What is the likely impact of this toxin on action potentials?

Question

A.  They will occur more frequently.
B.  They will be stronger and more unpredictable.
C.  Without ion gradients, action potentials are not possible.
D.  They will have longer refractory periods.

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.  Without ion gradients, action potentials are not possible.

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). Also remember that action potentials are “all-or-none” events that do not increase in amplitude (strength), but vary in frequency.

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 B)? Remember that ion gradients are necessary for the production of action potentials. If sodium can flow freely down its concentration gradient, then its gradient will be gone and there will be no force attracting it into the cell during an action potential (and thus no action potential will occur).