15.9:
Muscles that Move the Head
Multiple neck muscles help to balance the head and facilitate its movement at the atlanto-occipital joint.
For example, the bilateral sternocleidomastoid, or SCM, is a major head flexor along with the suprahyoid and infrahyoid muscles.
Its bellies originate at the sternum and clavicle and insert into the mastoid process of the temporal bone.
When the SCM contracts bilaterally, it helps to bend the head forward. In contrast, unilateral contraction facilitates lateral flexion on the same side or head rotation to the opposite side.
The lateral neck muscles — the anterior, middle, and posterior scalenes — run diagonally along the vertebral column.
They connect the cervical vertebrae to the upper two ribs and also facilitate lateral flexion.
The splenius capitis, a posterior neck muscle, originates from the nuchal ligament and the C7 to T3 spinous processes and inserts onto the occipital and temporal bones.
When contracted bilaterally, it aids head extension, whereas unilateral contraction assists lateral flexion and rotation to the same side.
15.9:
Muscles that Move the Head
The muscles that move the head are a dynamic and complex group of structures that work together to facilitate a wide range of head movements, including rotation, flexion, extension, and lateral bending.
The bilateral sternocleidomastoid, or SCM, and the suprahyoid and infrahyoid muscles are significant head flexors. The SCM muscles originate at the sternum and clavicle and attach to the mastoid process of the temporal bone. The SCM contracts bilaterally to bend the head forward, whereas unilateral contraction causes lateral flexion on the same side or head rotation to the opposite side.
The back of the neck is covered by muscles that connect the skull to the spinal column and pectoral girdle. These muscles can be categorized into three layers. The superficial layer includes the trapezius, splenius capitis, and splenius cervicis. The trapezius controls shoulder blade movements and assists in extending and tilting the head backward. The splenius capitis and splenius cervicis, originating from the lower cervical and upper thoracic vertebrae and inserting into the skull and upper cervical vertebrae, respectively, work together to extend the head and neck.
The deep layer includes the cervical transversospinalis muscles, such as the semispinalis capitis, semispinalis cervicis, and multifidus cervicis. These muscles primarily extend from the transverse processes of the vertebrae to the spinous processes of higher vertebrae or the occipital bone. The semispinalis capitis is particularly notable for its role in extending and rotating the head, contributing to the ability to look up and turn the head from side to side.
The deepest layer encompasses the suboccipital muscles, interspinales cervicis, and intertransversarii colli muscles. The suboccipital muscles, located just below the occipital bone, are crucial for fine motor control, aiding in minor adjustments of head position and proprioception — the sense of self-movement and body position.