Module 1: Introduction to Membrane Excitability

Lugi Galvani

• The first electrophysiologist

• Wanted to find the life force that powered biological organisms

• Used electricity to reanimate dead animals - showed lighting made frog legs twitch

What Did Galvani Show?

• Identified electricity as the innate force of life

Galvani’s Arch

• 2 metals in series

  • Forms a primitive battery when in constant contact with body tissues → Galvanism

Cult of Galvanism

• Giovanni Aldini continue his uncle’ on human cadavers

  • Used galvanic arch on George Forsters Body (murder)

Modern Galvanism

• Defibrillators

• Deep brain stimulation

Nernst Equation

• E_ion= RT ln[Ion]_o

  zF [Ion]_i

Nernst Equation: R

• Gas constant

  • 8.314 VCK^-1mol^-1

Nernst Equation: F

• Faraday constant

  • 9.648 × 10⁴ C mol^-1

Nernst Equation: T

• Absolute temperature *K

  • 273*K at 0*C

Nernst Equation: z

• Ion valency/ charge

  • ± 1, 2,3…

When [Ion]_o = [Ion]_i:

• E_ion = 0

  • Ln [1/1] = 0

• Polarity has no effect

When [Ion]_o > [Ion]_i:

• E_ion value dependent on ion charge

When [Ion]_i > [Ion]_o:

• E_ion value dependent on ion charge

Effect of Valence on E_ion Value

• When a divalent cation and a monovalent cation have the same [Ion]_o and [Ion]_i, E_ion for the divalent cation is half of that of the monovalent E_ion

Chemical Communication via Diffusion

• Effective over short distances

• Limited for long-distance signalling

Speed of Diffusion: Across Synaptic Gap (15-25nm)

• <1 us

Speed of Diffusion: Across Wide Dendrite

• 1 ms

Speed of Diffusion: Across Diameter of cell body

• 100ms

  • large distance - simple diffusion too slow