The chemical causing the transmission of nerve impulse across synapses is

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.

Parkinson's disease,characterized by tremors and rigidity of limbs,is caused by the degeneration of brain cells involved in movement control and the use of which neurotransmitter?

Identify the labelled parts $A, B$ and $C$ from the given diagram.

How long does the synaptic delay last (in $, ms$)?

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