2011 Membrane Potentials

2011 Membrane Potentials - C - 37Dr. Kennon M. Garrett...

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Unformatted text preview: C - 37Dr. Kennon M. Garrett MEMBRANE POTENTIALSReading: Widmaier et al., Vanders Human Physiology, 12th ed. pp. 142-147.Behavioral Objectives 1. List 2 forces that affect the movement of ions across the membrane. 2. Define the equilibrium potential of an ion. 3. Determine how chemical gradients of ions across the membrane affect the equilibrium potential using the Nernst equation. 4. List the equilibrium potentials for sodium, potassium and chloride. 5. Describe how both the equilibrium potential and permeability of individual ions affect the membrane potential and determine how changes in the permeability and concentration gradients of individual ions will alter the resting membrane potential. 6. Describe the role of the Na/K ATPase in maintaining the membrane potential. 7. Define depolarizing, hyperpolarizing and repolarizing. 8. Determine the direction of the movement of an ion and the effects on the membrane potential when given its equilibrium potential and the resting membrane potential. I. Resting membrane potential(Fig. 6-8) A. Introduction 1. Under resting conditions, all cells are negatively charged with reference to the outside of the cell. 2. The resting potential ranges from 5 to 100 mV depending on the type of cell, and is approximately 70 mV in neurons. C - 383. The magnitude of the resting potential is due to a. The concentration differences of ions across the cell b. The selective conductance of the ions 4. Ohm's law I = V/R a. I is current. In biological systems current is produced by movement of ions across the membrane (units are nanoamps or picoamps). b. V is potential difference (units are millivolts). c. R is resistance to current. Membranes have a high resistance due to lipids in the membrane (units are megaohms). d. conductance (g) = 1/R Changes inconductance (and resistance) are due to opening and closing of ion channels. C - 39B. Forces that affect the diffusion of ions across the membrane 1. Chemical - concentration gradient Concentrations of Ions in a Typical Nerve CellIonExtracellular concentrationIntracellular concentrationNa+145 mM 15 mM K+5 mM 150 mM Cl-110 mM 7 mM 2. Electrical - ions move toward the opposite charge (Fig. 6-7). Cations (positively charged ions) move toward negative charges and anions (negatively charged ions) move toward positive charges. 3. The movement of ions in cells is influenced by both the chemical gradients and electrical forces. The algebraic sum of the electrical and chemical forces is called the electrochemical potential for that ion. C - 40C. Equilibrium potential 1. Definition Each ion has an equilibrium potential. The equilibrium potential for an ion is the membrane potential where the driving force of the concentration...
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2011 Membrane Potentials - C - 37Dr. Kennon M. Garrett...

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