Semispinalis Cervicis

What is the Semispinalis Cervicis

Semispinalis cervicis, also known as semispinalis colli,  is a relatively small muscle belonging to the group of intrinsic back muscles. It is one of the three semispinalis muscles that constitute the deep layer of the intrinsic back muscles, along with the multifidus and rotatores muscles. Located in the neck and upper back region between the shoulder blades, it is one of the muscles that help with the movements of the head and neck.

Anatomy

Location and Attachments

Origin	Transverse processes of T1 to T6 vertebrae
Insertion	Spinous processes of C2 to C5 vertebrae

Origin

The muscle originates via narrow tendons from the transverse processes of the 1st to 6th thoracic vertebrae. As a relatively small muscle, its tendons travel upward as thin muscular fascicles, crossing the thoracic spine to reach the cervical spine.

Insertion

Once the fascicles reach the cervical spine, they insert into the posterior aspect of the spinous processes of the 2nd to 5th cervical vertebrae. The muscle fibers originating from T1 extend upward to insert into C2 (axis), while fibers originating from the successive thoracic vertebrae insert progressively lower on the cervical spine, with those from T6 inserting into C5. Conversely, the fascicle extending from T1 to C2 is often the thickest and most muscular part of the muscle.

Relations With Surrounding Muscles and Structures

The semispinalis cervicis is covered on its dorsal and lateral sides by the semispinalis capitis. The two create a muscular layer that covers the deeper intrinsic back muscles. It also has the splenius muscles lying superficially.

On the deep side, the muscle lies superficial to the multifidus muscles in the cervical and thoracic regions. Medially, the muscle is adjacent to the spinous processes of the cervical and thoracic vertebrae.

Function

Action

Extending, tilting, and rotating the head and neck

Semispinalis cervicis works with the semispinalis capitis and thoracis muscles to help with movements of the head and neck. When the muscle contracts bilaterally, or on both sides, it helps with extending the head and cervical spine – as you would do to look at something overhead. When it contracts unilaterally or only on one side, it assists in tilting the head to the same (ipsilateral) side and rotating the head and neck to the opposite (contralateral) side. 

Innervation

Nerve

Dorsal rami of the lower cervical nerves

The semispinalis cervicis muscle is innervated by the medial branches of the dorsal rami from the upper cervical spinal nerves, specifically C3 to C6.

Blood Supply

Artery

Occipital, vertebral, and deep cervical arteries

The muscle’s blood supply comes from the descending branch of the occipital artery, with the vertebral and cervical arteries being other key contributors. The dorsal rami of the upper posterior intercostal arteries provide additional blood supply.