Nerves of the Neck

• Is formed by the union of cranial and spinal roots.
• Has cranial roots that arise from the medulla oblongata below the roots of the vagus.
• Has spinal roots that arise from the lateral aspect of the cervical segment of the spinal cord between C1 and C3 (or C1 and C7) and unites to form a trunk that ascends between the dorsal and ventral roots of the spinal nerves in the vertebral canal and passes through the foramen magnum.
• Has both spinal and cranial portions, which traverse the jugular foramen, where they interchange fibers. The cranial portion contains motor fibers that join the vagus nerve and innervate the soft palate, pharyngeal constrictors, and larynx. The spinal portion innervates the sternocleidomastoid and trapezius muscles.
• Lies on the levator scapulae in the posterior cervical triangle and then passes deep to the trapezius.

• Is formed by the ventral primary rami of C1 to C4.

1. Cutaneous branches

Lesser occipital nerve (C2)

• Ascends along the posterior border of the sternocleidomastoid to the scalp behind the auricle.

Great auricular nerve (C2 to C3)

• Ascends on the sternocleidomastoid to innervate the skin behind the auricle and on the parotid gland.
  

Transverse cervical nerve (C2 to C3)

• Turns around the posterior border of the sternocleidomastoid and innervates the skin of the anterior cervical triangle.

Supraclavicular nerve (C3 to C4)

• Emerges as a common trunk from under the sternocleidomastoid and then divides into anterior, middle, and lateral branches to the skin over the clavicle and the shoulder.

2. Motor branches

Ansa cervicalis

• Is a nerve loop formed by the union of the superior root (C1 or C1 and C2; descendens hypoglossi ) and the inferior root (C2 and C3; descendens cervicalis ).
• Lies superficial to or within the carotid sheath in the anterior cervical triangle.
• Innervates the infrahyoid (or strap) muscles, such as the omohyoid, sternohyoid, and sternothyroid muscles, with the exception of the thyrohyoid muscle, which is innervated by C1 via the hypoglossal nerve.

Phrenic nerve (C3 to C5)

• Arises from the third, fourth, and fifth cervical nerves but chiefly from the fourth cervical nerve; contains motor, sensory, and sympathetic nerve fibers; and provides the motor supply to the diaphragm and sensation to its central part.
• Descends on the anterior surface of the anterior scalene muscle under cover of the sternocleidomastoid muscle.
• Passes between the subclavian artery and vein at the root of the neck and enters the thorax by crossing in front of the origin of the internal thoracic artery, where it joins the pericardiacophrenic branch of this artery.
• Passes anterior to the root of the lung and between the mediastinal pleura and fibrous pericardium to supply sensory fibers to these structures.

Twigs from the plexus

• Supply the longus capitis and cervicis or colli, sternocleidomastoid, trapezius, levator scapulae, and scalene muscles.

Accessory phrenic nerve (C5)

• Occasionally arises as a contribution of C5 to the phrenic nerve or a branch of the nerve to the subclavius (C5), descends lateral to the phrenic nerve, enters the thorax by passing posterior to the subclavian vein, and joins the phrenic nerve below the first rib to supply the
  diaphragm.

• Is formed by the union of the ventral primary rami of C5 to T1 and passes between the anterior scalene and middle scalene muscles.

1) Its roots give rise to the:

Dorsal scapular nerve (C5)

• Emerges from behind the anterior scalene muscle and runs downward and backward through the middle scalene muscle and then deep to the trapezius.
• Passes deep to or through the levator scapulae and descends along with the dorsal scapular artery on the deep surface of the rhomboid muscles along the medial border of the scapula, innervating the levator scapulae and rhomboid muscles.

Long thoracic nerve (C5 to C7)

• Pierces the middle scalene muscle, descends behind the brachial plexus, and enters the axilla to innervate the serratus anterior.

2) Its upper trunk gives rise to the:

Suprascapular nerve (C5 to C6)

• Passes deep to the trapezius and joins the suprascapular artery in a course toward the shoulder.
• Passes through the scapular notch under the superior transverse scapular ligament.
• Supplies the supraspinatus and infraspinatus muscles.

Nerve to the subclavius muscle (C5)

• Descends in front of the plexus and behind the clavicle to innervate the subclavius.
• Communicates with the phrenic nerve as the accessory phrenic nerve in many cases.