The Nervous System: Introduction, Spinal Cord, and Spinal Nerves (^237)
Dendrites
Cell body Nucleus
Axon terminals
Axon^
Impulse
Axon
Cell body (^)
Myelin sheath (^)
surrounding axon (^)
Impulse
(^) Dendrite (^)
Impulse
(^)
(^)
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®^
(^)
Axon terminals
Lear ni ng^
Lear n i ng^
(^)
Cenga ge^
Ceng age^
(A) (B) (C)
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Figure 10- 3 Three types of structural neurons. (A) Multipolar. (B) Unipolar. (C)
Bipolar.
(^) ®
Learning
Cengage
2016 ©
neurilemma. Narrow gaps in the sheath are the nodes of
Ranvier.
Functional Classification of Neurons.
Cells that conduct impulses from one part of the body to
another are called neurons. They may be classified by both
function and structure. The structural classi-fication
consists of three types of cells. Multipolar neu-rons are
neurons that have several (multi) dendrites and one axon.
Most neurons in the brain and spinal cord are this type. The
neuron studied in Chapter 5 is this type. Recall that the part
of the neuron with the
nucleus is called the cell body. The smaller exten-sions of
the cell body are the dendrites, and the single long
extension is called the axon. Single cells called Schwann
cells, also called neurolemmocytes (noo-row-leh-
MOH-sights), surround the axon at specific sites and form
the fatty myelin sheath around the axons in the peripheral
nervous system -(Figure 10-4). Gaps in the myelin sheath
are called nodes of Ranvier (NOHDZ of rahn-vee-A),
also called neurofibril nodes. These gaps allow ions to
flow freely from the extracellular fluids to the axons,
assisting in developing action potentials for nerve
transmission.