Provide the complete action of the Sternocleidomastoid SCM including single-sided and bilateral contraction?

Answer 1

STERNOCLEIDOMASTOIDEUS

Attached to the sternum (Greek - chest), clavicle (Latin - little key) and mastoid (Greek - breast-shaped) bone.

This muscle is a long strap muscle with two heads. It is sometimes injured at birth, and may be partly replaced by fibrous tissue that contracts t produce a torticollis (wry neck)

Origin

Sternal head: anterior surface of upper sternum

Clavicular head: medial third of the clavicle

Insertion

Mastoid process of the temporal bone (bony promenance just behind the ear)

Action

Contraction of both sides together (bilateral contraction): flexes neck (draws head forward). Raises sternum, and consequently the ribs, during deep inhalation.

Contraction of one side (single-sided contraction): tilts the head towards the same side. Rotates head to face the oppsite side (and also upwards as it does so).

Basic functional movement: Turning head to look over your shoulder. Raising head from pillow.

Sports that heavily utilise this muscle: Swimminh, Rugby scrummage, American football.

Movements or injuries that may damage this muscle: Extreme whiplash movements

Headache and neck pain are common problems when this muscle is chronically tight/shortened