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Unformatted text preview: Vertebrate Physiology Notes 1/21/10 • Action potential causes a pulse of electricity that causes the release of neurotransmitter • Neurotransmitter binds, and the positive current is injected into neuron carried by Na+ • This allows for a + charge in the new neuron to propogate an action potential • Synapse is where one cell connects to another cell • The point when the concentration force is balanced by the electrical force is called the equilibrium potential • In the example given it is the equilibrium potential for K+ • K+ is higher inside of the cell than outside and the membrane prevents movement of K+ from inside to outside • Semipermeable membranes occur when you have a specific type of channel that only allows one type of ion through • Efflux of K+ charges causes the inside of the cell to become more negative. • The building negativity inside causes K+ to transfer back into the cell through the channels also • Equilibrium potential of Potassium is E K • Nernst Equation predicts electrical potential across the membrane at electrochemical equilibrium • That potential is called the equilibrium potential for the ion • E ionx = RT/ZF x ln[ion] outside /[ion] inside o E is equilibrium potential o R is universal gas constant o T is temperature o Z is valence or electrical charge of ion o F is faraday constant • This simplifies to E ion = 58/Z x log [ion] outside /[ion] inside • If concentration of K inside cell were 10x higher than outside then Equation predicts equilibrium potential for K is -58 mV (inside negative) o Z = +1 o [ion] outside = 1 o [ion] inside = 10 • 6 things important to charge inside and outside cell o Which ion is the membrane permeable to o Where is it more concentrated in (inside or outside) o The ion must always move from high concentration to low concentration o What charge does it carry with it (+ or -) o What is the effect on the electrical potential of the charge movement o At what inside potential does the charges leaving equal the charges entering. Equilibrium potential. • The membrane is permeable to both Na+ and K+ but far more permeable to K+ than Na+ • The cell will never reach the Potassium Equilibrium potential due to the constant leakage of Sodium into the cell • Goldman-Hodgkin- Katz equation takes into account the relative permeability of the 3 major ions for calculating the cell’s actual membrane potential o V membrane potential = 58 log (P K [K] o + P Na [Na] o + P Cl [Cl] I ) / (P K [K] I + P Na [Na} I + P Cl [Cl] o ) o Make sure and notice that Chlorine is inside over outside, while Potassium and Sodium are outside over inside o Relative permeabilities is K+ = 1.0 Na+ = 0.01 Cl- = 0.10 o Equation used to determine that V membrane potential = -70.18 mV • Na-K pump o The Na/K ATPase pump accounts for 20-40% of the brain’s energy concsumption o How it works Na+ first binds to the pump ATP is hydrolyzed to ADP This causes the pump to close on the inside of the cell, and open on the outside of the...
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- Fall '08