. A research strain of mice has a mutation that causes voltage-gated sodium channels to take longer to return to the active state after a spike. What is the likely consequence for transduction of sensory stimuli?

Question

A.  There will be no effect on sensory perception, because sensory information relies on stimulus-gated ion channels and not voltage-gated ion channels.
B.  Sensory information will be incorrectly perceived as high intensity stimuli, due to the increased frequency of action potentials.
C.  The mutation will interfere with the ability of stimuli to create receptor potentials, and thus the neuron will fire with slow, broad action potentials, giving the animal enhanced sensory perception.
D.  Due to a longer refractory period, the neuron will be unable to conduct high frequency action potentials, and thus will not effectively transmit information about strong stimuli.


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

Gather Content
What do you already know about action potentials? What other information is related to the question?

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?

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

D.  Due to a longer refractory period, the neuron will be unable to conduct high frequency action potentials, and thus will not effectively transmit information about strong stimuli.


Clarify Question
What is the key concept addressed by the question?
        · What is the effect of the delay of a neuron to return to a resting state following an action potential?
What type of thinking is required?
            o This is an analyze question because you have to think about the whole process of an action potential to understand how slowing down part of that process can affect subsequent action potentials.

Gather Content
What do you already know about action potentials? What other information is related to the question?
        · You already know that action potentials are produced by the opening and closing of sodium and potassium channels. When a stimulus is applied, if it is strong enough to bring the neuron membrane potential above threshold, sodium channels are opened and the cell is depolarized. Shortly thereafter, the sodium channels close and potassium channels open, repolarizing the cell back toward the resting membrane potential. The time it takes to repolarize the cell is called the refractory period. If a mutation causes the sodium channels to stay open longer, then it will take much longer for the cell to be repolarized. A neuron needs to be repolarized before a subsequent action potential can fire. Thus, the longer the refractory period, the longer the time possible between action potentials, and thus a decrease in action potential frequency.

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
        · The mutation slowing voltage-gated sodium channels would produce a longer refractory period, thus preventing high frequency action potentials. As high frequency of action potentials represents stronger stimuli, the nervous system would not be able to transmit information about such stimuli. Although receptor potentials may not be affected as significantly as action potentials, receptor potentials lead to action potentials once they reach threshold. This, of course, would affect sensory perception.

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 Answering this question correctly depended not only on knowing the steps of an action potential including the refractory period, and knowing the difference between a receptor and action potential. If you got it wrong, which answer did you choose? Did you think that this mutation might affect both receptor and action potentials? Did you get the link between refractory period and frequency of action potentials (that is, the shorter the refractory period, the higher the potential frequency)?