Which one of the following is essential for the formation of the myelin sheath?

Which of the following is the structural and functional unit of the nervous system?

Neuroglia are

What are the Nissl's granules of a neuron composed of?

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?

Which one of the following pairs of structures distinguishes a nerve cell from other types of cells?