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MUSCLES-STERNOCLEDOMASTOID

Anatomy-Neck

MUSCLES-STERNOCLEDOMASTOID

1. Arises form the sternum + clavicle. A triangular interval exists b/w the two heads and the sternoclavicular joint, the IJV can be accessed here.

2. It is inserted along a curved line from the mastoid process to the superior nuchal line of the occipital bone.

3. Supplied by CN XI (spinal part), C1-6. IT IS ONE OF TWO SKELETAL MUSCLES THAT ARE SUPPLIED IPSILATERALLY. The reason is that when the (for example) the left UL muscles are being used (innervated by the right hemisphere), it is the right SCM (innervated by the right hemisphere) that turns the head to the left.

4. ACTIONS OF THE SCM
- Rotation: contralateral SCM + ipsilateral abductors (scalenus medius, semispinalis cervicis).
- Extension: bilateral SCM contracting.
- Flexion: bilateral SCM + flexion of cervical spine.
- Protraction: bilateral SCM + flexion of cervical spine + extension of atlanto-occipital joint.

5. SCM RELATIONS
- CN XI runs down below it to emerge in the posterior triangle.
- Deep to the upper lies the cervical plexus.
- Deep to the lower half is the carotid sheath overlying the scalenus anterior.


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REFERENCES

1. Mcminn. (2003). Last's Anatomy. Elsevier Australia. ISBN:0729537528. Read it at Google Books - Find it at Amazon
2. Netter, F. H. (2019). Atlas of human anatomy. Philadelphia, PA: Elsevier.
3. Image: no reference available.

Ⓒ A. Manickam 2018

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