Lab 1 Module 3: Posterior Triangle of the Neck - Page 4 of 5

Nerves of the Posterior Triangle

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The Cervical Plexus is a network of nerves formed by communications between the ventral rami of C1-C4. It has both motor and sensory components. The motor branches primarily innervate muscles in the anterior triangle of the neck, including the infrahyoid muscles (via the ansa cervicalis) and the diaphragm (C3-C5 by the phrenic nerve). The sensory branches emerges from deep to the sternocleidomastoid, pierce the investing layer of deep cervical fascia, and divide into four main cutaneous nerves supplying the skin of the neck and shoulder. These include:

	The Lesser Occipital Nerve (C2) ascends along the posterior border of the sternocleidomastoid, supplying the skin of the posterior scalp and the superior part of the auricle of the ear. (This nerve is not visible on this 3D model).
	The Greater Auricular Nerve (C2-C3) runs vertically across the sternocleidomastoid toward the parotid gland (located anterior to the ear). It supplies branches to the skin over the parotid region, posterior surface of the auricle of the ear, and over the mastoid area. (This nerve is not visible on this 3D model).
	The Transverse Cervical Nerve (C2-C3) passes transversely across the middle of the sternocleidomastoid toward the anterior triangle of the neck, supplying skin over the anterior and lateral neck. (This nerve is not visible on this 3D model).
	The Supraclavicular Nerves (C3-C4) arise as a common trunk that divides into three main branches: medial, intermediate, and lateral supraclavicular branches. These nerves descend superficial to the clavicle to supply the skin of the shoulder, superiormost thorax, and superior deltoid region.
	The Phrenic Nerve (C3, C4, C5), although closely associated with the cervical plexus, is not formally a branch of it. It descends obliquely across the anterior aspect of the anterior scalene muscle, passing into the thoracic cavity, and innervating the diaphragm, providing both motor and sensory fibers. (Mnemonic: "C3, C4, C5 keeps the diaphragm alive!").