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Laboratory Report

LABORATORY REPORT Activity: Name: Instructor: Date:

Action Potentials Nallanie Ramsarran J.Guers 07.23.2020

Predictions 1. Exceeding threshold depolarization at the trigger zone______the likelihood of generation of an action potential. decreases 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? Dendrite of the neuron

5. Where was membrane potential measured? axon and axon hillock

6. What was used to measure membrane potential? voltmeter

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.

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Laboratory Report

Location 0 V (no stimulation ) Axon hillock Axon

2V -68.9 -67.4

Stimulation Voltage 6V -56.2 -64.6

4V -63.7 -72.8

8V 29.9 29.9

29.9 29.4

b. Action Potential Generation. Location 0 V (no stimulation ) Action potential generated? Change in membrane potential with distance

Stimulation voltage 6V 8V

2V

4V

no

no

no

yes

yes

-1.5

9.1

8.4

0

0.5

Graph 1. Maximal depolarization of membrane potential at axon hillock and axon after different stimulation voltages. mV 20 0

1. no stimulus 2. 2 V 3. 4V 4. 6V 5. 8V

-20 -40 -60 -80 1

2

3

4

5

Resting membrane potential = -70 mV. 1. What was the resting membrane potential (no stimulation) recorded in Table 3? -70 mv 2. At which stimulation voltage(s) did you see decrimental conduction of graded potential from axon hillock to axon? 64.8 to 73.8

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

4. What was the membrane potential at the axon hillock when the action potential was generated? 30.2 at a hillock 6v

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

b) 4V sub-thread

c) 6V threshold

d) 8V threshold

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Laboratory Report

Table 4: Effect of Supra-Threshold Stimulation Frequency on Action Potential Generation. 25 Hz Period between stimulations (ms) Number of Action Potentials Produced Refractory period effect?

Frequency of the Five Supra-Threshold Stimuli 100 Hz 200 Hz 400 Hz 20 msec 10 msec 5 msec

50 Hz 40 msec

2.5 msec

5

5

3

1

1

no

no

yes

yes

yes

Graph 2. Number of action potentials generated at different times between stimulations. Number of action potentials produced 5 4

1. 40 msec(25 Hz) 2. 20 msec(50 Hz) 3. 10 msec(100 Hz) 4. 5 msec(200 Hz) 5. 2.5 msec(400 Hz)

3 2 1 0 1

2

3

4

5

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 msecs

d) 200 Hz 5 msecs

e) 400 Hz 2.5 msecs

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 same

c) 100 Hz shorter

d) 200 Hz shorter

e) 400 Hz shorter

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Laboratory Report

8. Estimate the length of the refractory period for the pyramidal neuron. 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 the threshold is met then the refractory period is needed . 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. It did not change. Unless the depolarization occurs, the sodium ions cannot enter created change. This only happens at the threshold.

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. It did not change .Unless the depolarization occurs the sodium ions cannot enter and created change. This only happens at the threshold. 4. In Experiment 2, explain why the number of action potentials generated varied with increased stimulation frequency. Time between the stimuli was shorter than refractory period 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 decrease the likelihood of generation of an action potential. Action potential amplitude does not change with distance Increasing frequency of stimulation to the trigger zone does not change number of action potentials.

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. In hyperkalemia, the resting membrane potential is decreased, and the membrane becomes partially depolarized . This increases membrane excitability but with prolonged depolarization, the cell membrane will become more refractory and less likely to fully depolarize

b. Explain how hypokalemia will initially affect the resting membrane potential and the generation of an action potential. The threshold cell membrane potential is reached when sodium permeability increases to the point that sodium entry exceeds potassium exit, depolarization becomes self-perpetuating, and an action potential develops.

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. TTX binds to the Na+ channel on the outside of the neuron and blocks the pore. Because of this blockage, neurons are not able to generate action potentials

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