MCAT Biology Question 47: Answer and Explanation

Home > MCAT Test > MCAT biology practice tests

Test Information

Question: 47

2. All of the following are associated with the myelin sheath EXCEPT:

  • A. faster conduction of nerve impulses.
  • B. nodes of Ranvier forming gaps along the axon.
  • C. increased magnitude of the potential difference during an action potential.
  • D. saltatory conduction of action potentials.

Correct Answer: C

Explanation:

Myelin is a white lipid-containing material surrounding the axons of many neurons in the central and peripheral nervous systems. It is arranged on the axon discontinuously; the gaps between the segments of myelin are called nodes of Ranvier, eliminating choice (B). Myelin increases the conduction velocity by insulating segments of the axon so that the membrane is permeable to ions only at the nodes of Ranvier, eliminating choice (A). The action potential jumps from node to node, a process known as saltatory conduction, eliminating choice (D). Action potentials are often described as being "all-or-nothing"; the magnitude of the potential difference in an action potential is constant, regardless of the intensity of the stimulus. Thus, myelin does not affect the magnitude of the potential difference in an action potential, making choice (C) the correct answer.

Previous       Next