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Review Sheet

Eliciting (Generating) a Nerve Impulse

1. Why don’t the terms depolarization and action potential mean the same thing?
   
A depolarization is any change in a neuron that makes it more positive than resting potential, but an action potential only occurs when the depolarization reaches the threshold level.

2. What was the threshold voltage in Activity 1?
   
3.0 V

3. What was the effect of increasing the voltage? How does this change correlate to changes in the nerve?
   
Increasing voltage results in depolarization of increasing numbers of neurons in a nerve.

4. How did the action potential generated with the unheated rod compare to that generated with the heated rod?
   
The action potential generated with the unheated rod was less than the action potential generated by the heated rod.

5. Describe the types of stimuli that generated an action potential.
   
Electrical, mechanical, thermal, and chemical stimuli are all capable of generating an action potential.

6. If you were to spend a lot of time studying nerve physiology in the laboratory, what type of stimulus would you use and why?
   
Although many different stimuli work, electrical stimulators are convenient because the voltage duration and frequency of the shock can be very precisely set for use.

7. Why does the addition of sodium chloride elicit an action potential? Hint: Think about the sodium permeability of the neuron (Figure 3.2e).
   
While the sodium-potassium pump is pumping sodium out of the cell and potassium into the cell, these ions are leaking back where they came from by diffusion. By adding sodium chloride, a more-than-normal amount of sodium will diffuse into the nerve, causing the resting membrane potential to reach the threshold value, bringing about a membrane depolarization.

Inhibiting a Nerve Impulse

8. What was the effect of ether on eliciting an action potential?
   
There was no effect it conducted the same

9. Does the addition of ether to the nerve cause any permanent alteration in neural response?
   
No, the ether has no lasting effect.

10. What was the effect of curare on eliciting an action potential?
   
Curare had no effect - an action potential

11. Explain the reason for your answer to question 10 above.
   
Curare stops Acetylcholine. It creates a depolarisation block. Disinhibition from blocking interneurons that express nicotinic accetylcholine receptors.

12. What was the effect of lidocaine on eliciting an action potential?
   
Lidocaine is an antagonist inhibitor that blocks sodium ion channels, when these are blocked there's no action potential (nerve impulses).

Nerve Conduction Velocity

13. What is the relationship between size of the nerve and conduction velocity?
   
A larger nerve will have a faster conduction velocity.

14. Keeping your answer to question 13 in mind, how might you draw an analogy between the nerves in the human body and electrical wires?
   
Larger electrical wire has less resistance to current flow and will conduct faster than smaller wire with increased resistance to current flow.

15. How does myelination affect nerve conduction velocity? Explain, using your data from Chart 1.
   
Myelination speeds up nerve conduction velocity by causing the nerve impulse to jump across the cell membrane from one internode to another rather than be conducted across the entire cell membrane.

16. If any of the nerves used were reversed in their placement on the stimulating and recording electrodes, would any differences be seen in conduction velocity? Explain.
   
No. Once a neural membrane is depolarized and the impulse is being conducted along the neural membrane, which direction is which does not matter. We state that a neural impulse is set up in the neuron’s trigger zone (mainly due to the large number of sodium channels there) but once the depolarization is set up, it not only travels down the axon but also around the soma of the cell.