Cervical plexus

Sensory

Branches of the cervical plexus include motor branches supplying muscles, and cutaneous branches innervating the skin of the anterolateral neck, the superior part of the thorax (superolateral thoracic wall) and scalp between the auricle (pinna) and the external occipital protuberance.

The sensory (posterior or cutaneous) branches of the plexus emerge around the middle of the posterior border of the sternocleidomastoid muscle. This area is clinically significant and recognized as the nerve point of the neck.

There are four sensory branches originating from the two loops formed between the anterior rami of spinal nerves C2 and C3, and C3 and C4. These are:

• Branches from the loop between C2 and C3:
  • Lesser occipital nerve (formed by C2)
  • Great auricular nerve (formed by C2 and C3)
  • Transverse cervical nerve (formed by C2 and C3)
• Branches from the loop between C3 and C4:
  • Supraclavicular nerves (formed by C3 and C4)

As highlighted in the names of those four sensory branches, a mnemonic to memorize the names can be derived from the bolded letters. Thus the mnemonic for the sensory branches is Let's Go To Sleep.

Motor

On the other hand, the motor branches of the cervical plexus form the ansa cervicalis (C1-C3), which is a nerve loop innervating the infrahyoid muscles in the anterior cervical triangle. 

They also form the phrenic nerve (C3-C5) which supplies the diaphragm and the pericardium of the heart. Additional muscular branches are also given off to provide innervation to several prevertebral, sternocleidmastoid and trapezius muscles. 

• Ansa cervicalis (mnemonic: Susan Saw Game Of Thrones)
  • Sternohyoid nerve (C1 – C3)
  • Sternothyroid nerve (C1 – C3)
  • Geniohyoid nerve (via hypoglossal nerve) (C1)
  • Omohyoid nerve (C1 – C3)
  • Thyrohyoid nerve (via hypoglossal nerve) (C1)
• Phrenic nerve (contributed mainly by C4, with little fibres from C3 and C5)
• Muscular branches to prevertebral, sternocleidomastoid and levator scapulae muscles 

You can easily remember the motor branches of cervical plexus by using the mnemonic MAP (Muscular branches, Ansa cervicalis, Phrenic nerve)

Find out more about the cervical plexus using the following study unit:

Sensory branches

• Lesser occipital nerve: This branch is formed by the second cervical nerve (C2) only, and courses to supply the skin of the neck and the scalp posterosuperior to the clavicle.
• Great auricular nerve: This sensory branch originates from the C2 and C3 nerves. It courses upwards in a diagonal fashion and crosses the sternocleidomastoid muscle onto the parotid gland. It then divides and innervates the skin over the parotid gland, the posterior aspect of the auricle, and an area of skin extending from the angle of the mandible to the mastoid process.
• Transverse cervical nerve: The transverse cervical nerve is formed by axons from the second and third cervical nerves. It supplies the skin covering the anterior triangle of the neck. This branch curves around the middle of the posterior border of the sternocleidomastoid muscle and crosses it deep to the platysma muscle.
• Supraclavicular nerves: These branches are formed by the C3 and C4 spinal nerves, and emerge as a common trunk under cover of the sternocleidomastoid muscle. This divides into three smaller branches (medial, intermediate and lateral) to the skin of the neck. Some branches also cross the clavicle to supply the skin over the shoulder.

Motor branches

• The ansa cervicalis: The five motor branches of the ansa cervicalis loop listed above, originate from C1 to C3 nerves. The ansa cervicalis is formed by two roots, superior and inferior, which are formed by the fibers from the anterior rami of the cervical spinal nerves. They supply the infrahyoid muscles in the anterior cervical triangle.
• The phrenic nerve: The phrenic nerve originates chiefly from the 4th cervical nerve (C4) but receives contributions from the 3rd and 5th cervical nerves (C3 and C5). It is formed at the superior part of the lateral border of the anterior scalene muscle, at the level of the superior border of the thyroid cartilage. The phrenic nerve contains motor, sensory, and sympathetic nerve fibres. It provides the sole motor supply to the diaphragm as well as sensation to its central part. In the thorax, the phrenic nerve innervates the mediastinal pleura and pericardium of the heart. The phrenic nerve descends obliquely across the anterior scalenus muscle, deep to the prevertebral layer of deep cervical fascia and the transverse cervical and suprascapular arteries. It runs posterior to the subclavian vein and anterior to the internal thoracic artery as it enters the thorax.