Lab 1 Module 3: Posterior Triangle of the Neck - Page 1 of 5

READINGS:

Gray's Anatomy for Students (Fourth Edition): Pages: 1012-1019

The neck is divided into several triangles for descriptive purposes. The two main divisions are the Anterior Triangle and the Posterior Triangle. Each of these triangles can be further subdivided into smaller sub-triangles. Let's first focus on the Posterior Triangle.

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	Begin with the Trapezius added to the shoulder.
	The Sternocleidomastoid (or SCM) divides the neck into the anterior and posterior triangles. The posterior triangle is bounded by the posterior border of the sternocleidomastoid muscle (anteriorly), the anterior border of the trapezius muscle (posteriorly), and by the middle one-third of the clavicle (inferiorly).

Origin - manubrium of the sternum and medial 1/3rd of the clavicle.

Insertion - mastoid process of the temporal bone the superior nuchal line of the occiput.

Innervation - (Spinal) Accessory Nerve (Cranial Nerve XI), with proprioceptive fibers from ventral rami of C2-C3.

Action - Unilaterally causes the contralateral rotation of the face and ipsilateral neck side bending. When acting bilaterally they help flex the neck and elevate the sternum during forced inspiration.

Remove the Sternocleidomastoid and add the Splenius Capitus, which runs from the ligamentum nuchae and spinous processes of the superior thoracic vertebrae to the mastoid process and superior nuchal line. *The splenius capitus will be covered during the Rheum block when we focus on the back muscles.*

Add the Posterior Scalene.

Origin - Posterior tubercles of transverse processes of C5-C7 vertebrae.

Insertion - external border of the second rib.

Innervation - ventral rami of C7 and C8 cervical nerves.

Action - laterally flexes the neck; elevates the second rib during forced inspiration.

Add the Middle Scalene.

Origin - Posterior tubercles of transverse processes of C5-C7 vertebrae.

Insertion - superior surface of the first rib, posterior to the groove for subclavian artery.

Innervation - ventral rami of cervical spinal nerves (C3-C8).

Action - flexes the neck laterally; elevates the first rib during forced inspiration.

Add the Anterior Scalene.

Origin - Transverse processes of C3-C6

Insertion - Scalene tubercle of 1st Rib

Innervation - ventral rami of C4-C6

Action - Flexes the head and assists with elevation of first rib during inspiration.

	The roots of the Brachial Plexus emerge between the anterior and middle scalene muscles and descend inferolaterally toward the axilla. This region is clinically important for performing brachial plexus nerve blocks during upper limb surgeries.
	The roof of the Posterior Triangle is formed by the investing layer of deep cervical fascia, which spans the space between the trapezius and sternocleidomastoid muscles. It is covered superficially by the skin, superficial fascia, platysma muscle, and superficial veins and cutaneous nerves.