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Question #47422
The Question
In a patient suffering from an autoimmune disorder that causes progressive demyelination of neurons in the central nervous system (such as Multiple Sclerosis), nerve impulse conduction eventually slows down and is completely blocked. Which of the following best explains the primary physiological reason for this conduction block?
Options
- A.
The internodal axolemma lacks a sufficient density of voltage-gated Na+ channels to sustain continuous action potential propagation.
- B.
The loss of myelin increases the axonal membrane resistance, preventing the rapid influx of Na+ ions during depolarization.
- C.
The Na+/K+ ATPase pumps are located exclusively on the myelin sheath and are destroyed during the autoimmune response.
- D.
Continuous conduction replaces saltatory conduction, leading to synaptic fatigue due to excessive Ca2+ influx at the nodes of Ranvier.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Nodes_of_Ranvier|Schwann_Cells|Voltage_Gated_Na_Channels
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often harbor the misconception that removing the myelin sheath simply converts a 'fast' myelinated neuron into a 'slow' unmyelinated neuron.
However, naturally unmyelinated neurons have an even distribution of voltage-gated Na+ channels along their entire length.
Myelinated neurons lack these channels in the internodal regions.
Therefore, demyelination does not just slow conduction; it causes a complete physiological block due to structural channel deficiency and current leakage.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Neural Control and Coordination - Class 11 |
| Concept | Saltatory Conduction Nodes |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |