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Question #47415
The Question
In a demyelinating pathology affecting the central nervous system, the destruction of the myelin sheath leads to a severe impairment of nerve impulse propagation. Why does the affected axon fail to simply adopt the continuous conduction mechanism seen in normal unmyelinated neurons?
Options
- A.
The loss of myelin decreases membrane capacitance and increases transverse electrical resistance, preventing the local current from reaching the threshold.
- B.
Voltage-gated Na+ channels are highly clustered at the Nodes of Ranvier; the newly exposed internodal membrane lacks sufficient channels and suffers from increased ion leakage, causing the current to decay.
- C.
Demyelination destroys the Schwann cells, which are directly responsible for maintaining the resting membrane potential via the Na+-K+ ATPase pump.
- D.
The exposed internodal axolemma undergoes a massive influx of Ca2+ ions, which permanently inactivates the voltage-gated Na+ channels.
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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|Voltage-gated Na+ channels|Multiple Sclerosis
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often assume that a demyelinated axon simply reverts to being a slow-conducting unmyelinated axon.
They fail to account for the spatial distribution of voltage-gated Na+ channels (clustered at nodes) and the biophysical changes (increased leakage) that cause the local current to decay below the threshold.
Additionally, Option C contains a classic location trap (Schwann cells in CNS instead of Oligodendrocytes).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Neural Control and Coordination - Class 11 |
| Concept | Resting Membrane Potential Ionic Flux |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |