Dr. Karius' Action Potential lecture Flashcards
Why do cells expand a huge amount of energy maintaining the membrane potential?
to store energy
What characteristics of the pore channel allow it to control flow?
charge of its amino acids
size of the pore
can open/close
pore channels can be controlled by
voltage changes
chemical binding
mechanical deformation
a “closed” channel has done what?
undergone a conformational change
inactivation and closure
inactivation is also a conformational change that cuts off pore movement but it’s not the same thing as closure because its not able to directly open from the inactivated state
The usual order for channels is
Open –> Inactivation —> Closed
What controls the direction in which ions flow?
the gradient
Voltage gated channels are used by
Na and K
ClC1 channels are used by
Cl- open at rest, closes with depolarization
K-leak channels are active when?
at rest
What happens to chlorine channels during depolarization?
they close
What channels are open at rest? What channels are closed at rest?
Na/K symporters, K leaky, and Cl- are all operational at rest
Na+ and K voltage gated channels are closed at rest
K+ leaky channel When open? What opens/closes? Ion? Inactivation?
open at rest/always
constitutive
K
No inactivation
ClC1 channels
When open?
What opens/closes?
Ion?
Inactivation?
open at rest
depolarization closes
Cl
Maybe inactivation?
Voltage gated Na
When open?
What opens/closes?
Ion?
Inactivation?
closed at rest, open during action potentiall
Opens during depolarization
Yes can be inactivated
voltage gated K channel
When open?
What opens/closes?
Ion?
Inactivation?
Closed at rest, opens during action potential
Opens during depolarization
K
Yes can be inactivated
The single highest user of ATP in the body is
the 3Na/2K pump, huge amounts of energy are
A local response is the
subthreshold
what is a subthreshold response?
a membrane depolarization that doesn’t achieve threshold
a sub-threshold is graded
they get larger with each new stimuli
what happens to local potentials after the stimulus is achieved?
they die away
Local responses have what kind of characteristic the further away they get from the site of stimulation?
they decay
Definition of excitable cells =
cells in which an action potential can be induced
there are ____ changes responsible for closing/opening a pore channel
2: both sides have to undergo a conformational change
“excitable cells”: definition is restricted to
neurons
skeletal muscle
cardiac muscle
smooth muscle
parts of an action potential:
subthreshold–> action potential (Depolarization) –> Repolarization–> hyperpolarization
After voltage gated ion channels are fully open, what two events occur?
sodium enters the cell and will make the Vm positive, overshooting the nernst potential
what happens during repolarization?
Na gates become inactivated and K gates are opening
they open slowly
K leaves cell
the cell repolarizes
how does the Na channel close?
repolarization has to achieve -90mV
What are the ionic events that produce the rapid unsweep of the action potential, repolarization, and the re-establishment of the resting Vm?
rapid upsweep
this is depolarization
opening of voltage gated sodium channels allowing sodium influx
What are the ionic events that produce the rapid unsweep of the action potential, repolarization, and the re-establishment of the resting Vm?
repolarization
opening of voltage gated sodium channels and K-efflux/inactivation of sodium channels
What are the ionic events that produce the rapid unsweep of the action potential, repolarization, and the re-establishment of the resting Vm?
resting
Na/K ATPase re-establishes resting concentrations
Threshold =
the Vm at which ALL the Na channels have opened
How does an action potential’s “shape” change during stimulus?
it doesnt. it’s just all or nothing
how can you increase or decrease the amount of Na going into a cell during an action potential?
you cant: you have to make new channels or change the Na concentration
Refractory period….
ABSOLUTE refractory period
Relative Refractory period
the period after an action potential in which it is impossible or more difficult to elicit a second action potential
AR: impossible to get a 2nd AP. Na channels open but inactivated
RR: more difficult to get a 2nd ap, some Na channels back to closer state
What is the role of the Na/K ATPase?
restablishes the resting gradient
the absolute refractory period makes up what “chunk” of the action potential?
the subthreshold, the depolarizaation, and a large portion of the repolarization
the relative refractory period makes up what portion of the action potential?
a chunk of the repolarization and the hyperpolarization period
Why don’t sodium channels close immediately after depolarization?
because the Vm is +
Voltage inactivation =
depolarization block
something is maintaining the Vm in (+) and it doesn’t get a chance to return to resting Vm
it’s more or less stuck in the AR stage
Subthresholds versus action potential propagation
Subthresholds die away the further they get from the origin of stimulus
action potentials do NOT die away
Propagation of the action potential (4 parts)
1) action potential goes along axon allowing Na influx
2) Na diffuses to other regions
3) those regions of the membrane are brought to threshold
4) action potential propagated
bigger/more myelinated axons —->
faster the conduction
Node of Ranvier
points where myelination are missing
Where are the Na/K channels located on a myelinated axon?
at the nodes
Myelin does what
it doesn’t allow the sodium to diffuse away, so it maintains the signal
What happens to sodium in an axon without myelination?
the sodium can leak out
subthreshold versus action potential: which is graded?
subthreshold, not AP
AP is All or None
how do ST and AP change with time?
ST die away, AP do not have a change in amplitude
how do ST and AP change with distance?
ST die away, APs do not have a change in amplitude
Define the following:
Saltatory conduction
in myelinated neurons, the action potential appears to hop from node of ranvier to node with little loss of Sodium in between: VERY FAST
Define the following:
Propagation
an action potential in one part of the membrane is sufficient to depolarize the neighboring membrane to threshold
Define the following:
Depolarization block
External force causes membrane potential to remain depolarized for longer periods of time: voltage gated sodium channels “stuck” in the inactive state
Define the time of the AR in an AP
beginning of AP to middle of repolarization
Define the time of the RR in an AP
End of ARP to some time after end of AP
RR and AR periods differ when they occur but also how they can be induced
during a AR a second AP cannot be induced no matter what
during a RR a second one can be induced with increasing stimulus
Mechanism of AR versus RR
in AR, all votage gated Na channels are either open or inactive
in RR, enough voltage gated Na channels have moved from inactive to closed state for a second potential to be induced
