Passive Electrical Flow in Neurons

Neurons are among the most important and interesting cells in the body. They are the fundamental building blocks of the central nervous system and hence responsible for motor control, cognition, perception, and memory, among other things. Although our understanding of how networks of neurons interact to form an intelligent system is extremely limited, one prerequisite for an understanding of the nervous system is an understanding of how individual nerve cells behave.

A typical neuron consists of three principal parts: the dendrites; the cell body, or soma; and the axon. The structure of some typical neurons is shown in Fig. 4.1. Den-drites are the input stage of a neuron and receive synaptic input from other neurons. The soma contains the necessary cellular machinery such as a nucleus and mitochondria, and the axon is the output stage. At the end of the axon (which may also be branched, as are the dendrites) are synapses, which are cellular junctions specialized for the transmission of an electrical signal (Chapter 8). Thus, a single neuron may receive input along its dendrites from a large number of other neurons, which is called convergence, and may similarly transmit a signal along its axon to many other neurons, called divergence.