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• Jenna Picard

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9/18/2019

PhysioEx Exercise 3 Activity 1

PhysioEx Lab Report Exercise 3: Neurophysiology of Nerve Impulses Activity 1: The Resting Membrane Potential Name: Jenna Picard Date: 18 September 2019 Session ID: session-ccc92275-1669-98c3-e024-770a75031589

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: 150 mM. 2 What is the approximate concentration of K+ outside a cell (extracellular concentration)? You correctly answered: 5 mM. 3 What is the approximate concentration of Na+ inside a cell (intracellular concentration)? You correctly answered: 5 mM. 4 What is the approximate concentration of Na+ outside a cell (extracellular concentration)? You correctly answered: 150 mM.

Experiment Results Predict Question 1 Predict Question: Predict what will happen to the resting membrane potential if the extracellular K+ concentration is increased. Your answer: The resting membrane potential will not change. Stop & Think Questions 1 What is the polarity of the resting membrane potential (voltage)? You correctly answered: negative. 2 What does it mean that the voltage just inside the membrane is negative?

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PhysioEx Exercise 3 Activity 1

You correctly answered: There are more negative charges than positive charges just inside the membrane. 3 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: out of the cell . 4 What effect does increasing extracellular K+ have on the net diffusion of K+ out of the cell? You correctly answered: It decreases the net diffusion of K+. 5 Which way would Na+ move across the membrane if there were open Na+ channels? You correctly answered: Na+ would diffuse into the cell. 6 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: Na+ channels are mostly closed. Experiment Data Extracellular Fluid (ECF)

Microelectrode Position

Voltage (mV)

Control

Cell body, extracellular

0

Control

Cell body, intracellular

-70

Control

Axon, extracellular

0

Control

Axon, intracellular

-70

High K+

Axon, intracellular

-40

High K+

Axon, extracellular

0

High K+

Cell body, extracellular

0

High K+

Cell body, intracellular

-40

Low Na+

Cell body, intracellular

-72

Low Na+

Cell body, extracellular

0

Low Na+

Axon, extracellular

0

Low Na+

Axon, intracellular

-72

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PhysioEx Exercise 3 Activity 1

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PhysioEx Exercise 3 Activity 1

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PhysioEx Exercise 3 Activity 1

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Post-lab Quiz Results You scored 100% by answering 3 out of 3 questions correctly. 1 A negative membrane potential was recorded when the tip of the microelectrode was https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex3/act1/

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You correctly answered: 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: an increase in extracellular K+. 3 Which of the following has the most negative voltage? You correctly answered: between the inside of the axon and the outside of the axon with control K+ ECF.

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: There is generally a higher amount of K+ inside the cell compared to the extracellular environment. So increasing the extracellular K+ decreases the concentration gradient which also decreases the net diffusion of K+. 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: The resting membrane potential is negative because there is a greater negative charge inside the cell than there is a positive charge outside of the cell. Increasing extracellular K+ results in the positive charge outside of the cell to increase as well. This in turn decreases the overall difference between the inside and outside of the cell. This did not match well with my prediction as I predicted that the membrane potential would remain the same. 3 Explain why a change in extracellular Na+ did not significantly alter the membrane potential in the resting neuron? Your answer: A change in extracellular Na+ does not significantly alter the membrane potential in the resting neuron because the plasma membrane of a neuron is only slightly permeable to Na+ because there is a less amount of Na+ leakage channels. This stops the net diffusion of Na+ into or out of the cell. 4 Discuss the relative permeability of the membrane to Na+ and K+ in a resting neuron. https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex3/act1/

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Your answer: The relative permeability of the membrane in a resting neuron to K+ is higher than that of Na+ because there are leak channels for K+ whereas there a very few leak channels for Na+ ions and the Na+ channels are closed. 5 Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential. Your answer: The membrane is more permeable to K+ so a change in K+ conductance would have a greater effect on the resting membrane potential than that of a change in Na+ conductance because the membrane is less permeable to Na+.

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