5 - Action Potentials Flashcards
ions require ___ ____ to move across the membrane
ion channels
Na flows _____ through an Na channel because of the large concentration and electrical gradient
inwardly
what is the membrane potential for many neurones?
-80mV
what is the equilibrium membrane potential for Na?
+60mV
The driving force for Na influx is simply (___-____). When this is _____ (in this case __mV) Na moves __wardly
The current carried by Na (Ina) is given by the expression:
INa = GNa (Vm - ENa)
what is Ina and Gna ?
The driving force for Na influx is simply (Vm - ENa). When this is negative (in this case - 140 mV) Na moves inwardly
The current carried by Na (Ina) is given by the expression:
INa = GNa (Vm - ENa)
Ina is Na current
Gna is Na conductance
K flows ____
outwardly
why does K flow outwardly?
the concentration gradient if outward and has an energy which exceeds the electrical gradient, which is inwards
the Vm is ___ to the equilibrium potential for K
positive
what is the the equilibrium (or reversal) potential of an ion
the equilibrium (or reversal) potential is the membrane potential where the net flow through any open channels is 0.
what is the equilibrium potential for K ?
-100mv
what is the equation that gives the equilibrium potential of an ion?
nernst
The driving force for K efflux is simply (___-____). When this is _____ (in this case __mV) K moves __wardly
The current carried by Na (Ina) is given by the expression:
IK = GK (Vm - EK)
The driving force for K efflux is simply (Vm- Ek). When this is positive (in this case 20mV) K moves outwardly
The current carried by Na (Ina) is given by the expression:
IK = GK (Vm - EK)
within a cell at membrane potential is more ___ than outside the cell membrane
negative
what is the effect of opening Na selective or K selective channels upon the membrane potnetial>?
the potential is driven towrds the equilibrium potential of the ion -
+ 16 for Na and -100 for K
ion channels can be ___- gated, ___ - gated or opened by ___ ___ e.g. ___, ___
voltage gates, ligand gated (opened by chemical substances) or opened by physical stimuli e.g. mechanical, thermal
what are the ion channels responsible for the action potential in neurones ?
Voltage-activated Na+ channels (Nav) (depolarizing)
Voltage-activated K+ channels (Kv) (hyperpolarizing)
what is responsible for the period of undershoot in an action potential?
K channels open and close slowly so too many K ions diffuse out of the cell causing hyperpolarisation
what happens to the magnitude and velocity of APs as they propagate along nerve cell axons?
stay the same
why is the ENa never reached during upstroke?
because the K pores dont allow this - by inward trickle
opening of voltage activates Na channels and depolarisation is a ____ feedback system.
Depolarisation causes an ___ in Na conductance causing the ___ movement of Na ions
positive, increase, inward
opening of voltage activates K channels and depolarisation is a ____ feedback system.
depolarisation causes an ___ in K conductance causing the ___ movement of K and thus ______
negative, increase, outward, repolarisation
although VA Na channels initially open in response to depolarisation, what happens during maintained depolarisation?
they enter a non-conducting, inactivated state
what are the three states of the Na channels?
- open state (conducting)
- inactivated state (non- conducting)
- closed state (non-conducting)
____ is required for the Na channels to enter the closed state in readiness for opening and the generation of a further action potential
repolarisation
