What is the likely impact of this toxin on the resting potential of a neuron?

Question

A.  The resting potential will require more energy to maintain.
B.  The resting potential will be more negative.
C.  It will destroy the ion gradients necessary for the resting potential.
D.  The resting potential will promote action potentials with a larger depolarization.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content/Choose Answer
· What do you already know about sodium and potassium? What other information is related to the question?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  It will destroy the ion gradients necessary for the resting potential.

Clarify Question
· What is the key concept addressed by the question?
        o Sodium and potassium ion flow and equilibrium.
· What type of thinking is required?
        o This is an analyze question because you have to consider the normal distribution of ions across a cell membrane, and then predict the result of free movement of these ions.

Gather Content/Choose Answer
· What do you already know about sodium and potassium? What other information is related to the question?
        o To solve this problem, you’ll need to understand that sodium normally has a greater concentration outside the cell and potassium has a greater concentration inside the cell. If a channel is locked open, this would allow free flow of sodium and potassium. Sodium will rush into the cell, and potassium will rush out of the cell, down their concentration gradients. This would reduce the ionic gradients and prevent the formation of action potentials (caused by sodium rushing into the cell) leading to paralysis, as well as prevent the maintenance of the resting membrane potential (which is largely caused by the equilibrium potential of potassium). Resting membrane potential is negative (usually about -60 to -70 mV), because there are more positively charged ions inside the cell than outside. Although leaky potassium channels allow a small amount of potassium to flow out of the cell continually, having sodium-potassium channels locked open would allow potassium to flow out rapidly, which would increase the resting membrane potential (i.e., make it less negative).

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o If you figured out the correct answer, good job! If not, where did you go wrong? Did you remember that the distribution of sodium and potassium across the cell membrane are opposite of each other, and that sodium has a greater concentration outside of the cell, whereas potassium has a greater concentration inside the cell. Did you recall that ions always flow down their electrochemical gradients? Did you recall that action potentials are “all-or-none” responses such that larger depolarizations would not be possible (answer D)? Also, did your remember that the sodium-potassium pump requires energy in the form of ATP? If the pump is locked open, it will not be utilizing ATP and so the resting potential would require more energy to maintain (answer A), but with the channels locked open it is not able to.