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Understanding Membrane Potentials and Resting Membrane Potential

Learn the physiology of membrane potentials and resting membrane potential. Understand electrochemical potential, Nernst equation, and Goldman equation to estimate resting membrane potential. Explore excitable tissues, nerve impulses, types of channels involved, and basic physics of membrane potentials.

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Understanding Membrane Potentials and Resting Membrane Potential

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  1. Membrane potentials and Resting Membrane Potential

  2. Objectives ♦Goal /Aim By the end of this session students should be able to understand the Physiology of Membrane potentials and Resting Membrane Potential Student should be able to • Define the electrochemical potential difference (Δμ) Use the Nernst equation to determine whether an ion is in equilibrium across a membrane. • Compute the equilibrium transmembrane electrical potential difference across a membrane that is permeable to only one ionic species. • Estimate a cell’s resting membrane potential by the Nernst equation & Goldman equation

  3. Lesson contents • Membrane potentials • DEFINITIONS • Excitation • Stimulus • Excitable Tissues • Nerve impulse • Types of Channels involved in Various Excitable Tissues • Basic Physics of Membrane Potentials • Nernst potential • Distribution of Ions across the membrane • Goldman Equation • Resting Membrane Potential • Origin of RMP

  4. DEFINITIONS • Excitation: • the process of eliciting the action potential • Stimulus: • Anything that excites “Any Change inthe environment” TYPES: a. Electrical b. Mechanical & c. Chemical

  5. DEFINITIONS • Excitable Tissues: • Any tissue that is capable of generating rapidly changing electrochemical impulses at their membranes • Tissues which are capable of responding to stimuli to highest degree than other tissues of the body in the form of electrical signals. These include • Nerve & • Muscle • Excitable tissues have LOW Threshold of Stimulation

  6. DEFINITIONS • Electrical potentials exist across the membranes of virtually all cells of the body • Change in Electrical Potential • nerve or muscle membranes • Nerve impulse • Propagated Action Potential • Local • glandular cells, macrophages, and ciliated cells • Transmission= • Conduction

  7. Types of Channels involved in Various Excitable Tissues Na+ • Voltage gated channels (fast) K+ • Slow Ca++- Na+ Channels • Ligand Gated Channels • Na+ - K+ Pump • Mechanical Gated Channels (Hair Cells ) • Na+ - K+ Leak Channels

  8. Basic Physics of Membrane Potentials

  9. Assessment Q.1 • What is meant by Excitable Tissues?

  10. Basic Physics of Membrane Potentials • Membrane Potentials Caused by Diffusion • "Diffusion Potential" Caused by an Ion Concentration Difference on the Two Sides of the Membrane • Nernst Potential: • Relation of the Diffusion Potential to the Concentration Difference

  11. Nernst potential • Definition: The diffusion potential level across a membrane that exactly opposes the netdiffusion of a particular ion through the membrane is called the Nernst potential for that ion • Magnitude of Nernst potential: • determined by • ratio of the concentrations of that specific ion on the two sides of the membrane. • Directly proportional

  12. Distribution of Ions across the membrane • Na+ mainly extracellular--- 142 mEq/L (ICF: 14 mEq/L) • K+ mainly intracellular----- 140 mEq/L (ECF: 4 mEq/L) • Cl- mainly extra cellular– 103 mEq/L(ICF: 4 mEq/L) • Non-diffusible intracellular anions. -- HPO4 – -- SO4-- • ---Intracellular proteins • (4times as in the plasma)

  13. Nernst Potential • EMF=± 61log • EMF is electromotive force • at normal body temperature of 98.6°F (37°C): • For univalent ion • +ve for –ve ion • Conc. Inside= Ci • Conc. Outside= Co Conc. inside Conc. outside

  14. Assessment Q.2 • Calculate Nernst Potential for Potassium ions.

  15. Calculation of Nernst Potential for K+ • EMF=± 61log • Conc. Inside= Ci=140 mEq/L • Conc. Outside= Co= 4 mEq/L • EMF= -61 log (140/4) • EMF= -61 log (35) • EMF= -61 (1.544) • EMF= -94 mv Conc. inside Conc. outside Log of 35= 1.544

  16. Diffusion Potential of Na+ and K+ • POTASSIUM :94 millivolts, with negativity inside the fiber membrane. • SODIUM: 61millivoltspositive inside the fiber.

  17. Goldman Equation(Goldman-Hodgkin-Katz equation) • EMF=-61log • P= Permeability • More than one ion • Potential in ECF outside cell membrane= zero (CNa+i PNa+) + (CK+iPk+) + (CCl-o PCl-) (CNa+o PNa+) + (CK+oPk+) + (CCl-i PCl-)

  18. Assessment Q.3 • Calculate Nernst Potential for Sodium ions.

  19. Calculation of Nernst Potential for Na+ • EMF=± 61log • Conc. Inside= Ci=14 mEq/L • Conc. Outside= Co= 142 mEq/L • EMF= -61 log (14/ 142) • EMF= -61 log (0.0986) • EMF= -61 (-1.00616031) • EMF= 61.366 mv Conc. inside Conc. outside Log of 0.0986= -1.006

  20. Resting Membrane Potential(RMP) Definition: The resting membrane potential is the electrical potential difference across the plasma membrane of a normal living cell in its unstimulated state. In most cells RMP is close to Nernst Potential for K+

  21. Channels involved in origin of RMP

  22. Potassium leak channel

  23. Contribution to RMP • Contributed by • K+ Diffusion Potential = -94 mv • Na+ Diffusion Potential = +61mv • Na+ K+ Pump = -4mv Large nerve fibers= -90 mv

  24. Origin of RMP Contribution by K+ Diffusion Potential Contribution by Na+ Diffusion Potential Contribution by Na+ and K+ Diffusion Potential (Goldman Equation) Contribution by Na+ K+ Pump -4 mv Net RMP

  25. Types of Disturbances across the Cell Membrane • TWO Types: • Non-Propagated Potentials: • Synaptic • Generator • Propagated • Action Potential Action Potential

  26. Summary • Electrical potentials exist across the membranes of virtually all cells of the body • Nernst potential is thediffusion potential level across a membrane that exactly opposes the netdiffusion of a particular ion through the membrane is called the Nernst potential for that ion • Diffusion Potential of POTASSIUM is -94 millivolts, and of SODIUM is +61millivolts • Goldman Equation is used to calculate diffusion potential if more than one ions are taken into consideration • Resting Membrane Potential (RMP) is defined as the electrical potential difference across the plasma membrane of a normal living cell in its unstimulated state. • In case of large myelinated nerve fibers Contribution to RMP by K+ Diffusion Potential is -94 mv, by Na+ Diffusion Potential is +61mv; and Na+ K+ Pump contributes -4mv. The final calculation is done by putting the values in Goldman Equation

  27. Assessment Q.4 • In case of large myelinated nerve fibers how much is the Contribution to RMP by • K+ Diffusion Potential • Na+ Diffusion Potential, and • Na+ K+ Pump

  28. Next topic

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