Action Potential Lecture Flashcards
action potentials ____ proportional to the stimulus size
ARE NOT proportional to the stimulus size
can action potentials act locally?
NO - they DO NOT act locally
do action potentials die out with distance? attentuate?
NO - they do not attenuate
T/F: you can generate LOCAL potential in any given cell
TRUE
Do action potentials spread in both directions?
NO they do not spread in both directions
can action potentials be generated in any given cell?
NO - they do not happen in many different cells
action potentials can only be generated AND propagated in ___ and __
neurons (at the axon) and muscles - propagation is just as important as the generation
what types of channels are mostly found on the axon and axon hillock
voltage gated channels
what is another name for the axon hillock
the trigger zone
do we have VG channels in axon or soma?
yes! but we just don’t have enough of them
describe the sodium voltage gated channels
sodium voltage gated channels have TWO gates so it makes it a little more complicated; activation gate and the inactivation gate
describe the potassium voltage gated channels
a simple gate - opened or closed
will sodium ions pass through if the activation gate is closed and the inactivation gate is open?
NO - the channel is still closed
will sodium ions pass through if the activation gate is open and the inactivation gate is closed?
NO - the channel is still closed
how do we open the sodium voltage gated channel
BOTH the activation gate and the inactivation gate have to be OPEN for the channel as a whole to be open and for sodium ions to pass through
at resting state: all the channels are ___
CLOSED; despite the fact that the inactivation gate is open on the sodium voltage gated channel; only way to move is leak channels or generating a local potential
when do the voltage gates change their status
upon depolarization and ONLY after reaching a threshold
channels will open up at a given potential - what number
-55 mV
inactivation gates ___, activation gate ___ and potassium channel ____ after reaching threshold
inactivation gate closes, activation gate opens and potassium channel opens
sodium activation gate is a ___ gate and the sodium inactivation gate is a ___ gate ; the potassium gate is a ____ gate
fast, slow, slow; 0.5 ms delay that occurs with the slow closing gates that allows the sodium channel to be open
4 step graph for action potential
- all channels are closed at resting membrane potential - (the sodium inactivation gate is open but it doesn’t matter)
- stimulus added and the channel opens and sodium ions move in
- Depolarization ; -70 become -68 - (local graded potential)
- Eventually threshold is reached if we have enough sodium ions
- inactivation gates close really slowly and activation gates open really fast, so sodium channel is OPEN for a small amount of time
- increasing on the depolarization (2) event as more ions move in (positive feedback chain)
- peak of depolarization is reached when the inactivation gates finally CLOSED
- repolarization (3) potassium gates are finally opened up, so potassium leaves and cell is losing positive charge and is repolarizing
- undershoot beyond -70 (hyperpolarization) is caused by the slow closing of the potassium channels to close completely
- go back to resting membrane potential - SPP restores the gradient and resting membrane potential
T/F: action potential starts with a local graded potential
true
once the first sodium voltage gated channel is open why can the stimulus go away?
because a positive feedback loop is started and each VG channel opens the next one
when does depolarization stop
when the inactivation gate finally closes and as a result closes the channel
