Action Potential Flashcards
At resting membrane potential describe the ion concentrations inside and outside the cell
OUTSIDE
[Na+]o = 140mM
[K+]o = 5mM
INSIDE
[Na+]i = 10mM
[K+]i = 140mM
Passive diffusion of potassium
Moves from a high concentration inside the cell to the outside
From a low concentration outside the cell to the inside
Describe a cell that is only permeable to potassium
The potassium equilibrium will be negative
Passive diffusion of sodium
Moves from a high concentration outside the cell to the inside
From a low concentration inside the cell to the outside
Describe a cell that is only permeable to sodium
The sodium equilibrium will be positive
Origin of the resting membrane potential
A very small number of K+ ions diffuse out of the cell down their concentration gradient
Because K+ ions are not accompanied by anions, charge separation occurs and the electrical potential of the cell interior becomes negative with respect to the extracellular solution.
AT REST, that the membrane is slightly permeable to Na+ (50 times less than K+)
At rest describe membrane permeability
AT REST, that the membrane is slightly permeable to Na+ (50 times less than K+)
Ohm’s Law
V = IR
Resting Membrane Potential
-70 mV
K+ equilibrium potential
-100 mV
Na+ equilibrium potential
60 mV
Depolarisation
A change from a negative potential to a more positive potential.
Repolarisation
A change from a more positive potential to more negative potential.
Hyperpolarisation
Movement of a cell’s resting membrane potential to a more negative value
Characteristics of the action potential
- The initial depolarisation must reach a critical threshold
- Once the threshold is attained, the depolarising upstroke is regenerative.
- The potential depolarises, overshoots zero and peaks around +30 mV.
- The response is all-or-none
- The potential repolarises from the peak of the overshoot back to the resting level
Describe membrane permeability changes
At rest PNa:PK = 1/50
Upstroke is associated with a rapid increase in
sodium permeability (x600)
Repolarisation is associated with a delayed 10
fold increase in PK
Voltage gated sodium channel action
At resting potential (-70mV)
Closed but capable of opening
From threshold to peak potential (-50mV to +30mV)
Open (activated)
From peak to resting potential (+30mV to -70mV)
Closed but not capable of opening (inactivated)
Voltage gated potassium channel action
At resting potential
Closed
Delayed opening triggered at threshold; remains closed to peak potential (-70mV to +30mV)
From peak potential through after hyper polarisation
(+30mV to -80mV)
Describe positive feedback
Na+ channels open
Increased Na+ permeability
Increased flow of Na+ into the cell
Membrane depolarisation
Na+ channels closed
If a cell is only permeable to potassium ions, what electrical potential would be recorded inside the cell ?
Negative
If a cell is only permeable to sodium ions, what electrical potential would be recorded inside the cell ?
Positive
If a cell is only permeable to chloride ions, what electrical potential would be recorded inside the cell ?
Negative
Since the normal transmembrane potential is usually a negative number, which ion is likely to have the greatest resting permeability ?
K+
What would happen to the resting membrane potential if the potassium permeability increased ?
Hyperpolarisation
