Dr. Karius' Vm lecture Flashcards
Resting membrane potential of all living cells is
lower than outside
Vm is the
difference of electrical potential between inside and outside cell and right at the membrane itself
if a cell’s Vm is 0 that means there is
no difference between the inside and the outside of the cell
-90 and +90 Vm mean
the two charges are equal in magnitude but opposite in polarity
hyperpolarization =
the membrane potential becomes more negative (moves farther away from zero)
Depolarization =
the membrane potential becomes less negative (moves closer to zero)
an ionic gradient exists when two conditions are met
1) there is an electrical gradient and
2) there is a chemical gradient working a particle
an ionic equilibrium may be achieved when
the combined forces of the concentration gradient and the electrical gradient are balanced, even if on their own they do not appear to be balanced
Two things are required to make an ionic gradient
a selectively permeable membrane and a Na/K ATPase
Lipophilic–Hydrophilic Polar–Non polar: which of the three can passively diffuse across a membrane?
the lipophilic and the nonpolar
Na+ =
low permeability
K+ =
higher permeability at rest (100X of sodium)
Ca++
low permeability at ret
Cl-
moderate permeability at rest
intracellular proteins have what kind of charge?
negative
proteins create a
electrical gradient because they are negatively charges
negative ions outside the cell are
repelled because of the net negative charge inside the cell, so positive charges are attracted
What are the TWO ways a selective permeability helps create the membrane potential
1) by keeping the proteins (with their negative charges) in the cell
2) by not allowing certain ions (e.g. sodium) to enter the cell
the Na/K ATPase pumps out more
+ from than into the cell (3Na out, 2K in)
what is the Na/K ATPase described as?
electrogenic
Sodium is higher
outside the cell than inside
Potassium is higher
inside the cell than outside
Chloride is higher
outside the cell than inside
Calcium is higher
outside the cell than inside
electrogenic means the cell
pumps out more (+) than (-)
the most important role of the Na/K ATPase is
producing a concentration gradient
what happens if you poison the Na/K pump?
the cell depolarizes immediately because of the loss of electrogenic effect of the ATPase, then more slowelr because the concentration gradient begins to equalize
how much voltage in a neuron is lost if you poison the Na/K pump?
around 5 mV
what is a chemical expression of electrogenicity?
3Na/2K
Effect on cell if Na/Ka is poisoned: initial and final
cell death
1) initial 5-10 mV
2) slower depolarization to 0
Importance of electrogenicity and Na/K in what cells?
neurons, skeletal muscle CRITICAL
other cells types not as critical
part 1: proteins do what
attract positive (K) ions to the interior of the cell
part 2: Na/K does what
pumps out 3 Na for every 2 K it pumps it takes in
part 3: the membrane doesn’t allow ____ to cross the membrane readily
ions
Muscle cells have a resting Vm is
-70 mv to -90 mv
the electrical and chemical gradient of Na
e: pulls Na into the cell
c: pulls Na into the cell
the electrical and chemical gradient of K
e: pulls K into the cell
c: repels K from the cell
the electrical and chemical gradient of Cl
e: repels Cl
c: attracts Cl
the electrical and chemical gradient of Ca
e: attracts Ca
c: attracts Ca
What happens if the Nernst potential is more negative than the membrane potential?
ions will move out of the cell
what happens if the nernst potential is less negative than the membrane potential?
ions will move from the outside to the inside
what happens if the nernst potential is equivalent to the membrane potential?
nothing moves because the electrical gradient and the chemical gradient are equal in opposite directions
At normal conditions, the equilibrium potential is ____ than the membrane potential
less than
if Vm is less negative than the equilibrium value, which direction does the gradient go?
out of the cell
if the Vm is more negative than the equilibrium value, which direction does the gradient go?
into the cell
V (DF) = Vm - Veq
DF is driving force
driving force = membrane potential minus nernst (equilibrium potential)
results of Vm larger than Veq?
cation OUTWARD flow; anion inward flow
Ved is positive
result when Vm is smaller than Veq?
cation inward flow, anion outward flow
Ved is negative
Vm = Veq ?
no net flow in either direction
What happens when the depolarization voltage nears V(Na) ?
The potassium channels are activated
Does the V(Na) ever get achieved?
no, just below it
What happens when hyperpolarization voltage nears V(k)?
V begins to depolarize slightly until it arrives at Vrest (Vm)
Does hyperpolarization ever reach Vk?
no
Hey now
Does this work?
