Effect of Frequency of Stimulation on Action Potential Generation 1. Dependent Variable membrane potential

Lab Report-Nursing homework Assignment

Task5-revisions.docx
LABORATORY REPORT

Activity: Action Potentials

Name: Jennifer Sollena

Predictions 1. Exceeding threshold depolarization at the trigger zone —-the likelihood of generation of an action potential. Increases

2. Action potential amplitude does not change with distance

3. Increasing frequency of stimulation to the trigger zone does not change number of action potentials.

Materials and Methods Experiment 1: Effect of Stimulus Strength on Action Potential Generation 1. Dependent Variable membrane potential

2. Independent Variable stimulus strength (voltage)

3. Controlled Variables frequency of stimulation, type of neuron

Experiment 2: Effect of Frequency of Stimulation on Action Potential Generation 1. Dependent Variable membrane potential

2. Independent Variable frequency of stimulation

3. Controlled Variables stimulus strength (voltage), type of neuron

4. Which part of the neuron was stimulated? The dendrite was stimulated.

5. Where was membrane potential measured? The membrane potential was measured at the axon, and axon hillock.

6. What was used to measure membrane potential? Patch clamp electrodes and voltage dependent fluorescent dye was used to measure membrane potential.

Results Table 3: Change in Membrane Potential From Axon Hillock to Axon a. Values of maximal depolarization of membrane potential (mV) at different stimulation voltages, by location. Location Stimulation Voltage 0 V (no stimulation) 2 V 4 V 6 V 8 V Axon hillock -67.7 -64.1 -56.6 31 29.7

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Location Stimulation Voltage 0 V (no stimulation) 2 V 4 V 6 V 8 V Axon -67.6 -73.1 -64.9 31.3 29.4

b. Action Potential Generation. Location Stimulation voltage 0 V (no stimulation) 2 V 4 V 6 V 8 V Action potential generated? no no no yes yes Change in membrane potential with distance -0.1 9 8.3 -0.3 0.3

Graph 1. Maximal depolarization of membrane potential at axon hillock and axon after different stimulation voltages.

Resting membrane potential = -70 mV. 1. What was the resting membrane potential (no stimulation) recorded in Table 3? Axon Hillock -67.7. Axon -67.6.

2. At which stimulation voltage(s) did you see decrimental conduction of graded potential from axon hillock to axon? 6 volts.

3. At what stimulus voltage(s) did an action potential occur? 6 volts.

4. What was the membrane potential at the axon hillock when the action potential was generated? 31.

5. For each of the stimulation voltages, indicate whether it was sub-threshold, threshold, or suprathreshold. a) 2V sub-threshold

b) 4V sub-threshold

c) 6V threshold

d) 8V threshold

Table 4: Effect of Supra-Threshold Stimulation Frequency on Action Potential Generation. Frequency of the Five Supra-Threshold Stimuli 25 Hz 50 Hz 100 Hz 200 Hz 400 Hz Period between stimulations (ms) 40 msec 20 msec 10 msec 5 msec 2.5 msec Number of Action Potentials Produced 5 5 3 1 1

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Frequency of the Five Supra-Threshold Stimuli 25 Hz 50 Hz 100 Hz 200 Hz 400 Hz

Refractory period effect?

no no yes yes yes

Graph 2. Number of action potentials generated at different times between stimulations.

6. State the amount of time between stimulations for each frequency of stimulation. a) 25 Hz 40 msec

b) 50 Hz 20 msec

c) 100 Hz 10 msec

d) 200 Hz 5 msec

e) 400 Hz 2.5 msec

7. For each frequency of stimulation, indicate whether the period between stimulation is longer or shorter than the length of an action potential. Length of action potential in pyramidal neuron is about 15-20 milliseconds (msec). a) 25 Hz longer

b) 50 Hz longer

c) 100 Hz shorter

d) 200 Hz shorter

e) 400 Hz shorter

8. Estimate the length of the refractory period for the pyramidal neuron. 10 msecs

Discussion

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1. In Experiment 1, discuss why the amplitude of the action potential did not increase as stimulation voltage increased above threshold. The amplitude of the action potential did not increase as stimulation voltage increased above threshold because of the all or nothing law that applies to neuronal action potential. Once a threshold is met, there is a necessary refractory period.

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. The membrane potential between the axon hillock and axon did not change with the subthreshold stimulus. This is because depolarization needs to occur in order for sodium ions to enter, and this only happens with a threshold stimulus.

3. In Experiment 2, 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. The membrane potential between the axon hillock and axon did not change with the subthreshold stimulus. This is because depolarization needs to occur in order for sodium ions to enter, and this only happens with a threshold stimulus.

4. In Experiment 2, explain why the number of action potentials generated varied with increased stimulation frequency. The number of action potentials varied with increased stimulation frequency because of the all or nothing law. (“dictionary.com,” 2002, 2001, 1995) Even with an increase in stimulation, the refractory period must be met, in order for an action potential to be generated. So with increased stimulation frequency, the number of action potentials actually decreased, because the mandatory refractory period was not met.

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. Exceeding threshold depolarization at the trigger zone increases the likelihood of generation of an action potential. This is correct. Action potential amplitude does not change with distance. This is correct. Increasing frequency of stimulation to the trigger zone does not change number of action potentials. This is correct.

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 depolarizes muscle cells, reducing the membrane potential. This is because there is a higher amount of K inside the cell, and this decreases the resting membrane potential. (Walter A. Parham, MD, Ali A. Mehdirad, MD, FACC, Kurt M. Biermann, BS, and Carey S. Fredman, MD, FACC [Tex Heart Inst J. ], 2006) This brings the membrane potential closer to the threshold for generation of an action potential. Hyperkalemia will increase excitability, because a lesser depolarizing stimulus is required to generate an action potential. Within the body this will cause rhythm irregularities, muscle aches, fatigue, difficulty breathing, and if left untreated death.

b. Explain how hypokalemia will initially affect the resting membrane potential and the generation of an action potential. This brings the membrane potential further from the threshold. There is a higher concentration of potassium outside of the cell. This causes a faster level of diffusion. Meaning, more positively charged K will flow out than normal, causing the inside of the cell to be negative. Lower potassium levels will cause hyperpolarization of the resting membrane potential. This means the body will be more tired, showing signs of fatigue, muscle weakness, irregular heart rythms, and decreased GI motility. (“Antanick,” )

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. Tetrodotoxin is a naturally occurring sodium channel blocker that is found in several of the puffer fish species. (Garud & Kulkarni, 2017) This is poisonous to humans because it blocks voltage-gated sodium channels in nerve membranes. This means that sodium ions cannot enter the cell, so signals are not transmitted, and this can cause a rapid and progressive paralysis. This can be fatal because it could cause paralysis of the respiratory muscles.

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References

all-or-none law. (2002, 2001, 1995). Retrieved from https://www.dictionary.com/browse/all-or-none-law

Garud, M. S., & Kulkarni, Y. A. (2017). Natural Remedies for the Treatment of Cancer Pain. Retrieved from https://www.sciencedirect.com/topics/neuroscience/tetrodotoxin

Walter A. Parham, MD, Ali A. Mehdirad, MD, FACC, Kurt M. Biermann, BS, and Carey S. Fredman, MD, FACC. (2006). Hyperkalemia Revisited. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1413606/

What is Hypokalemia? (). Retrieved from https://antranik.org/what-is-hypokalemia/

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