Compound Action Potentials Essay Example

threshold is reached, causing an action potential, or it’s not. Right after an action potential, the membrane does not respond to any stimulation because the sodium gates aren’t activated, but the potassium gates are active. This period is called the absolute refractory period.

A little later, another action potential can be produced, but the stimulus must be greater than the threshold because during this time, not all of the sodium gates are activated. This is the relative refractory period. At the beginning of this period, a stimulus largely greater than the threshold is required to produce an action potential, but as time goes on the nerve cell membrane will need a smaller and smaller stimulus to cause an action potential. By the end of the relative refractory period, only a slightly above threshold stimulus will get the job done.

Once initiated near the soma, action potentials grow and distribute down the axons. The movement of action potentials all the way down an axon is caused by positive charges in the cell leaking to an unstimulated region. Action potentials only take place in the nodes of myelinated cells because the insulation keeps the action potential currents from leaking out of the membrane. Materials and Methods Frog Dissecting board Forceps Scissors Fine tipped glass rod Ringer’s Solution Thread Recording Nerve Bath with lid Power Lab Lab Tutor Computer Stimulating Electrodes Recording Electrodes

The frog was dissected in order to expose the sciatic nerve. The sciatic nerve was then removed and placed in a bath of Ringer’s solution. The nerve is then placed in a nerve bath that is connected to the Power Lab in order to receive stimuli. The computer

recorded the data. There were three parts to this experiment: threshold voltage and maximal compound action potential amplitude, refractory period, and conduction velocity of the nerve. Results The first part of this experiment was to dissect a frog and remove it’s sciatic nerve. The animal was secured to a dissecting board with its ventral side up and placed in a dissecting pan.

With scissors, the frog’s skin was cut around its abdomen and peeled downward and off of the legs. Using the forceps, the urostyle was grabbed and cut free, exposing the nerve plexus just below it. With the glass hook, the sciatic nerve was located and lifted from the sciatic artery and cut from the spinal cord. Thread was tied around the free end and after cutting the leg from the abdomen, the rest of the nerve was cut from the calf muscle. The second step to this experiment was the proper set up of the equipment. The stimulating electrodes are connected to the nerve bath first.

They are connected at the end where the coils are closer together and the BNC connectors plug into the Power Lab output connectors. There are two sets of recording electrodes that need to be connected to the nerve bath as well. The first set are connected here. The second set of recording electrodes are connected here. The positive and negative BNC connectors of the stimulating leads shoud be connected to the analog outputs on the Power Lab. The first set of recording electrodes should be connected to Input 1, and the second set should be connected to Input 2 on the Power Lab as shown.

Discussion The result of exercise

1 was not what it should have been. There should have been a point where the amplitude of the compound action potential stopped increasing. The maximal stimulus, however, was never reached. The constant increasing of the amplitude at higher stimulus voltages is because of additional axons within the nerve reaching their individual threshold. In exercise 2, the results were fine. In the graph, you can clearly see the intervals increasing as the amplitude was staying mostly the same.

The use of two stimuli both of which are near maximal, helped determine both refractory periods. At the beginning of the refractory period, a big stimulus was needed in order to trigger an action potential. Gradually, the stimulus needed was weaker and weaker. In exercise 3, the nerve used for this experiment died during the test. Conduction velocity was supposed to be determined. This sciatic nerve contains several different types of nerve fibers, each having their own conduction velocity. The difference varies according to different diameters as well as different levels of myelination of the nerve fibers.

The difference between type A and B fibers is due to the difference in diameter, and the difference in conductance velocity between type B and C fibers is based on different states of myelination. With this exercise, the differences in conduction velocity amongst the different types of nerve fibers should have been apparent. Conclusion Action potentials and their creation is one of the most important aspects of the nervous system. It is the basis of neuronal communication. Thoughts, feelings, and movement are only a few of the important things that require action potential.

Nerves are made of different nerve fibers, all of which

have their own threshold voltage. The frog’s sciatic nerve represents this. Taking the sciatic nerve from a “living” frog made sure that the nerve was viable and would serve the purpose of these experiments. Each experiment was supposed to show different things. Being able to determine the threshold voltage, the maximal compound action potential, the absolute and relative refractory periods, and the conduction velocity with one nerve is truly advancement in science.