The Muscles of the Cranium

Epicranial Aponeurosis also referred to as the Galea Aponeurotica or the aponeurosis epicranialis is a broad tendon and is the intermediate section of the occipitofrontalis muscle. It runs from the superior portion of the frontal bone and covers the parietal bones to the lambdoid suture. It is in between the frontalis muscle that lies on the frontal bone and the occipitalis muscle that lies on the occipital bone. Occiptalis muscle, frontalis muscle, and epicranial aponeurosis are collectively known as occipitofrontalis muscle. Together they draw the eyebrows up and wrinkle the forehead. The frontal belly, as seen above, originates on the epicranial aponeurosis and inserts on the skin of the eyebrow and forehead. It is innervated by the temporal branches of Cranial Nerve VII, the facial nerve. It gets its blood supply from the frontal branch of the superficial temporal artery, the supra-orbital artery, and the supratrochlear artery. The occipital belly, as seen below, originates on the superior nuchal line of the occipital bone and inserts on the epicranial aponeurosis. It is innervated by the posterior auricular nerve, which arises from Cranial Nerve VII, the facial nerve. The occipital artery and posterior auricular artery supply the occipital body with blood. They both play a role in elevating the eyebrows, wrinkling the forehead, and moving the scalp. The frontal belly furrows the brow and the occipital belly unfurrows the brow.

Temporoparietalis originates on the fascia superior to the auricule and inserts anterolateral epicranial aponeurosis. Temporoparietalis draws the epicranial aponeurosis towards the front of the cranium. It is innervated by the temporal branches of Cranial Nerve VII, the facial nerve. It is supplied by the superficial temporal artery and the posterior auricular artery.

The temporalis muscle originates on the temporal fossa of the temporal bone. It inserts on the ramus and coronoid process of the mandible. The vertical part elevates the mandible and the horizontal part plays a part in retracting the mandible and chewing. It is innervated by the anterior branch of the deep temporal nerve and the posterior branch of the deep temporal nerve. The superficial temporal artery, the maxillary artery, and the posterior deep temporal artery supplies temporalis with blood.

SUPRAHYOID AND INFRAHYOID MUSCLES
The suprahyoid and infrahyoid muscles of the neck, except hypoglossus, will perform at least one of the 4 movements: elevation, depression, protrusion, and retraction. The movements in combination with each other can perform complex movements such as swallowing and phonation. The corresponding muscles on both sides of the neck contract together to achieve their desired outcome. 

SUPERFICIAL ANTERIOR MUSCLES OF THE NECK

The two superficial muscles of the anterior neck, platysma, and sternocleidomastoid, contribute to 4 main actions: cervical spine flexion, lateral flexion of the cervical spine, cervical spine rotation, and depression/stabilization of the Mandible. The right and left sternocleidomastoid muscles can contract individually to rotate the cervical spine or flex laterally. When they contract together, neck flexion occurs.

MUSCLES SURROUND THE LARYNX

The muscles surrounding the larynx either insert or originate on the laryngeal skeleton or the hyoid bone. This means that these muscles aid in swallowing and positioning the vocal cords. 

INTRINSIC MUSCLES OF THE THYROID CARTILAGE

The intrinsic muscles of the larynx are deep to the thyroid cartilage and the median thyrohyoid ligament. The actions of these muscles dictate the voice. 

The internal and external thyro-artyenoid muscles change the vocal pitch by either contracting or relaxing. In isolation, the contraction of these muscles lowers the resonant frequency of the vocal folds.

POSTERIOR CERVICAL MUSCLES

Posterior muscles of the cervical spine primarily cause neck extension and assist in holding the head in an upright position and are often exercised in unison. All muscles have mirror images on the left and right side of the neck and when both are activated at the same time, the head and neck will move as indicated in the table below. However, when used separately, each muscle can move the head in a lateral motion (ipsilateral, same side of the body) with the angle depending on points of origin and insertion.

In the table below muscles are grouped by their location (superficial to deep, medial to lateral and superior to inferior) and function. The Trapezius (truh-pee-zee-uh-s) and Levator Scapula (see Figure below) are relatively superficial and both cause neck movement as well as the elevation of the scapula.

The trapezius is a vast muscle and extends from the skull to lower thoracic spine. Functionally the trapezius can be divided into Descending Portion (upper), Transverse Portion (central, laterally stretching) and Ascending Portion (lower). In the table below, we are looking at the Descending Portion of the Trapezius (pars descendens musculi trapezii), please click here for more on the central and lower portions.

When activated, the descending trapezius causes neck extension and hyper-extension, and with activation on one side, the descending trapezius can cause lateral neck flexion as well as shoulder elevation.

