2 - The neurone

Abstract

This chapter discusses the structure and functions of neurons. The neuron or nerve cell is the functional unit of the nervous system. It consists of a cell body and a number of nerve fibers. The function of the neuron is to carry information in the form of nerve impulses from one point to another. As with any other cell in the body, cytoplasm forms the major part, with a nucleus at its center. Surrounding the nucleus are the Nissl granules that contain RNA and are thought to produce protein for the cells. The cells come in a variety of shapes and, compared with other cells in the body, are relatively large. The red blood cell is about 7–5 μm in diameter, whereas the neuron may vary from 10–100 μm. The nerve cell body is essential for the life of the nerve and if it is destroyed, it cannot regenerate. Attached to the cell body are the nerve fibers. These are of two types that include (1) the dendrites, which are short, branching fibers receiving information, of which there may be one or more, and (2) the axon, which may be short or more than a meter long and of varying thickness. The axon transmits information away from the nerve cell. It may give off branches along its length, and at its far end has several small branches. Within these nerve endings are vesicles containing chemical transmitter substances, necessary to produce another impulse in the connecting neuron, or to act on the muscle cell.