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Ion+Channels+Glossary-1 - This is from the Ion Channels...

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1 This is from the Ion Channels course at Cold Spring Harbor Lab, and is a useful reference even if all the terms may have not been discussed in class. Ion Channels Glossary Nelson Spruston, Mark Farrant, Jeff Diamond I. Basic electricity Charge: The fundamental property of matter that is responsible for electrical phenomena. Charge (Q) is measured in Coulombs (C). Elementary charge, e = 1.602 x 10 -19 Coulombs (C) Valence: a term to describe the charge of a particle. Na+ and Ca++ have positive valence, while Cl- has negative valence. Moreover, Na + is monovalent, and Ca++ is divalent. In the Nernst equation and the GHK voltage equation, valence is represented by the variable z. Anion: a negatively charged particle. Cation: a positively charged particle. Current: The rate of charge movement. Current (7) is measured in amperes (A), which is equivalent to coulombs per second (C/s). I = ! Q/ ! t = Coulombs/sec = Amps (A) Voltage: The force created on a charge caused by the separation of charge. Voltage (F) is measured in volts (V). Voltage is equivalent to potential difference. Potential Difference: The same as voltage. Another definition is the difference in potential energy experienced by a charged particle in two locations (the work required to move a charge from point A to B). Potential difference (E) is measured in volts (V). E = Joules/Coulomb = Volts (V) Conductance: The ability of something (e.g. a wire or an ion channel) to pass current. Conductance (G) is measured in Siemens (S). Resistance: The inverse conductance. That is, the ability of something to impede current. Resistance (R) is measured in Ohms ( ! ). Conductivity: The ability of a substance to pass current. For a membrane, the conductivity (Gm) is measured in units of S/cm 2 and G=Gm*area. For a cable (e.g. axon or dendrite), the conductivity (G,, for intracellular conductivity) is measured in units of S/cm and G=Gi*length/area (i.e. cross-sectional area).
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