Please enable JavaScript.
Coggle requires JavaScript to display documents.
Ionic basis for cell excitability: resting membrane potential (8) - Coggle…
Ionic basis for cell excitability: resting membrane potential (8)
Resting Membrane Potential
at rest, inside of cell is negative compared to outside
excitable cells about -70 mV
non-excitable cells about -30 mV
Unequal Distribution of Ions
Potassium - inside 140 mM, outside 5 mM
sodium - inside 15 mM, outside 150 mM
calcium - inside 0.0001 mM, outside 2 mM
chloride - inside 10 mM, outside 120 mM
protein (-) - inside 145 mM, outside 37 mM
osmotic potential of intra and extracellular solution is the same
each bulk solution is electroneutral
Selective Ion Permeability
ion channels - transmembrane proteins that act as selective pores
selective cation channels discriminate between sodium, potassium, calcium, etc
selective anion channels discriminate chloride
Electrochemical gradients
each permeant ion is subjected to two forces
chemical - ions flow from high to low concentration
electrical - ions flow toward regions of opposite charge
if a membrane is impermeable to all ions, no potential difference, if permeable, potential difference can occur
if ion channel only for potassium opens, potassium will flow along chemical gradient to area of lower concentration, however, as inside of cell becomes more negative, electrical gradient for potassium increases and positive ions are attracted back to the inside of the cell
at the reversal/equilibrium/Nernst potential (Ek) net flux of ions is zero
flux down chemical gradient (Fc) is equal and opposite to flux down electrical gradient (Fe)
Equilibrium potential
if cell becomes only permeable to potassium, electrochemical gradient outwards, so cell becomes more negative
if cell becomes permeable only to sodium, electrochemical gradient inwards, so cell becomes more positive
Resting membrane potential is determined by potassium ions
in neurones at rest, the plasma membrane is 100x more permeable to potassium than other ions
this means cell tries to reach electrochemical equilibrium for potassium
thus resting membrane potential lies near to, or at the equilibrium potential for potassium
cell communication can occur by changing selective permeability of membrane
if only permeable to sodium, depolarisation
if only permeable to potassium, repolarisation
cell membranes behave like an electrical circuit
membrane lipid bilayer is capacitor (stores charge)
ion channel acts as resistor (resists current/ion flow)
battery is the electrochemical gradient