Anatomy & Physiology: Membrane Potential
Anatomy & Physiology: Membrane Potential ANPS 019
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This 3 page Class Notes was uploaded by Olivia may on Wednesday October 12, 2016. The Class Notes belongs to ANPS 019 at University of Vermont taught by Sean Flynn in Fall 2016. Since its upload, it has received 15 views.
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Date Created: 10/12/16
Lecture Objectives 14 1. Define the basic principles of bioelectricity Current (I) - the flow of electrical charge measured in amperes (A) - Charge carried by chemical ions - Current always flows in a complete circuits Resistance (R) - hindrance to charge flow by substance through which current must pass measured by ohms - Cellular membrane - Extracellular/intracellular membrane Voltage (potential) (delta V) - measured of potential energy generated by separated electrical charges measured in volts (V) - Separation is most often a physical barrier - Membrane potential (Vm) is the voltage difference between intracellular and extracellular spaces - Vm = Vin - Vout - Vout is defined as zero 2. Explain ohm’s law relates to biological membranes I = V/R or Delta V = IR ***Current is directly proportional to voltage ***Current is inversely proportional to resistance 3. Define membrane potential and describe how membranes are designed to establish membrane potentials Membrane potential - voltage across a membrane Functions of the plasma membrane that contribute to the membrane potential: 1. Mechanical Barrier - separates two of the bodies fluid - phospholipid bilayer prevents the movement of ions - creates resistance (R) - separates two of the bodies fluid 2. Selectively permeability - Determines manner in which substance enter or exit cells - Leakage channels ie. potassium leakage channels - ionic concentrations gradients establish resting membrane potential - Active transport maintains resting membrane potential - 3. Electrochemical gradient - Ions want to achieve both chemical and electrical equilibrium and will move rapidly when allowed - driving force - the combined forces of the concentration and electrical gradient of a given ion in a specific environment 4. What membrane proteins are important for membrane potential Transport proteins ie. potassium leakage channels, sodium leakage channels NaK pump 5. Describe the relationship between intracellular and extracellular ion concentration Nernst Equilibrium Potential - the membrane potential for an individual ion at which the sum of forces pushing an ion at which the sum of forces pushing an ion out of the cell equals the sum the force pushing the ion onto the cell. Veq. = RT/zF *ln ([Xout]/[Xin]) (important part for this course) Goldman-Hodgkin-Katz equation - The membrane potential that results from the contribution of all ions that can cross the membrane Concentration gradient - ions will diffuse passively from an area of higher chemical concentration to an area of lower chemical concentration Electrical Gradient - ions will move toward an area of opposite electrical charge More sodium outside the cell than inside, more potassium inside the cell than outside 6. Describe electrochemical gradients/driving force and equilibrium potentials Electrochemical gradient - Ions want to achieve both chemical and electrical equilibrium and will move rapidly when allowed - driving force - the combined forces of the concentration and electrical gradient of a given ion in a specific environment Equilibrium potentials (Eion) - when chemical and electrical forces are equal 7. Describe why gradients and equilibrium for ions important in normal cell function Without equilibrium and gradients Osmotic balance might be disrupted, causing hypertonic or hypotonic cells. Osmotic is in reference to pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane. It is also defined as the measure of the tendency of a solution to take in water by osmosis. 8. Describe how neurons establish and maintain resting membrane potential Ionic concentrations gradients establish resting membrane potential Active transport maintains resting membrane potential - 9. Explain how we measure membrane potential Membrane potential is measured based on relative potential charges. Relative charge scale (extracellular fluid set to zero) is used no the absolute charge scale which can not be easily measured.
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