Action Potential Flashcards
action potentials begin
as a large depolarization that elicits a further depolarizaiton and complete reversal of membrane potential across plasma membrane
graded potentials
changes in membrane potential that are small and local
excitatory or inhibitory
strength of initial graded potential correlates with
strength of triggering event
graded potentials dissipate with distance because
K+ leak channels are always open (basically)
phase 4
resting phase
phase 0
depolarization
Phase 3
re-polarization
hyperpolarization
refractory period (extra negative)
threshold
membrane potential at which AP will certainly occur
ion channel characteristics
mostly passive
leaky
gates restrict ion movements (voltage-gated, ligand-gated, signal-gated, mechanically-gated)
depolarization mechanism
increase in permeability of membrane to Na
voltage-gated Na channels open rapidly
after MINIMAL delay, channels close automatically
Na leak channel gates
activation gate (threshold opens this) inactivaiton gate (closes pore after a slight delay)
phases of voltage gated Na channels opening
resting - A closed I open
Activation - A open I open
Inactivation - A open I closed
cannot be moved until membrane potential returns to near resting
positive feedback loop of voltage-gated Na channels
local triggering opens some channels
More Na channels open
More spread
Loop is broken at +30mV because Na channels close
absolute refractory period
Na channels are either open or the inactivation gate is closed and cannot reopen
another Ap cannot be generated
relative refractory period
inactivation gate is open and activation gate is closed
K+ permeability is fairly high and overshoots K leaving the cell, membrane becomes slightly more negative than resting membrane potential
AP may be stimulate but requires stronger stimulus
what three events occur at threshold potential
rapid opening of voltage gated Na channel activation gates
Slow closing of voltage gated Na channel inactivation gates
Slow opening of voltage gated K channel gates
hypokalemic periodic paralysis
periodic dips in blood K levels
Dorps in blood K triggers events, but blood K levels are normal between attacks
membrane hyperpolarized, harder to reach threshold
repolarizatino occurs more quickly
Hyperkalemic periodic paralysis
excessive K+ in blood
unable to compensate like normal person would
prolonged depole and absolute refractory periods
attacks managed by mild exercise, potassium-wasting diuretics, glucose management
permeability to sodium increases ______ while potassium permeability is _____
increases rapidly
K permeability is slower to increase
