Laboratory Report
8. Estimate the length of the refractory period for the pyramidal neuron.
Estimate length of refractory period for pyramidal neuron is appx 10 msecs.
Discussion
1. In Experiment 1, discuss why the amplitude of the action potential did not increase as stimulation voltage increased above threshold.
Once a neuron hits its stimulation threshold, it goes into a refractory period where the action potential doesn’t increase. The neurons communicate with the nervous system function. Either the neurons fires or not. This means that the intensity of the stimulus doesn't affect the magnitude of the action potential. Instead, it only affects the frequency at which they generate the impulses.
2. In Experiment 1, explain why the membrane potential between the axon hillock and axon either changed or did not change with subthreshold stimulus. Differences of 1.0 mV or less are not significant.
When sodium ions hit a cell, they only cause a change if the neuron depolarizes at the threshold stimulus. This happens because it opens up the voltage-gated Na+ channels, which lets more Na+ into the cell and makes the membrane less charged. A subthreshold shock won't change the membrane potential if there isn't any depolarization.
3. In Experiment 1, explain why the membrane potential between the axon hillock and axon either changed or did not change with threshold stimulus. Differences of 1.0 mV or less are not significant.
When the threshold stimulus was applied, there was no change in the membrane potential between the axon hillock and axon. However, depolarization occurs once the threshold is reached. At this point, sodium ions are permitted to pass through, causing the necessary alteration.
4. In Experiment 2, explain why the number of action potentials generated varied with increased stimulation frequency.
As stimulation frequency increased, action potentials changed. Short trigger intervals were shorter than system response time. Once the threshold stimulus is reached, all stimuli above it must refractory before causing another action potential. Since the requisite refractory period is not satisfied, action potentials decrease with stimulation frequency. As stimulation frequency increases, action potentials shift. This is because action potentials require refractory periods.
5. Restate your predictions that were correct and give the data from your experiment that supports them. Restate your predictions that were not correct and correct them, giving the data from your experiment that supports the correction.
Due to refractory period, boosting voltage from 6V to 8V barely enhanced signal amplitude. Once the threshold is reached, stimulus strength does not affect membrane events. Positive feedback loops from depolarization cause action potentials. Amplitude change down the axon was 0.4 and 0.3. A stimulus location determines non-refractory membrane conductivity. Cells fire action potentials. Each cell has an all-or-none threshold, thus stimulus strength or frequency does not enhance output.
Application
1. ECF potassium levels affect resting membrane potential. Hyperkalemia (excessive levels of potassium in the blood) and hypokalemia (abnormally low blood potassium levels) both affect the function of nerves and muscles.
a. Explain how hyperkalemia will initially affect the resting membrane potential and the generation of an action potential.
Hyperkalemia is a metabolic issue caused by excess potassium in the blood. It can cause irregularities in muscles, including the heart, fatigue, and breathing difficulties. It decreases the resting membrane potential, leading to partial depolarization and making the membrane more excitable. This affects the flow of potassium and sodium in and out of cells, making it hard to trigger an action potential.
b. Explain how hypokalemia will initially affect the resting membrane potential and the generation of an action potential.
Cells are negative and less likely to ignite with low potassium. Cell excitation is eliminated by hyperkalemia. The transport of potassium affects intracellular and extracellular ratios differently than total body potassium. When the resting membrane potential decreases, it disrupts the flow of potassium and sodium, making it harder to trigger action potentials. Accumulation of potassium outside the cell during repolarization hinders the concentration gradient, preventing action potentials.
2. Tetrodotoxin, a toxin found in puffer fish, acts by inhibiting voltage-gated sodium channels. Eating improperly prepared puffer fish sushi can be fatal because of interference with action potential generation. Explain how tetrodotoxin interferes with action potential generation.
Toxins from Tetrodotoxin fish targets sodium channels, and can lead to neurological and gastrointestinal issues. The skin, viscera, ovaries, and liver of the fish are the main sources of this toxin. Tetrodotoxin works by binding to voltage-gated sodium channels in the neuronal membrane, which stops Na+ from entering the cell. This prevents depolarization and maintains a negative resting membrane potential, which prevents an action potential.
Laboratory Report/ Kristin Bautista/ Action Potentials/ Kim Shahi/ 08.24.2023/ Page [4] of [4]
