Physioex 8.0 Lab Exercise #3

Exercise 3: Neurophysiology of Nerve Impulses Worksheet
Assignment Due: Week 4

Student instructions: Follow the step-by-step instructions for this exercise found in your text and record your answers in the spaces below. Submit this completed document by the assignment due date found in the Syllabus.

Please make sure that your answers are typed in RED.

Please type your Name and Student ID Number here: Charles Coon 4048223

Eliciting a Nerve Impulse
Activity 1: Electrical Stimulation

1. Do you see any kind of response on the oscilloscope screen with 1.0 volts? No a flat line was observed 2. What was the threshold voltage, or the voltage at which you first saw an action potential? 3.0 volts 3. How do the tracings generated with higher voltages compare to the one that was generated at the threshold voltage? The tracings traveled in the same fashion but had a higher peak of the action potential as you increased the threshold voltage 4. What reason can you give for the change? The increase in voltage creates the nerve to depolarize. 5. Record this maximal voltage here: 6.0 volts

Activity 2: Mechanical Stimulation

1. When the glass rod is touching the nerve, what do you see on the oscilloscope screen? The nerve’s action potential to stimuli 2. How does this tracing compare with the other tracings you have generated? The tracings follow the same pattern as the threshold voltage tracing

Activity 3: Thermal Stimulation

1. What happens when the heated rod touches the nerve? The action potential is generated 2. How does this trace compare to the trace that was generated with the unheated glass bar? Be specific! The tracings followed the same patterns but when the heated bar touched the nerve the action potential increased causing the nerve to start depolarization 3. What explanation can you provide for this? The heated bar caused a stronger nerve impulse with a higher action potential.

Activity 4: Chemical Stimulation

1. Does the sodium chloride generate an action potential? Yes action potential generated 2. Does this tracing differ from the original threshold stimulus tracing? If so, how? No the tracings are identical at the threshold voltage 3. Does the hydrochloric acid generate an action potential? Yes action potential generated 4. Does this tracing differ from the original threshold stimulus tracing? If so, how? No the tracing are identical at the threshold voltage 5. To summarize your experimental results, what general kinds of stimuli can elicit an action potential? Any stimulus that has a strong enough threshold stimulus regardless if it is physical stimulus or chemical stimulus will have an action potential on the nerve.

Inhibiting a Nerve Impulse
Activity 5: Testing the Effects of Ether

1. Was a nerve impulse inhibited? Yes there was no action potential at the threshold voltage 2. What has happened to the nerve? Nerve transmission was blocked by the ether 3. How long does it take for the nerve to return to normal? 6 minutes

Activity 6: Testing the Effects of Curare

1. Do you see that an action potential was generated or not? Yes action potential was generated 2. What explains this effect? The curare affects the acetylcholine and block neurotransmission. This will affect single neurons, you can have single neurons that are paralyzed in the nerve but unless all the neurons are paralyzed you will have action potential in the nerve. 3. What do you think would be the overall effect of Curare on the organism? The overall effect on an organism would be fatal if directly introduced into the bloodstream.

Activity 7: Testing the Effects of Lidocaine

1. Was a nerve impulse generated? No there was no action potential 2. Why does Lidocaine have this effect on nerve fiber transmission? Lidocaine is a sodium ion channel antagonist which in turn will block the sodium channels from opening. When this happens it will inhibit any action potential taking place

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? About 8.94 m/sec 3. Which nerve of the four has the fastest conduction velocity? Rat Nerve #2 4. What was the speed of the nerve? About 46.74 m/sec 5. What is the relationship between nerve size and conduction velocity? What are the physiological reasons for this relationship? The relationship between axon diameter and conduction velocity is that larger diameter nerves will conduct faster. The plasma membrane depolarizes to its threshold which will create the action potential. 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? Myelinated nerves that are larger will conduct faster when the action potential is propagated. Myelination creates lining on the axons in the neuron that prevents ions from leaking through the membrane increasing conduction velocity.