What is a synapse? What happens at the synapse between two neurons? How are the messages carried across a synapse? Explain with the help of a labelled diagram.

In the nervous system, the synapse is a junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter. Synapse between two neurons allows electrical impulses to pass in one direction only. The process is as follows: When the receptor sends an electrical impulse, it reaches at the end of the axon of sensory neuron. Then this electrical impulse releases a chemical, known as neurotransmitter, in very small amount into the synapse between two adjacent neurons. Neurotransmitter crosses the synapse and starts a similar electrical impulse in the dendrite of the next neuron. By this way, the electrical impulse passes from one neuron to the next across the synapse.