#nerve plexus

Basicaly, a nerve plexus is a system of connected nerve fibers that link spinal nerves with specific areas of the body. Fibers in a plexus connect the spinal cord and the body by grouping themselves into one larger nerve. The human body consists of several nerve plexuses, including the brachial plexus, the cervical plexus, the coccygeal plexus, the lumbar plexus, the sacral plexus, and the solar plexus.

The main function of a nerve plexus is to ensure that all areas of the body are innervated, thereby equipping each region with the ability to send and receive messages from the peripheral nervous system. The different plexuses are charged with innervating different portions of the body and help to control the functions unique to each portion. A nerve plexus is formed during development, when disparate muscles of the skeleton fuse together and result in large muscles requiring innervation

4 major nerve plexuses are found, which - together with their peripheral nerves are described below:

1.  Cervical plexus:

- Arises from the ventral rami of C1 - C5

- Supplies muscles of the shoulder and neck

- Major motor branch is the phrenic nerve

- Arises from C3 - C5

- Innervates the diaphragm

“The primary danger of a ‘broken neck’ is that the phrenic nerve may have been severed, leading to paralysis, cessation of breathing and death …”

2.  Brachial plexus

- Arises from ventral rami of C5 - C8, and T1

- Subdivides into 5 major peripheral nerves which are:

A) Axillary nerve

Serves the muscles and skin of the shoulder, e.g. deltoid muscle

Damage causes paralysis and atrophy of deltoid

B) Radial nerve

Large peripheral nerve which innervates all extensor muscles of the arm, forearm and hand; and all the skin along the way;

E.g. triceps brachialis

Damage causes wrist drop and inability to extend hand at wrist;

C) Median nerve

Runs down anterior of the arm

Supplies most of the flexor muscles in the forearm and several muscles in the lateral part of the hand;

Damage causes inability to pick up small objects due to decrease ability to flex and abduct thumb and index finger;

D) Musculocutaneous nerve

Innervates the arm muscles that flex the forearm and of the skin of the lateral surface of the forarm;

Damage leads to decreased ability to flex the forearm;

E) Ulnar nerve

Runs down along the postero-medial surface of the arm;

Supplies the flexor carpi ulnaris muscle and all intrinsic muscles of the hand not served by the median nerve;

Damage causes typical “clawhand” with inability to spread fingers apart;

3.  Lumbar plexus

- Arises from the central rami of L1 - L4;

- Innervates the lower abdominal region and the anteromedial thigh;

- The largest nerve of this plexus is the femoral nerve;

- Innervates the anterior thigh muscles, lower abdomen, buttocks,  and the skin of the anteromedial leg and thigh;

- Damage causes inability to extend leg and to flex the hip;

- Another important nerve associated with this plexus is the obturator nerve;

- Innervates the adductor muscles of the medial thigh and small hip muscles; also serves the skin of the medial thigh and hip joint;

- Damage leads to inability to adduct the thigh;

4.  Sacral plexus

- Arises from L4 - S4

- Peripheral nerves of this plexus innervate the buttock, the posterior thigh and virtually all of the leg and foot;

- The major nerve of this plexus is the sciatic nerve;

- It is the largest nerve of the human body!

- Travels through the greater sciatic notch of the hip bone down to the posterior thigh;

- Innervates the lower trunk and the posterior surface of thigh and leg;

- Damage leads to inability to extend hip and to flex the knee –> “sciatica”

- Divides in the popliteal region into the:

A) Common fibular nerve

Innervates the lateral aspect of the leg and foot;

Damage leads to inability to dorsiflex the foot –> “footdrop”

      B) Tibial nerve

Innervates the posterior aspect of the leg and foot;

Damage leads to inability to plantar flex and invert the foot –> “shuffling gait”;

Another important nerve of this plexus is the superior and inferior gluteal nerve;

Innervates the gluteal muscles of the hip;

Source: WiseGeek - “What is a Nerve Plexus?”: http://www.wisegeek.com/what-is-a-nerve-plexus.htm