Chapter 5 Part 2 Membrane Potential

# Chapter 5 Part 2 Membrane Potential - d The Equilibrium...

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Miguel Alvarez LS2 PLF Winter 10 Week 8 Chapter 5 Part 2: Membrane Potentials ***There are 3 important concepts that we have to cover regarding Membrane potentials: 1. Diffusion of an ion . a. Selectively permeable membrane (i.e. permeable to K, only K will be able to go through the membrane). i. Permeability: willingness for the membrane to let “things” go through. b. An ion will naturally diffuse down its concentration gradient, until it reaches equilibrium (the state where the rate of entry = rate of exit). 2. Equilibrium Potential (EP) a. There are EP’s for ions, such as sodium and potassium. b. [Na+] is higher outside the cell than inside the cell. c. Unit of measuring electric pressure: mV (millivolts) i. Because of concentration gradient, Na will want to go in (influx) ii. Because of the positive voltage in the cell created by the excess of + charge inside, Na will go out (efflux). iii. At this point, the potential across the membrane is the Equilibrium potential for the ion (in this case it’s Na (sodium)).

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Unformatted text preview: d. The Equilibrium potential values for Na and K are: i. Na=+50mV ii. K= -80 mV e. The charge of the ion doesn’t matter when calculating the Eq. Potential. What does matter is the direction of the substance. f. Q: Why does K (potassium) have a negative E.P. is it’s a positive ion just like Na? g. A: Since there is more K+ inside the cell, it will want to go OUT! As it leaves, there will be a DEFICIT of this ion inside the cell and thus become negative negative EP. 3. Membrane Potential (MP) a. Refers to: electric potential of the cell’s interior relative to the exterior (which is assigned 0). b. Resting potential: -70mV i. De polarization: away from the resting potential (usually towards the positive end) ii. Re polarization: back to the resting potential iii. Hyper polarization: a bit “under” the resting potential Miguel Alvarez LS2 PLF Winter 10 Week 8 c. MP depends on the relative permeabilities of the membrane....
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Chapter 5 Part 2 Membrane Potential - d The Equilibrium...

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