1. What was your observed threshold voltage? The voltage at which I first observed an action potential was 3.0V 2. How does this tracing compare to the one that was generated at threshold voltage? The small increase in voltage causes a small increase in the height of the action potential peak. 3. What reasons can you give for your answer?
Recruitment of the nerve’s neurons. Increasing the voltage will cause most of the neural fibers to experience depolarization. 4. At what voltage did you no longer observe an increase in the peak of the action potential trace? Maximum voltage or the point beyond which no further increase occurs in the peak of the action potential trace was 4.0V
1. What did you observe when the glass rod contacted the nerve? An action potential is generated as I touch the rod to the nerve. 2. How does this tracing compare with the other tracings you have generated? The tracing is identical to the tracing generated at the threshold voltage. 3. What did you observe when the heated glass rod contacted the nerve? An action potential is generated when you touch the heated rod to the nerve, through a thermal stimulus. 4. How does this trace compare to the trace that we generated with the unheated glass rod? The tracing shows the action potential peaking slightly higher than the peak generated by the unheated rod. 5. What did you observe when you added sodium chloride and hydrochloric acid solutions to the nerve? Dropping hydrochloric acid on the nerve generates an action potential, through a chemical stimulus. 6. 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.
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1. What are the effects of ether on the nerve? The screen displays a flat line, indicating no nerve response. The nerve has been anesthetized by the ether, thus preventing any impulses of the nerves. 2. How long did it take for the nerve to return to normal?
It required about 2 min to return to normal. Activity 6:
1. What effect did adding curare have on the action potential? There is no overall effect, still an action potential. 2. Explain this effect. Nerve transmission is unaffected because curare works on the synaptic ends of the nerve. 3. What do you think would be the overall effect of curare on an organism? Curare would eventually kill the organism by blocking nerve transmission. More specifically, stunt the nerves in their diaphragm, preventing respiration.
1. Does adding lidocaine to the nerve generate an action potential? No action potiential with the addition of lidocaine. 2. Explain why lidocaine has this effect on nerve fiber transmission. It is a local anesthetic, which closes the Na+ channels, preventing depolarization.
Record Your Data:
Nerve Earthworm (small) Frog (medium, myelinated) Rat nerve 1 (medium, unmyelinated) Rat nerve 2 (large, myelinated) Threshold voltage
Elapsed time from stimulation to action potential
1. Which nerve in the group has the slowest conduction velocity? Earthworm 2. Which nerve of the four has the fastest conduction velocity? Rat 2, myelinated. 3. Explain the relationship between nerve size and conduction velocity. Larger diameter is faster than smaller diameters. 4. What are the physiological reasons for this relationship? Unmyelinated = continuous conduction 5. What are the effects of myelination on conduction velocity? Myelinated fibers are faster than unmyelinated fibers 6. What are the physiological reasons for you conclusion?
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7. What are the evolutionary advantages achieved by the myelination of neurons?
Mylein: less current leakage, insulation, faster conduction of impulse. Larger diameter more electricity can flow, less resistance, faster conduction.