The gap between two adjacent myelin sheaths is called ........

Choose the correct statements about Nissl's granules from the codes given below:
$I.$ There are regular masses of ribosomes
$II.$ There are irregular masses of ribosomes and $ER$
$III.$ There are granular bodies
$IV.$ They synthesise proteins in the cell

Neurons with long axons are called

Where are the $Nissl$ granules found?

Identify $P, Q,$ and $R$ in the given neuron.

What is the function of neurons?