The movement of the nerve impulse across the synaptic cleft is primarily

Identify the correct sequence of action potential transmission as it arrives at the axon terminal from the choices given below:

Which of the following hormones act as neurotransmitters?

How is the synaptic cleft formed?

Parkinson's disease (characterized by tremors and progressive rigidity of limbs) is caused by the degeneration of brain neurons that are involved in movement control and make use of the neurotransmitter:

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.