$GABA$ (Gamma-aminobutyric acid) is a:

True about electrical synapses:
$(I)$. Pre and postsynaptic neurons are in very close proximity.
$(II)$. Pre and postsynaptic neurons are separated by a synaptic cleft.
$(III)$. Impulse transmission is very fast.
$(IV)$. Electrical synapses are common in our system.
Select the correct option.

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.
$\quad\quad\quad P\quad\quad\quad Q$

What is the primary function of acetylcholine?

The brief delay in the transmission of an impulse through a synapse is called .........

The parasympathetic nervous system functions through the secretion of which substance?