Page 348 - Atlas of Histology with Functional Correlations

FIGURE 9.8 ■ Motor neurons: anterior horn of the spinal cord. Stain:
hematoxylin and eosin. High magnification.

FUNCTIONAL CORRELATIONS 9.2 ■ Neurons,

Interneurons, Axons, and Dendrites

Functionally, neurons are classified as afferent (sensory), efferent (motor),
or interneurons. Sensory or afferent neurons conduct impulses from
receptors in the internal organs or from the external environment to the CNS.
Somatic afferent fibers conduct impulses from the body surface and body
organs, such as muscles, tendons, and joints. Visceral afferent fibers

conduct impulses from internal organs, glands, and blood vessels. Motor, or
efferent, fibers convey impulses from the CNS to the effector muscles or
glands in the peripheries. Interneurons constitute the majority of the neurons

in the CNS. They serve as intermediaries or integrators of nerve impulses and
connect neuronal circuits between sensory neurons, motor neurons, and other
interneurons in the CNS.

Neurons are specialized for irritability, conductivity, and production or
synthesis of neurotransmitters and neurohormones. After a mechanical or

chemical stimulus, these neurons react (irritability) to the stimulus and
transmit (conductivity) the information via axons to other neurons or
interneurons in different regions of the nervous system. Strong stimuli create
a wave of excitation, or nerve impulse (action potential), which is then

propagated along the entire length of the axon (nerve fiber).

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