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