Figure 11-3. A neuromuscular junction.
(1) Motor neuron. The axon of a motor neuron ends as it reaches a striated
muscle fiber (of a skeletal muscle). At this point, it has a terminal bulb. Within this bulb
are synaptic vesicles (bundles of neurotransmitter). The presynaptic membrane lines
the surface of the terminal bulb and lies close to the muscle fiber.
(2) Synaptic cleft. The synaptic cleft is a space between the terminal bulb of
the motor neuron and the membrane of the muscle fiber.
(3) Muscle fiber. The terminal bulb of the motor neuron protrudes into the
surface of the muscle fiber. The membrane lining the synaptic space has foldings and
is called the postsynaptic membrane. Beneath the postsynaptic membrane is a chemi-
cal which inactivates the used neurotransmitter.
Section III. THE HUMAN CENTRAL NERVOUS SYSTEM
The major divisions of the human nervous system are the central nervous
system (CNS), the peripheral nervous system (PNS), and the autonomic nervous