Nissl bodies are mainly composed of

Which of the following statements is true?

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

Where are the "Nodes of Ranvier" found?

On nerve fibres,to prevent the leakage of an impulse,a layer of ...... is found.

Mark the following statements as true/false and choose the correct option from the codes given below:
$I.$ Neuroglial cells are the packing and supporting cells found in the brain and spinal cord.
$II.$ Oligodendrocytes are a category of glial cells that form myelin sheaths around the axon.
$III.$ Microglia provide mechanical support to the neurons.
$IV.$ Astrocytes communicate with one another through potassium channels.