The synapse is the functional relationship of contact between the ends of nerve cells. It's a concept that comes from a Greek word which means 'union' or 'link '.
This communicative process between neurons is started by a chemical-electrical discharge in the sending (presynaptic) cell membrane. When this nerve impulse reaches the end of the axon (nerve fibre), the neuron secretes a substance that fits into the synaptic space between this neuron transmitter and the receiver (postsynaptic) neuron. It is for this neurotransmitter to excite another neuron.
Regarding the type of transmission of the nerve impulse, the synapse can be either electrical or chemical. In the case of the electrical synapse, processes pre and postsynaptic are continuous because the cytoplasmic union by tubular protein molecules, which allow stimulation to move from one cell to another without the need for chemical mediation. Thus, the electrical synapse offers low resistance between neurons and minimum delay in synaptic transmission since there is no chemical mediator.
The chemical synapse is the most common type of synapse. In such cases, the neurotransmitter is used, so to speak, of vehicle between two neurons, and then spreads into the synaptic space to attach to receptors, which are special molecules of proteins located in the postsynaptic membrane.
The union of the neurotransmitters and receptors of the postsynaptic membrane generates changes to the level of the permeability of the membrane, while the nature of the neurotransmitter and receptor molecule determines whether the effect is excitation or inhibition of the postsynaptic neuron.