Neurophysiology

I

Introduction

Neurophysiology, the study of how nerve cells, or neurons, receive and transmit information.

II

Anatomy

In the nervous system there are two main types of cell, the neuron and the neuroglia. Neurons relay information to and from the central nervous system (the brain and spinal cord) in the form of electrical impulses and are specialized to perform the functions of the nervous system. They sense changes occurring inside and outside the body, control thinking and feeling, and control muscles and glands in the body. Neuroglia do not usually convey electrical signals but lie close to the neurons and serve to support and protect them, especially in the central nervous system.

A

Neurons

A neuron is a cell with a thick central area containing the nucleus (the cell body or perikaryon). The cell body usually has one long process called an axon that in the human body can be as short as 1 mm or as long as 1 m, and one or more short, bushy processes called dendrites. Axons conduct impulses away from the cell body to stimulate other cells, for example, another neuron, a gland cell, or a muscle. Dendrites, on the other hand, conduct impulses initially generated at another site in the body towards the cell body of the neuron.

B

Axons

The axon contains a number of neurofibrils, which are fibrils running the length of the axon and made of long, thin filaments called microtubules. The cytoplasm of the axon, the axoplasm, is surrounded by a membrane known as the axolemma. At the end of the axons are bulbous structures known as end feet (or synaptic boutons), which are important in the conduction of impulses from the neuron to a neighbouring cell (another neuron, a gland, or a muscle). Dendrites receive impulses from other neurons. The exceptions are sensory neurons, such as those that transmit information about temperature or touch—for example, from the skin to the brain—in which the signal is generated by specialized receptors in the skin at the end of the dendrite.