Experiment Results
Predict Question:
Predict Question: What effect will the increased stimulus intensity have on the frequency of action potentials?
Your answer : b. The frequency of action potentials will remain the same.
Stop & Think Questions:
4. At the site of stimulation, the stimulus keeps the membrane of the axon at threshold for a long time, but this depolarization
does not spread to the recording electrode. After one action potential has been generated and the axon has fully recovered
from its absolute and relative refractory periods, the stimulus is still present to generate another action potential
Measure the time (in milliseconds) between action potentials. This interval should be a bit longer than the relative refractory
period (measured in Activity 5).
Click Measure to help determine the time between action potentials. A thin, vertical yellow line appears at the first action
potential. You can move the line in 10 millisecond increments by clicking the + and - buttons beside the time display, which
shows the time at the line. Subtract the time at the first action potential from the time at the second action potential to
determine the interval between them.
Enter the interval between action potentials in the field below and then click Submit to display your answer in the data
table.
You answered: .10 milliseconds
5. The interval between action potentials is sometimes called the interspike interval (ISI). Action potentials are sometimes
referred to as spikes because of their rapid time course.
From the ISI, you can calculate the action potential frequency. The frequency is the reciprocal of the interval and is usually
expressed in hertz (Hz), which is events (action potentials) per second. From the ISI you entered, calculate the frequency of
action potentials with a prolonged (500 msec) threshold stimulus intensity. Frequency = 1/ISI. (Convert the ISI to seconds
before calculating the frequency.)
Enter the frequency in the field below and then click Submit to display your answer in the data table.
You answered: 0.100 Hz
7. Enter the interval between action potentials (the ISI) in the field below and then click Submit to display your answer in
the data table.
Click Measure to help determine the time between action potentials. A thin, vertical yellow line appears at the far left side of
the oscilloscope screen. You can move the line in 10 millisecond increments by clicking the + and - buttons beside the time
display, which shows the time at the line.
You answered: .10 milliseconds
8. From the ISI you entered, calculate the frequency of action potentials with a prolonged (500 msec) 30 mV stimulus
intensity. Frequency = 1/ISI.
Enter the frequency in the field below and then click Submit to display your answer in the data table.
You answered: 0.100 Hz
11. Enter the interval between action potentials (the ISI) in the field below and then click Submit to display your answer inthe data table.
Click Measure to help determine the time between action potentials. A thin, vertical yellow line appears at the far left side of
the oscilloscope screen. You can move the line in 10 millisecond increments by clicking the + and - buttons beside the time
display, which shows the time at the line.
You answered: .10 milliseconds
12. From the ISI you entered, calculate the frequency of action potentials with a prolonged (500 msec) 45 mV stimulus
intensity. Frequency = 1/ISI.
Enter the frequency in the field below and then click Submit to display your answer in the data table.
You answered: 0.100 Hz
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