The semispinalis capitis is the largest of the deep cervical muscles, forming a thick cylindrical mass on either side of the cervical spinous processes beneath the splenius group. It is the primary extensor of the head and upper cervical spine and is tonically active during any upright posture, making it one of the most continuously loaded muscles in the body. The greater occipital nerve pierces through it on its way to the scalp, making semispinalis capitis tightness a cause of greater occipital nerve entrapment.
| Origin | Transverse processes of C7 through T6 and the articular processes of C4 through C6 |
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| Insertion | Between the superior and inferior nuchal lines of the occipital bone |
| Nerve Supply | Posterior rami of the cervical spinal nerves |
| Blood Supply | Deep cervical artery; Occipital artery |
| Actions | Extension of the head; Contralateral rotation of the head; Maintains upright head posture against gravity |
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Its broad origin from thoracic transverse processes allows it to exert a long-lever extension force on the head and neck with significant torque capacity, crucial for maintaining the head erect against gravity during seated and standing work.
Greater occipital nerve entrapment within the semispinalis capitis is a significant cause of occipital headache and scalp hypersensitivity. Sustained semispinalis capitis tension from prolonged forward head posture is a primary contributor to chronic cervicogenic headache. The suboccipital triangle, deep to the semispinalis capitis, contains the greater occipital nerve and vertebral artery.
The semispinalis capitis is palpable as the thick bilateral muscle column immediately lateral to the cervical spinous processes deep to the trapezius, becoming firm during resisted head extension.
Acute injury from whiplash or forced flexion producing deep posterior cervical pain with extension restriction, often involving concurrent greater occipital nerve irritation from muscle swelling within the nerve's penetrating tunnel.
