Membrane+Action potentials Flashcards
Flux def
The number of molecules that cross a unit area per unit of time (number of particles).
i.e. molecules.m−2.s−1
Equilibrium potential def
Equilibrium potential: the potential at which electrochemical equilibrium has been reached. It is the potential that prevents diffusion of the ion down its concentration gradient
What are the most important ions for determining a neurons resting potential?
What does the nernst equation describe?
Used to calculate equilibrium potential using temp and ion concentrations
What is the Goldman-Hodgkin-Katz (GHK) equation and what does it describe?
The GHK equation describes the membrane potential (Em) using ion permeability and concentration more accurately; P is permeability or channel open probability (0 = 100% closed, 1 = 100% open, 0.5 = open 50% of time), Subscript on P indicates the ion,
[K+], [Na+] and [Cl-] represent concentration and the subscript i or o indicates inside or outside the cell.
What is proportional to each ions’ contribution to membrane potential?
Each ion’s contribution to membrane potential is proportional to how permeable the membrane is to the ion at any time.
Calculate membrane potential at:
All channels are open all the time (PK = 1, PNa = 1, PCl = 1
Em = -61 * log((1[0.15] + 1[0.01] + 1[0.11])/(1[0.005] + 1[0.15] + 1[0.005]) )
= -61 * log(0.27 / 0.16)
= -61 * 0.225
= -14 mV
Calculate membrane potential at:
K+ channels open, Cl- and Na+ channels closed (PK = 1, PNa = 0, PCl = 0)
Em = -61 * log ((1[0.15] + 0[0.01] + 0[0.11]) / (1[0.005] + 0[0.15] + 0[0.005]))
= -61 * log(0.150 / 0.005)
= -61 * 1.477
= -90 mV (Ion concentration has not changed BUT Em moved to EK)
What does depolarisation, repolarisation, overshoot and hyperpolarisation mean?
How does the size of an action potential change as it travels along an axon and why?
How are the variety of nerve stimulations differentiated?
They are ‘graded’
-Some depolarise, some hyperpolarise, controlling what happens next
Do ion pumps control the change in membrane potential during an action potential?
NO
What is the permeability of ions(Na+,K+) like at resting potential and why?
PK > PNa
Membrane potential nearer equilibrium potential for K+ (-90mV) than that for Na+ (+72mV)
What occurs at the start of threshold potential?
K+ channels start opening slowly(Pk increases)-Still less than Na+ leaving the axon so potential is still becoming more positive
What must happen for an action potential to be generated?
The membrane must reach threshold potential
How does the release of K+ at an action potential vary with distance from the site of depolarisation?
Where are voltage gated channels mostly located on myelinated axons?
Nodes of ranvier
What factors increase/decrease conduction velocity?
How does hyperkalaemia affect an action potential curve?
Resting potential is more positive, so easier to reach a threshold potential-but retains the same peak voltage on the upstroke
How does hypernatraemia affect an action potential curve?
Hypernatraemia increases the amount of sodium efflux that occurs, so a larger upstroke occurs.
