What is the $Axon$ $hillock$?

With which system are dendrites associated?

The medullary sheath of the nerve fibre is interrupted at intervals by

Four healthy people in their twenties were involved in injuries resulting in damage and death of a few cells of the following types. Which of these cells are least likely to be replaced by new cells?

Which of the following structures distinguishes a neuron from other cells?

Four healthy individuals suffer an injury at the age of $20$ years,which results in the damage and death of some cells. Which of the following cells will show the least amount of regeneration?