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Unformatted text preview: always talking of direction of current/cation). this positive
charge want to flow up, gets to inside membrane, cancel the negative charge. then positive charge directly above
that is no longer held by the negative charge and is free to move away. for capacitance (nothing is crossing the
membrane, just electrostatic attraction and repulsion).
****membrane has depolarize: charges flow out across the membrane, through membrane capacitance,
depolarizes the cells**** Potentials are graded (vary with stimulus strength)
and local (decay exponentially with distance). I V1 V2 V3 + ECF ++ ++
-- -ICF + V1 I V2 V3 V4 Length
constant (λ) is
to 1/e (37%)
value. misconception: the depolarization of action potential is due to sodium influx. the influx of sodium depolarizes the cell because you are adding positive cell (making inside positive). Except
now realize that there's no way you can stuff a bunch of positive charge inside without a complete circuit. a miilion charge in, a million charge has to be out.
-truth: those positive charge coming in cause other charge to come out. when the other positive charge flow out across the membrane, this depolarize membrane capacitance. from BISC 220 Ionic Basis of the Action Potential -when you depolarize voltage-gated sodium channel open rapidly. v-gated sodium channel have 2 responses to depolarization: they open (activation) and close in the next millisecond (deactivation).
-during the time vgated sodium channel open, there's an increase in permeability to sodium and inward sodium current because sodium is so far out of equilibrium, creating a large negative driving force.
-sodium ions come in and flow out somewhere else, depolarize the cell. (3 to 5)
-about milisecond after v-gated sodium channel open, they close. when they close, the inward current of sodium start cut off. with a slight delay, potassium channels (which have lower probability of
opening with depolarization) will open. and there's a slight increase in potassium permeability which help bring membrane potential back down to Ek. if permeability ion increase selectively, membrane
potential will approach equilibrium potential. ENa Na+
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- Spring '09