Sternocleidomastoid Muscle

Sternocleidomastoid Muscle

The sternocleidomastoid is 1 of the 2 large, supf muscles of the neck

Origin

sternal head	· tendinous · arises from superolat part of front of manubrium sterni
clavicular head	· musculotendinous · arises from med 1/3 of upper surface of clavicle

Insertion

It is inserted by:

1. a tendon into mastoid process of the temporal bone

2. a thin aponeurosis into lat part of sup nuchal line of occipital bone

Nerve Supply

spinal part of accessory n	motor
ventral rami of C2 & C3	sensory (proprioceptive)

Blood Supply

by branches from occipital artery

Actions

When both muscles contract:

1. extend head at atlanto-occipital jt

2. flex cervical part of vertebral column

When 1 muscle contracts:

1. tilt the head towards the shoulder

2. rotates head so that the face looksupwards on the oppo side

If the head is fixed, the 2 muscles can also act as accessory muscles of inspiration

Relations

Supf

1. skin 2. fascia & platysma 3. ext jugular vein (EJV) 4. great auricular, tnvs cut & med supraclavicular nerves 5. supf cervical LN along EJV 6. parotid gland

Deep

1. carotid sheath & its contents: common & ICA, IJV & vagus n 2. muscles: sternohyoid, sternothyroid, omohyoid, scaleni ant, med & post levator scapulae, splenius capitis & post belly of digastric 3. besides common carotid art (CCA) & int carotid art (ICA) there are also    1. ext carotid art (ECA)    2. occipital art    3. subclavian art & suprascapular art 4. besides int jugular vein (IJV), there are also     1. ant jugular vein     2. facial vein     3. lingual vein 5. besides vagus nerve there also:     1. accessory nerve     2.cervical plexus     3. upper part of brachial plexus     4. phrenic n & ansa cervicalis 6. deep cervical LN

Clinical Notes

1. the sternocleidomastoid divides the neck into ant & post triangles

2. congenital torticollis

3. spasmodic torticollis