Membrane Potential Flashcards
What is chemical potential?
concentration gradient
What is electrical potential?
charge differential
What is electrostatic potential?
cumulative forces that act on charged ions
What causes a membrane potential?
asymmetrical distribution of charges across a semipermeable membrane
What determines changes in membrane potential?
changes in permeability of membrane ion channels
What is the equilibrium potential?
membrane potential that just opposes the chemical potential for a given ion across a semipermeable membrane
What equation describes equilibrium potential for a given ion? Explain each variable
Nernst equation - R = universal gas constant T = temperature z = valence (+1 for Na and +2 for Ca) F = Faraday's constant [ion]o = conc of ions outside [ion]I = conc of ions inside
What are the approximate equilibrium potentials of potassium, sodium and chlorine?
potassium = -95mV sodium = +65mV chlorine = -64mV
What determines resting membrane potential?
Na+/K+ ATPase and leak channels (K+ leak channels dominate, but small Na+ leak draws membrane potential toward it)
What equation describes resting membrane potential?
Goldman-Hodgkin-Katz Equation:
What is the physiological importance of resting membrane potential?
important for action potentials and heart beating
driving force for ion transport
What is the medical importance of membrane potential?
inhibition of ion channels or too much leakage of ion channels can be deadly
What is a graded potential?
local transient changes in membrane potential invoked by neurotransmitters
What determines the intensity of a graded potential?
distance away from stimulus (further means smaller)
strength of stimulus (stronger means larger)
What is EPSP?
excitatory post synaptic potential: depolarizes membrane
by signaling of ionotropic glutamate receptors that conduct Na+ or Ca2+
What is EPP?
end plate potential - depolarizes membrane
by signaling of acetylcholine receptors that conduct Na+ and Ca2+
What is IPSP?
inhibitory post synaptic potential - hyperpolarizes membrane
by signaling of GABA receptors that conduct Cl-
What is the difference of function of GABA receptors during development?
developing neurons have high Cl- in the cell so GABA receptors depolarize the cell by letting Cl- out
What is the threshold potential?
membrane depolarization needed to trigger an action potential
What is the safety factor?
amount that a graded potential depolarizes a cell more than the threshold potential
What is myosthenia gravis?
loss of acetylcholine receptors at EP so safety factor is lost
muscle can’t generate as many action potentials
What is an action potential?
dynamic all or nothing changes in membrane potential
Describe the sequence of events in an action potential.
- ESPSs sum to reach threshold depolarization
- voltage gated Na+ channels activate letting Na+ into the cell (MP to 35mV)
- at 35mV, voltage gated K+ ion channels activate to repolarize cell (-90mV)
- Na+ channels are inactivated after a short time and remain that way until repolarization of membrane
- often overshoots, so cell has to depolarize to get to resting membrane potential
What is the absolute refractory period?
the cell cannot undergo another action potential during this time
