Measurement of Compound Action Potentials from the Frog Sciatic Nerve Essay


The aim of this experiment was to look at how the compound motion potentials propagate down the sciatic nerve of a frog based mostly on various stimuli. Earlier than the nerve could possibly be examined it wanted to be extracted from the thigh of the frog after which submerged in saline. A number of various stimuli have been used and recorded by a software program bundle. The second experiment requires a relentless stimulus with various reference pin areas. From this the rate of the motion potential propagated will be decided.

The experiment revealed that because the depth of the stimulus elevated so did the depth of the compound motion potential (CAP).


As taught to us throughout class totally different stimuli are going to have totally different results on the pressure the muscle generates. The muscle first needed to be extracted. Dissection concerned the usage of scalpels, scissors, and tweezers to chop and take away each the pores and skin and the muscle. Whereas eradicating the This experiment will permit us to investigate how the motion potentials generated by a nerve from a frog adjustments in response to variations in amplitude of a stimulus from a voltage supply.

By analyzing the adjustments in motion potential, we will decide whether or not there's a sure development within the motion potentials and whether or not or not the nerve will attain a saturation level at which there'll now not be a change within the worth of the motion potential. Additionally, we'll analyze the change in velocity of the propagation of the motion potential on account of alterations in amplitudes of the stimuli. We predict this velocity of propagation to be between zero and 80 meters per second.


At first of this lab, a frog was soaked in a paralyzing agent after which pithed. That is executed to not create any discomfort for the frog and euthanize them within the quickest and least painful manner potential. After the animal is pithed, the dissection can start. First, the pores and skin of the animal have to be eliminated off the legs. Merely reduce across the torso and “de-pants” the frog by pulling the pores and skin down the legs exposing the muscle tissues. After this, the sciatic nerve have to be discovered by separating the 2 muscle tissues within the higher leg. The sciatic nerve is white and a vein is working along-side it. To extract it, tie a knot round it proper above the knee and hint it up the torso into the central nervous system.

When the part is giant sufficient, one other knot needs to be tied across the nerve. The nerve ought to then be reduce above the knots to allow them to be utilized to assist take away the part. The nerve could have a number of braches which have to be eliminated to correctly extract the nerve. The most important part potential needs to be extracted to correctly span the testing tray. After extracted soak the nerve in saline and correctly join the results in their correct locations on the testing tray, configuration proven in Determine 1 under. After connections are made, the nerve needs to be set on the tray ensuring that it spans from the primary to the final connector. That is very important for correct outcomes. Set your pulse width to .05 and set stimulus to solely hearth when the button is pressed. Be certain to maintain the nerve moist on the tray so the cells within the nerve don't die.

Determine 1: Configuration for Testing Tray

The primary experiment that needs to be executed is to differ the stimulus depth creating totally different motion potentials and the second is to check the rate that the nerve propagates motion potentials. This may be executed first working a sure stimulus depth via nerve like earlier after which shifting the +R connector down one pin. Then ship the identical stimulus via the nerve and measure the space between pin to help in figuring out the rate. V=(distance between pins)/(time distinction between two identical intenity samples)


Desk 1: The amplitude of the stimulus and the change within the depth of the compound motion potential. Amplitude (V)∆ CAP Depth (mV)


Desk 1 reveals the amplitude of the stimulus utilized within the first column. The second column is the outcomes of the change within the depth of the compound motion potential. A fast commentary of the desk reveals that because the stimulus is elevated the bigger the depth of the CAP. When the amplitude reaches .3V saturation is revealed. It was additionally famous that because the amplitude of the stimulus elevated the CAP obtained wider and its period elevated.

The rate of the motion potential propagating via the nerve was decided by discovering the distinction of the peaks with the identical stimuli of 1 volt however with totally different reference nodes. That is proven within the equation under:

V=X/∆t=(four*〖10〗^(-Three) m)/((.75-.5)*〖10〗^(-Three) s)=(four m)/(.25 s)=16 m/s

No additional conduction velocities could possibly be evaluated due to nerve loss of life.


The CAP is the sum of all particular person fiber motion potentials of the given nerve. Because the power of the stimulus will increase the, extra fibers are recruited. Addition of fibers, produce extra motion potentials to supply a CAP with a bigger curve. That is why the CAP depth grew bigger because the stimulus was strengthened. As soon as the stimulus power reached a sure stage saturation occurred. This might have occurred for 2 causes. One purpose is that every one the fibers within the nerve have been excited and are conducting motion potentials. The second purpose could possibly be as a result of the software program IWORX has a acquire of 1000, which implies the depth can not go above 5 mv.

The outcomes present that the very best CAP depth reached 5.167 mv this could possibly be the IWORX trying to restrict the voltage. Easy motion potential is an all or none phenomenon, which implies that there aren't any grades of response. Both the motion potential happens or it doesn't. Both a stimulus is greater than threshold in a single fiber and motion potential happens, or it's too low and there's no motion potential. Compound motion potential considers the response of a complete nerve. Your entire nerve consists of many fibers of various sorts: small, giant diameter, absence or presence of myelin, every of which have totally different thresholds. So, given a selected stimulus some fibers could produce motion potentials whereas some could not. Therefore there's a gradation in response relying upon the variety of fibers excited which produces the compound motion potential.

Figure1: Pattern response of nerves CAP

The supply of the stimulus artifact as proven if determine 1, is from the enter. The artifact is outcomes from the just about instantaneous unfold of stimulating electrodes to the recording electrodes. This half doesn’t contain the fiber simply but, that’s why it’s sooner than the CAP. The conduction velocity of 16 m/s will be most precisely recognized because the response from the big quantity of Aδ fibers being excited within the frog nerve. In keeping with Wikipedia, that is cheap on condition that conduction velocities of Aδ fiber vary from Three-30 m/s.

Whereas the outcomes are cheap we can't be positive if the information is completely appropriate. Just one trial for conduction velocity was executed. Correct information requires a number of trials. Additionally the errors may have affected the information. An error could possibly be from the anesthetic used within the experiment. The anesthetic injected within the frog may have blocked motion potentials from being produced. A second supply of error could possibly be the period of the experiment. Because the experiment went on; nerve loss of life was occurring. The deterioration of the nerve may have decreased the quantity of motion potentials being produced.


Total the lab was a hit. The connection of stimulus depth and compound motion potential have been examined. The lab revealed that because the power of the stimulus elevated; the bigger the compound motion potential. For future labs a much less potent anesthetic, needs to be used to make sure motion potentials have been being propagated. Extra expertise in dissecting, would lengthen the lifetime of the nerve; extending the period of the experiment permitting us study the totally different conduction velocities of the nerve. We may additionally swap the enter results in see how the conduction velocities of the nerve evaluate in reverse instructions.