The chapter next drops down to the cellular level, with a discussion of the neuron, the basic unit of communication in the nervous system. The neuron is composed of dendrites, a cell body, and an axon, with glial cells helping neurons to connect properly and to communicate quickly.
Neurons come in several varieties, including sensory neurons, motor neurons, and interneurons.
When a neuron's resting potential is disturbed by excitation and the stimulus exceeds threshold, the neuron fires and the resulting electrochemical changes propagate down the axon.