland to secrete an activating hormone to another gland. If a signal is transmitted to a gland, indicating low blood levels of its hormone, it secretes additional amounts into the blood stream. Once the optimal level is restored, the gland stops secreting the hormone. In this way the endocrine system plays its critical role in metabolism, growth, sexual development, reproduction, and responding to stress. Figure 2.14 shows the locations of the major glands.\r\n\r\n \r\n\r\n\"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/9\/9d\/Illu_endocrine_system_New.png\"\r\n

Figure 2.14 Major gland locations<\/em><\/p>\r\n \r\n\r\nThe [pb_glossary id=\"2867\"]pituitary gland[\/pb_glossary] connects to the base of the hypothalamus and is often referred to as the master gland since it secretes several different hormones impacting upon other glands involved in maintaining homeostasis. Hormones secreted by the pituitary control growth, blood pressure, water balance, temperature regulation, and pain relief. The [pb_glossary id=\"2869\"]pineal gland[\/pb_glossary] is located at the base of the cortex between the two hemispheres and next to the thalamus. It influences the sleep-wake cycle by secreting the hormone melatonin when stimulated by light. The [pb_glossary id=\"2870\"] thyroid gland [\/pb_glossary] is located in the neck by the larynx (voice box) and affects metabolism by controlling the rate at which energy is expended. It is one of the glands under the control of the pituitary which secretes thyroid-stimulating hormone (TSH). The pituitary in turn is controlled by the hypothalamus through the release of thyrotropin-releasing hormone (TRH). Humans usually have four [pb_glossary id=\"3381\"] parathyroid glands [\/pb_glossary] located on the rear surface of the thyroid gland. These control the amount of calcium in the blood and bones. The [pb_glossary id=\"2871\"] thymus [\/pb_glossary] is located below the thyroid gland in the middle of the chest. It is an important part of the immune system. Damage, such as through contracting the HIV virus, can result in increased susceptibility to infection (e.g., AIDS). The [pb_glossary id=\"2872\"] spleen [\/pb_glossary] lies toward the bottom of your rib cage and is involved in the removal of red blood cells. The [pb_glossary id=\"2873\"] adrenal glands [\/pb_glossary] are located on top of the kidneys and through the release of epinephrine (adrenalin) are significantly involved in the body\u2019s \u201cfight-or-flight\u201d response in reaction to danger. The [pb_glossary id=\"2874\"] sex glands [\/pb_glossary] (ovaries for the female and testes for the male) secrete hormones controlling the development of the reproductive sex organs and secondary sex characteristics (e.g., pubic hair) during puberty.\r\n\r\n \r\n\r\nAttributions<\/strong>\r\n\r\nFigure 2.7 \"Human nervous system\"<\/a> is licensed under CC BY-SA 3.0<\/a><\/span><\/strong>\r\n\r\nFigure 2.8 \"Autonomic nervous system\"<\/a> by Geo-Science-International<\/a> is licensed under CC BY 1.0<\/a><\/span><\/span><\/strong>\r\n\r\nFigure 2.9 \"The neuron\"<\/a> is licensed under CC BY-SA 4.0<\/a><\/span><\/span><\/strong>\r\n\r\nFigure 2.10 \"Synapse\"<\/a> by Dwindrim<\/a> is licensed under CC BY-SA 1.0<\/a><\/span><\/strong>\r\n\r\n<\/span>Figure 2.11 \"Neurotransmitters\"<\/a> is licensed under CC BY-SA 3.0<\/a><\/span><\/strong>\r\n\r\n<\/span>Figure 2.12 \"Human brain\"<\/a> by Bruce Blaus<\/a> is licensed under CC BY 3.0<\/a><\/span><\/strong>\r\n\r\nFigure 2.13 \"Brain lateralization\"<\/a> is licensed under CC BY-SA 3.0<\/a><\/span><\/strong>\r\n\r\nFigure 2.14 \"Major endocrine glands\"<\/a> by US Government<\/a> is in the Public Domain, CC0<\/a><\/span><\/span><\/strong>\r\n\r\n \r\n\r\n \r\n\r\n ","rendered":"

The Nervous System: Connecting Sensation and Movement<\/strong><\/h2>\n

As we consider the human genotype, we will start by providing an overview of the nervous system<\/a> (see Figure 2.7), those structures which transmit information regarding external and internal stimulation and coordinate behavior.<\/p>\n

 <\/p>\n

\"Datoteka:NSdiagram.svg\"<\/p>\n

Figure 2.7\u00a0 Overview of human nervous system<\/em><\/p>\n

 <\/p>\n