The Neuron Is the Major Functional Unit of the Nervous System
The major functional unit of the nervous system is the neuron, a cell type whose shape varies considerably with its location in the nervous system. Almost all neurons have an informationreceiving area of the cell membrane, usually called the dendrite; a cell body, or soma, containing the organelles for most cell metabolic activity; an information-carrying extension of the cell membrane, called an axon; and a presynaptic terminal at the end of the axon to transmit information to other cells.
The axon is often covered with a fatty coating called the myelin sheath that enhances the speed of information transfer along the axon s length.The other cell type in the nervous system is the glial cell (Greek for “glue”), originally thought to primarily provide structural support. Glial cells do not produce action potentials, but growing evidence indicates that they can indirectly monitor the electrical activity of neurons and use this information to modulate the effectiveness of neural communication. In addition, glial cells play important roles in producing the myelin sheaths of axons, modulating the growth of developing or damaged neurons, buffering extracellular concentrations of potassium and neurotransmitters, and participating in certain immune responses of the nervous system.