Question

Node of the Ranvier is the place where

• A. Myelin sheath and neurilemma are discontinuous
• B. Axolemma is absent
• C. Axolemma is discontinuous
• D. Myelin sheath is discontinuous

Answer 1

The correct option is D

Myelin sheath is discontinuous

The correct option is D.

Explanation for the correct option:

Option D:

1. The periodic gap in the insulating sheath (myelin) on the axon of certain neurons that serves to facilitate the rapid conduction of nerve impulses is referred to as a node of Ranvier.
2. The presence of Ranvier nodes causes the myelin sheath to be discontinuous.
3. To enable saltatory conduction, the myelin sheath is not continuous.

Explanation for the incorrect options:

Option A:

1. A protective layer or sheath called myelin develops around nerves, including those in the brain and spinal cord.
2. A nerve axon's neurilemma is its thin protective covering (including myelin where this is present).
3. Neurilemma and myelin sheath are discontinuous: to have a Ranvier node, myelin sheath must be absent, but neurilemma does not have to be.
4. Myelin sheath is discontinuous, when the myelin sheath is discontinuous, the Node of Ranvier forms.
5. Because of the Ranvier nodes, the myelin sheath is discontinuous.
6. Nodes of Ranvier, a recurring opening in the myelin sheath that surrounds the axon of some neurons, help nerve impulses to travel more quickly.
   

Option B:

1. An axon's plasma membrane for a brief period of time following the passage of a nerve impulse along with a nerve fibre, while the axolemma remains depolarized, a second stimulus, no matter how powerful, is unable to excite the nerve.
2. Additionally, axolemma can be found at Ranvier's nodes.
   

Option C:

1. In an axon's plasma membrane while the axolemma is still depolarized after the passage of a nerve impulse along with a nerve fibre, a second stimulus, no matter how strong, is unable to excite the nerve.
2. Nodes of Ranvier, sometimes referred to as myelin-sheath gaps in neurology and anatomy, appear along a myelinated axon where the axolemma is exposed to the extracellular environment.

Final answer: The node of the Ranvier is the place where the myelin sheath is discontinuous.