Synaptic fatigue is due to

The following figure shows the structure of a neuron. Which of the following parts contains neurotransmitters?

$A$ synapse is formed by

What happens if $GABA$ is released at the synapse?

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

The pre-synaptic part is: