A Neurophysiologist Is Investigating Nerve Reflexes in Two Different Animals

Multiple Choice

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.