[PhysioEX Chapter 3 exercise 4] PEX-03-04

Solved by ramonistry

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

Voltage-gated Na+ channels are membrane channels that open
You correctly answered: b. when the membrane depolarizes.
When open, Na+ channels allow
You correctly answered: a. Na+ ions to diffuse into the cell.
Which of the following is true of an action potential?
You correctly answered: d. All of these answers are correct.
Which of the following can reduce the likelihood of an action potential?
You correctly answered: d. All of these can reduce the likelihood of an action potential.

Experiment Results
Predict Question:
Predict Question 1: If you apply TTX between recording electrodes R1 and R2, what effect will the TTX have on the action
potentials at R1 and R2?
Your answer : c. TTX will block the response at R2 but have no effect at R1.
Predict Question 2: If you apply lidocaine between recording electrodes R1 and R2, what effect will the lidocaine have on
the action potentials at R1 and R2?
Your answer : c. Lidocaine will block the response at R2 but have no effect at R1.
Stop & Think Questions:

Enter the peak value of the response at R1 and R2 in the field below and then click Submit to record your answer in the
lab report.
You answered: 100 μV
With a slower timescale, the appearance of the action potentials generated at R1 and R2 will appear to
You correctly answered: c. be compressed in time but have the same peak value of response.
Why do you think TTX is not used during dental procedures?
You correctly answered: c. TTX irreversibly blocks voltage-gated sodium channels in axonal membranes.
Experiment Data:
Condition Stimulus
Voltage (mV)
Electrode Peak Value
of Response
(μV) 2 sec
Peak Value
of Response
(μV) 4 sec
Peak Value
of Response
(μV) 6 sec
Peak Value
of Response
(μV) 8 sec
Peak Value
of Response
(μV) 10 sec
Control 30 R1 100 100 100 100 100
Control 30 R2 100 100 100 100 100
TTX 30 R1 100 100 100 100 100
TTX 30 R2 100 100 0 0 0
Lidocaine 30 R1 100 100 100 100 100
Lidocaine 30 R2 100 100 100 0 0

Post-lab Quiz Results
You scored 100% by answering 4 out of 4 questions correctly.

In the control, the amplitudes of the action potentials at R1 and R2 are the same. Which of the following explains this?
You correctly answered: d. All of these are reasonable explanations.
Blocking the voltage-gated Na+ channels between R1 and R2 with TTX blocks
You correctly answered: d. the propagation of the action potential from R1 to R2.
When voltage-gated Na+ channels between R1 and R2 are blocked with TTX, an action potential is still recorded at R1
because
You correctly answered: b. the voltage-gated Na+ channels between the stimulus and R1 are unaffected by the TTX.
Puffer fish must be prepared carefully and properly before they can be eaten. Eating puffer fish can cause numbness of
the lips, probably because
You correctly answered: a. action potentials from sensory neurons in the lips are blocked.

Review Sheet Results

What does TTX do to voltage-gated Na+ channels?
Your answer:
TTX blocks the diffusion of Na+ across the channel.
What does lidocaine do to voltage-gated Na+ channels? How does the effect of lidocaine differ from the effect of TTX?
Your answer:
TTX and lidocaine they all block the diffusion of Na+ across the channel. Effect of TTX is irreversible while that of lidocaine
is reversible.
A nerve is a bundle of axons, and some nerves are less sensitive to lidocaine. If a nerve, rather than an axon, had been
used in the lidocaine experiment, the responses recorded at R1 and R2 would be the sum of all the action potentials (called
a compound action potential). Would the response at R2 after lidocaine application necessarily be zero? Why or why not?
Your answer:
The response in R2 with lidocaine would be greater than zero because it is recording total action potential. Some axons
remain unaffected. The nerve response would be greater than zero.
Why are fewer action potentials recorded at recording electrodes R2 when TTX is applied between R1 and R2? How
well did the results compare with your prediction?
Your answer:
TTX applied to R1 have no effect because a stimulus has already passed through the axon at that channel. However, the
TTX have an effect at R2 as predicted.
Why are fewer action potentials recorded at recording electrodes R2 when lidocaine is applied between R1 and R2?
How well did the results compare with your prediction?
Your answer:
It had no effect on R1 but blocked the response of R2 like TTX.
Pain-sensitive neurons (called nociceptors) conduct action potentials from the skin or teeth to sites in the brain involved
in pain perception. Where should a dentist inject the lidocaine to block pain perception?
Your answer:
Dentists should inject the lidocaine to the receptor of nociceptors.