Question

The area where the myelin sheath is absent in the nerve fiber is called:
A. Schwann cells
B. Schwann nodes
C. Nissls granules
D. Node of ranvier

Answer 1

Hint: Myelin is an insulating layer, or sheath that wraps the nerves associated with the brain and spinal cord. It is made from protein and cerebrosides. This myelin sheath lets in electric impulses to transmit speedy and effectively alongside the nerve cells. If myelin is damaged, those impulses gradual down. This can cause sicknesses consisting of a couple of sclerosis.

Complete answer:
Option: A - Schwann cells are the major glial cells and are known to form the myelin sheath. So, Schwann cells do not designate the area where myelin sheath is absent in the nerve fiber.
So, Option A is not the correct answer.
Option: B - Schwann nodes are nothing in reality i.e., no such structure is present in a nerve fiber hence it cannot be the region of the nerve fiber where the myelin sheath is absent.
Thus, Option B is also not correct.
Option C - Nissl's granules are present in the cyton(cytoplasm) of the neurons and are the sites of protein synthesis in neurons. Thus, in any way it is not related with myelin sheath.
Thus, Option C is also incorrect.
Option D - A node of ranvier is the gap between two adjacent Schwann cells. Since Schwann cells form the myelin sheath, a node of ranvier will be the area on the neuron or nerve fiber where the myelin sheath is actually absent.
Thus, Option D is the correct answer.

Hence, Option D. Node of Ranvier is the correct answer.

Note:
Nervous system consists of a large number of nerve fibers composed of cells called neurons. A neuron typically consists of an axon, cyton and the dendrites. All the three structures help in the conduction of nerve impulses through nerves. Based on their function’s neurons are classified into motor neurons, sensory neurons and interneurons. Neurons may also be classified based on the presence or absence of myelin sheath.