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Exercise 3: Neurophysiology of Nerve Impulses: Activity 5: The Action Potential: Measuring Its Absolute and Relative
Refractory Periods Lab Report
Pre-lab Quiz Results
You scored 100% by answering 4 out of 4 questions correctly.
- Which of the following occurs after the peak of the action potential?
You correctly answered: d. All of these occur. - What is meant by Na+ channel inactivation?
You correctly answered: b. The Na+ channel no longer allows Na+ ions to pass through it. - What happens when voltage-gated K+ channels open?
You correctly answered: d. All of these occur. - It is harder to generate a second action potential soon after the first action potential because
You correctly answered: d. All of these make it harder to generate a second action potential.
Experiment Results
Predict Question:
Predict Question: If you further decrease the interval between the stimuli, will the threshold for the second action potential
change?
Your answer : c. The threshold for the second action potential will be higher (requiring a larger depolarization).
Stop & Think Questions:
Threshold can be defined as the minimum voltage needed to generate an action potential. Is the threshold for the first action
potential the same as, or different from, the threshold for the second action potential with a 60 msec interval?
You correctly answered: a. The threshold for the first action potential is lower than the threshold for the second action
potential.
Experiment Data:
Interval Between Stimuli (msec) Stimulus Voltage (mV) Second Action Potential?
250 20 Yes
125 20 Yes
60 20 No
60 25 No
60 30 Yes
30 30 No
30 35 No
30 40 No
30 45 Yes
15 60 Yes
7.5 60 Yes
3.75 60 No
Post-lab Quiz Results
You scored 100% by answering 5 out of 5 questions correctly.
- What is the original threshold for this neuron?
You correctly answered: a. A 20 mV depolarization to -50 mV. - As the interval between stimuli decreases, the depolarization needed to generate the second action potential
You correctly answered: a. increases. - Judging from your results, what time period after the first action potential best describes the relative refractory period
(the time when a second action potential can be generated only if the stimulus intensity is increased)?
You correctly answered: c. 7.5 ms-60 msec - At what interval between stimuli did the second action potential fail, regardless of the stimulus intensity?
You correctly answered: d. 3.75 msec - What is the absolute refractory period for this neuron?
You correctly answered: d. 3.75 msec
Review Sheet Results
- Define inactivation as it applies to a voltage-gated sodium channel.
Your answer:
Inactivation of voltage-gated sodium channel refers the status that it can not diffuse Na+. - Define the absolute refractory period.
Your answer:
Whether stimulus strong or not action potential can not be generated in refractory period. - How did the threshold for the second action potential change as you further decreased the interval between the stimuli?
How well did the results compare with your prediction?
Your answer:
As the interval between stimuli was decreased, the threshold for the second action potential change increased. Prediction
was right. - Why is it harder to generate a second action potential during the relative refractory period?
Your answer:
The refractory period is the period during which initiation of a second action potential is inhibited. Because voltage-gated K+
channel that oppose depolarization is open during the refractory period.