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Spinalis Muscle Anatomy

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Origin
  • Spinalis capitis: spinous processes of C6-T2 vertebrae or the nuchal ligament
  • Spinalis cervicis: spinous processes of C7-T1 vertebrae or the nuchal ligament
  • Spinalis thoracis: spinous processes of T11-L2 vertebrae
Insertion
  • Spinalis capitis: the 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 the cervical and thoracic spine
  • Unilateral contraction: lateral flexion of the trunk and neck at the cervical and thoracic spine
Nerve
  • Posterior rami of the lumbar, thoracic, and cervical spinal nerves
Artery
  • Dorsal branches of posterior intercostal arteries
  • Deep cervical artery
  • Vertebral artery
  • Dorsal branches of lumbar arteries
Last updated: Estimated Reading Time: 11 min

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 longissimus. The erector spinae muscles are deep muscles of the back that run in a vertical direction, parallel to the vertebral column. The spinalis is the most medial of these muscles and blends with the longissimus thoracis laterally.[1]

The spinalis muscle is also composed of three sections: the capitis, cervicis, and thoracis. The capitis is the most superior section, the cervicis is in the middle, and the thoracis is the most inferior.[1] The spinalis cervicis and capitis portions also vary between people. Some people may have cervicis and capitis portions that are blended with the semispinalis muscle, some people may have distinct cervicis and capitis portions that do not blend into the semispinalis muscle, and some people may be missing one or both of these muscle portions entirely, or a portion may be present on just one side. More details about this can be found in the Origin & Insertion section below.[2]

spinalis muscle
Here, we can see the spinalis muscle by itself.
spinalis sections highlighted
This picture shows the different sections of the spinalis muscle. The capitis is highlighted in yellow, the cervicis in purple, and the thoracis in green.
erector spinae muscles
Displayed here are the erector spinae muscles, without any color coding or labels.
erector spinae muscle with the iliocostalis, longissimus and spinalis labeled
Here, we can see each of the erector spinae muscles highlighted in different colors for clarity. The spinalis is highlighted in yellow, the longissimus in purple, and the iliocostalis in green.

Origin & Insertion

The spinalis muscle’s origins 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 vertebrae T2-T8.[1]

spinalis thoracis origin and insertion points
In this image, we can observe the origin and insertion points of the spinalis thoracis muscle. The origins are highlighted in red, while the insertions are colored blue.
Note: For the sake of simplicity, only the left side of the muscle is displayed here. However, the origins and insertions are duplicated on the right-hand side as well.

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.[2]

spinalis cervicis section origin and insertion
This image shows the origin and insertion sites of the spinalis cervicis section. The red markings indicate the muscle’s origins, while the blue markings represent its insertions.
Note: For the sake of simplicity, only the left side of the muscle is displayed here. However, the origins and insertions are duplicated on the right-hand side as well.
nuchal ligament
This image displays the nuchal ligament, which serves as a point of origin for the spinalis cervicis and spinalis capitis sections. The nuchal ligament is located at the back of the neck and extends from the external occipital protuberance to the seventh cervical vertebra.

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 entirely absent in 70.3% of people.[2]

spinalis capitis origin and insertion
Displayed here are the origin and insertion points of the spinalis capitis muscle. The muscle’s origins are marked in red, and its insertions are marked in blue.
Note: For the sake of simplicity, only the left side of the muscle is displayed here. However, the origins and insertions are duplicated on the right-hand side as well.
spinalis origins and insertions
Here, we can see the origins and insertions of the spinalis thoracis, cervicis, and capitis, with origins highlighted in red and insertions in blue. The capitis has a yellow highlight around it, the cervicis has a purple highlight, and the thoracis has a green highlight.
Note: For the sake of simplicity, only the left side of the muscle is displayed here. However, the origins and insertions are duplicated on the right-hand side as well.

Actions

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.[3]

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.[3]

The cervicis 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.[3]

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.[3]

Image of a person demonstrating the movement of trunk extension.
This image shows an example of trunk extension, which involves arching or bending the spine, torso, or back backward. The opposite of trunk extension is trunk flexion. The spinalis thoracis section is involved in trunk extension. The extension is the result of a bilateral contraction.
Image of a person demonstrating the movement of trunk lateral flexion.
This image demonstrates trunk lateral flexion, which involves bending the torso to the side. The spinalis thoracis section is involved in trunk lateral flexion. The lateral flexion is the result of a unilateral contraction.
Image of a person demonstrating the movement of neck extension.
This image demonstrates neck extension, which involves bending the neck backward. The opposite of neck extension is neck flexion. The spinalis cervicis and capitis sections are involved in neck extension. The extension is the result of a bilateral contraction.
Image of a person demonstrating the movement of neck lateral flexion.
This image demonstrates neck lateral flexion, which involves bending the neck to the side. The spinalis cervicis and capitis sections are involved in neck lateral flexion. The lateral flexion is the result of a unilateral contraction.

Innervation

The spinalis muscle is innervated segmentally by the posterior rami of spinal nerves. This means that the nerve supply comes from spinal nerves close to the vertebral levels where each part of the muscle is located, rather than from one single named peripheral nerve. As part of the erector spinae group, the spinalis receives branches from posterior rami across the cervical, thoracic, and upper lumbar regions.[3,4]

The spinalis thoracis is supplied mainly by posterior rami from thoracic and upper lumbar spinal nerves. The spinalis cervicis and spinalis capitis are supplied by posterior rami from cervical and upper thoracic spinal nerves. These posterior rami also supply other intrinsic back muscles, which is why the spinalis is usually described as having a regional, segmental nerve supply.[3,4]

spinal nerves anatomy
Here, we can see a cross-section of a lumbar vertebra. One of the labeled parts is the ‘dorsal ramus’, which is also known as the ‘posterior ramus’. Each segment of the erector spinae muscles receives innervation from the posterior ramus of the corresponding spinal nerve. In other words, the part of the muscle aligned with a specific spinal segment is innervated by that specific spinal nerve’s posterior ramus.

Blood Supply

The blood supply of the spinalis muscle is regional because the muscle extends through the cervical, thoracic, and upper lumbar parts of the back. In the cervical region, it receives muscular branches from vessels such as the vertebral and deep cervical arteries, with possible contribution from descending branches of the occipital artery. In the thoracic region, spinalis thoracis is supplied mainly by dorsal branches of the posterior intercostal arteries. In the lower thoracic and upper lumbar region, dorsal branches of the lumbar arteries can also contribute.[4]

The dorsal branches of the posterior intercostal arteries pass posteriorly toward the deep muscles of the back. Their medial branches supply the spinalis and longissimus thoracis, along with nearby skin. This segmental arrangement means that the spinalis does not rely on a single artery; instead, it receives blood from arteries near the spinal level of each muscle portion.[4]

References

  1. [1] 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/
  2. [2] 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.
  3. [3] Dalley AF, Agur AMR. Moore’s Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
  4. [4] Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Amsterdam: Elsevier; 2021.

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