BIOS252 Week 3 PowerPhys4 Lab Report 2

Topics: Action potential, Neuron, Membrane potential Pages: 5 (973 words) Published: November 18, 2014

Activity 4: Generation of Action Potentials


1. Exceeding the threshold depolarization at the trigger zone DECREASES the likelihood of generation of action potential.

2. Action potential amplitude: DOES NOT CHANGE with distance

3. Increasing frequency of stimulation to the trigger zone: DOES NOT increase the production of action potentials.


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
Type of neuron
Stimulus Strength (voltage)

4. Which part of the neuron was stimulated? Action potential is first generated in the dendrites of the neuron, or where the neuron receives the action potential of other neurons.

5. Where was membrane potential measured?

6. What was used to measure membrane potential?


See Table 3: Membrane Potentials at Different Stimulation Voltages, by Location See Graph 1: Maximal depolarization of membrane potential at axon hillock and axon after different stimulation voltages.

1. What was the resting membrane potential (no stimulation) recorded in Table 3? The Resting Membrane Potential Voltage =-70 mV

2. At which stimulation voltage(s) did you see decrimental conduction of graded potential from axon hillock to axon? At 2V the graded potential went from 64.8 – 73.8

3.At what stimulus voltage(s) did an action potential occur? Action potential occurred at 6V

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

5. For each of the stimulation voltages, indicate whether it was sub-threshold, threshold, or suprathreshold. 2 V Subthreshold
4 V Subthreshold
6 V Threshold
8 V Threshold

See Table 4: Effect of Supra-Threshold Stimulation Frequency on Action Potential Generation. See Graph 2: Number of action potentials generated at different times between simulations.

6. State the amount of time between stimulations for each frequency of stimulation. 25 Hz 40 msecs
50 Hz 20 msecs
100 Hz 10 msecs
200 Hz 5 msecs
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) 25 Hz longer

50 Hz same
100 Hz shorter
200 Hz shorter
400 Hz shorter

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

The length of refactory period was approximately 10 msecs between the 15-20 increasing the action potentials almost doubling them from 3 to 5.


1. In Experiment 1, discuss why the amplitude of the action potential did not increase as stimulation voltage increased above threshold. All-or-nothing theory…..Once the threshold is met, a refactory period is needed. All and then nothing, repeat…..

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....
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