Neurons may be classified structurally based on the number of processes extending from the perikaryon or they may be classified functionally based on the direction the nerve impulse is carried.
The three types of structural neurons are: multipolar neurons, bipolar neurons, and unipolar neurons.
Multipolar neurons have many dendrites and one main axon. Bipolar neurons will have only one axon and only one dendrite. Unipolar neurons consist of a cell body and one process which is usually referred to as an axon, though the portion carrying impulses toward the perikaryon is sometimes called a dendrite.
The three types of functional neurons are: sensory (afferent) neurons, motor (efferent) neurons, and connector (association) neurons. Sensory neurons conduct an impulse toward the spinal cord or brain. Motor neurons conduct an impulse away from the spinal cord or brain to effectors (muscles and glands). Connector neurons are found only within the central nervous system and serve to connect sensory and motor neurons and one another.
Figure 21.1 shows three different types of neurons. Using your textbook as a guide, fill in the labels on the figure from the list of words given.
Study the model of the motor neuron. Identify the following structures on the model: axon, dendrites, mitochondria, myelin sheath, neurofibrils, neurolemma, Nissl bodies, nodes of Ranvier, nucleus of the perikaryon, nucleus of the Schwann cell, perikaryon, and Schwann cell.
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