[PhysioEX Chapter 3 exercise 3] PEX-03-03

Solved by ramonistry

Exercise 3: Neurophysiology of Nerve Impulses: Activity 3: The Action Potential: Threshold Lab Report
Pre-lab Quiz Results
You scored 100% by answering 4 out of 4 questions correctly.

1. Axons are
   You correctly answered: d. long, thin structures that extend from a neuronal cell body.
2. Which of the following is easier?
   You correctly answered: a. extracellular recordings of the action potential
3. An action potential is usually initiated in an axon at or near
   You correctly answered: d. all of the above
4. The initiation of an action potential in a sensory neuron in the body normally
   You correctly answered: a. follows a sufficiently large depolarizing receptor potential.

Experiment Results
Predict Question:
Predict Question: How will the action potential at R1 (or R2) change as you continue to increase the stimulus voltage?
Your answer : b. The peak value of the action potential will increase.
Stop & Think Questions:
Why is the action potential recorded by the second recording electrode (R2) delayed relative to the action potential recorded
by the first recording electrode (R1)?
You correctly answered: c. The action potential had to propagate from R1 to R2.
An increase in extracellular K+ would depolarize a neuron. This depolarization would occur if neurons were damaged. From
what you have just learned about generating an action potential, what effect would this have on nearby axons? The nearby
axonal membranes will ___________.
You correctly answered: b. be depolarized to values near or above threshold voltages.
Experiment Data:
Stimulus Voltage (mV) Peak Value at R1 (μV) Peak Value at R2 (μV) Action Potential
10 0 0 No
20 100 100 Yes
30 100 100 Yes
40 100 100 Yes
50 100 100 Yes

Post-lab Quiz Results
You scored 100% by answering 3 out of 3 questions correctly.

1. The threshold voltage in an axon is usually
   You correctly answered: a. less negative than the resting membrane potential.
2. If a graded receptor potential made the resting membrane potential of the axon more negative (for example, -70 mV
   changes to -75 mV), you would expect
   You correctly answered: d. it to be more difficult for this axon to reach the threshold voltage.
3. Failure to reach the threshold voltage in the axon of a sensory neuron could be caused by
   You correctly answered: d. all of the above.

Review Sheet Results

1. Define the term threshold as it applies to an action potential.
   Your answer:
   Only when potential reaches to threshold, action potential can occur.
2. What change in membrane potential (depolarization or hyperpolarization) triggers an action potential?
   Your answer:
   Depolariztion is the trigger of action potential.
3. How did the action potential at R1 (or R2) change as you increased the stimulus voltage above the threshold voltage?
   How well did the results compare with your prediction?
   Your answer:
   Action potential didn't change as the stimulus voltage increased. Threshold is the only point. and action potential is fixed
   whenever it occurs.
4. An action potential is an "all-or-nothing" event. Explain what is meant by this phrase
   Your answer:
   There is just two way that it occurs or not. When it occurs its potential value is always same.
5. What part of a neuron was investigated in this activity?
   Your answer:
   The axon.