Unformatted text preview: els Depolarization EK
vibration of vili amplify current. larger vibration=better hearing.
Q: epithelial cell in the inner ear: <ICF [K+]=150 mM, negative resting potential (-50mV)> <ECF [k+]=4mM, 0mV> the solution above apical membrane (endolymph [k+]=150mM, 100mV) is not same as
basolateral membrane (ECF).
1. WHAT IS APPROX VALUE OF Ek ACROSS THE APICAL MEMBRANE?
use Nerst equation: 0. the concentration of potassium inside and outside is same. log 1=0
2. if K+ channels open in the apical membrane, will K+ flow into or out of the cell?
flow into the cell. first way: think about forces that move ions: the concentration gradient is zero, but there's an electrical gradient (the inside of cell is negative with respect to endolymph, potassium move in.
the magnitude of electrical gradient in Vm is 150 mV (note for basolateral, it's 50 mV). remember: the force driving the ion is the driving force=membrane potential (-150)-equilibrium potential (0, from
eariler).=-150 mV, meaning potassium is moving in the cell. the current=conductance times driving force. I=g(vm x ek) pK 3. would the current in b hyperpolarize or depolarize the cell?
depolarize. because inward current (direction of current is cation, if direction of ion is anion, then direction of current is opposite). inward current carry by chloride means chloride is moving out of cell. inward
current by potassium means potassium is moving into cell. (exception: potassium flow in and depolarizes (inward current always depolarizes), instead of flow out and hyperpolarize the cell) remember that a nerve cell, there are hundreds of ion channels. each one can only be open or close, flip instanenously. when you depolarize, probability of ion channel open increases.
-action potential show the ionic currents and resulting potential changes in one fix location as a function of time. this figure with a piece of axon, depict action potential as a function of distance (as oppose
to time, at one fixed location) at one instant in time. action potential is moving to right. the green part show sodium influx. the right is where the peak of action potential have not happen yet. to the left of
white arrow is AP occur already. the arrows represent ionic c...
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- Spring '09
- ECF, Positive charge