Posterior Neck - LO1
1. What muscles (and other structures) form the boundaries of the posterior (=lateral) triangle (and sub-triangles)? What are the high-yield contents of these triangles? What are the actions of these muscles? What are the innervations of these muscles?
The posterior cervical triangle is bounded anteriorly by the posterior border of the sternocleidomastoid m., posteriorly by the superior part of the trapezius m., and inferiorly by the clavicle.
The posterior cervical triangle may be subdivided into two triangles. Both triangles are bordered anteromedially by the sternocleidomastoid m., posterolaterally by the upper fibers of the trapezius m., and these triangles are divided from one another by the inferior belly of the omohyoid m. They are the:
occipital triangle: the superior-most triangle; typically contains the nerve point of the neck (Erb’s point) and its branches and the accessory n. (CN XI).
subclavian (omoclavicular) triangle: the inferior-most triangle; typically contains the ultimate connection between the external jugular v. and subclavian v., and supraclavicular lymph nodes.
Sternocleidomastoid m.:
Trapezius m.:
Trapezius and SCM mm. are both efferently (motor) innervated by the accessory n. (CN XI). The accessory n. is strictly efferent (motor); therefore, afferent (sensory) supply to these muscles comes from ventral primary rami of cervical nerves (C2-C4). Typically, C2-C3 (sometimes C4) afferently serve the SCM, whereas C3-C4 afferently serve the trapezius. It is likely that C2-C4 also carry some motor fibers.