Membrane Potential Lecture Flashcards
ion channels
the door which ions can move in or out
there are 4 types of ion channels
- Leak channels
- Chemically (Ligand) gated channels
- Voltage gated channels
- Mechanically gated channels
what is a leak channel
they are always open; BUT not everything can move through the channel - still very specific; size and charge matters - sodium cant move through potassium leak channels and vice versa
what drives ions to move in or out of the membrane
the electrochemical gradient - higher concentration of certain ions on the outside versus inside
always go from ___ to ___ gradient when ions move
higher to lower area
ions have charges which is why the driving force is called the _______ gradient
electrochemical - electrical AND chemical ; the combination of the two
there is a ___ concentration of potassium K+ in the cytosol than in the ECF
HIGHER inside the cell than it is outside the cell
will the CHEMICAL gradient drive K+ in or out of the cell
OUT - wants to go from higher to lower concentration
how is K+ going to leave the cell
through K+ leak channels
where does the majority of the negative charge in the inside of cell come from?
the negatively charged proteins that are inside the cell - not from the negative N ions
the plus potassium and negatively charged proteins are ___ nicely so why does K+ want to move out
balanced ; they want to move because of the CHEMICAL gradient
what happens when potassium leaves the cell and proteins stay in?
more of an electrical gradient, and the more K+ that leaves the cell and tries to solve the CHEMICAL the greater the ELECTRICAL gradient becomes
so as K+ leaves to go be with other K+s there is now a force calling them ____ to the cell
back to the cell ;
the more potassium that leaves, the more ___ that will want to come back into the cell
potassium
in the tug of war between electrical and chemical - who wins
usually the chemical wins out
we decided that the measure membrane potential by measuring the inside of the cell and comparing it to the outside
cytosol compared to ECF
what would the electrical membrane potential that will counteract the outflow of K+
it will be more negative relative to the outside, so the answer is negative
what is reversal potential
the reversal potential of a given ion is the membrane potential at which the net flow of the ion across the membrane = 0
how does reversal potential happen
this happens when the electrical gradient has become as strong as the chemical gradient so that there is still flow of an ion in/out of the cell, but they are flowing in/out at the same rate, meaning the NET FLOW is 0
T/F: each ion has its own reversal potential and is completely independent of other reversal potentials
true
does permeability have anything to do with reversal potential
nope
Synonyms for reversal potential
Nerst equation and equilibrium potential
reversal potential is NOT the resting membrane potential
TRUE
sodium is found in higher concentrations on the ___ of the cell compared to the ___ of the cell
higher Na+ concentrations outside of cell (in ECF) than inside the cell (in cytosol)
the CHEMICAL gradient will drive Na+ ___ the cell
inside
what will the electrical reversal potential be to counteract the Na+ flow
it has to be positive because it was negative then the Na+ ion would WANT to stay - positive rejects positive, so we need positive to PUSH Na+ out of the cell
what is resting membrane potential
it is the membrane potential of a given membrane when there is no stimulus and all the gated channels are closed
Na+ and K+ are the two major ions that contribute to membrane potential - so what is numeric resting membrane potential
-70 mV ; puts together -88 mV and 60 mV
T/F : sodium barely has an effect on the resting membrane potential value of -70mV
True - sodiums membrane potential is positive 60 mV and RMP is -70mV
why does sodium not contribute as much to the resting membrane potential ; why is the value so close to potassium’s value?
the membrane is not as permeable to sodium as it is to potassium ; a much lower concentration of sodium leak channels than potassium leak channels - not many windows in the wall for sodium, but lots for potassium
resting membrane potential is mainly dependent on the potassium electrochemical gradient and it is ___
negative
concentration is not changed by much in order to affect the potential - T/F?
