CERVICAL PLEXUS: LOCATION, BRANCHES AND FUNCTIONS - ANATOMY AND PHYSIOLOGY - 2024

The cervical plexus is a set of nerve fibers that innervates some parts of the neck and trunk. It is located in the back of the neck and reaches the middle of the sternocleidomastoid muscle.

It is formed by the ventral branches of the first four cervical nerves, that is, it goes from segment C1 to C4. However, there are authors who include part of C5 to the cervical plexus, since it participates in the formation of one of the motor branches: the phrenic nerve.

Distribution of the dermatome of the trigeminal nerve (superficial cervical plexus visible in purple, in the lower central part). Source: Henry Gray / Henry Vandyke Carter (1918) Anatomy of the Human Body. Public Domain File, via Wikimedia Commons

In addition, the cervical plexus has an anastomosis (surgical connection) with the accessory nerve, the hypoglossal nerve, and the sympathetic trunk.

The cervical plexus primarily controls the movement of the neck. It also innervates the upper part of the shoulders and chest, as well as some muscles and the skin of the head. It is part of the peripheral nervous system, constituting the highest nervous plexus.

The concept "nerve plexus" is used to define a complex network of interlocking axons that start from the spinal cord.

Location

Cervical plexus Source: Henry Gray / Henry Vandyke Carter (1918) Anatomy of the Human Body. Public Domain File, via Wikimedia Commons

The cervical plexus is located in the neck, lying below the sternocleidomastoid muscle. It is in the anterolateral part of the levator scapulae, and in the middle of the scalene muscles.

The spinal nerves exit each vertebra of the spinal cord through the intervertebral foramina (intervertebral foramen).

Each nerve of the cervical plexus communicates with the others in a superior-inferior way, close to the place where it originates. That is, the C2 connects with the fibers from C1 and C3. This structure also connects to the sympathetic trunk of the sympathetic nervous system.

Except for the fibers coming out of C1, the others divide into an ascending and descending branch. They then join with branches of the adjacent cervical nerve to form the loops of the cervical plexus.

Branches and functions of the cervical plexus

The cervical plexus differentiates into two branches: superficial and deep branches.

Shallow branches

Also called superficial cervical plexus, it is located on the sternocleidomastoid, having merely sensitive functions. Through the sensitive or cutaneous branches, it provides sensitivity to areas of the head, neck and upper part of the thorax.

These sensitive bouquets are:

- Greater occipital nerve (C2), which occupies the skin on the back of the skull.

- Lesser occipital nerve (C2). Also called the mastoid nerve, it is located in the skin of the mastoid area. As well as in the lateral area of ​​the skull, posterior to the ear. It arises between the second and third cervical vertebrae, together with the greater occipital nerve.

- Atrial nerve (C2-C3). It is responsible for innervating the skin of the pinna, that is, of the ear or external ear.

- Cutaneous nerve of the neck (C2-C3): it is located in the skin surrounding the hyoid bone.

- Supraclavicular nerve (C3-C4). It innervates the skin on the upper side of the trunk.

- Supra-acromial nerve (C3-C4): sensitizes the skin of the acromion bone of the shoulder, the outermost area of ​​the shoulder blade.

Deep branches

The deep branches constitute the deep cervical plexus. It differs from the previous one in that it is of the motor type, except for the phrenic nerve that has some sensory fibers. Its branches are divided into:

- Medial branches: these are those that allow the movements of the long muscles of the head and neck.

- Lateral branches: innervate the muscles that elevate the scapula and the rhomboids (C3-C4). Some of its branches are part of the cranial nerve XI (accessory nerve), which is what gives movement to the sternocleidomastoid muscle (C2). The latter is involved in the rotation of the neck.

The lateral branches also innervate the trapezius muscle (C3-C4), which serves to lift the shoulders.

- Ascending branches: they activate the rectus anterior muscles and the lateral rectus of the head.

- Descending branches: here the fibers that are involved in cervical flexion converge. They come from the roots C1, C2 and C3 and the hypoglossal, forming the loop of the hypoglossal. Specifically, the innervated muscles are those located in the subhyoid area (such as the omohyoid, the sternothyroid, the sternohyoid, the thyrohyoid and the geniohyoid).

On the other hand, the phrenic nerve is made up of the root of C4 and part of C5 and C3. The nerve descends in a straight line anterior to the scalene muscle, lateral to the sympathetic trunk, and under the sternocleidomastoid muscle.

Then it reaches the thorax, spreading to the right and left side of the body. It passes through the diaphragm, and into the aortic arch.

Sensory sub-branches leave the phrenic nerve that innervate the pleural dome, the pleura, and the pericardium. Thus, it produces motor innervation of the diaphragm, in addition to giving it sensitivity.

On the other hand, there are two additional branches that arise from the posterior roots of the spinal nerves. They are the preauricular nerve (which come from the posterior roots of C2 and C3) and the postauricular nerve (from the posterior roots of C3 and C4).

Cervical plexus blockage or involvement

Injuries to the cervical plexus produce different symptoms depending on the damaged nerve fibers. They generally cause paralysis and lack of sensation in areas of the upper body, neck, and head.

Generally, a cervical plexus block would inhibit the transmission of nerve impulses, impeding skin perception and movement. This block is often used as a local anesthetic for surgical operations.

To do this, anesthetic agents are injected into several areas along the posterior border of the sternocleidomastoid muscle.

If the phrenic nerve ruptures, diaphragm paralysis can occur. The nerve can also be temporarily blocked by injecting an anesthetic around this nerve, near the anterior scalene muscle.

A surgical intervention that affects the phrenic nerve leads to a prolonged period of paralysis. This can occur, for example, weeks after surgery for a diaphragmatic hernia.

On the other hand, a nerve that is very vulnerable to injury is the supraclavicular nerve. This can be damaged after clavicle fractures, especially if they involve the middle third of the clavicle.

If this nerve is damaged, the ability to laterally rotate the humerus at the shoulder is lost. These people are also unable to begin limb abduction.

References

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2. Cervical plexus. (sf). Retrieved on April 10, 2017, from Wikipedia: en.wikipedia.org.
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4. Cervical Plexus. (sf). Retrieved on April 10, 2017, from Ken Hub: kenhub.com.
5. The cervical plexus. (sf). Retrieved on April 10, 2017, from Teach me Anatomy: teachmeanatomy.info.