Extend From A Neuronal Cell Body

Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 Axons are You correctly answered: long, thin structures that extend from a neuronal cell body. 2 Which of the following is easier? You correctly answered: Extracellular recordings of the action potential. 3 An action potential is usually initiated in an axon at or near You correctly answered: all of the above. 4 The initiation of an action potential in a sensory neuron in the body normally You correctly answered: follows a sufficiently large depolarizing receptor potential. Experiment Results Predict Question 1 Predict Question: How will the action potential at R1 (or R2) change as you continue to increase the stimulus voltage? Your answer: The peak value of the action potential will increase. Stop & Think Questions 1 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: The action potential had to propagate from R1 to R2. + 2 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 _______. You correctly answered: be depolarized to values near or above threshold voltages. Experiment Data Stimulus Voltage (mv) 10 Peak Value at R1 (μV) Peak Value at R2 (μV) 0 0 Action Potential No 20 100 100 Yes 30 100 100 Yes 40 100 100 Yes 50 100 100 Yes Post-lab Quiz Results You scored 100% by answering 3 out of 3 questions correctly. 1 The threshold voltage in an axon is usually You correctly answered: 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 You correctly answered: 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: all of the above. Review Sheet Results 1 Define the term threshold as it applies to an action potential. Your answer: The inside of the neuron needs to reach threshold in order for an action potential to occur. If the inside of the neuron at the trigger zone, the beginning of the axons, if the inside of the neuron at that region does not reach threshold, than an action potential will not occur. Basically, the threshold is the minimum stimulus used to generate an action potential but only if the neuron reaches it. 2 What change in membrane potential (depolarization or hyperpolarization) triggers an action potential? Your answer: The reason why the membrane potential change is because the movement of the potassium ion leaked causing the membrane potential to depolarize that 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: I predicted that the peak value of the action potential will increase. As soon as I kept increasing the stimulus voltage I noticed that there was no change happening. Even though threshold was happening, it was always at the same point that it reaches and action potential was set whenever it occured. Therefore, my prediction was wrong because the peak value did not change when it was increasing each time we went higher on the voltage. 4 An action potential is an "all-or-nothing" event. Explain what is meant by this phrase Your answer: An action potential is an "all-or-nothing" event because the action potential either occurs completely or it does not occur at all. If the threshold is reached than the AP will happen. If the graded potentials are not strong enough to bring the membrane to the threshold, then an AP will not happen. 5 What part of a neuron was investigated in this activity? Your answer: The part of a neuron that was investigated in this activity was the axon.