Question

1. An electrophysiologist is studying the electrical properties of an isolated squid neuron placed in normal extracellular fluid. She places a recording electrode inside the cell to record the potential difference across the membrane. She records a resting membrane potential of -70 mV.

She then applies an electric current across the membrane and records a slight change in the membrane potential. When she increases the current and stimulates the cell again, she notices a rapid reverse in the membrane potential to +30 mV followed by a drop in membrane potential to -75 mV before it returns to -70 mV. When she increases the current some more and stimulates the cell again, she records the same electrical pattern that is the same as what was obtained with the previous current that was applied.

2. What name can be given to the small change in membrane potential seen with the first electrical current applied?

3. Given the type of stimulus, what triggered this change in membrane potential?

4. What is the name given to the electrical pattern obtained with the next current used?

5. What allowed this stimulus to work but not the previous one?

6. Explain the type of feedback mechanism that occurs when this pattern was initiated.

7. Describe the cellular mechanisms that account for the rise and then fall in this electrical pattern

8. Why did the pattern remain the same when the highest stimulus was applied?

Answer 1

B. it is called as a local potential ( produced by sub-threshold stimulus)

C. opening of sodium channels allowed the entry of sodium into the cell.

D. Action potential

E. because the second stimulus was strong enough so that the potential reached firing level or threshold potential

F. after reaching the firing level, there is a positive feedback on the voltage gated sodium channels by the sodium influx.

G- rise in potential is called as depolarisation which is due to opening of sodium channels and entry of sodium to the cells.

fall in potential is called as repolarisation which is due to opening of potassium channels and potassium efflux. sodium channels begins to close at the beginning of repolarisation.

H. any stimulus more than the threshold stimulus will cause the same action. the strength of stimulus doesn't matter once it reach the threshold stimulus.