ACTIVITY 1
2. Click Single Stimulus. Do you see any kind of response on the oscilloscope screen? At 1.0 V, there is no response—the screen displays a flat line.
What was the threshold voltage, that is, the voltage at which you first saw an action potential? 3.0 V
4. How does this tracing compare to the one trace that was generated at the threshold voltage? (Hint: Look very carefully at the tracings.)
The slight increase in voltage results in a slight increase in the height of the action potential peak.
What reason can you give for the change?
At threshold voltage, the smaller fibers in a nerve are stimulated and an action potential
is seen. Increasing the voltage will cause most, if not all of the neural fibers to undergo
depolarization. A given nerve is made up of literally thousands of neuron processes
(axons) so this slight increase is noted when all fibers in the nerve fire.
5. Record this maximal voltage here: 4.0 V
ACTIVITY 2
2. Using the mouse, click the glass rod located on the bottom shelf on the left side of the screen, and drag it over to the nerve. When the glass rod is over the nerve, release the nerve. What do you see on the oscilloscope screen?
An action potential is generated when you touch the rod to the nerve.
How does this tracing compare with the other tracings that you have generated?
The tracing is identical to the tracing generated at the threshold voltage.
ACTIVITY 3
Click on the glass rod and drag it to the heater, releasing the mouse button. Click on the Heat button. When the rod turns red, indicating that it has been heated, click and drag the rod over the nerve and release the mouse button. What happens?
An action potential is generated when you touch the heated rod to the nerve.
How does this trace compare to the trace that was generated with the unheated glass rod?
The tracing shows the action potential peaking slightly higher than the peak generated by
the unheated rod.
What explanation can you provide for this?
Thermal stimulation can also elicit a nerve response. Heat generates action potentials in
more of the neurons in a nerve than are generated by touch.
ACTIVITY 4
1. Click and drag the dropper from the bottle of sodium chloride (salt solution) over to the nerve in the chamber and then release the mouse button to dispense drops.
Does this generate an action potential?
Yes, dropping sodium chloride on the nerve generates an action potential.
2. Look back at Activity 1 for the voltage you determined. Set the voltage at that level, and click Single Stimulus to stimulate the nerve.
Does this tracing differ from the original threshold stimulus tracing?
No, the tracing does not differ from the original threshold stimulus tracing.
4. Click and drag the dropper from the bottle of hydrochloric acid over to the nerve, and release the mouse button to dispense drops.
Does this generate an action potential?
Yes, dropping hydrochloric acid on the nerve generates an action potential.
Does this tracing differ from the one generated by the original threshold stimulus?
No, the tracing does not differ from the original threshold stimulus tracing.
6. To summarize your experimental results, what kinds of stimuli can elicit an action potential?
Electrical, mechanical, thermal, and chemical stimulation are all capable of generating an
action potential in a nerve.
ACTIVITY 5
2. Look back at Activity 1 for the voltage you determined. Set the voltage at that level, and click Single Stimulus to stimulate the nerve.
What sort of trace do you see? The screen displays a flat line, indicating no nerve response.
What has happened to the nerve? The nerve has been anesthesized by the ether.
4. How long does it take for the nerve to return to normal? 2 min.
ACTIVITY 6
2. Look back at Activity 1 for the voltage you determined. Set the voltage at that level, and click Single Stimulus to stimulate the nerve. Does this generate an action potential?
There is no change to the action potential tracing.
What explains this effect?
Nerve propagation is unaffected because curare works on the synaptic ends of the nerve.
What do you think would be the overall effect of curare on the organism?
Curare would ultimately kill the organism by blocking nerve transmission.
ACTIVITY 7
1. Click and drag the dropper from the bottle of lidocaine and position it over the nerve between the stimulating and recording electrodes. Release the mouse button to dispense drops. Does this generate a trace? No
2. Look back at Activity 1 for the voltage you determined. Set the voltage at that level, and click Single Stimulus to stimulate the nerve. What sort of tracing is seen? Flat line
Why does lidocaine have this effect on nerve fiber transmission?
It is a Na-channel antagonist—if Na channels cannot be opened, then there can be no change in membrane potential.
ACTIVITY 8
5. At what threshold voltage do you first see an action potential generated? 5 V
11. Which nerve in the group has the slowest conduction velocity? Earth worm
What was the speed of the nerve? 8.85 m/sec
Which nerve in the group of four has the fastest conduction velocity? Rat 2 – myelinated
What was the speed of the nerve? 45.74 m/sec
What is the relationship between nerve size and conduction velocity? Larger diameter is faster than smaller diameters
Based on the results, what is your conclusion regarding conduction velocity and whether the nerve is myelinated or not? Myelinated fibers are faster than unmyelinated fibers.
What is the major reason for the differences seen in conduction velocity between the myelinated nerves and the unmyelinated nerves? Unmyelinated = continuous conduction
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