When an impulse moves down the axon,
a. sodium ions first rush out of the cell.
b. a small part of the axon momentarily reverses its polarity.
c. the resting potential of the cell does not change.
d. potassium ions are pumped into the axon.
B?
OK, thanks!
Yes, the correct answer is B.
To understand why, let's break down the process of an impulse moving down the axon.
During resting state, the cell membrane is polarized, meaning there is a difference in electrical charge between the inside and outside of the cell. The inside of the cell has a negative charge, while the outside has a positive charge.
When an impulse travels down the axon, there is a sudden increase in the electrical charge at a specific point of the cell membrane. This is called an action potential. The action potential occurs due to the movement of ions across the cell membrane.
In response to the electrical change, sodium (Na+) channels on the cell membrane open. This allows sodium ions to rapidly rush into the cell, causing a depolarization of the membrane. As a result, the small section of the axon associated with the action potential momentarily reverses its polarity, with the inside of the axon becoming positively charged and the outside becoming negatively charged. This is known as depolarization.
Option A is incorrect because sodium ions, in fact, rush into the cell, not out of it.
Option C is incorrect because the resting potential of the cell does change during an action potential. It temporarily becomes depolarized.
Option D is incorrect because potassium ions (K+) are not pumped into the axon during an action potential. The movement of potassium ions occurs later in the repolarization phase, where the cell membrane returns to its resting state.
Therefore, the correct answer is B, a small part of the axon momentarily reverses its polarity.