Predictions 1. Exceeding threshold depolarization at the trigger zone —-the likelihood of generation of an action potential. IncreasesExperiment 2: Effect of Frequency of Stimulation on Action Potential Generation 1. Dependent Variable membrane potential
.
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?
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