Sternocleidomastoid Muscle Anatomy
Origin:
Sternal Head: Upper part of the anterior surface of the manubrium
Clavicular Head: Superior surface of the medial one-third of the clavicle
Insertion: Lateral surface of the mastoid process, the lateral half of the superior nuchal line
Actions:
Unilaterally: Rotation of head to the opposite side, lateral flexion of the neck on the same side
Bilaterally: Stabilizes the head, flexion of the head and neck, checkreins backward motion of the head and neck
Innervation: Accessory nerve: cranial nerve XII and ventral rami of the (C2, C3)
Blood Supply: Branches from the vertebral artery
Primary Actions of the Sternocleidomastoid
Primary Actions of the Sternocleidomastoid
1. Extension of the head and cervical spine when posterior fibers act bilaterally
Agonists:
- Longissimus Capitis
- Spinalis Capitis
- Splenius Capitis
- Semispinalis Capitis
Antagonists:
- Longus Capitis
- Sternocleidomastoid (anterior fibers)
2. Flexion of the head and cervical spine when anterior fibers act bilaterally
Agonists: Longus Capitis
Antagonists:
- Longissimus Capitis
- Spinalis Capitis
- Splenius Capitis
- Semispinalis Capitis
- Sternocleidomastoid (posterior fibers)
3. Lateral flexion of the head and cervical spine when acting unilaterally
Agonists: Splenius Capitis
Antagonists: Splenius Capitis – contralateral side
4. Contralateral rotation of the head and cervical spine when acting unilaterally
Agonists:
- Semispinalis Capitis
- Trapezius (upper part)
Antagonists:
- Splenius Capitis – contralateral side
- Trapezius (upper part)
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For Pain and Symptom Information See: Sternocleidomastoid Muscles: Head, Eyes, Sinus, Ears, Throat Pain
An excellent book for those beginning the study of anatomy. Coloring helps memory retention.
For intermediary anatomy students learning skeletal and muscle structure.
For beginning and intermediary anatomy . Muscle overlays on the human body. Excellent visuals!