Figure. Posterior Cervical Muscles Superficial and Mid-Layers

Figure. Posterior Cervical Muscles Deep Layers. (See Below for Spinal Muslces)

Table 1: Overview of Cervical Muscles from Superficial to deep, medial to lateral and superior to inferior. (For deep cervical spine muscles, click here); PDF File of Table

Below is an image giving perspective on how the many muscles of the head attach to the skull. Some of these groupings include muscles for movement of the head and neck, for mastication (chewing), and for some facial movements.

Figure X. Muscle attachment points on the inferior surface of skull, mandible removed (Norma basalis). Groupings of muscles with nerves noted. n.= nerve, m.= muscle (singular), mm.= muscles (plural)

Add to your learning of the muscles that move the head and neck:        https://www.getbodysmart.com/neck-muscles

Deep muscles associated with the cervical region

Intervertebral muscles: The intervertebral muscles main function is to provide motion to the spine. Please refer to Table 1 for specific Origins, Insertions, Actions, and Innervations, of the intervertebral muscles.

Cervical interspinales: In the cervical region the interspinales muscles are the most distinct which consist of 6 pairs. They are found between the spinous processes of the vertebrae. The shape is also small narrow bundles. In the cervical region, they range from the inferior part of the axis’s spinous process down to the interspinales muscles between C7 and T1. In the thoracic region, they are found between T1-T2, T11-T12 and sometimes T2-T3. In the lumbar region, interspinales muscles are found between all the lumbar vertebrae, and sometimes between T-12-L1 and L5-S1.

                         Figure 7: Cervical Intervertebral muscles

Cervical intertransversarii: In the cervical region the intertransversarii muscles are small muscles placed between the transverse processes of vertebrae. These muscles also span most of the spinal column but do not appear between thoracic vertebrae T1-T9. These muscles have seven pairs. There is an anterior and posterior intertranserverarii between each transverse process and are separated by a cervical nerve that runs between each intertransversarii.

Mutifidus muscles: In the cervical region the multifidus muscles are long and thin muscles that are found on the articular processes of the bottom 4 vertebrae. The multifidus muscles span nearly the entire length of the vertebral column from the sacrum to the axis. They are very thin muscles that fill up the groove between the spinous processes of vertebrae. They play an important role in stabilizing joints within the spine. The multifidus muscles are bilateral in nature and span three joint segments.

Rotatores group: (rotatores brevis, longus, capitis, thoracis, and lumborum): In the cervical region that rotatores muscles run up and down the spine and lie beneath the multifidus muscles. The rotatores muscles include the rotatores capitis, rotatores cervicis (brevis and longus), and rotatores thoracis. At the cervical level and lumbar level, the rotatores may not be as obviously present and may be represented by a deeper bundle of tissues like the multifidus muscles. The Rotatores muscles are small and quadrilateral in shape and are also are involved in proprioception and postural control.

Deep suboccipital and anterior cervical muscles

Suboccipital muscles: The suboccipital muscles in the cervical region are named according to their position below the occipital bone. Their primary function is to stabilize the head and neck. Please refer to Table 2 below for specific Origins, Insertions, Actions, and Innervations of the suboccipital muscles and the deep anterior cervical muscles Longus Colli and Longus Capitis.

Rectus capitis posterior minor: The rectus capitis posterior minor is a postural muscle that acts at the atlanto-occipital joint and that monitors that position of the head. It is considered to be a sensory organ as well as a muscle that extends the head and neck.

                                  Figure 8: Suboccipital cervical muscles

Rectus capitis posterior major: The rectus capitis posterior major muscle acts at the atlanto-occipital joint allowing for extension and rotation of the head. This muscle forms the superior part of the suboccipital triangle.

Obliquus capitis superior: The obliquus capitis superior muscle is a small muscle that forms the lateral part of the suboccipital triangle. It is deep to the trapezius

Obliquus capitis inferior: The obliquus capitis inferior muscles are the larger muscle in this group of two muscles. This muscle forms the inferior part of the suboccipital triangle. It is also deep to the trapezius and semispinalis capitis. Although the muscles named “capitis” it doesn’t actually connect to the cranium.

Deep anterior cervical muscles

Longus Colli: The longi colli muscles are made up of three parts (the superior oblique portion, the medial vertical portion, and the inferior oblique portion). It is found on the anterior part of each vertebra between the atlas and third thoracic vertebrae. This muscle is broad in the middle and narrow at either end. These muscles are often injured in rear whiplash accidents (This will be covered further in the common injury section).

                              Figure 9: Deep anterior cervical muscles

Longus capitis: The longus capitis is broad at the superior end and narrow below where it attaches to the tubercles of the anterior transverse processes.

Table 1: Cervical Spine Intervertebral Muscles

Table 2: Deep suboccipitals and deep anterior cervical muscles