Membrane potential III Flashcards
There is an excess of negative charge inside of the cell that gives rise to a
resting negative potential.
the potential difference resulting from this imbalance is large, the actual difference in the number of cations versus anions inside the cell is relatively small.
the number of excess anions in a typical cell is _____ compared to the total number of _____.
small
anions
bulk solutions are always electrically _____.
neutral
Principle of Electrical Neutrality states that
bulk solutions have equal concentrations of anions and cations.
Equilibrium, in the case of ions, depends on
differences in both ion concentration and in electric potential between the inside of the cell and the extracellular fluid.
Equilibrium is achieved when a balance
between the concentration gradient and the electric gradient is reached.
Nernst equation:
E=(60/z) log (Coutside/Cinside)
Osmotic balance
osmolarity between the inside and outside of the cell must be equal
charge neutrality
the concentration of anions must equal that of cations in both the intra and extra cellular fluids
Nernest equations explains that
when dealing with ions, the effect of charge and electric force must be considered
Dannons rule is
when two permeating ions are, the equilibrium potential (E) must satisfy both ions.
Dannon’s rule equation is
[K+]outside x [Cl-]outside =[K+]inside x [Cl-]inside
With each cycle of the sodium pump, ____ K+ ions are pumped into the cell and ____ Na+ ions are pumped out of the cell. This is accomplished with energy from the ____
two
three
splitting of ATP.
Equilibrium is a state in
which no energy is required to move ions across membranes to maintain the state.
Even if the concentrations are not the same on both sides of the membrane, for every ion that comes into the cell
another will leave without net use of energy.
In contrast, a steady state requires an input of energy to maintain
the composition of the ICF.
This constant input of energy is derived from metabolism. Like equilibrium, the concentrations of ions are not changing over time.
membrane potential depends on
relative, not absolute, permeabilities to ions.
Different cells throughout the body have different membrane potentials, this is due to
differences in the relative permeability of ions in these cells.
K ions and Na ions are always struggling to attain their equilibrium potential, and how close they can come depends on the
relative number of channels for that ion.
A glial cell has very few ___ channels compared to __ channels, so it is essentially permeable only ____, thus the membrane potential of these cells is very close to the ____
Na
K
to K
Ek
The Na/K pump has a maximum rate cannot be
significantly adjusted, thus it is integral in establishing long term stability of membrane potential but not the short term changes in potential.
the primary short term determinant of membrane potential is not the Na/K pump, but the:
relative membrane permeabilities to the different ions.
what determines short term membrane potential?
The amount of a given ion flowing across the membrane
a cell that is very leaky to K and Na ions can have the same membrane potential as a cell that is tight, if the cells have the same proportion of ion channels, so the relative number of ions moving is the same.
The driving force of an ion is the:
the difference between membrane potential and the equilibrium potential of that ion
driving force is the extent to which an ion wants to enter a cell.
Neurons and other excitable cells, potential is sensitive to small changes in ____ but not _____
[K+]o,
[Na+]o
Changes in the ECF concentration of Na have little effect on cells because:
the membrane is relatively impermeable to Na
changes in Na concentration have little to no effect on:
membrane potentials.
____ is the dominant cation in the ECF.
Na
Because there isn’t very much K in the ECF, An increase in ECF concentration of K will result in
less efflux of K ions from the cell.
So small changes in extracellular concentration can greatly affect membrane potential.
Concerning hyperkalemia:
- Name the most common source of the extra potassium
- One important sign
- Two major strategies for reducing the potassium concentration in the ECF.
ICF
EKG change
uptake by cells and removal from body.
