A neurophysiologist is investigating nerve reflexes in two different animals: a crab and a fish. Action potentials are found to pass more rapidly along the fish's neurons. What is the most likely explanation?
A) The fish's axons are smaller in diameter; small axons transmit action potentials faster than large axons do.
B) Unlike the crab, the fish's axons are wrapped in myelin; myelination increases the speed of action potential transmission.
C) There are more ion channels in the axons of the crab compared with fish axons.
D) Unlike the crab, the fish's axons are wrapped in myelin, and the fish's axons are smaller in diameter; small axons transmit action potentials faster than large axons do.

Question

Quizplus · Accepted Answer

Myelination increases the speed of action potential transmission, and the fish's axons are wrapped in myelin. This is the most likely explanation for the faster action potential transmission in fish neurons compared to crab neurons. Option A is incorrect because small axons do not necessarily transmit action potentials faster than large axons. Option C is incorrect because having more ion channels would not necessarily increase the speed of action potential transmission. Option D is partly correct, but the size of the axon is not the main reason for the faster transmission in fish neurons.

A Neurophysiologist Is Investigating Nerve Reflexes in Two Different Animals