What is a synapse? How many types of synapses are found? Discuss the conduction of a nerve impulse through a synapse with a diagram.

(N/A) synapse is a junction through which a nerve impulse is transmitted from one neuron to another.
There are two types of synapses:
$(i)$ Electrical synapses
$(ii)$ Chemical synapses
$(i)$ Electrical Synapses:
In electrical synapses,the membranes of pre- and post-synaptic neurons are in very close proximity. Electrical current can flow directly from one neuron into the other across these synapses. Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. Electrical synapses are rare in our system.
$(ii)$ Chemical Synapses:
In chemical synapses,the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft. The pre-synaptic neuron transmits an impulse across the synaptic cleft to the post-synaptic neuron. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. The axon terminals contain vesicles filled with these neurotransmitters. When an impulse arrives at the axon terminal,it stimulates the movement of the synaptic vesicles towards the membrane,where they fuse with the plasma membrane and release their neurotransmitters into the synaptic cleft. The released neurotransmitters bind to their specific receptors present on the post-synaptic membrane. This binding opens ion channels,allowing the entry of ions which can generate a new potential in the post-synaptic neuron. The new potential developed may be either excitatory or inhibitory.