Ions, Permeability and the Resting Potential Flashcards
What are the three most important factors which determine the ‘passive’ movement of ion across the membrane?
electrical gradient, concentration gradient, membrane permeability
What is the Nernst equation (the equilibrium potential)?
Ex=61 log10[X]1/[X]2
Describe the origin of the resting membrane potential
more K+ than Na+ gates are open, making the membrane more permeable to K+ (therefore a negative value)
If the K+ permeability increased by a factor of 50, how would the Em be affected?
It would be hyperpolarised
If the sodium permeability increased by a factor of 100, how would Em be affected?
Depolarisation
What is the threshold potential?
The minimum membrane potential that must be reached in order for an action potential to be generated.
What is the effect of increasing the extracellular K+ concentration to 10mV?
depolarisation and movement of the resting membrane potential nearer to threshold
What is the effect of decreasing the extracellular K+ concentration to 2mV?
Hyperpolarisation and movement of the resting membrane potential away from the threshold
What is the effect of varying the extracellular K+ concentration on Em?
increasing the extracellular K+ concentration rapidly increases the membrane potential (mV) (becoming more positive)
What is the effect of varying the extracellular Na+ concentration on Em?
increasing the extracellular Na+ concentration only increases the membrane potential (mV) slightly
Resting potential of cardiac action
-90mV
What is the time called during which another action potential is impossible; limits maximal firing rate?
absolute refractory period
How does repolarisation of ventricular cells differ to neurons?
Not as quick as neurons
What causes cardiac depolarisation?
associated with opening of fast sodium channels
What keeps the depolarisation phase of cardiac cells open for longer?
increased calcium permeability
What closing of sodium channels triggers?
opening of calcium channels
(when calcium permeability increases) where calcium binds
receptors on the ER
What causes a muscle contraction?
caused by release of intracellular calcium
What is the cause of K+ channels opening in cardiac cells?
closing of calcium channels
What is Na+ channel reactivation dependent on?
both time and voltage
What is the effect of giving KCl to patient?
by preventing repolarisation back to the membrane potential, the high extracellular K+ inhibits the reactivation of the Na+ channels and further action potentials - therefore heart can’t beat again
Why does changing the extracellular concentration of K+ have a greater effect on the membrane potential than changing the extracellular Na+ concentration?
the membrane is more permeable to K+ than it is to Na+
concentration of extracellular K+ that Em=0mV
140mM
why 140mM of K+ gives an Em = 0
the intracellular and extracellular K+ concentrations are equal
(peak of the action potential) 30mV
membrane is more permeable to Na+ than it is to K+
