Week 07 Bioelectronics Lecture Flashcards
What is resting membrane potential?
an eletrical potential difference between intra and extracellular spaces that all cells maintain via manipulation of cytosolic ion concentrations
- generally between -30 and -90 mV
What is the general relationship between Na+, K+ and Cl- ions inside and outside cells?
Intracellular: higher K+
Extracellular: higher Na+ and Cl-
How do uncharged particles move across cell membranes?
What is the equation for neutral particle flow?
- small, uncharged particles move via diffusion
- flow from high to low concentrations in order to increase entropy
- based on the intensive property of chemical potential, which is basically concentration gradient
In the case of charged particles (ions), what must be taken into account in relation to their diffusion?
What is the equation for charged particle diffusion?
the intensive property of electrochemical potential, a thermodynamic measure of chemical potential taking into account the energy contribution of electrostatic forces
- expressed in J/mol
What is the permeability constant?
a coefficient dependent on the porous nature of the membrane
calculated as
P = D/d
where D is the diffusion constant
and d is the thickness of the membrane
What is Donnan equilibrium?
- a phenomenon that occurs when small, permeating charged particles near a semi-permeable membrane fail to distribuite evenly across the membrane
- usually results when a non-permeating charged particle creates an uneven electrical charge
ex: in the figure below, negatively charged proteins cause an uneven distribution of K+ and Cl- ions
How does donnan equilibrium affect osmotic pressure?
it results in extra osmotic pressure attributable to cations (Na+ and K+) attached to dissolved plasma proteins
What three conditions form the basis of the electrodiffusive transport model for membrane potential?
- Membrane is at rest, but without equilibrium between intra/extracellular spaces
- Membrane potential (volts) is constant (net ion flow = zero)
- Potential gradient (net difference in elect. charge, so Coulombs) in the membrane is constant
What is the Goldman-Hodgkin-Katz equation?
an equation for determination of the reversal potential across a cell’s membrane
- takes into account all of the ions that are permeant through the membrane
- version below can be simplified by removing Cl-
What is reversal potential?
- a membrane potential value, specific to an ionic species, at which there is no net flow of that particular ion from one side of the membrane to the other
ex: in post-synaptic neurons, the reversal potential is the membrane potential at which a neurotransmitter causes no net flow of ions through the neuron’s ion channels
What is depolarization in relation to resting membrane potential?
What is an example in the body of this?
Depolarization occurs when the cell suddenly becomes more permeable to certain ions and the resting membrane potential equalizes (going from its resting slightly negative value towards zero)
ex: hair cell stimulation in the inner ear
What is **hyperpolarization **in relation to cell membrane potential?
What is an example of it in the body?
- a change in membrane permeability that causes the potential to become more negative
- usually an efflux of K+ or influx of Cl-
-
inhibits action potentials by increasing stimulus required to move membrane potential to the threshold value
ex: photochemical effect hyperpolarizing rod cells in the retina
What is the equation for the time constant of the membrane (as if it were an RC circuit)?
What is the equation for the space constant of the membrane?
How does the graph of action potential depolarization/repolarization look?
Draw it.
lines A and B do not reach the threshold potential
line C reaches threshold and rapidly depolarizes to a peak as a result of Na+ influx
