Explain what happened to the CAP amplitude as voltage applied to the neuron was

Question

1. Explain what happened to the CAP amplitude as voltage applied to the neuron was changed. Be specific with your results and explain why the amplitude was smaller with some voltages and larger with other voltages. B.Describe the effect that temperature had on the conduction velocity, time delay, duration and enzyme activity of the nerve. C.Discuss what happend to the second CAP as the interval was changed between the shocks. Explain why these results were seen in relationship to absolute and relative refractory periods.

Explanation / Answer

With a low initial stimulus amplitude, no CAP will be visible, but you will see a brief, biphasic deflection near the beginning of the display. This is the stimulus artifact, which results from virtually instantaneous, passive current spread from stimulating electrodes to recording electrodes. As we slowly increase the stimulus voltage, using the control knob on the stimulator, at a certain point a second deflection will appear in the displayed waveform. This is the Compound Action Potential of the nerve. As we increase stimulus voltage further, observe the corresponding changes in the CAP shape and amplitude s, the reason that the cAP increases is due to the following reasons. 1. Large diameter axons require less intense stimulation to activate than smaller axons. (So at a low intensity, you are only triggering APs in large axons. As you increase intensity, you also begin triggering APs in smaller axons. Thus the compound action potential increases). 2. Axons that are close to the site of stimulation are activated at lower intensity than those that are farther away. (So at low intensity, you only recruit neurons near the electrode, and as you increase intensity, neurons further away also begin firing).

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