Deep branches of cervical plexus

The cervical plexus gives off superficial (sensory) and deep (motor) branches.

The deep branches of cervical plexus primarily supply motor innervation to various neck muscles and the diaphragm. They also form connections with the autonomic nervous system via the sympathetic trunk. These include:

Motor branches to neck muscles

1. Direct branches to prevertebral muscles

• Innervate the rectus capitis anterior, rectus capitis lateralis, longus capitis, and longus colli muscles, which are anterior to the cervical vertebral column.

2. To sternocleidomastoid and trapezius (C2–C4)

• Some fibers contribute to the accessory nerve (cranial nerve XI) for innervating the sternocleidomastoid and trapezius muscles.

3. To geniohyoid and thyrohyoid muscles (C1)

• The cervical plexus also gives a communicating branch from C1 spinal nerve to the hypoglossal nerve which almost immediately leaves to supply the geniohyoid and thyrohyoid muscles.

4. To diaphragm via phrenic Nerve (C3–C5, predominantly C4)

• The phrenic nerve is a prominent branch of the cervical plexus. It travels inferiorly, running on the scalenus anterior, and supplies motor innervation to the diaphragm. It also carries sensory fibers to parts of the pericardium, mediastinal pleura, and the diaphragm's central tendon.

Motor branches via the ansa cervicalis

The ansa cervicalis is a loop of nerves derived mostly from C1 to C3, which provides motor innervation to the infrahyoid muscles (except the thyrohyoid).

• The superior root arises from C1, hitchhiking with the hypoglossal nerve (cranial nerve XII).

• The inferior root arises from C2 and C3.

• Together, these roots join to loop around the internal jugular vein.

The ansa cervicalis supplies the:

• Omohyoid,

• Sternohyoid, and

• Sternothyroid muscles.

Note: The thyrohyoid and geniohyoid muscles are supplied by fibers of C1 traveling through the hypoglossal nerve (as mentioned above).

Autonomic connections to the sympathetic trunk

• Communicating branches from the superior cervical ganglion, called the gray rami communicans, connect the sympathetic trunk with the anterior rami of cervical nerves, thus establishing a connection with the cervical plexus.