The figure shows an axon terminal and synapse. Select the option giving correct identification of labels $A-D$.

What is the difference between electrical transmission and chemical transmission?

How is the synaptic cleft formed?

Muscle contraction is initiated by a signal sent by the central nervous system by the release of . . . . . . .

Arrange the following events in proper sequence during impulse transmission across a chemical synapse:
$(a)$ Fusion of synaptic vesicles with the cell membrane of the presynaptic neuron.
$(b)$ $Ca^{++}$ channels open and $Ca^{++}$ diffuses into the synaptic knob from the extracellular fluid.
$(c)$ Neurotransmitter binds with receptors of the postsynaptic cell.
$(d)$ Release of neurotransmitter by exocytosis.

What is an electrical synapse?