Electrical Phenomenain

Biological Structures

Information transfer in the brain

Excitation conduction in the heart

Sensory information acquisition and processing

Nerve pulse conduction

Electromechanical activity

Electrical Phenomena in the Body

12/23/16 3

Electric Current

Conductors:

- presence of free electrons- low resistance to the current of electrons

Insulators:

- lack of free electrons- high resistance to the current of electrons

4

Electric Current - Ohm’s Law

Unit: Coulomb/second (C/s) = Amperes (A)

I – current (A)R – resistance (Ω)

Power of the Electric Current (Watts)

For a voltage V (volt ) across resistor

Electrical circuit in of bodyTransport of ions (charges)

through cell membraneLipid bilayer membrane

Nuerons

6

Biological Membranes as Parallel plate Capacitors

High resistance and a low dielectric constant

Capacitor

Plasmamembranefattyphospholipidbilayerinsulator

Capacitor

The property of the capacitor

Relationship between thecharge and the potentialdifference V across the plates

Dielectricpermittivity

Capacitance

Platearea

2212 ./1085.8 mNCx -

Diffusion across membranes

Non-charged particles/molecules• The concentration gradient is the main driving force

From high → low concentration• Diffusion of one compound is independent of others• When the net diffusion stops ?

- concentration on both sides is equal.- equilibrium is reached.- No net change (Net diffusion : diffusion on both directions is equal )

10

Membrane Potential and Charged particles

Equilibrium(electrostatic force)

• Membranepotential:separationofoppositechargesacrosstheplasmamembrane.

• Allanimalcellsareelectricallypolarized(maintainvoltagedifferenceacrossthecell’splasmamembrane).Ihasanelectrochemicalgradient.

• Membranepotentialischaracterizedbyaslightexcessofpositivechargesoutsidethecellandnegativechargesinside

Equilibrium Potential (E) for ions

Intracellularfluid(Inside)

Extracellularfluid(Outside)

Inorganismsionsareresponsibleforcarryingchargeinbodyfluids• UnequaldistributionofkeyionsbetweenICFandECF.• Themembraneisimpermeaple tolargeICFproteinanions• Selectivemovementoftheseionsthroughplasmamembrane

NernstequationTemperature(K)Gasconstant

Faraday’sconstantIonvalence

Concentrationofionoutside

Concentrationofioninside

Example 1: Calculate the equilibrium potentials at normal bodytemperature for potassium K+ and sodium Na+ in neurons. Theconcentration of potassium is 5 mmol/L outside and 140 mmol/Linside. For sodium 1.5 mmol/L inside and 120 mmol/L outside.

Example 2: Calculate the equilibrium potentials at normal bodytemperature for calcium Ca2+ with typical external concentration of1.5 mM and internal concentration of 10-4mM

14

Ion Distribution Across the Membrane

Resting Membrane Potential Vm

EquilibriumpotentialforsingleionRestingmembranepotentialbycontributionofseveralions

ECFECF ICF

(Goldman-Hodgkin-Katz Equation)

Relativemembranepermeabilities:easewithwhichionscrossthemembrane

Example4: calculatethemembranerestingpotentialforpartialpermeabilitiesof1,0.03,0.1forK,Na,andClionsrespectively

Currentamperes(A)

Conductanceinsiemens(S)

Membranevoltage(restingpotential)(V)

Equilibriumpotentialofionx

Whathappenstopassapulse/spikeSignaltransferinneuronswhenstimulated

IncreaseinthepermeabilityofNa+todepolarize

18

Stimulating an excitable cellChanges in the Resting Membrane Potential

Whatistheperiodoftheactionpotential?

20

Electrical Processes

Conductor Cell (neuron)

Cable Axon

Free electrons Electrochemical gradient

Zero potential Resting potential

Electrical current Ion current across along the cable the membrane

Battery (source) Pacemaker cell

• Exercise1: usetheconcentrationsbelowtocalculatetheequilibriumpotentialatnormalbodytemperatureofeachionfortheplasmamembraneandforthemembranewiththeinterstitialfluid.

Eercise 2: Typical Nernst equilibrium potential for Cl- (z =-1) at 37oC is -0.090 V. if laboratory results showed that extracellularchlorine was 120 mM find the intracellular concentration

(Think about it until next lecture)