Zivistan PhysioEx Exercise 3 Activity 1

9/24/23, 11:08 AM PhysioEx Exercise 3 Activity 1 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex3/act1/ 1/8 PhysioEx Lab Report Exercise 3: Neurophysiology of Nerve Impulses Activity 1: The Resting Membrane Potential Name: Zivistan Fidan Date: 24 September 2023 Session ID: session-e56709c6-24c6-7c14-3822-b605474d4296 Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. Experiment Results Predict Question Stop & Think Questions What is the approximate concentration of K inside a typical cell (intracellular concentration)? You correctly answered: 150 mM. 1 + What is the approximate concentration of K outside a cell (extracellular concentration)? You correctly answered: 5 mM. 2 + What is the approximate concentration of Na inside a cell (intracellular concentration)? You correctly answered: 5 mM. 3 + What is the approximate concentration of Na outside a cell (extracellular concentration)? You correctly answered: 150 mM. 4 + 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 become less negative. 1 + What is the polarity of the resting membrane potential (voltage)? You correctly answered: negative. 1 What does it mean that the voltage just inside the membrane is negative? 2

9/24/23, 11:08 AM PhysioEx Exercise 3 Activity 1 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex3/act1/ 2/8 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 You correctly answered: 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: out of the cell . 3 + + + 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 . 4 + + + Which way would Na move across the membrane if there were open Na channels? You correctly answered: Na would diffuse into the cell. 5 + + + 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. 6 + + + + +

9/24/23, 11:08 AM PhysioEx Exercise 3 Activity 1 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex3/act1/ 4/8

9/24/23, 11:08 AM PhysioEx Exercise 3 Activity 1 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex3/act1/ 5/8

9/24/23, 11:08 AM PhysioEx Exercise 3 Activity 1 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex3/act1/ 7/8 Review Sheet Results A negative membrane potential was recorded when the tip of the microelectrode was You correctly answered: both inside the cell body and inside the axon. 1 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 . 2 + 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. 3 + Explain why increasing extracellular K reduces the net diffusion of K out of the neuron through the K leak channels. Your answer: Increasing extracellular K+ reduces the net diffusion of K+ out of the neuron through the K+ leak channels because the gradient concentration is reduced in between the extracellular and intracellular fluid. This indicated that less K+ will want to diffuse out of the neuron. 1 + + + 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: Increasing extracellular K+ causes the membrane potential to change to a less negative value because the positive charge outside of the cell gets increased. Therefore, the inside of the cell becomes more negative. 2 + Explain why a change in extracellular Na did not significantly alter the membrane potential in the resting neuron? Your answer: At a resting neuron, the membrane is highly permeable to K+ because of the number of K+ leak channels that are open. The membrane has a low permeability t ions since there are few Na+ leak channels, and Na+ channels are closed. 3 + Discuss the relative permeability of the membrane to Na and K in a resting neuron. Your answer: 4 + +

9/24/23, 11:08 AM PhysioEx Exercise 3 Activity 1 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex3/act1/ 8/8 The membrane is highly permeable to K+ at rest since the K leak channels are open. There is low permeability to Na ions since there are few Na leak channels and Na channels are closed. Discuss how a change in Na or K conductance would affect the resting membrane potential. Your answer: An alteration in K+ conductance would have a larger effect on resting membrane potential than an alteration in Na+ conductance because the membrane is more permeable to K+. 5 + +