GENERAL FEATURES OF NERVE TISSUE & THE NERVOUS SYSTEM

ØA. Two Classes of Cells: Nerve tissue consists of the neurons that transmit impulses and the supporting cells that surround them. It contains little extracellular material.

Ø1. Neurons. These cells are highly specialized to carry out nerve tissue functions. Neurons receive, integrate, and transmit electrochemical messages. Each has a cell body, also called the soma ("body") or perikaryon ("around the nucleus"), comprising the nucleus and the surrounding cytoplasm and plasma membrane. Each neuron has a variable number of dendrites, cytoplasmic processes that collect incoming messages and carry them toward the soma, and a single axon, a cytoplasmic process that transmits messages to the target cell. Axons of most neurons have a myelin sheath formed by supporting cells and interrupted by gaps called nodes of Ranvier. Myelinated axon segments between the gaps are called internodes. 2. Supporting cells. These cells are called neuroglia ("nerve glue") or glial cells. Their functions include structural and nutritional support of neurons, electrical insulation, and enhancement of impulse conduction velocity along axons.