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Sternocleidomastoid muscle: Origin| Insertion| Applied anatomy

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    What is sternocleidomastoid muscle?

    The sternocleidomastoid muscle is the principal muscle of the neck region. It obliquely extends across the side of the neck region & dividing the anterior and posterior triangle of the neck.

    Origin and insertion

    Origin:

    • Sternal head: Upper part of the anterior surface of the manubrium of the sternum.
    • The clavicular head of SCM: Superior surface of medial 1/3rd of the clavicle.

    Insertion

    • Sternal head: Lateral one-half of superior nuchal line.
    • The clavicular head of SCM: lateral surface of the mastoid process.

    Sternocleidomastoid muscle

    Nerve supply

    • Accessory nerve [ XI ]
    • Branches from anterior rami of C2 to C3 (C4).

    Blood supply

    Arterial supply

    • Upper part: Posterior auricular artery & occipital artery.
    • Middle part: Superior thyroid artery.
    • Lower part: Suprascapular artery.

    Actions of the sternocleidomastoid muscle

    • Unilateral contraction
    • Bilateral contraction

    Individually — will tilt head toward the shoulder area on the same side rotating head to turn face to the opposite side; acting together, draw head forward.

    Relations of the sternocleidomastoid muscle

    • The investing layer of deep cervical fascia present outside the sternocleidomastoid muscle. 
    • Four sternomastoid arteries and spinal accessory nerve pierced this muscle. 
    • There are the following superficial & deep relations are below; 

    Superficial Relations

    • Skin
    • Platysma
    • Three cutaneous nerves
      • Great auricular
      • Transverse cervical
      • Medial supraclavicular
      • Lesser occipital
    • External jugular vein
    • Superficial cervical lymph nodes
    • Parotid gland

    Deep Relations

    In the upper part

    • Muscle: 
      • Posterior belly of digastric
      • Longissimus capitis
      • Splenius capitis
    • Artery: Occipital artery

    In the middle part

    • Muscles: 
      • Levator scapulae muscle
      • Scalenus anterior muscle
      • Scalenus medius muscle
      • Scalenus posterior muscle
      • Splenius capitis muscle
      • Inferior belly of the omohyoid muscle

    Arteries: 

    • Common carotid artery
    • Internal carotid artery

    Veins: 

    • Internal jugular vein
    • anterior jugular vein

    Nerves: 

    • Vagus nerve
    • Spinal accessory nerve
    • Cervical plexus nerve 
    • Brachial plexus (upper part)
    • Ansa cervicalis (inferior root)

    Glands: 

    • The thyroid gland
    • Lymph nodes

    In the lower part

    Muscles: 

    • Sternohyoid muscle
    • Sternothyroid muscle
    • Scalenus anterior muscle

    Arteries: 

    • Suprascapular artery 
    • Transverse cervical artery

    Veins: 

    • Anterior jugular veins

    Nerves: 

    • Brachial plexus (lower part)
    • Phrenic nerve

    Applied anatomy 

    • Torticollis or wry neck
    • Sternomastoid tumor

    Torticollis or wry neck

    • It occurs due to a spasm of the trapezius muscle and sternocleidomastoid muscle in the neck.
    • Spasmodic torticollis:
      • Repeated painful contraction muscles
      • Caused by exposure to cold & maladjustment of pillow during sleep. 
    • Reflex torticollis:
      • It occurs due to irritation of the spinal accessory nerve caused by inflamed or suppurating lymph nodes.
    • Congenital torticollis: 
      • Due to birth injury to muscles. 

    Sternomastoid tumor

    • The Middle Third of the sternocleidomastoid muscle swelling due to edema & ischemic necrosis caused by trauma at birth. 

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