Spinalis

The spinalis (Latin: musculus spinalis) is one of the muscles forming the erector spinae - a muscle group of the deep back muscles. The other two are the longissimus and iliocostalis. The spinalis is the most medial of the three erector spinae muscles.

The spinalis mainly originates from and inserts into spinous processes of cervical and thoracic vertebrae, but its upper part also attaches to the occipital bone.

This muscle`s actions provide extension and lateral flexion of the cervical and thoracic parts of the spine.

The spinalis is innervated by the lateral branches of the posterior rami of the spinal nerves.

It receives blood supply via the dorsal branches of the posterior intercostal arteries, the deep cervical artery, and the muscular branches of the vertebral artery. 

Thie spinalis is formed of three parts: capitis, cervicis, and thoracis.

Spinalis capitis

Origin

The spinalis capitis originates from the spinous processes of the C7 to T1 vertebrae.

Insertion

It inserts into the occipital bone, near its midline.

Action

Upon bilateral contraction, the spinalis capitis extends the head and neck, while upon unilateral contraction, it provides lateral flexion of the cervical spine to the same side (ipsilaterally).

Innervation

The muscle is innervated by the lateral branches of the posterior rami of the spinal nerves.

Spinalis cervicis

Origin

The spinalis cervicis originates from the spinous processes of the C7 to T1 vertebrae and the nuchal ligament.

Insertion

The fibers of the spinalis cervicis insert into the spinous processes of the C2 to C4 vertebrae.

Action

Upon bilateral contraction, the spinalis cervicis extends the cervical spine, while upon unilateral contraction, it provides lateral flexion of the cervical spine to the same side (ipsilaterally).

Innervation

The muscle is innervated by the lateral branches of the posterior rami of the spinal nerves.

Spinalis thoracis

Origin

The spinalis thoracis arises from the spinous processes of the T11 - L2 vertebrae.

Insertion

The thoracic part of the spinalis muscle inserts into the spinous processes of the T2 to T8 vertebrae.

Action

A bilateral contraction of the spinalis thoracis provides an extension of the thoracic spine, while a unilateral contraction provides lateral flexion of the thoracic spine to the same side (ipsilaterally).

Innervation

The muscle is innervated by the lateral branches of the posterior rami of the spinal nerves.