Page 346 - Atlas of Histology with Functional Correlations

FIGURE 9.7 ■ Ultrastructure of typical axodendritic synapses in the CNS.
Transmission electron micrograph. Courtesy of Dr. Mark Desantis, Professor

Emeritus, WWAMI Medical Program, University of Idaho, Moscow, ID.
×75,000.

FUNCTIONAL CORRELATIONS 9.1 ■ Synapses

Synapses are specialized membrane junctions where transmissions of nerve
impulses are conveyed unidirectionally from a presynaptic neuron to a
postsynaptic membrane of a neuron; effector cells, such as muscle fibers; or

gland cells. The synapses process and convert an impulse from the
presynaptic cell into a signal that affects the postsynaptic cell membranes and
initiates stimulatory neuronal activities. Most synapses in mammals release
chemical neurotransmitters from the presynaptic portion of one axon or
dendrite to the postsynaptic membrane of another cell. Numerous

neurotransmitters exist, including amino acids such as glutamate,
catecholamines, acetylcholamine, and others. Neurotransmitter chemicals
first cross the synaptic cleft, bind to specific neurotransmitter receptors on

the postsynaptic membrane, and produce either an excitatory response or an
inhibitory response at the postsynaptic membrane. The final generation of

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