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Membrane potentials and Resting Membrane Potential

Membrane potentials and Resting Membrane Potential. 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

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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

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