Which lipid-rich layer surrounds the nerve fiber?

Which organelle is absent in a mature neuron?

With which system are dendrites associated?

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

The junction between two adjacent Schwann cells in a myelinated nerve fiber is known as:

Which of the following is regarded as a unit of nervous tissue?