The nervous system is responsible for short-term immediate control of the human body and for communication between various body systems. Although the endocrine system achieves long-term communication and control via chemical (hormonal) mechanisms, the nervous system relies on a faster method of alternating chemical and electrical transmission of signals, and commands through a network of specialized neural cells (neurons).

There are three differing types of neurons including sensory neurons, neurons associated with transmission of impulses, and effecter neurons such as motor neurons that transmit nerve impulses to specialized tissues (e.g., motor neurons to muscle tissue) and glands. In addition to neurons, there are a number of cell types that play a supportive role in the nervous system. Principal among these neuron-supporting cells are Schwann cells associated with an insulating myelin sheath that wraps around specific types of neural fibers or tracts.

Neurons contain...