Semispinalis Muscles

What Are the Semispinalis

The semispinalis group comprises three long, narrow muscles: the capitis, cervicis, and thoracic. They form the deep layer of the intrinsic back muscles along with the multifidus and rotatores. These 5 muscles together form the transversospinales group, one of the most important muscle groups in the human back. 

The semispinalis, located along both sides of the thoracic and cervical spine, play a vital role in the movement of the head, neck, and back.

Names and Basic Anatomy of the Semispinalis Muscles

As is common with most other intrinsic back muscles, the 3 semispinalis are named after their points of insertion. Here’s a comparative overview of each:

Name	Origin	Insertion	Action	Innervation	Blood Supply
Semispinalis Capitis	Articular processes of 4th-7th cervical vertebrae (C4-C7), and transverse processes of 7th cervical to 6th thoracic vertebrae (C7-T6)	On the occipital bone, between the superior and inferior nuchal lines	Extending, tilting, and rotating the head and neck	Dorsal rami of 1st to 5th cervical nerves (C1 to C5)	Occipital artery
Semispinalis Cervicis	Transverse processes of 1st-6th thoracic  vertebrae (T1-T6)	Spinous processes of 2nd-5th cervical vertebrae (C2-C5)	Same as semispinalis capitis	Dorsal rami of the lower cervical nerves (C3 to C6)	Occipital, vertebral, and deep cervical arteries
Semispinalis Thoracis	Transverse processes of 6th-10th thoracic vertebrae (T6-T10 )	Spinous processes of 6th cervical to 4th thoracic vertebrae (C6-T4)	Extending, tilting, and rotating the head, neck, and body trunk	Dorsal rami of cervical and thoracic nerves	Dorsal rami of the posterior intercostal arteries

Semispinalis thoracis, with attachment to the lower thoracic vertebrae, is the only semispinalis muscle that participates in the movement of the entire body trunk.

The sternocleidomastoid muscle at the front of the neck, which helps flex the neck forward to bow your head, is antagonistic to the semispinalis muscles, as they extend the neck to bring the head back to an upright position.