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-inward current where sodium ion enter the cell through open sodium channel (complete circuit so it will flow out). once inside the cell, the current is carried by whichever charge most abundant in cell (here
potassium ion) and there's chloride going to opposite direction.
-most current is capacitance, so ions are not physically moving but charges. outward current ahead of AP depolarizes the cell. AP regenerate by continuous depolarize the membrane ahead, opening
newsodium channel ahead (tap into energy stored by sodium-potassium pump) Action Potential Conduction behind the AP (there's as much current flowing back and front). current flow out of membrane
(have RC resistance, it can go through either resistance or capacitance, but remember AP
already pass here, so there's a lot of open potassium channel (v-gated or leakage). so we have
lots of currents flowing down the axon. remember: as AP move, it depolarize membrane ahead,
and behind repolarizing/reestablishing the resting potential by outward current flow. by the time
AP move far enough away, that location is back to original (after hyperpolarization occur).
-the limitation set limit on firing of signal (150 hz). membrane need time to reset itself. refractory
period (cannot get AP)-AP never backs up (zone of inactivated sodium channel and open
potassium channel, make up refractory period).
time needed to reset itself is just right so that the back flow is never enough to trigger another
AP (multiple schloresis=AP trailing after traveling AP).
-how fast is the conductance? one meter per second. giant axon in invertebrate conduct faster
because lower longitudinal resistance, the further the current ahead of AP can spread the axon
before they leak out of membrane and depolarize the membrane. big axon have sufficient
current flowing out across membrane to trigger AP farther down the axon, so whole thing move
faster (squid develop large axon in escape nerve) Na+ -- +++ --- K+ ++
+ Raxoplasm ∝ 1 / r2 Rasband MN (2011) Sem cell dev biol 22:178-184 ++++ ---- Na 0 mV
Compress, Flip resting potential in some axons of vertebrae, the glial cell not only wrap around axon but also wrap in layers. the myelin sheath leaves areas of exposed axon (node of ranvier). ion channel is not uniformaly distributed...
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- Spring '09
- ECF, Positive charge