[PhysioEX Chapter 3 exercise 9] PEX-03-09

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Exercise 3: Neurophysiology of Nerve Impulses: Activity 9: The Action Potential: Putting It All Together Lab Report
Pre-lab Quiz Results
You scored 100% by answering 4 out of 4 questions correctly.

1. Sensory neurons respond to an appropriate sensory stimulus with a change in membrane potential that is
   You correctly answered: b. graded with the stimulus intensity.
2. If the depolarization that reaches the axon is large and suprathreshold, the result in the axon is
   You correctly answered: c. action potentials at higher frequency.
3. At the axon terminal, each action potential causes the release of neurotransmitter. This neurotransmitter diffuses to the
   receiving end of an interneuron, where it binds to receptors and causes
   You correctly answered: a. ion channels to open, so that the receiving end of the interneuron depolarizes.
4. Interneurons respond to chemical (neurotransmitter) stimulation with a change in membrane potential that is
   You correctly answered: b. graded with the stimulus intensity.

Experiment Results
Predict Question:
Predict Question 1: If you apply a very weak, subthreshold stimulus to the sensory receptor
Your answer : a. a small, depolarizing response will occur at R1, and no responses will occur at R2, R3, and R4.
Predict Question 2: If you apply a moderate stimulus to the sensory receptor
Your answer : a. a larger, depolarizing response will occur at R1, and an action potential will be generated at R2 and maybe
at R4.
Predict Question 3: If you apply a strong stimulus to the sensory receptor
Your answer : a. a large, depolarizing response will occur at R1 and R3, and action potentials will occur at R2 and R4.
Stop & Think Questions:
Observe the two neurons in the petri dish. What do you think is the resting membrane potential at the receiving end of the
sensory neuron (sensory receptor) and the receiving end of the interneuron?
You correctly answered: c. -70 mV
Why is there no response at R3 when you apply a very weak stimulus to the sensory receptor?
You correctly answered: c. The very weak stimulus does not depolarize the axon of the sensory neuron to threshold.
Why is there a larger, depolarizing response at R1 when you apply a moderate intensity stimulus?
You correctly answered: c. The stimulus induces a graded receptor potential at R1.
Experiment Data:
Stimulus Sensory Neuron
Membrane Potential
(mV) Receptor
Sensory Neuron
AP Frequency
(Hz) in Axon
Sensory Neuron
Vesicles Released
from Axon Terminal
Interneuron
Membrane Potential
(mV) Receiving End
Interneuron
AP Frequency (Hz)
in Axon
None -70 -70
Weak -60 0 0 -70 0
Moderate -40 16.6 4 -50 5
Strong -25 33.3 6 -40 10

Post-lab Quiz Results
You scored 100% by answering 5 out of 5 questions correctly.

1. What determines the amplitude of the depolarization at the sensory receptor (R1)?
   You correctly answered: a. The strength of the stimulus applied to the sensory receptor.
2. What determines the frequency of action potentials in the axon of the sensory neuron (R2)?
   You correctly answered: a. The amplitude of the depolarization at the sensory receptor (R1).
3. Which of the following directly determines the amount of neurotransmitter released at the axon terminal of the sensory
   neuron?
   You correctly answered: c. The amount of calcium that enters the sensory receptor.
4. Which of the following directly or indirectly determines the amount of neurotransmitter released at the axon terminal of
   the sensory neuron?
   You correctly answered: d. All of the above play a role in determining the amount of neurotransmitter released.
5. Which of the following directly or indirectly determines the frequency of action potentials in the axon of the interneuron?
   You correctly answered: d. All of the above play a role in determining the frequency of action potentials in the axon of the
   interneuron.

Review Sheet Results

1. Why is the resting membrane potential the same value in both the sensory neuron and the interneuron?
   Your answer:
   because value of the membrane potential in neurons is typical regardless of the types.
2. Describe what happened when you applied a very weak stimulus to the sensory receptor. How well did the results
   compare with your prediction?
   Your answer:
   There was a small depolarizing response at R1 with no responses occuring at R2-R4, as predicted.
3. Describe what happened when you applied a moderate stimulus was to the sensory receptor. How well did the results
   compare with your prediction?
   Your answer:
   There was a larger depolarizing response at R1 with action potentials at R2 and two AP's occuring at R4, as predicted.
4. Identify the type of membrane potential (graded receptor potential or action potential) that occurred at R1, R2, R3, and
   R4 when you applied a moderate stimulus (view Experiment Results to view the response to this stimulus).
   Your answer:
   graded receptor potentials occured at R1 and R3, and action potentials occured at R2 and R4.
5. Describe what happened when you applied a strong stimulus to the sensory receptor. How well did the results compare
   with your prediction?
   Your answer:
   a larger depolarizing response occurred at R1 and R3, and action potentials occured at R2 and R4.