Answer:
Nerve impulses, which are electrical, do not jump across the synaptic gap at synapses. Instead, the arrival of a nerve impulse at the axon terminal triggers the release of chemicals called neurotransmitters from the axon terminal into the synaptic gap. The neurotransmitter molecules diffuse across the gap to the membrane of the postsynaptic cell, in effect serving as chemical messengers. There are molecules called receptors that stick off the membrane of the postsynaptic cells. In order to have any effect on the postsynaptic cell, a neurotransmitter molecule must fit onto a receptor. There are specific receptors for specific neurotransmitters, and the neurotransmitter molecule must fit onto the receptor precisely, as a key fits into a lock. When a neurotransmitter successfully fits ont a receptor, it causes changes in the postsynaptic cell, making it more (or less) likely to fire off a nerve impulse of its own.