Question

Which one of the following statements is TRUE?

• A. A myelinated axon has a greater ATP requirement than an unmyelinated axon of the same diameter and length
• B. An unmyelinated axon has a greater ATP requirement than a myelinated axon of the same diameter and length
• C. An unmyelinated axon has the same ATP requirement as a myelinated axon of the same diameter and length
• D. An unmyelinated axon always has a greater ATP requirement than a myelinated axon irrespective of their diameter and length

Hint:

Myelination reduces ATP consumption by limiting depolarization to small nodes, while unmyelinated fibers depolarize along their entire length.

Answer 1

The Correct Option is B

Step 1: Understanding ATP usage in axons.
ATP is required primarily for restoring ion gradients after an action potential. The more membrane surface area that undergoes depolarization, the higher the ATP consumption.
Step 2: Compare myelinated vs. unmyelinated axons.
In myelinated axons, action potentials occur only at the Nodes of Ranvier, so only small membrane segments need ion pumping. This reduces ATP usage drastically.
In unmyelinated axons, the entire axonal membrane undergoes depolarization, increasing sodium–potassium pump activity and thus ATP demand.
Step 3: Conclusion.
For axons of equal diameter and length, an unmyelinated axon always requires more ATP than a myelinated one.
Therefore, the TRUE statement is (B).