Resting Membrane Potential

what is membrane potential?

a voltage or electrical charge across the plasma membrane.
more negative in inside

resting membrane potential in neurons

-70mV

resting membrane potential in muscle cells

-90mV

resting membrane potential in red blood cell

-30mV

what is the effect of having an ion concentration gradient

an electrochemical gradient established - molecules move by diffusion or active transport.

Inorganic ions that establish electrochemical gradient?

K+ Na+ Ca2+ Cl-

where is potassium concentration highest?

inside the neuron

why don't charged particles just move in and out of a neuron freely?

membrane is impermeable to charges particles because it is non polar.

At resting potential which channels are open

K+ channels to allow some out that there is a bit of net diffusion, sodium channels as well.
Na+/K+ pump to maintain gradient.

what is actually happening to maintain resting potential?

mostly K+ moving out as membrane very permeable to K+ - potassium channels open inside axon is negative.

Sodium channels also slowing a small influx of Na+ down its conc gradient.

Na+/K+ pump maintains conc gradient of both ions using Na+/K+ ATPase (3 out 2 in)

what is the diffusion potential?

the voltage at which the electrostatic force on an ion is equal and opposite to the chemical force from the concentration gradient.
K+ conc higher on inside so moves out, but move -ve on inside due to anions so K+ wants to stay.

what is steady state in a neuron/cell?

- no net force no ion flow
- no further change in ion conc at plasma membrane
- no further change in charge dist or membrane potential

what is the diffusion potential for K+ and sodium

Ek = -90
ENa = -70mV

what does it mean for sodium to have a lower diffusion potential than potassium?

membrane is more permeable to potassium

what is the Nernst equation about

Calculates equilibrium potential (E_ion) for a single ion species

what is the Ek for potassium?

-90mV

what ways do sodium and potassium move in a pump in a neuron?

Na+ in to depolarise (membrane potential is smaller than diffusion potential)

K+ out to depolarise (membrane potential is greater than diffusion potential)

how does Na+/K+ ATPase work?

transports 3 Na+ out for every 2 K+ that are transported into the cell at the expense of one ATP.

replenishes lost K+. Removes accumulated Na+ in cell and maintains the resting potential.

what inhibits sodium potassium pump?

digoxin - reversibly inhibits the pump due to its positive inotropic effects.

What are diffusion rates determined by

Concentration

Membrane potential (Vm) is influenced by what

ion concentration and their permeability

what is the Vm and what does it reflect

The voltage where total ionic current is zero, but individual ion movements continue.

it reflects steady-state potential where no net ion flow occurs

What drives ion movement across the plasma membrane

Concentration gradietn and voltage gradient

If Vm > E_K (depolarised),

K+ flows out to bring Vm back to E_K.

If Vm < E_K (hyperpolarised),

K+ flows in to bring Vm back to E_K.