Membrane Potential Flashcards
Is extracellular or intracellular [Na+] higher?
Extracellular
Is extracellular or intracellular [K+] higher?
Intracellular
Is extracellular or intracellular [Ca+] higher?
Extracellular
Is extracellular or intracellular [Mg2+] higher?
Extracellular
Is extracellular or intracellular [Cl-] higher?
Extracellular
Concentration (mM) x valence = ?
mEQ
Why can’t a a cell with only a lipid membrane have a membrane potential?
Bulk electroneutrality and ions cannot cross the membrane
What is being balanced when K+ leak channels reach an equilibrium state?
Concentration gradient of the higher intracellular potassium and the electric resistance to flow (inside becomes more negative)
Abbreviated Nernst Equation
Ek=(61)(mV)log(Ko/Ki)
Equation describing the resting equilibrium state of a membrane with more than one permeable ion
Goldman Equation (G-H-K equation)
The external membrane surface typically has a negative or positive charge?
negative (despite the extracellular fluid itself being relatively positive)
Do monovalent or divalent cations bind to the negative charges on the extracellular membrane leaflet?
Divalent. Monovalent “not charged enough” to bind.
Decreases in extracellular Ca2+ and Mg2+ are called what, respectively?
Hypocalcemia and hypomagnesemia
“unscreened” negative charges on the cell membrane outer surface have what affect on the charge difference across the membrane?
Reduce the total charge difference. Resting potential less negative
Ease of movement of a substance through the cell membrane
Membrane Permeability (Pm)
Determined by the number of open ion channels in the membrane
Ion membrane permeability
Ease of movement of electric charge through the cell membrane.
Membrane conductance
Unit for membrane conductance
Siemens (S)
Relationship between membrane conductance and resistance
Resistance is the inverse of conductance
Rate of charge flow across the cell membrane
Membrane current (measured in Amperes - A)
Total net difference in electrical charge distribution across the cell membrane
Membrane potential (measures in Volts - V)
How is the driving force for an ion determined?
Difference between membrane potential and an ion’s equilibrium potential
ΔVion = (Vm - Eion)
(Driving Force) x (Conductance) = ?
current
Outward current. Makes the cell interior more negative or positive?
More negative (efflux of cations or influx of anions)
Inward current. Makes the cell interior more negative or positive?
More positive (influx of cations or efflux of anions)
Positive current is outward or inward?
Outward
Negative current is outward of inward?
Inward
Capability (of the membrane) to store electrical charge
Membrane Capacitance (measured in Farads - F)
Describes the lag between current flow and change in membrane potential. Determined by total membrane resistance (Rm) and total membrane capacitance (Cm)
Membrane Time Constant
Why does membrane potential change slower than membrane current?
Membrane current changes instantaneously if there’s a change in driving force or conductance but it takes time to rearrange the the charges stored on the cell membrane.
Two determinants of membrane capacity to store charge
Surface area (pos relationship) and thickness (neg relationship)
Membrane Time Constant = ?
(resistance) x (capacitance)
total membrane conductance is the product of… (2)
(number of open channels) x (individual channel conductance)
Increasing Rm will have what effect on the time constant
increases the time constant
Increasing Cm will have what effect on the time constant
increases the time constant
Describes the decay in effect over distance along a cylindrical membrane area. Higher value means more current flow.
Length Constant (λ)
Determinants of the length constant (2)
membrane resistance (Rm) and axial resistance (Ra)
Resistance to current flow along cylindrical area of membrane
axial resistance
Does higher axial resistance increase or decrease the length constant
decrease
Large diameter axons have a larger or smaller axial resistance?
Small Ra
Small diameter axons have a larger or smaller axial resistance?
Large Ra
