Nodes of Ranvier are found in

Some cells in our body can be over a foot long. They are:

Select the correct option for dendrites and axons.
$I -$ Short fibers,$II -$ Long fibers,$III -$ Transmit impulses away from the cell body,$IV -$ Transmit impulses towards the cell body,$V -$ Highly branched fibers,$VI -$ Unbranched fibers
Dendrites $\quad$ $\quad$ Axon

What is the myelin sheath derived from?

Which of the following statements are correct for a nerve cell?
$(I)$. Each neuron has a cell body
$(II)$. Each neuron has a single axon
$(III)$. Neurons are the functional units of the nervous system
Select the correct option.

Neurons with long axons are called