phdindustrialengineering

Lecture: Mysteries Of Bioelectricity

Enrico M. Staderini

Everything You Always Wanted to Know About BIOELECTRICITY* (*But Were Afraid to Ask)

Electrical current is a flow of electric charges displacing under an electric field. Well, this is generally true but what if electrical charges, of both signs, are transported by heavy carriers in an environment plenty of obstructions of many kinds? There is no metal in biological tissues, and free electrons (like insects flying freely in the air) are not present there. Instead, heavy and cumbersome ions (like donkeys loaded with heavy goods) are struggling to move (back and forth depending on the electric field sign AND the carried charge sign) under an electric field, in a medium filled up with many obstacles which impose a substantial friction on their displacement. And what happens at the interface between a biological tissue and a metallic wire used to inject or gather an electrical current from the body? Conventional electrotechnicalsimplifications(namely the linearity property) are often wrong and useless to understand these phenomena: this is where the mysteries of “bioelectricity” come out.

The course encompasses a preliminary recall of the not so trivial basic concepts of biological tissues electricity phenomena, before starting a practical in‐depth discussion on the physics and chemistry of electrodes and bioelectrical signals. A very interesting part of the course is dedicated to the electrical stimulation of excitable tissues (nerves and muscles): after the linear and theoretical derivation of the historically celebrated Lapicque curve, a presentation is given to its neglected non‐ linear extension which is at the base of the babel of (generally misunderstood) recipes for stimulation currents and waveforms used in FES (Functional Electrical Stimulation) and the so‐called electrostimulation and “musculation” biomedical devices. The course requires a good preliminary knowledge of physics and chemistry at bachelor level.

This is a short list of topics:

Preliminary recall of not so trivial and basic concepts

  • Cell membrane and membrane potential
  • Membrane currents and electrical excitation
  • The volume electrical conductor and the volume electrical source

Such things considered so trivial that nobody cares to explain (nor to fully understand)

  • Electrodes
  • Amplifiers

Models of bioelectrical sources

  • ECG, EEG, EMG, EOG

Electrical muscle stimulation

  • Current generators
  • Electrodes for muscle stimulation
  • The derivation of the Lapicque curve and its validity conditions
  • The babel of stimulation currents and waveforms