Membrane Potentials and Action Potentials Dr Arwa Rawashdeh
Membrane Potentials and Action Potentials Dr. Arwa Rawashdeh
objectives • • • Resting membrane potential (RMP) Achieving constant membrane potential Electrochemical equilibrium Nernst equation (ion equilibrium potential ) Goldman Hodgkin (GHK) equation (diffusion potential ) Combination of nernst and GHK Donnan potential Voltage gated ion channels, gating states Basic of action potential (AP) terminology
Membrane potential • Biological function and one of the examples is Action potential • Muscle contraction • Signal transduction
Achieving RMP and Electrochemical equilibrium
• Na+ (outside): 142 m. Eq/L • Na+ (inside): 14 m. Eq/L • K+ (outside): 4 m. Eq/L • K+ (inside): 140 m. Eq/L
Sodium and potassium pump versus sodium and potassium channels Sodium and potassium channels • No net flow • Thermodynamic downhill • No energy required Sodium potassium pump • thermodynamic uphill • It is required energy 40% of the energy used in your body
Gibbs Donnan potential • Presence macromolecules negatively charged that cannot escape cause to membrane negative potential • Thermodynamic equilibrium
Nernst equation R is the universal gas constant and is equal to 8. 314 J. K-1. mol-1 (Joules per Kelvin per mole) T is the temperature in Kelvin (K = °C + 273. 15). z is the valence of the ionic species. +1 for K+, . F is the Faraday's constant and is equal to 96485 C. mol-1 (Coulombs per mole). In the natural lograthmeis difference betwwen the conc [X]out is the concentration of the ionic species X in the extracellular fluid. Note that the concentration unit must match that of [X]in is the concentration of the ionic species X in the intracellular fluid. Note that the concentration unit must match that of [X]out. Typically, but not always, the concentrations are noted in m. M.
Goldman Hodgkin Equation (GHK)
Nernst equation • Calculate one ion • No energy GHK equation • All ions • Permeability • Concentrations • Intra and extra conc • Net flow • Well , adequately explains living cells • Requires energy
Combination of nernst and GHK equations
Combination of nernst and GHK equations • When the permeability for a given ion increases dramatically the resting membrane potential is going to get closer to the given ion equilibrium
Factors to resting membrane potentials • Diffusion potential (GHK) • Pumps of sodium and pottasium • Gibbs and Donnon potential negative 12 to 20 m. V
186000 miles/sec 100 min/sec in thickest myleinated nerve cell
Action potential (AP) • Short event in which membrane potential dramatically changes
• 1 AP for every heart beat so how many action potential the heart can generate in beats/min; the heart beats is 200 per a min; 1 AP/0. 3 sec * 60 sec/1 min= 200 AP/ min. • This number is very important to know your maximum cardiac output you can go with to increase your endurance Which is 80% or 70% of your heart
How can we apply this clinically? Hypokalemia anorexia (the people who don't eat) bulimia (when somebody eats and enforce himself to vomit). diuretics (increase urine output) hyperaldosteronism (hormone regulates sodium and potassium). vomiting and diarrhea especially in infants the
Hyperkalemia Kidney failure • Hypoaldosteronism • Excessive IV drip of k chloride instead of sodium chloride •
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