The nervous system—the brain, spinal cord, and nerves—is made up of nervous tissue. Nervous tissue is made up of large, complex cell groups called neurons, which transmit nerve impulses, and supporting cells—including astrocytes, Schwann cells, and other neuroglia cells—that support and work in conjunction with the neurons. Figure 36-52 shows a neuron and its associated structures.

In addition to the cell body, neurons have two types of cytoplasmic extensions that transmit impulses. A dendrite is a short extension that normally carries inbound impulses to the cell body from nearby cells and axons. An axon is a long extension that normally carries impulses from the cell body to remote dendrites and cells.