PEX-03-01 - Physio Ex 9.1 PDF

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Physio Ex 9.1...

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Name: Steffany A. Rivera 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

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Experiment Results Predict Question: Predict Question: Predict what will happen to the resting membrane potential if the extracellular K+ concentration is increased. Your answer : c. The resting membrane potential will not change. Stop & Think Questions: What is the polarity of the resting membrane potential (voltage)? Your answer : a. positive Correct answer: 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+

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

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

High K+ High K+ High K+ Low Na+ Low Na+ Low Na+

Axon extracellular Cell body extracellular Cell body intracellular Cell body intracellular Cell body extracellular Axon extracellular

0 0 -40 -72 0 0

Low Na+

Axon intracellular

-72

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Post-lab Quiz Results You scored 33% by answering 1 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? Your answer: d. between the inside of the axon and the outside of the axon with High K+ ECF Correct answer: c. between the inside of the axon and the outside of the axon with control K+ ECF

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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: The concentration of K+ inside the neuron is already high so increasing the concentration of the ECF does not change in ICF concentration 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 K+ concentration started diffusing to the inside of the cell creating a more negative membrane potential. 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 and do not allow the diffusion of Na+ in or out of the cell. 4. Discuss the relative permeability of the membrane to Na+ and K+ in a resting neuron. Your answer: In resting neuron the resting membrane potential is unchanged because there is no exchange in ions. The permeability is not good since there is no diffusion. 5. Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential. Your answer: Any diffusion of NA+or K+ in or out of the cell changes the resting membrane potential because the concnetration of the ions dictate the relative - or + membrane potential.

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