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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 cells 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 brains 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