Biologic Membranes and Membrane Potential Flashcards
describe diffusion
passive movement of a molecule through a membrane; the net movement of molecules; gases
in order to diffuse through the lipid bilayer, what must a molecule be? (2) give 3 examples
- lipid soluble
- non-charged
examples are alcohol and gases and steroid hormones
describe carrier-mediated transport
active process of moving molecules through a membrane that would not otherwise diffuse through that membrane
what kind of molecules must utilize carrier-mediated transport to get through the lipid bilayer? (2)
- non-lipid soluble
- charged
are transport proteins fast enough to where their movement of charged molecules can affect the moment to moment membrane potential? if not, is something else used?
channels are not fast enough to make real time changes in membrane potential; in order for ions to make real time changes to membrane potential channels are needed!
what is the resting cell membrane potential?
-70mV
what does the charge of the membrane potential refer to?
refers to the inner surface of the cell membrane
what is meant by hyperpolarizing?
a change in the membrane potential away from 0 (more negative)
what is meant by depolarizing?
a change in the membrane potential towards 0 (more positive; less negative)
why is the fact that the membrane is a great capacitor relevant?
it is relevant because, although there are many other charged molecules in and outside of the cell, the membrane can account for those charges, so we only need to consider the movement of a few ions close to the membrane and it only takes a few ions to make drastic changes to membrane potential
describe the relative concentrations of sodium inside and outside of the cell at resting membrane potential; how does sodium flow relative to the membrane
more sodium outside the cell at rest; sodium tends to flow into the cell
what is the equilibrium potential of sodium?
+56
give the relative concentrations of potassium inside and outside of the cell at resting membrane potential
more potassium inside the cell at rest; potassium tends to flow out of the cell
what is the equilibrium potential of potassium?
-102
give the relative concentration of chloride inside and outside of the cell at rest
more outsidegi
give the equilibrium potential of chloride
-76
describe the relative concentration of calcium inside and outside of the cell at rest
almost 0 inside the cell and also very little outside the cell
give the equilibrium potential of calcium
+125
do the relative concentrations of sodium, potassium, chloride, and calcium change during an action potential?
not really
what causes the unequal distribution of ions across the membrane?
the selective permeability of the membrane
when controlling membrane potential, what is in charge?
permeability of the membrane
what is equilibrium potential?
the electrical potential at which the measured concentration of an ion inside and outside the cell would be at equilibrium; where ion concentrations have equal flux into and out of the cell (assuming an ion can pass through a channel in the membrane)
what keeps all the potassium ions inside the cell?
the resting negative charge inside the cell
are there a lot of sodium channels?
nope; only very few
does the sodium potassium ATPase pump contribute to moment-moment changes in membrane potential? why or why not? what does it do?
is too slow to contribute to moment-moment changes; instead just establishes the concentration gradients of sodium and potassium
what happens with the more permeable the membrane is to an ion?
the closer the membrane potential moves to that ion’s equilibrium potential (so if a membrane is super permeable to potassium, the closer the membrane potential will move to potassium’s equilibrium potential)
what 2 things do open channels see/evaluate?
- size
- charge
describe the forces pushing calcium through open channels versus potassium and sodium
calcium is more charged than sodium and potassium so it has a much greater force pushing it through the open channels and is preferentially carried through those open channels
what are ligand-gated channels?
channels that open in response to a chemical molecule binding to the channel and causing a conformational change
what are 5 types of ligand-gated channels?
- ionotropic
- metabotropic
- mechanoreceptors
- heat receptors
- visual receptors
what are voltage-gated ion channels? what do they generate?
those that open or close when the membrane potential changes; generate an action potential
what happens to membrane potential when sodium channels open?
depolarization (more positive in, closer to 0)
what happens to membrane potential when sodium channels close
no change because sodium does not really cross a resting membrane
what happens to membrane potential when potassium channels open?
hyperpolarization (potassium floods out so + leaves and cell becomes more negative/away from 0)
what happens to membrane potential when potassium channels close?
depolarization (allows the few sodium and calcium channels to have a greater influence as potassium no longer in flux and the movement of some sodium/+ in can depolarize closer to 0)
what happens to membrane potential when calcium channels open?
depolarization (lots of + influx, closer to 0)
what happens to membrane potential when calcium channels close?
no change as the membrane is hella impermeable to calcium
what happens when we change ion concentrations OUTSIDE the cell?
equilibrium potential becomes less negative, meaning there is less force pushing potassium out, leading to depolarization and other dramatic effects
what is the equilibrium potential of normal potassium levels?
-96mV
what is the result of high extracellular potassium levels on membrane potential?
membrane potential goes from -96mV (normal) to -78mV (depolarized)
what is the result of VERY high extracellular potassium levels on membrane potential?
membrane potential goes from -96mV (normal) to -53mV (depolarization)
what is the general result of high or very high extracellular potassium levels on the cell?
decreasing the amount of potassium flowing out of the cell due to high EC concentrations traps positive charge inside the cell and the cell becomes less negative and MORE active; can lead to fibrillation of the heart
what is the effect of low extracellular potassium levels on membrane potential and the cell?
membrane potential goes from -96mV (normal) to -114mV (hyperpolarized) and cell becomes less active
give 3 diseases that can cause hyperkalemia
- addison’s disease
- renal failure
- massive injury
give 3 diseases/drugs that can cause hypokalemia
- diuretics
- vomiting/diarrhea
- diabetes
what are the 3 diseases/deficiencies that can cause hypercalcemia?
- hyperparathyroidism
- vitamin D toxicity
- renal disease
what are 2 diseases that can cause hypocalcemia?
- parturient paresis
- hypoparathyrodisim
what happens when extracellular concentrations of calcium change? why?
there is little effect on the equilibrium potential when extracellular calcium concentrations change since free calcium levels in the cell are extremely low
how does calcium impact membrane potential?
calcium interferes with sodium channels!!
