Semispinalis Capitis O, I, A
Origin: Articular processes of vertebrae C4-C7, transverse processes of vertebrae T1-T6
Insertion: Between superior and inferior nuchal lines of occipital bone
Actions: Extension of the head and cervical spine
Innervation: Descending branches of greater occipital nerve (C2) and spinal nerve C3
Blood Supply: Descending branches of the occipital artery
Primary Actions of the Semispinalis Capitis
1. Extension of the head and cervical spine when acting bilaterally
Agonists:
- Longissimus capitis
- Spinalis capitis
- Splenius capitis
- Sternocleidomastoid (posterior fibers)
Antagonists:
- Longus capitis
- Sternocleidomastoid (anterior fibers)
2. Contralateral rotation of the head and cervical spine when acting unilaterally
Agonists:
- Trapezius (upper part)
- Sternocleidomastoid
Antagonists: same muscles on the contralateral side
- Trapezius (upper part)
- Sternocleidomastoid
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Secondary Actions of the Semispinalis Capitis
2. Assists with lateral flexion of the head and cervical spine when acting unilaterally
Agonists:
- Splenius capitis
- Sternocleidomastoid
Antagonists: same muscles on contralateral side
- Splenius capitis
- Sternocleidomastoid
Information about cause and effect of Semispinalis Capitis pain: Semispinalis Capitis Neck and Head Pain