Posterior neck muscles

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Major muscles of facial expression and mastication, and neck muscles.

The posterior neck muscles are located on the posterior aspect of the neck and connect the skull to the vertebral column and pectoral girdle. They can be subdivided into three groups: superficial, deep and deepest. 

The superficial layer is composed of the trapezius and the two splenius muscles (capitis and cervicis). The trapezius primarily functions to produce lateral flexion and contralateral rotation of the head if contracting unilaterally, or extension of the head if contracting bilaterally. It also stabilizes and moves the scapula in different directions, depending on which fibers contract. The splenius muscles cause lateral flexion and ipsilateral rotation of the head and neck when contracting unilaterally, or extension of the head and neck when contracting bilaterally.

The deep layer is composed of the transversospinales muscles of the cervical region: semispinalis capitis, semispinalis cervicis and multifidus cervicis. The primary function of this group lateral flexion and contralateral rotation of the head and neck when contracting unilaterally and extension the head and neck when contracting bilaterally.

The deepest layer consists of the suboccipital muscles (rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis superior, obliquus capitis inferior), interspinales cervicis and intertransversarii colli. The primary function of the suboccipital muscles is to produce movements of the head (extension, lateral flexion and rotation) as well as maintaining posture. Due to their small size, the interspinales cervicis and the intertransversarii colli muscles are primarily proprioceptive and stabilizer muscles, however they also assist other muscles in extension and lateral flexion of the neck, respectively.