Action Potentials 1 Flashcards
resting phase
Na+ ions more numerous outside of membrane
K+ ions more numerous inside membrane
positive charge outside and negative charge inside
Established by the sodium-potassium pump
sodium potassium pump
Sodium-potassium pump pumps 3 Na+ ions out of cell for every 2 K+ ions it pumps into the cell
Resting membrane potential
= -70 mV
na+/k+ pump
K+ ions can leak through membrane through ion channels; Na+ cannot because its ion channels are closed
polarized resting potential
neuron more negatively charged inside than outside
excitatory signals
cause threshold to be reached and action potential to fire
inhibitory signals
inhibit action potential from firing
threshold
-55 mV
absolute refractory period
the period of time after an action potential is initiated in which it’s impossible to initiate another action potential
1 msec
spike initiation zone
part of neuron where axon originates from soma
axon hillock
voltage at resting potential
-70 mV
voltage to reach threshold
-55 mV
structure of voltage gated sodium channel
four domains with each six transmembrane alpha helices
four domains clump together to form pore, closed at negative resting potential
selectivity filter that makes it permeable to na+ but not k+
ion-water complex
what causes sodium channels to open
depolarization twists s4 after entire segment is forced to move by changing membrane potential
conformational change causes gates to open
membrane potential from -65 to -40
what causes potassium channels to open
when membrane is depolarized and functions to diminish any further depolarization by giving k+ ions a path to leave the cell across the membrane
what happens when potassium channels open
k+ ions flow out of cell, down concentration gradient, until inside is negative
electrical current created
Vm = Ek
relative refractory period
period after end of absolute refractory period
relatively difficult to initiate another action potential (several msecs)
amount of current required to depolarize neuron to action potential threshold elevated above normal
why is it important for cell to repolarize and return quickly to resting potential
so cell is prepared to generate another action potential as soon as it needs to
what happens to axons in multiple sclerosis
how does this impact message transmission
MS attacks myelin sheaths of bundles of axons in brain, spinal cord, and optic nerves
slows message transmission
how do local anesthetics stop you from feeling pain during surgery
temporarily block action potentials in axons, especially small ones
some bind to voltage gated sodium channels and interfere with flow of na+ that normally results from depolarizing channel
what determines whether or not to fire action potential
cell body
APs direction
can only travel in one direction because of inactivated sodium channels
local anesthetic ex
novacaine
na+ have what as chaperone
water molecule
ttx affects
na+ channel
