Week 07 Bioelectronics Lecture Flashcards Preview

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Flashcards in Week 07 Bioelectronics Lecture Deck (16)
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1
Q

What is resting membrane potential?

A

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
2
Q

What is the general relationship between Na+, K+ and Cl- ions inside and outside cells?

A

Intracellular: higher K+

Extracellular: higher Na+ and Cl-

3
Q

How do uncharged particles move across cell membranes?

What is the equation for neutral particle flow?

A
  • 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
4
Q

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?

A

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
5
Q

What is the permeability constant?

A

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

6
Q

What is Donnan equilibrium?

A
  • 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
7
Q

How does donnan equilibrium affect osmotic pressure?

A

it results in extra osmotic pressure attributable to cations (Na+ and K+) attached to dissolved plasma proteins

8
Q

What three conditions form the basis of the electrodiffusive transport model for membrane potential?

A
  1. Membrane is at rest, but without equilibrium between intra/extracellular spaces
  2. Membrane potential (volts) is constant (net ion flow = zero)
  3. Potential gradient (net difference in elect. charge, so Coulombs) in the membrane is constant
9
Q

What is the Goldman-Hodgkin-Katz equation?

A

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-
10
Q

What is reversal potential?

A
  • 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
11
Q

What is depolarization in relation to resting membrane potential?

What is an example in the body of this?

A

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

12
Q

What is **hyperpolarization **in relation to cell membrane potential?

What is an example of it in the body?

A
  • 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
13
Q

What is the equation for the time constant of the membrane (as if it were an RC circuit)?

A
14
Q

What is the equation for the space constant of the membrane?

A
15
Q

How does the graph of action potential depolarization/repolarization look?

Draw it.

A

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

16
Q

How do ions flow into and out of the cell at different points during the action potential?

Which ions move where at which point during the potential?

A

voltage-gated ion channels open and close to allow ion flow

  • initial depolarization - some stimulus opens Na+ channels, slightly depolarizing cell
  • post-threshold depolarization - once threshold voltage is met, many more Na+ ion channels open, depolarizing cell to positive voltages
  • repolarization - at peak voltage, Na+ channels close and K+ channels to allow K+ efflux and repolarization