Name: Ori Baronin Exercise 3: Neurophysiology of Nerve Impulses: Activity 3: The Action Potential: Threshold Lab Report Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. Axons are You correctly answered: d. long, thin structures that extend from a neuronal cell body. 2. Which of the following is easier? You correctly answered: a. extracellular recordings of the action potential 3. An action potential is usually usually initiated in an axon at or near You correctly answered: d. all of the above 4. The initiation of an action potential in a sensory neuron in the body normally You correctly answered: a. follows a sufficiently large depolarizing receptor potential.
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Experiment Results Predict Question: Predict Question: How will the action potential at R1 (or R2) change as you continue to increase the stimulus voltage? Your answer : b. The peak value of the action potential will increase. Stop & Think Questions: Why is the action potential recorded by the second recording electrode (R2) delayed relative to the action potential recorded by the first recording electrode (R1)? You correctly answered: c. The action potential had to propagate from R1 to R2. An increase in extracellular K+ would depolarize a neuron. This depolarization would occur if neurons were damaged. From From what you have just learned about generating an action potential, what effect would this have on nearby axons? The nearby axonal membranes will ___________. You correctly answered: b. be depolarized to values near or above threshold voltages. Experiment Data: Stimulus Voltage (mV) 10 20 30 40 50
Peak Value at R1 (µV) 0 10 0 10 0 10 0 10 0
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Peak Value at R2 (µV) 0 10 0 10 0 10 0 10 0
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Action Potential No Yes Yes Yes Yes
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Post-lab Quiz Results You scored 66% by answering 2 out of 3 questions correctly. 1. The threshold voltage in an axon is usually You correctly answered: a. less negative than the resting membrane potential. 2. If a graded receptor potential made the resting membrane potential of the axon more negative (for (for example, -70 mV changes to -75 mV), you would expect You correctly answered: d. it to be more difficult for this axon to reach the threshold voltage. 3. Failure to reach the threshold threshold voltage in the axon of a sensory neuron could be caused by Your answer: a. generation of a receptor potential that makes the axonal resting membrane potential more negative. Correct answer: d. all of the above.
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Review Sheet Results 1. Define the term threshold as it applies to an action potential. You did not answer this question. 2. What change in membrane potential (depolarization or hyperpolarization) triggers an action potential? You did not answer this question. 3. How did the action potential at R1 (or R2) change as you increased the stimulus voltage above the threshold voltage? How well did the results compare with your prediction? You did not answer this question. 4. An action potential is an "all-or-nothing" event. Explain what is meant by this phrase You did not answer this question. 5. What part of a neuron was investigated in this activity? You did not answer this question.
