Four healthy people in their twenties faced injuries resulting in damage and death of a few cells given below. Which of the cells are least likely to be replaced by new cells?

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.

The axon contains in its axis cylinder a fibrillar component of $90 \ \mathring{A}$ thick called

$A$ structure of neuron comprises of

Differentiate between medullated nerve fibers and non-medullated nerve fibers.

The axon part of the neuron is highly modified for which of the following functions?