The receptors of neurotransmitters are present on/in the

In $P$,the membranes of pre-synaptic and post-synaptic neurons are in very close proximity,whereas in $Q$,there is a space between the membranes of pre-synaptic and post-synaptic neurons.
$\quad\quad\quad P\quad\quad\quad Q$

Which of the following is released by the parasympathetic nervous system?

Explain the process of transport and release of neurotransmitter with the help of a labelled diagram,showing complete neuron,axon terminal and synapse.

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?

$A$ synapse is formed by