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Eliciting a Nerve Impulse
Activity 1: Electrical Stimulation
1. Do you see any kind of response on the oscilloscope screen? No
2. What was the threshold voltage, or the voltage at which you first saw an action potential? 3.0V
3. How does this tracing compare to the one that was generated at the threshold voltage? This tracing moved in the same pattern however it was slightly higher at the top peak and slightly lower at the bottom peak.
4. What reason can you give for the change? As the voltage increases the range of the trace will expand until the threshold is reached.
5. Record this maximal voltage here: 4.0V
Activity 2: Mechanical Stimulation
1. When the glass rod is touching the nerve, what do you see on the oscilloscope screen? The oscilloscope shows the nerve’s reaction to stimulus
2. How does this tracing compare with the other tracings you have generated? The tracing travelled in the same pattern as the other tracings and was at the same high and low as the 3.0V test.
Activity 3: Thermal Stimulation
1. What happens when the heated rod touches the nerve? The trace shows a slightly higher reaction to the heated glass rod as opposed to the cold glass rod.
2. How does this trace compare to the trace that was generated with the unheated glass bar? This trace had an approx. 0.5V higher reaction.
3. What explanation can you provide for this? Since the glass rod was heated it generated a slightly higher nerve impulse.
Activity 4: Chemical Stimulation
1. Does the sodium chloride generate an action potential? Yes.
2. Does this tracing differ from the original threshold stimulus tracing? If so, how? Yes, it is 1.0V lower than the original threshold from activity 1.
3. Does the hydrochloric acid generate an action potential? Yes.
4. Does this tracing differ from the original threshold stimulus tracing? If so, how? Yes, it is 1.0V lower than the original threshold from activity 1.
5. To summarize your experimental results, what kinds of stimuli can elicit an action potential? A direct electric pulse of 3.0V to 4.0V as well as chemical stimuli, such as sodium chloride or a physical stimuli, such as heat.
Inhibiting a Nerve Impulse
Activity 5: Testing the Effects of Ether
1. What sort of trace do you see? The trace is a flat line.
2. What has happened to the nerve? The ether blocked the nerve transmission.
3. How long does it take for the nerve to return to normal? The nerve returns to normal at 6 minutes and then flat lines and returns to normal every two minutes following the initial vertical spike.
Activity 6: Testing the Effects of Curare
1. Does this generate an action potential? There is no change.
2. What explains this effect? The nerve impulse is unchanged, due to curare affecting the synaptic ends of the nerve.
3. What do you think would be the overall effect of Curare on the organism? Ultimately the organism would die, due to curare inhibiting nerve transmissions.
Activity 7: Testing the Effects of Lidocaine
1. Does this generate a trace? No.
2. What sort of tracing is seen at the threshold voltage? The trace is plat lined.
3. Why does Lidocaine have this effect on nerve fiber transmission? Lidocaine is sodium based and prohibits the channel from opening, stopping any action potential from initiating.
Nerve Conduction Velocity
Activity 8: Measuring Nerve Conduction Velocity
1. Which nerve in the group has the slowest conduction velocity? Earthworm.
2. What was the speed of the nerve? 8.94m/sec
3. Which nerve of the four has the fastest conduction velocity? Rat2
4. What was the speed of the nerve? 53.09m/sec
5. What is the relationship between nerve size and conduction velocity? What are the physiological reasons for this relationship? The nerve is similar to a water pipe, the larger the pipe the faster the flow. For the nerve, a larger the nerve has greater conduction velocity than a smaller nerve and myelinated nerves are faster than unmyelinated nerves.
6. Based on the results, what is your conclusion regarding the effects of myelination on conduction velocity? What are the physiological reasons for your conclusion? The action potential of myelinated nerves jumps from the nodes to the Ranvier to the next node, as opposed to continuous conduction in the unmyelinated nerves.
7. What are the evolutionary advantages achieved by the myelination of neurons? Myelinated nerves allow for faster conduction, which would result in faster impulses and action potential, which would allow for faster reaction.
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