Lecture 3: Cell Potentials Flashcards
1. Write Ohm's law, define the factors, and state an analogy for each factor 2. Calculate the equilibrium potential for an ion at 37C 3. State the fundamental reason for the passive segregation of ions across a cell membrane 4. State the role of active transport in the segregation of ions across a cell membrane 5. List the relative intracellular and extracellular concentration of the major ions 6. State why the resting membrane potential is often near the potassium equilibrium potential 7.
What does Ohm’s law tell us?
Ohm’s law describes the relationship between the flow of electrons (ions), the force driving the flow, and the resistance the flow encounters
What is Ohm’s law (equation) and what does each variable represent?
I= E/R or E = I x R E= potential, the driving force or "pressure" on electrons to move R= resistance, the opposition to flow that the electrons encounter I = current, the number of electrons that are moving for a given driving force (E) and resistance to flow (R)
What is found using the Nernst equation?
E = -60/z x log10 [Xz]i/[Xz]o
** the relationship btwn concentration difference and potential it exerts on a membrane at equilibrium **
Chemical Potential- the chemical energy (or work) of moving an ion Xz from one concentration inside a cell to another concentration outside the cell (concentration dependent)
Electrical Potential- the electrical energy (or work) of moving an ion Xz through an electrical potential across the membrane (E, measured outside relative to inside)
Equilibrium- The ion will come to equilibrium when the electrical work is equal to the chemical relationship.
How does intracellular protein pass through the cell membrane?
Trick question.. it doesn’t. Protein is impermeable therefore its net charge is negative. Negative likes Positive so protein holds K+ ions inside the cell.
What is the reason for passive segregation of ions across a cell membrane?
The concentration gradient actively segregates the ions and by doing so moderates the water balance through this ion distribution. Naturally, water would want to balance the charges across the membrane so by manipulating the ions on each side of the membrane the cell can moderate the amount of water within it. Pretty impressive cell.. i see u ;)
How does active segregation occur?
Active transport of ions can occur electrogenically by producing concentration gradients or by moving net charge.
As seen by Na+/K+ ATPase pump and the Calcium pump.
What are the Intracellular and Extracellular concentrations and the Membrane Potentials (Ex) for: K+, Na+, Cl-, A- (protein)?
Ions Intracellular(mM) Extracellular(mM) Ex(mV)
K+ 150 5 -89
Na+ 15 150 60
Cl- 10 110 -62
A- 74 13 —-
*protein doesn’t have a membrane potential because it can’t cross the membrane DUH!
At resting state, how does the charge within the cell change as it is depolarized vs hyperpolarized?
Depolarization makes the charge more positive by increasing Na+ within the cell through sodium channels during an action potential.
Hyperpolarization occurs after the action potential as K+ ions exit the cell making it more negative. K+ ions leave to offset the excessive positive charge within the cell brought about by the Na+ ions.
