The primary movements of the head result from the action of paired muscles located in the neck and upper back. These muscles cause flexion, extension and rotation of the neck and head. The primary muscles of head movement are the sternocleidomastoid, splenius capitis, semispinalis capitis, and longissimus capitis muscles. When these paired muscles work on one side they share the function of lateral flexion (bending to one side) or rotating the head. The sternocleidomastoid, when acting in tandem, flexes the head. The other muscles, when both sides are functioning, extend the head. The upper fibers of the trapezius muscle are also weakly active in extension.

Various smaller muscles also share responsibility for these actions. The rectus capitis posterior major and minor, oblique capitis superior, and oblique capitis inferior are very small muscles at the back of the neck and upper back that are considered together as the suboccipital group. In addition there are three other small and deep neck muscles called the rectus capitis anterior, rectus capitis lateralis, and the longus capitis. The name 'capitis' refers to these posterior neck muscles having their common insertion on the occipital bone, which they share with the splenius, semispinalis, and longissimus capitis muscles mentioned above.

Sternocleidomastoid and Trapezius Muscle

The sternocleidomastoid is a muscle on both sides of the neck that arises on the sternum and upper clavicle and inserts on the mastoid process. When one side contracts alone the head is turned to the opposite (ipsilateral) side. When both sides work together the head is flexed. The sternocleidomastoid is also able to raising the sternum when the head is held in a fixed position by other muscles. This assists in forceful respiration, making the muscle and accessory muscle of inspiration. The trapezius muscle is synergistic with the sternocleidomastoid in neck movements and its upper fibers extend the head.

The Capitis Group of Muscles

The splenius capitis is a broad and powerful muscle on each side of the posterior of the neck which originates on the spinous processes of the lower cervical and upper thoracic vertebrae and inserts on the mastoid process. When one side acts singly it produces rotation and lateral flexion of the head. Acting together the muscles extend the head into an upright position. Together with the levator scapula, semispinalis capitus, cerviscus and trapezius muscles it has been called a "checkrein" against forward bending of the head so that it keeps the head from falling forward when one is looking downwards for long periods. Making this muscle very active along with the semispinalis capitus, ceviscus, splenii and trapezi while looking down at a book or working at a computer.

The semispinalis capitis is a broad and sheetlike muscle which originates on the lower cervical and upper thoracic vertebrae and inserts on the occipital bone. This muscle bends or rotates the head to one side when acting unilaterally and extends the head when acting in tandem.

The longissimus capitis muscle is a narrow band that arises on the lower cervical and upper thoracic vetebra and inserts onto the mastoid process. It also has the role of lateral flexion and rotation when acting unilaterally and exension of the head and vertebral column when acting bilaterally.

The rectus capitis anterior and the rectus capitis lateralis both flex the head and help to stabilize the atlantooccipital jont. The longus capitis flexes the head.

The suboccipital group is four tiny muscles on each side of the posterior neck. These muscles form a triangle over the cervical spine and beneath the occipital bone. The groups is made up of the rectus capitis posterior major and minor, oblique capitis superior, and oblique capitis inferior. As a pair the rectus capitis posterior major muscles extend the head and unilaterally rotates it to the same side. The rectus capitis posterior minor muscle only extends the head. The oblique capitis superior extends the head and flexes it laterally and the oblique captitis inferior rotates the first cervical vertebra (C1) on the cranium, known as the atlanto-axial joint.