Human Physiology - Appendix: A Brief Review of Electricity

Appendix: A Brief Review of Electricity

- force

- electrical charge: a fundamental property of matter

- force equation:

- K: proportionality constant (9 x 10⁹ N·m² / columb²)

- Q: amount of charge on the particles

- r: distance between the particles

- direction of force depends on polarity, which is assigned by convention

- protons: (+) charge

- electrons: (-) charge

- quantification

- columb: unit of charge (total charge associated with 6.25 x 10¹⁸ protons or electrons)

- Avogadro’s number: definition of a mole (6.023 x 10²³ units/L)

- Faraday’s constant: amount of charge carried by 1 mole of ions (9.65 x 10⁴ coulombs)

- potential energy

- work: energy used to produce movement (W = F·s)

- potential energy: the potential to do work (W = ΔPE)

- current

- cations: migrate towards the negative electrode (cathode)

- anions: migrate towards the positive electrode (anode)

- current: movement of charge (by convention, movement of positive charge)

- current from (+) movement from anode to cathode = (-) movement from cathode to anode

- ampere: unit of current (1 amp = 1 C/s past a point)

- Ohm’s law

- conductance:

- resistance:

- Ohm’s law:

- circuit diagrams

- resistance in series

- current:

- resistance:

- resistance in parallel

- current:

- composite resistance:

- capacitors

- capacitance: the capability for charge storage on parallel plates

- potential:

- charge:

- capacitance:

- : dielectric constant (property of the medium separating the charge plates)

- biological membranes: ≈ 1 μF/cm²

- A: area of the interface

- d: distance between the plates

- biological membranes

- circuit diagram: battery with resistor and capacitor in parallel, and a switch

- defines the simple case of a single compartment, single cell membrane

- assumes potential is identical at any point along the membrane

- charge application

- current flows until the capacitor is charged to its maximum potential

- at this point, resistance across the capacitor is infinite, and all current flows through the resistor

- time dependence (τ) of charging a capacitor

- τ: time required to charge a capacitor to 1/e (approximately 1/3) of its final steady state value

- shape: asymptoting exponential function

- becomes important in formation of action potentials and propagation

- allows inference of membrane properties from observation of τ