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Frog Sciatic Nerve Cap

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Submitted By mrphillips76
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1. How does a CAP differ from a single action potential? Single action potentials follow the "all or none" rule. That is, if a stimulus is strong enough to depolarize the membrane of the neuron to threshold, then an action potential will be fired. Each stimulus that reaches threshold will produce an action potential that is equal in magnitude to every other action potential for the neuron.

Compound action potentials do not exhibit this property since they are a bundle of neurons and have different magnitudes of AP's. Thus compound action potentials are graded. That is, the greater the stimulus, the greater the action potential.

2. Action potentials are said to be all or none responses. Why does the frog sciatic nerve give a graded response? The frog sciatic nerve gives a graded response because the nerve is a bundle of axons (CAP) and not a single axon (thus it does not show the all or none response of an axon-either generating an action potential or not). If one axon is generating an action potential then a small nerve impulse is witnessed, if all axons are simultaneously generating action potentials then a large nerve impulse is witnessed. Thus the nerve impulse is graded (it can be none, small, medium, large, larger, maximal). 3. What was the smallest voltage required to produce the maximum (largest) CAP? What proportion of the nerve fibers were excited to produce this maximal response? A minimum of 140 mV is required to produce the maximum Cap. 100% of the excitable nerve fibers were excited to produce the maximal response. We know this because all of the A-alpha fibres making up the nerve have been excited and are conducting action potentials. Even if you were to increase the voltage past 140 mV, the AP would not continue to increase in amplitude. 4. In this exercise, you examined the effect of…...

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