membrane and action potentials Flashcards
what is the resting membrane potential in a typical nerve cell
-70 mV
what is the sodium equilibrium potential
+60 mV
what is the potassium equilibrium potential
-90 mV
what is equilibrium potential
when the conc. gradient and electrical gradient balance out each other (equilibrium)and no net movement of ion occurs, the potential that would exist at this equilibrium is known as the equilibrium potential
what is the relative membrane permeabilities of sodium and potassium ions
Na+: 100
K+:1
what is the value for the sodium, potassium and chloride ion concentrations inside and outside the cell
inside and outside:
Na+ : 15 mM,150mM
K+ :150 mM, 5 mM
Cl- : 7 mM,110 mM
what is the Nernst equation for calculating equilibrium potential
Eion= 61 log 10 [ion]o/[ion]i
state the Goldman-Hodgkin-Katz equation to calculate membrane potential
Em= 61 log Pk [K+]o+ PNa [Na+]o/Pk [K+]i + PNa [Na+]i
log base 10, Pk=1 PNa=0.01
why are the resting membrane potential and potassium equilibrium potential not identical?
Due to the slight inward leak of Na+ into the cell (down the Na+-electrochemical gradient)
increases membrane potential from Ek
The plasma membranes of all cells are polarised electrically
true or false
true
The plasma membranes of all cells are electrically neutral
true or false
false
concentration gradient for Na+ is outward/inward
inward
concentration gradient for K+ is outward/inward
outward
At resting potential the membrane is ___ times more permeable to K+ than Na+.
100
At resting potential the membrane is 100x more permeable to __ than __
K+, Na+
The 2 opposing forces acting on K+:
______ gradient -tending to move K+ out of the cell
_______ gradient -tending to move K+ into the cell)
concentration, electrical
the Na+-K+ pump generates a hyperpolarizing current
true or false
true
3 +ve go out for 2 in, net 1+ve goes out- leaves -ve overall charge in
what is depolarization
the inside of cell becomes less negative ( more +ve)
what is hyperpolarization
the inside of the cell becomes more negative
Na+ selective ion channel effects the membrane potential by
Depolarization
Inward current: Vm is driven toward ENa+:becomes more +ve
K+ selective ion channel effects the membrane potential by
Hyperpolarization
Outward current:Vm is driven to EK+: becomes more -ve
what is neuronal action potential
they are electrical signals which momentarily reverse the polarity of the nerve cell membrane
what is threshold
To generate an action potential, the cell needs to reach threshold
about -55 mV, they are all or none
what is upstroke and downstroke
upstroke: rise during depolarization till 0 mV
downstroke: fall from 0 mV during hyperpolarization
what is overshoot and undershoot
overshoot: peak of action potential from 0 mV
undershoot: fall of action potential from resting potential
Na+ ion channel in its closed stage is
non- conducting
inactivation gate is open, activation gate is closed
Na+ ion channel in its open stage is
conducting
Na+ ion channel in its inactivated stage is
non-conducting
inactivation gate is closed, activation gate is open
this allows for a refractory period
what is an absolute refractory period?
no stimulus can elicit a secondary action potential
all Na+ channels are inactivated and membrane is depolarized and repolarized
what is a relative refractory period?
a stronger than normal stimulus may elicit a secondary action potential
some Na+ channels are closed not inactivated now, and membrane is hyperpolarized
how does an impulse propagate in a myelinated nerve fibre?
saltatory conduction
it “jumps” from each node- nodes of raniver–> occurs due to local current flow
how does an impulse propagate in a un-myelinated nerve fibre?
contiguous conduction or passive conduction
List the 3 types of gated ion channels
.membrane voltage: voltage-gated ion channels (VGICs)
.chemical substances:ligand-gated ion channels (LGICs)
.physical stimuli e.g., mechanical, thermal
The ion channels responsible for the action potential in neurones are ____ gated ion channels
voltage
Driving force for Na+ influx
-130 mV
Vm- ENa+= -70-60=-130 mV
since its negative causes inward movement
Driving force for K+ efflux
+20 mV
Vm-EK+= -70-(-90)= 20 mV
since it’s +ve causes outward movement
what causes upstroke in action potential
upstroke (depolarizing phase) is mediated by the opening of voltage-activated Na+ channels
what causes downstroke in action potential
downstroke is due to the opening of voltage-activated K+ channels and the inactivation of voltage-activated Na+ channels
what causes undershoot in action potential
undershoot is due to delayed closure of voltage-activated K+ channels
ways to increase passive conduction
- increase diameter of axon
- decrease leak of current by insulating material- myelin–> schwann cells in PNS and ogliodendrocytes in CNS
schwann cells and ogliodendrocytres are both types of macroglia
how does the activation of Na+ ion channels work?
The activation of Na+ channels is self-reinforcing – the opening of a few channels causes further channels to open, causes further depolarization
positive feedback
what causes activation of Na+ ion channels ?
depolarization.
how does activation of K+ ion channels work?
The activation of K+ channels is self-limiting – outward movement of K+ causes repolarization which turns off the stimulus for opening This is negative feedback
what causes activation of K+ ion channels?
depolarization
