neuromuscular junction has an organization identical to a synapse. However, the knob
is much larger. The postsynaptic membrane is also larger and has foldings to increase
its surface area.
Figure 5-3. A neuromuscular junction.
(1) Motor neuron. The axon of a motor neuron ends as it reaches a skeletal
muscle fiber. At this point, it has a terminal knob. Within this knob are synaptic vesicles
(bundles of neurotransmitters). The presynaptic membrane lines the surface of the
terminal knob and lies close to the muscle fiber.
(2) Synaptic cleft. The synaptic cleft is a space between the terminal knob
of the motor neuron and the membrane of the muscle fiber.
(3) Muscle fiber. The terminal knob 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
chemical that inactivates the used neurotransmitter.
5-7. PROCESS OF NEUROTRANSMISSION
a. The dendrites receive the impulse and transfer it to the nucleus. The nucleus
will then cause a change in the permeability of the membrane surrounding the axon.
Potassium, which is normally present in high concentrations within the axon, will diffuse
out. Sodium, which is usually present in high concentrations outside the axon, will rush