At a chemical synapse a synaptic cleft separates the pre- and postsynaptic cells so they are not electrically coupled. Within the cytoplasm of the synaptic terminal of a presynaptic cell are numerous synaptic vesicles containing thousands of neurotransmitter molecules. The neurotransmitter diffuses to the postsynaptic membrane where it binds to specific receptors, causing ion gates to open. Depending on the type of receptors and the ion gates they control, the neurotransmitter may either excite the membrane by depolarization or inhibit the postsynaptic cell by hyperpolarization. The neurotransmitter molecules are quickly degraded by enzymes and the components recycled to the presynaptic cell.
Chemical synapses allow transmission of nerve impulses in only one direction.
Synaptic vesicles and their neurotransmitter molecules are found only in the synaptic terminals at the tip of axons. Receptors for neurotransmitters are located only on postsynaptic membranes. Neurotransmitters and Receptors Dozens of different molecules are known to be neurotransmitters and many others are suspected to function as such. Must be present in and discharged from synaptic vesicles in the presynaptic cell when stimulated and affect the postsynaptic cell's membrane potential. Must cause an IPSP or EPSP when experimentally injected into the synapse.