Review of Trapezius & Sternocleidomastoid Muscle + their Relation to Investing Fascia

Review of Trapezius:

- An extrinsic or superficial muscle of the back.

Functions: Assist in rotating the scapula during the abduction of the humerus above the horizontal; Upper fibres elevate, middle fibres adduct and lower fibres depress scapula.

Sri: The classification of the fibres are based on their structure i.e. upper fibres are descending fibres; middle fibres transverse & lower fibres are ascending.

Origin: Superior nuchal line, external occipital protuberence, ligamentum nuchae, spinous processes of CVII to TXII.

Insertion: Lateral 1/3 of clavicle, acromion, spine of scapula

Innervation: Motor - accessory nerve(CN XI); Proprioception - C3 and C4

Review of Sternocleidomastoid (aka Sternomastoid muscle)

Function: Individually - tilts head towards shoulder on same side; rotates head to turn face to opposite side, Acting together - draw head forwards

Origin: Sternal head- Upper part of anterior surface of manubrium
Clavicular head- Superior surface of medial 1/3 of the clavicle

Insertion: Lateral 1/2 of superior nuchal line, Lateral surface of mastoid process

Innervation: Accessory nerve (CN XI) and branches from anterior rami of C2 to C3 (C4)

Relations to Investing Fascia:

Posteriorly, the investing fascia attaches to the ligamentum nuchae and the spinous process of CVII. As this fascial layer moves anteriorly, it splits to enclose the trapezius muscle, reunites into a single layer to form the roof of the posterior triangle, spilts again to surround the sternocleidomastoid muscle, and reunites again to join its twin from the other side.

Contributed by John Lee

Source: Gray's Anatomy for Students