The Resting Membrane Potential

9/29/2020 PhysioEx Exercise 3 Activity 1 PhysioEx Lab Report Exercise 3: Neurophysiology of Nerve Impulses Activity 1: The Resting Membrane Potential Name: Date: 29 September 2020 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 become less negative. Stop & Think Questions 1 What is the polarity of the resting membrane potential (voltage)? You correctly answered: negative. i 1/8 9/29/2020 PhysioEx Exercise 3 Activity 1 2 What does it mean that the voltage just inside the membrane is negative? 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 ll l i 2/8 9/29/2020 PhysioEx Exercise 3 Activity 1 Low Na+ Axon, intracellular -72 i 3/8 9/29/2020 PhysioEx Exercise 3 Activity 1 i 4/8 9/29/2020 PhysioEx Exercise 3 Activity 1 i 5/8 9/29/2020 PhysioEx Exercise 3 Activity 1 Post-lab Quiz Results You scored 100% by answering 3 out of 3 questions correctly. i 6/8 9/29/2020 PhysioEx Exercise 3 Activity 1 1 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. 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: It changes the diffusion. 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 results was accurate to my prediction. It causes it to change to a less negative value because it changes the diffusion. 3 Explain why a change in extracellular Na+ did not significantly alter the membrane potential in the resting neuron? Your answer: Because the Na channels are mostly closed. 4 Discuss the relative permeability of the membrane to Na+ and K+ in a resting neuron. Your answer: K+ has leaky channels and Na+ channels are mostly closed. 5 Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential. i 7/8 9/29/2020 PhysioEx Exercise 3 Activity 1 Your answer: high concentration of K+ out of the cell decreases the net diffusion of K+ and Na+ channels are mostly closed so it doesn't make a huge difference. i 8/8