True - think about the beach analogy - sand in eye is super bothersome but only one grain from a beach of millions left the sand
what would happen if there wasn’t a gradient
ions wouldn’t want to move
what creates the gradient in the first place? what causes the difference in the concentrations of ions?
the sodium - potassium pump; the hardest working protein in our body ; it actively (requires ATP) working against the concentration gradient - it throws sodium out and throws potassium in - important for creating AND maintaining the gradient
how does sodium potassium pump maintain the resting potential
it will bring gradient back to normal / maintain resting membrane potential
in reality not a huge amount of ions flow T/F
True - 0.006% of K+ ions move
T/F: The membrane is much more permeable to K+ than to Na+
True.
T/F: the electrical gradient counteracts the chemical gradient and the ions reach equilibrium (NET FLOW = 0)
True.
T/F: The Na+/K+ pump maintains the chemical gradient and is essential in creating/maintaining a negative resting membrane potential
True.
what is a chemically (ligand) gated channel
they are opened by ligand which is a compound/chemical they can be ion-specific or not ion specific (in terms of permeability) but they ARE SPECIFIC to the ligand that binds to receptor and opens the channel (ex. the Ach receptor at the neural muscular junctions is permeable to both Na+ and K+)
what is a voltage-gated channel
they open or close depending on the voltage/potential surrounding them; a change in the voltage (membrane potential) is what stimulates it to open/close; they are ion selective channels ; their gates can open and close at different speeds;
what are mechanically gated channels
carousels in ears are mechanically gated channels - they are found in sensory receptors (ex. in ears we have stream of fluid that is pushing those hairs and opening mechanically gated channels and as a result ions move in)
how do the three gated channels differ?
they differ in how they respond to a stimulus
in resting membrane potential it is ___
negative
we can change membrane potential by changing the gate’s status through ___
polarization
depolarize
making the cell less polarized or closer to 0 (ex. -70 to -60)
hyperpolarize
making it further away from 0 (ex. -70 to -90)
how do we polarize ?
with a stimulus - electrical, chemical or mechanical
what happens to little amount of sodium coming through leak channels
it gets booted back out by SPP
what is a local or graded potential?
a short-range change (ex. -70 to -65) in a membrane potential upon a stimulus (ex. ligand gated channels opening and positive sodium ions moving into the cell leading to depolarization)
sodium ligand gated channels opening upon stimulus leads to ___ of the cell
depolarization
T/F: adding ions outside the membrane changes the electrical gradient
FALSE - you changed the CHEMICAL gradient but not the electrical gradient (remember the beach example)
can the graded/local potential be increased? HOW?
YES! A local potential can be increased with a stronger stimulus (as in the Ach - not the ions that are already there for a ligand channel)
if I add a bunch of sodium and did not open the ligand gated channels will it affect the resting membrane potential
No - its like grains of sands to the beach ; the membrane is not very permeable to it; just a few leak channels but otherwise it cannot flow
if I add a bunch of potassium will it affect the resting membrane potential even if the channels are closed
yes - more so than sodium because membrane is highly permeable to the potassium and potassium can flow easily
is the SPP continuous
yes
the stronger stimulus affects the graded potential which is why we call it a graded solution
TRUE
why does a graded/local potential weaken
the response to the graded/local potential is diffusing/moving along the membrane because cations will move towards the negative charge to the left and right of where the local potential occured; the site next to the original depolarization site will also depolarize but not by as much because it didn’t have the same amount of influx of ions as did the original site causing it to slowly weaken
why does a graded/local potential weaken
& the SPP is pumping them back out and some diffuse toward middle of cell and their effect is less; the response to the graded/local potential is diffusing/moving along the membrane because cations will move towards the negative charge to the left and right of where the local potential occured; the site next to the original depolarization site will also depolarize but not by as much because it didn’t have the same amount of influx of ions as did the original site causing it to slowly weaken
what is an example of a stimulus that could lead to hyperpolarization
opening Cl- ligand gated channels (they are higher in concentration outside the cell like Na+) or opening K+ channels (they would leave the cell but they’re cations so it would lead to hyperpolarization)
