Dr. Martin's notes

Monday September 12, 2016

PERIPHERIAL NERVOUS SYSTEM (PNS)

The PNS begins in the brain by having 12 cranial nerves come off the upper part of the spinal cord. They control your facial muscles, your hearing, eye movements, tongue movements and other cranial activity. There is one pair of nerves that come off the spinal cord for each of the vertebrae and the sacrum and coccyx. There is one extra pair at the top of the spine between the first cervical and the occipital bone. (8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal)

The main set of nerves of the upper extremity are formed by the spinal nerves from C5-T1. These nerves join and separate in a complex pattern (the cervical plexus). It is located in the upper shoulder muscle area. By the time this plexus reaches the shoulder, it has formed the three major nerves of the arm, the radial, medial and ulnar nerves. These nerves pass down the arm, through grooves in the elbow and serve the arm, hands and fingers.

There is also a lumbar plexus that is made up of the T12-L4 nerve roots, and essentially makes up the Sciatic nerve into the leg. There is a sacral plexus that consists of L4-S3, and serves the back of the calf, lateral side of the foot, and the gluteal muscles.

All of the nerves as they come off the spine serve a certain area on the body. These can be measured on the skin surface and are called dermatomes. (This means the path of the nerves). Dermatome sensitivity can be measured by a cotton ball, pin prick or a pin wheel.

When a nerve is injured or severed, it can regenerate, usually starting within 24 hours after injury. The nerve filaments (tiny fibers that make up the nerve) can grow at the rate of about 1.5 mm per day. The nerve forms a tube between the severed surfaces and fills with cells to help join the areas together.

The best way to test for upper perpheral nerve injury is by using hand/finger tests.

Median N. Thumb to little finger, both extended.
Ulnar N. Abduct and adduct extended fingers
Radial N. Hand flat on table, extend wrist

Nerves basically have two functions, motor (meaning they make something move or happen) and sensory (for feeling).

If time permits, discuss physiology of pain.