Approximately one third of these cells are neurons, i.e. afferent neurons, interneurons, or efferent neurons. The rest, approximately two thirds, of the cells are a class of cells called glia . Glial cells carry out metabolic functions in the nervous system. It is important to remember that receptors are not neurons or glia. The unit of function in the nervous system is the nerve impulse.
Neurons receive input from dendrites .
The dendrites project from the cell body of the neuron. Within the cell body is a nucleus , where the chromosomes, which carry DNA, are located. Projecting from the cell body is the axon . Nerve impulses are received by the dendrites. If a certain threshold of excitation is achieved, then the neuron fires through the terminal endings .