There are two types of synapses - electrical synapses and chemical synapses.
Conduction and transmission of nerve impulse across a synapse : The theory of chemical transmission or synaptic transmission states that a chemical substance, acetylcholine, is liberated at the synapse and it diffuses through the synaptic transmission occurs in the following way :
(a) Release of a neurotransmitter substance at the tip of axon from the synaptic vesicles through presynaptic membrane.
(b) Diffusion of this chemical substance, acetylcholine cross the synaptic cleft.
(c) Combination of acetylcholine with a chemireceptor on the post synaptic membrane.
(d) Depolarization of the post synaptic membrane by neuro-transmitter substance initiate a fresh impulse or action potential passing through the neurons.
(e) Inactivation of acetylcholine by an enzyme acetylcholine esterase in the post synaptic membrane.