The pre-synaptic part is:

The following figure shows the axon terminal and synapse. What is the function of $P$?

Five events in the transmission of a nerve impulse across a synapse are given below:
$a.$ Certain ion channels open,allowing ions to enter and generate a new action potential in the post-synaptic neuron.
$b.$ Neurotransmitter molecules bind to receptors on the post-synaptic membrane.
$c.$ Synaptic vesicles fuse with the pre-synaptic membrane,and the neurotransmitter is released into the synaptic cleft. Depolarization of the pre-synaptic membrane is induced.
$d.$ An action potential reaches the axon terminal.
What is the correct sequence of these events?

The neurotransmitter which communicates between two neurons or between a neuron and a muscle is

What is a neurotransmitter?

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?