Peripheral Nervous System Health Article

The enteric nervous system

The enteric nervous system is made up of nerve fibers that supply the viscera of the body: the gastrointestinal tract, pancreas, and gallbladder.

Regulation of the autonomic nervous system

The involuntary ANS is controlled in the hypothalamus, while the somatic system is regulated by other regions of the brain (cortex). In contrast, the somatic nervous system may control motor functions by neural pathways that contain only a single axon that innervates an effector (i.e., target) muscle. The ANS is comprised of pathways that must contain at least two axons separated by a ganglia that lies in the path between the axons.

ANS reflex arcs are stimulated by input from sensory or visceral receptors. The signals are processed in the hypothalamus (or regions of the spinal cord) and target effector control is then regulated via myelinated preganglionic neurons (cranial and spinal nerves that also contain somatic nervous system neurons). Ultimately, the preganglionic neurons terminate in a neural ganglion. Direct effector control is then regulated via unmyelinated postganglionic neurons.

The principal neurotransmitters in ANS synapses are acetylcholine and norepinephrine.

General PNS disorders

General PNS disorders include loss of sensation or hyperesthesia (abnormal or pathological sensitivity). Sensations such as prickling or tingling without observable stimulus (paresthesia) or burning sensations are also abnormal.

Stabbing or throbbing pains are often due to neuralgia (e.g., trigeminal neuralgia, also known as tic douloureux). Neuritis (an inflammation of the nerve) can be caused by a number of factors, including trauma, infection (both bacterial and viral), or chemical injury.

BOOKS

Goldman, Cecil. Textbook of Medicine, 21st ed. New York: W. B. Saunders Co., 2000.

Guyton & Hall. Textbook of Medical Physiology, 10th ed. New York: W. B. Saunders Company, 2000.

Tortora, G. J., and S. R. Grabowski. Principles of Anatomy and Physiology, 9th ed. New York: John Wiley and Sons Inc., 2000.

Brian Douglas Hoyle, PhD

Paul Arthur