Page 305 - Atlas of Histology with Functional Correlations

are the myelinated motor nerves (3) and their branches, the axons (1, 5, 10).

The motor nerve (3) courses within the muscle, branches, and distributes its
axons (1, 5, 10) to the individual muscle fibers (6, 7). The axons (1, 5, 10)
terminate on individual muscle fibers as specialized junctional regions called
motor endplates (4, 9). The small, dark, round structures seen in each motor
endplate (4, 9) are the terminal expansion of the axons (1, 5, 10). Some axons (1)

are also seen without motor endplates as a result of tissue preparation.

FIGURE 8.7 ■ Skeletal muscles, nerves, axons, and motor endplates. Stain:
silver. High magnification.

FUNCTIONAL CORRELATIONS 8.1 ■ Skeletal

Muscles

Skeletal Muscle and Motor Endplates

Skeletal muscles are voluntary because the stimulation for their
contraction and relaxation is under conscious control. Large motor nerves or

axons innervate skeletal muscles. Near the skeletal muscle, the motor nerve
branches, and a smaller axon branch individually innervates a single muscle
fiber. As a result, skeletal muscle fibers contract only when stimulated by an

axon. Also, each skeletal muscle fiber exhibits a specialized site where the
axon terminates. This neuromuscular junction, or motor endplate, is the
site where the impulse from the axon is transmitted to the skeletal muscle
fiber.

The terminal end of each efferent (motor) axon contains numerous small

vesicles that contain the neurotransmitter acetylcholine. Arrival of a nerve
impulse, or action potential, at the axon terminal causes the synaptic

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