Biophysics labs Theory

• Processes in the human body are inherently electric
• The cellular fluid is an electrolyte (a liquid composed of free electrons and ions), therefore, it is sensitive to external electric current
• Even a relatively small, 100 mA current may be fatal
• Impairing effects of electric current

  • Heat effects (burns)
  • Neural and cardiac malfunction
  • Muscle contraction and twitches
• Therapeutic effects of direct current

  • Used in physiotherapy (galvanic treatment)
  • Changes conductivity of nerves
  • Stimulates sensory nerves, increases stimulus threshold, analgesic effect
  • Vasodilating and metabolic-enhancing effects, promote absorption of harmful tissue fluids, restore muscle tone
• Iontophoresis


  Electric charge used to deliver medicine through the skin
• Different tissues have different resistance to flow of ions
• Electric charge


  The movement or flow of charges is called an electric current
• Direct current (DC)


  Always flows in the same direction between the two poles
• In the case of direct current, the density, the velocity, and the charge of the particles in the flow space are constant
• Quantity


  Shows the amount of work (W) done by the electric field by moving a charge Q=1 C (coulomb) from one point in the field to another
• Voltage (potential difference)


  Shows the amount of work (W) done by the electric field by moving a charge Q=1 C (coulomb) from one point in the field to another
• Electric current


  Shows the amount of charge (Q) flowing through the unit cross-section of the conductor in 1 second
• Resistance


  The property of a substance that impedes the flow of electric current
• Electrical work


  Work required to move charge Q in time t
• Power


  The amount of work done by a circuit element in 1 second
• Ohm's law


  The current (I) flowing through a conductor is directly proportional to the potential difference (voltage, V) between the two ends of the conductor; the constant of proportionality is resistance (R)
• Resistance can always be calculated from the Ohm's law formula, but it can be defined more accurately (measurement error can be reduced) by drawing a graph of current vs. voltage
• Series connection of resistors

  The same current flows through all of the components while the magnitude of the voltage drop depends on each resistor
• Parallel connection of resistors

  The reciprocals of the resistance values add up, so total resistance can be calculated by the following equation
• Skin resistance


  The dry epidermal layer (stratum corneum) is considered to be a good insulator, whereas the wet layer and the sweat glands increase the electrical conductivity of the skin
• Bioelectrical impedance analysis (BIA)


  Body fat measuring devices use the difference between the resistance of muscle and adipose tissue for the calculation
• The more muscle, the lower the resistance of the body
• Multimeter


  A device for measuring (meter) various types of (multi) quantities; for instance, current, voltage, and resistance, both in the case of direct and alternating current circuits