The Action Potential - Threshold Lab Report

Exercise 3: Neurophysiology of Nerve Impulses: Activity 3: The Action Potential: Threshold Lab Report Pre-lab Quiz Results You scored 75% by answering 3 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 initiated in an axon at or near Your answer : a. the axon hillock Correct answer: 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. 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 what you have just learned about generating an action potential, what effect would this have on nearby axons? The nearby axonal membranes will ___________. Your answer : d. be further depolarized to values below threshold voltages. Correct answer: 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) 0 100 100 100 100 Peak Value at R2 (µV) 0 100 100 100 100 Action Potential No Yes Yes Yes Yes Post-lab Quiz Results You scored 33% by answering 1 out of 3 questions correctly. 1. The threshold voltage in an axon is usually Your answer: d. the same value as the resting membrane potential. Correct answer: 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 example, -70 mV changes to -75 mV), you would expect Your answer: a. it to be easier for this axon to reach the threshold voltage. Correct answer: d. it to be more difficult for this axon to reach the threshold voltage. 3. Failure to reach the threshold voltage in the axon of a sensory neuron could be caused by You correctly answered: d. all of the above. Review Sheet Results 1. Define the term threshold as it applies to an action potential. Your answer: The magnitured or intensity that must be exceeded for a certain reaction or condition to occur or be manifested. 2. What change in membrane potential (depolarization or hyperpolarization) triggers an action potential? Your answer: depolarization triggers an action potential 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? Your answer: The peak values actually stay the same as the stimulus increases. The prediction made earlier is not supported by the data. 4. An action potential is an "all-or-nothing" event. Explain what is meant by this phrase Your answer: That action potential must reach the threshold in order to occur, if the threshold is not reached there is not action potential. Either it goes all in into an action potential or it does not. 5. What part of a neuron was investigated in this activity? Your answer: The trigger zone in the axon hillock,