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Instrumentation & Membrane Potential. Dinaz Lahewala 2011 Biol 125. What We Did. Potential Gradient Exercise Simulated a cell and observed change in membrane potential caused by a change in [ion]. Familiarize ourselves with recording and displaying software and hardware
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Instrumentation & Membrane Potential DinazLahewala 2011 Biol 125
What We Did • Potential Gradient Exercise • Simulated a cell and observed change in membrane potential caused by a change in [ion]. • Familiarize ourselves with recording and displaying software and hardware • Computer programs – LabChart6 • Powerlab, Bio amp, force transducer
Instrumentation • What does a force transducer do? • Which units are appropriate and when? • Capturing Biological Signaling • Provide the pathway ADI Instruments
Potential Gradient Excercise • Concepts: Potential Gradient • The potential gradient is the voltage difference between the inside and the outside of a membrane and is expressed in millivolts (mV).
Potential Gradient • The Experiment • We created an artificial cell. • Inside 0.1 M KCl was added. • Outside 0.01 M KCl was added. • Membrane selectively allows K+ to pass through, but not Cl-. • K+ will travel down their [gradient] leaving a higher [Cl-] on the inside.
Potential Gradient • The Experiment • Creates a disparity of charge on opposites sides • consequently creates a potential gradient. • The voltage on the inside is less positive than the voltage outside. • A few milliliters of 0.1 M KCl was added to the outside compartment. This caused the membrane voltage (mV) to increase further from zero
Potential Gradient • How does this relate to the cell? • A potential gradient is created across the membrane by the Na-K pump. This pump exudes 3 Na+ ions for 2 K+ ions. There is a net removal of a positive ion from the cell with each cycle • This leads to a negative charge in the cytoplasm and a positive charge in the ECF. • *Na-K pump is said to be electrogenic because… • It pumps unequal amounts of ions in opposite directions.
Potential Gradient Nernst Potential: EX
What About Cl- ? • Calculate the value from the Nernst Potential So based on what you recorded, and what is calculated, which ion do you think the membrane is permeable to? EX
Potential Gradient • Action Potentials • For an action potential to be possible in an excitable cell, the membrane must be depolarized (increase in membrane potential). • If the voltage increases past threshold, the cell will “fire”, meaning an action potential will occur
Lecture Questions 4. Which protein involved in the movement of substances across the membrane, will actually bind to that substance? • C) carrier protein 6. The Na/K pump is said to be “electrogenic” because _____. D) it pumps unequal numbers of ions in opposite directions • 10. The conductance of voltage-gated K channels is greatest during the _____. • C) Repolarization phase of the AP. • 11. The threshold potential for an AP is ____ • A) reached by depolarization from the resting membrane potential
Lecture Questions • 13. Graded potentials _____. A) are found along axons B) are found in the membrane of axon terminals C) are small changes in membrane potential D) degrade with distance along the membrane E) C and D • E) C & D • 14. During the absolute refractory period _____. A) all channel types in the membrane are closed B) a second stimulus will not result in an action potential C) a second stimulus may result in an additional AP if the stimulus is strong enough • B • T or F: A neuron will always respond with an action potential if the stimulus is large enough. • False – Not if it is in its absolute refractory period.
Lecture Questions • How does the cell membrane act as a capacitor? • Identify a channel type that acts as a variable resistor. • What activity results in the hyperpolarization period of an action potential?
