What is a synapse and what does it do?

Synapse ( or neuronal junction) is the site of transmission of nerve impulse between two neurons.

The synapse along with its neurotransmitters acts as a physiological valve, directing the conduction of nerve impulses in regular circuits and preventing random and chaotic stimulation of nerves.

The arrival of a nerve impulse at the presynaptic terminal causes a movement towards the synaptic vesicles. These fuse with the membranes and release neurotransmitters. A single neurotransmitter may elicit different responses from different receptors.

The neurotransmitter transmits the nerve impulse to the post synaptic fibre, by diffusing across the synaptic cleft and binding to receptor molecules on the post synaptic membrane.

This results in a series of reactions that open "channel shaped " protein molecules. Electrically charged ions then flow through the channels in or out of the neurons. If the net flow of positively charged ions is large enough, it leads to the generation of a new nerve impulse called action potential.

Later the neurotransmitter molecules are deactivated by enzymes in the synaptic cleft.