Interspinales muscles are short, paired muscles that belong to the deepest layer of the intrinsic muscles of the back. They extend between adjacent spinous processes of the vertebral column.
Even though they span the entire length of the vertebral column, they are only properly developed in the cervical and lumbar spine, whereas in the thoracic spine they are underdeveloped or often completely absent.
Interspinales muscles serve to aid other intrinsic muscles of the back to extend the spine. However, it’s more important role is to stabilize the spine during movement and maintain normal posture of the body.
This article will discuss the anatomy and functions of the interspinales muscles.
Interspinales cervicis: Superior aspect of spinous processes of vertebrae C3-T1
Interspinales thoracis: Superior aspect of spinous process of vertebrae T2, T11 & T12 (variable)
Interspinales lumborum: Superior aspects of spinous processes of vertebrae L2-L5
Interspinales cervicis: Inferior aspect of spinous processes of vertebrae C2-C7
Interspinales thoracis: Inferior aspect of spinous processes of vertebrae T1, T10 & T11
Interspinales lumborum: Inferior aspects of spinous processes of vertebrae L1-L4
|Function||Extension of cervical and lumbar spine|
|Innervation||Posterior rami of spinal nerves|
Interspinales cervicis: vertebral artery, deep cervical artery, occipital artery, transverse cervical artery
Interspinales thoracis: superior intercostal artery, posterior intercostal arteries, subcostal artery
Interspinales lumborum: lumbar arteries
Origin and insertion
The interspinales muscles are small muscles that connect the spinous processes of adjacent spinal vertebrae. They are comprised of paired muscle fascicles, one on each side of the interspinous ligament. The interspinales muscles are divided based on the region of the vertebral column into:
- Interspinales cervicis: consists of six pairs of muscles that originate at the superior aspect of the spinous processes of vertebrae C3-T1, and insert at the inferior aspect of the spinous processes of the cranially adjacent vertebrae C2-C7, respectively.
- Intererspinales thoracis: these muscles are generally underdeveloped or even absent, with only some segments having distinct muscle fascicles. Usually they consist of three pairs of muscles that originate at the superior aspect of spinous processes of vertebrae T2, T11 and T12, and insert at the inferior aspect of the spinous processes of the cranially adjacent vertebrae T1, T10 and T11, respectively.
- Interspinales lumborum: consists of four pairs of muscles that originate at the superior aspects of spinous processes of vertebrae L2-L5, and insert at the inferior aspect of the spinous processes of the cranially adjacent vertebra L1-L4, respectively.
Interspinales comprise the deep layer of the intrinsic muscles of the back. They are found lateral to the interspinous ligament, passing inferiorly on each side of the ligament, and are located medial and deep to the attachments of the multifidus and rotatores muscles, which also belong to the deepest layer of the intrinsic muscles.
Like the other intrinsic muscles of the back, interspinales muscles are innervated by the posterior rami of the respective spinal nerves.
The interspinal muscles are supplied by the dorsal branches of the respective segmentally extending arteries. The supplying arteries are prone to variation, but generally they include:
- Interspinales cervicis: branches of the vertebral artery, deep cervical artery, occipital artery and transverse cervical artery.
- Interspinales thoracis: branches of the superior and posterior intercostal arteries and subcostal artery.
- Interspinales lumborum: branches of the lumbar arteries.
Venous drainage of the interspinales muscles occurs via the corresponding veins of the aforementioned arteries.
The actions of interspinales are not well established. Most authors consider these muscles incapable of generating enough force to produce significant movement of the vertebral column. However, they are thought to assist with extension in the cervical and lumbar spine, and they are best developed in these regions.
Interspinales muscles have a pronounced density of muscle spindles, which are proprioceptors that monitor and adjust muscle tension and posture. Thus they provide stability to the spine, controlling the position of the vertebral column.
To learn more about the anatomy of the dorsal trunk, check out the following resources:
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