PhysioEx 9.1 Lab 3 Activity 1

Exercise 3: Neurophysiology of Nerve Impulses: Activity 1: The Resting Membrane Potential Lab Report
Pre-lab Quiz Results
You scored 100% by answering 4 out of 4 questions correctly.
1. What is the approximate concentration of K+ inside a typical cell (intracellular concentration)?
You correctly answered: a. 150 mM
2. What is the approximate concentration of K+ outside a cell (extracellular concentration)?
You correctly answered: b. 5 mM
3. What is the approximate concentration of Na+ inside a cell (intracellular concentration)?
You correctly answered: b. 5 mM
4. What is the approximate concentration of Na+ outside a cell (extracellular concentration)?
You correctly answered: a. 150 mM

09/25/13

page 1

Experiment Results
Predict Question:
Predict Question: Predict what will happen to the resting membrane potential if the extracellular K+ concentration is increased. Your answer : b. The resting membrane potential will become less negative.
Stop & Think Questions:
What is the polarity of the resting membrane potential (voltage)?
You correctly answered: b. negative
What does it mean that the voltage just inside the membrane is negative?
You correctly answered: b. There are more negative charges than positive charges just inside the membrane.
The membrane of most cells, including neurons, contains passive, open,
K+ leak channels. Given the normal K+ concentrations and the resultant concentration gradient, which direction would K+ be expected to move (diffuse) through these leak channels?
You correctly answered: b. out of the cell
What effect does increasing extracellular K+ have on the net diffusion of K+ out of the cell?
You correctly answered: b. It decreases the net diffusion of K+ .
Which way would Na+ move across the membrane if there were open Na+ channels?
You correctly answered: a. Na+ would diffuse into the cell.
The membrane has open K+ channels, and changing extracellular K+ concentration results in a change in membrane potential. Changing the extracellular Na+ concentration does not significantly change the membrane potential. What do your results suggest about the number or state (open or closed) of Na+ channels in the resting membrane of a neuron?
You correctly answered: b. Na+ channels are mostly closed.
Experiment Data:
Extracellular Fluid (ECF)
Control
Control
Control
Control
High K+
High K+
High K+
High K+
Low Na+
Low Na+
Low Na+
Low Na+

Microelectrode Position
Cell body extracellular
Cell body intracellular
Axon extracellular
Axon intracellular
Axon intracellular
Axon extracellular
Cell body extracellular
Cell body intracellular
Cell body intracellular
Cell body extracellular
Axon extracellular
Axon intracellular

09/25/13

page 2

Voltage (mV)
0
-70
0
-70
-40
0
0
-40
-72
0
0
-72

09/25/13

page 3

09/25/13

page 4

09/25/13

page 5

09/25/13

page 6

Post-lab Quiz Results
You scored 66% by answering 2 out of 3 questions correctly.
1. A negative membrane potential was recorded when the tip of the microelectrode was
Your answer: b. just inside the cell body.
Correct answer: d. both inside the cell body and inside the axon.
2. Which of the following caused a change in membrane potential from -70 to -40 in the cell body?
You correctly answered: a. an increase in extracellular K+
3. Which of the following has the most negative voltage?
You correctly answered: c. between the inside of the axon and the outside of the axon with control K+ ECF

09/25/13

page 7

Review Sheet Results
1. Explain why increasing extracellular K+ reduces the net diffusion of K+ out of the neuron through the K+ leak channels. Your answer:
Increasing the extracellular K+ causes the membrane potential to change to a less negative value because when K+ ions diffuse out across the membrane they are leaving behind a net negative charge.
2. Explain why increasing extracellular K+ causes the membrane potential to change to a less negative value. How well did the results compare with your prediction?
Your answer:
Potassium ions diffuse out across the membrane, leaving behind a net negative charge.
3. Explain why a change in extracellular Na+ did not significantly alter the membrane potential in the resting neuron?
Your answer:
There are less leakage sodium channels than leakage potassium channels, and more of the potassium channels are open.
4. Discuss the relative permeability of the membrane to Na+ and K+ in a resting neuron.
Your answer:
Membrane permeability to sodium is very low because there are only a few sodium leakage channels. Sodium ions slowly diffuse inward, down their concentration gradient. Left unchecked, such inward leakage of sodium would eventually destroy the resting membrane potential. The sodium potassium pumps offset the small inward sodium leak and outward leak of potassium leak.
5. Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential.
Your answer:
The resting period potential is a potential difference between the inside of the cell and the outside of the cell across the membrane. It depends on the resting permeability of the membrane to ions and on the intracellular and extracellular concentrations of those ions to which the membrane is permeable.

09/25/13

page 8