L7 Action Potentials Flashcards
K+ equilibrium potential
-90mV
Big conc gradient favors efflux \+ Small electrical gradient favors influx = Weak outward driving force but w/ high permeability
Na+ equilibrium potential
+65mV
Big conc and electrical gradients favor influx
=strong inward driving force
But with low permeability
What would happen if permeability to Na+ suddenly increased? And then permeability to K+ increased?
Drives it right toward its equilibrium potential (65) very quickly, depolarize
Drives it back towards its equilibrium potential (-90) very quickly, repolarizes
Action potentials are always the _____ magnitude and move in what direction?
SAME
only move in one direction
Action potentials take place as a result of?
A triggered opening and subsequent closing of two specific channels
All are triggered at the same threshold!
Over or under -55mV
What are the triggered channels involved in action potentials?
Voltage gated Na+ activation gate
Voltage gated Na+ inactivation gate
K+ voltage gated channel
Na+ activation gate
Opens to allow Na+ to move outside in initially when triggered by -55mV
Opens rapidly
is open from threshold to peak (-55 to +30mV)
At rest , it’s closed
Na+ inactivation gate
Stops further influx of Na+ when triggered by -55mV (same time as activation)
Closes slowly
Is closed from peak to resting (30mV to -70mV)
Doesn’t completely close until peak is reached
At rest, it’s open
K+ voltage gated channel
Triggered at threshold to open (-55mV)
Delayed opening
Not fully opened until peak (30mV)
Open through peak to after hyperpolization (30 to -80)
Positive-feedback cycle for opening of Na+ channels at threshold
The passive spread of current from adjacent site that’s already depolarized spreads down membrane causing further depolarization/decrease in membrane potential because moving further away from threshold point and can’t reset to rest to trigger another action potential
Refractory period
Ensures one way propagation of action potential
Limits frequency (impossible to get two at same time)
Absolute refractory period
Interval during which NO stimulus can elicit an action potential
Most voltage gated Na+ channels are inactivated
Relative refractory period
Interval when a SUPRANORMAL stimulus is required to elicit an action potential ( in hyperpolarized state)
Just have generate more depolarization (-80 to -55 instead of -70 to -55)
Due to elevated gK coupled with the residual inactivation of voltage gated Na+ channels
Hyperkalemia
Depolarizes, so it’s easier to get an action potential because it’s closer to -55mV
If hyperkalemia is severe what happens
membrane depolarizes so much and Can’t back get to threshold (-55mV) and stuck in absolute refractory period
Paralysis- permanent or periodic
In periodic- Na+-K+ ATPase pump can reset levels to below -55mV and action potentials can fire again
What factors determine speed of conduction?
Diameter
Myelination
What’s the relationship between diameter of fiber and speed of conduction?
Larger diameter=less resistance =rapid fibers
Motorneurons
Smaller diameter=more resistance=slow fibers Internal organs (gut, glands)
Myelination
Lipid insulator
Keeps charges inside axon and greatly increases the conduction velocity
Myelinated vs unmyelinated fibers
Myelinated axons are always faster
Even with smaller diameter
Contiguous conduction
Conduction in unmylienated fibers
Action potential spreads along every portion of the membrane
Takes a long time
Saltatory conduction
50x faster
Impulses jump over sections of fiber covered with insulating myelin
Action potential jumping from one node of ranvier to next
All or nothing principle
If a stimulus exceeds threshold
An action potential will be initiated
An action potential will always be same magnitude because they only have one trigger
Either triggered or not
Stimulus strength is produced by
Rate of stimulus, NOT magnitude
Lower amplitude of graded potentials = slower rate of action potentials= weaker stimulus
Higher amplitude of graded potentials= high rate of action potentials = stronger stimulus
