|Origin||Spinalis capitis: spinous processes of C6-T2 vertebrae or nuchal ligament|
Spinalis cervicis: spinous processes of C7-T1 vertebrae or nuchal ligament
Spinalis thoracis: spinous processes of T11-L2 vertebrae
|Insertion||Spinalis capitis: occiput|
Spinalis cervicis: spinous processes of C2 or C3 vertebrae
Spinalis thoracis: spinous processes of T2-T8 vertebrae
|Action||Bilateral contraction: extension of the trunk and neck (at cervical and thoracic spine)|
Unilateral contraction: lateral flexion of the trunk and neck (at cervical and thoracic spine)
|Nerve||Posterior rami of the lumbar, thoracic, and cervical nerves|
|Artery||Dorsal branches of the posterior intercostal artery, deep cervical artery, muscular branches of vertebral artery|
Location & Overview
The spinalis muscle is situated in the middle and upper back as well as the neck, running parallel to the spine. It plays an important role in extending the back and neck, while also aiding in lateral flexion movements. The spinalis muscle is a member of the erector spinae muscle group. The erector spinae muscles consist of the spinalis, iliocostalis, and the longissimus. The erector spinae muscles are deep muscles of the back which run in a vertical direction, parallel to the vertebral column. The spinalis is the most medial of these muscles and blends with longissimus thoracis laterally.
The spinalis muscle is also comprised of three sections, the capitis, cervices and thoracis. The capitis is the most superior of these sections, the cervices is in the middle, and the thoracis is the most inferior . The spinalis’ cervices and capitis portions also have variations between people. Some people may have a cervices and capitis which is blended with the semispinalis muscle, some people may have a distinct cervices and capitis which does not blend into the semispinalis muscle, and some people may be missing one of both of these muscle portions entirely or it may be present on just one side. More details about this can be found in the origin and insertion section below .
Origin & Insertion
The spinalis muscle’s origin and insertions are different for each section of the muscle. There are also individual variations between people as outlined below:
The spinalis thoracis originates on the spinous processes of T11-L2 and inserts onto the spinous processes of the upper thoracic vertebra of T2-T8 .
The spinalis cervicis muscle originates from the nuchal ligament or the spinous processes of the lower cervical to upper thoracic vertebrae (C7 and T1) and inserts onto the spinous processes of the second or third cervical vertebra. This muscle is distinct and separate from the semispinalis capitis in 46.1% of individuals. However, in 18% of cases, the fibers of the spinalis cervicis are blended with those of the semispinalis cervicis. In such instances, the spinalis cervicis originates from the same location, but the fibers blend with those of the semispinalis cervicis before inserting onto the spinous processes of C2 or C3. In 35.9% of individuals, the spinalis cervicis muscle is entirely absent .
The spinalis capitis muscle originates from the spinous processes of C6 to T2 or the associated nuchal ligament and inserts onto the occiput. This muscle is distinct and separate from the semispinalis capitis in 1% of individuals. However, in 28.7% of cases, the fibers of the spinalis capitis are blended with those of the semispinalis capitis. In such instances, the spinalis capitis still originates from the spinous processes of C6 to T2 or the associated ligamentum nuchae, but the fibers blend with those of the semispinalis capitis before inserting onto the occiput. The spinalis capitis muscle is absent entirely in 70.3% of people .
The actions of the spinalis muscle vary based on which portion is contracting and whether one side or both sides of the muscle contract simultaneously. Unilateral contraction refers to the contraction of one side, while bilateral contraction refers to the contraction of both sides together .
The thoracis section spans from L2 to T2 and affects the vertebrae in this area. Bilateral contraction results in trunk extension, while unilateral contraction causes lateral flexion of the trunk .
The cervices portion, located between T1 and C2/C3, influences the corresponding vertebral region. Bilateral contraction leads to extension of the cervical vertebrae, thereby extending the neck. Unilateral contraction, on the other hand, causes ipsilateral lateral flexion of the neck .
Similarly, the spinalis capitis segment stretches from T2 to the occiput and also affects the cervical vertebrae. Bilateral contraction results in neck extension, while unilateral contraction causes ipsilateral lateral flexion of the neck .
The thoracic portion of the spinalis muscle is innervated by the posterior rami of the thoracic and upper lumbar nerves. The cervicis and capitis portions are innervated by the posterior rami of the cervical and upper thoracic nerves.
The spinalis muscle is supplied with blood by the dorsal branches of the posterior intercostal artery, the deep cervical artery, and the muscular branches of the vertebral artery.
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|↑1, ↑2, ↑4||Henson B, Kadiyala B, Edens MA. Anatomy, Back, Muscles. [Updated 2022 Aug 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537074/|
|↑3, ↑5, ↑6||Greiner TM, Bedford ME, Walker RA. Variability in the human m. spinalis capitis and cervicis: frequencies and definitions. Ann Anat. 2004 Apr;186(2):185-91. doi: 10.1016/S0940-9602(04)80039-6. PMID: 15125051.|
|↑7, ↑8, ↑9, ↑10||Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017.|