membrane potentials

Question 1

3 ways electrical events are measured

Answer 1

intracellular-electrode inside cell
extracellular - electrode outside cell
patch clamping - electrode sealed to surface.
electrical recording with fluid-filled glass capillary tube with microelectrode

Question 2

EMG

Answer 2

electron myography - record activity by skeletal muscle –> electromyogram

Question 3

EEG

Answer 3

electroencephalogram = record activity of the brain. electrodes on scalp

Question 4

why are electrochemical gradients established

Answer 4

1. pump moves ions against gradient
   2.restricted ion movement through channels
   3 membrane stores and separates charges on inner and outer surfaces - it is a capacitor

Question 5

what is voltage (within context)

Answer 5

measure electrical work done in separating charges across membrane

Question 6

what is osmotic work done by the conc gradient

Answer 6

pump derives energy from hydrolysis of ATP - create concentration gradients.
creates electrical back-drag in opposite direction

gradients = [C]out/[C]in

Question 7

Explain the idea behind the Nernst equation

Answer 7

• force of conc gradient pushing K out=electrical force pulling back in.
• results in no net movement of K. electrical force which balance osmotic force = equilibrium potential. this can be determined if conc gradient is known from Nernst

Question 8

what is the Nernst eqn

Answer 8

E = (R.T/z.F) . in([C]out/[C]in)

R.T/z/F has units of joules per coulomb - expressed in volts
R and F are consents - monovalent ions the equine

Question 9

how is Nernst different if monovalent ions are used

Answer 9

chemical group with a valence of one, which thus can form one covalent bond. e.g. Na and H

E = 58 (mV) x log [C]out / [C]in

Question 10

intra and extracellular conc of Na and K?

Answer 10

intra
K=140mM, Na=10mM

extra
K=4mM
Na=140mM

Question 11

cell potentials to top K leaving and Na entering

Answer 11

-90 to stop K leaving
+60 to stop Na entering

conc Nernst eqn shows

Question 12

describe Vm(membrane voltage)

Answer 12

closer to Ek than E(Na) because membrane is 50times more permeable to K than Na

Question 13

what happens at constant Vm

Answer 13

net flow of ions is zero. passive leak of K out is matched by Na in

Question 14

what is the driving force on ion

Answer 14

Vm - E(eq)

e.g. for K+ = -70mV – (-90 mV) = +20 mV
For Na+= -70mV – (+50mV) = -120 mV

Question 15

what is Goldman Hodgkin Katz eqn and how is it different to Nernst

Answer 15

considers relative permeabilities of monovalent ions.

Nernst deals with one ion at a time, makes no assumptions about relative permeabilities