human phys lec 3 - Biophysical...

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iophysical basis for electrical activity Biophysical basis for electrical activity of cells and tissues
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Electricity review Opposite charges attract, same charges repel parating pposite charges quires nergy Separating opposite charges requires energy Moving like charges closer together requires energy Charged particles can move through materials called conductors , which gives rise to electric current. Charged particles do not move through materials called insulators (also known as dielectric materials). Main conductor in the body is H 2 O A phospholipid bilayer is an insulator (high dielectric constant)
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Review of important equations in electricity I = V/R where I is current, V is voltage (potential), R is resistance (Ohm’s Law) G I = VG where G is conductance (1/ R ). Another form of Ohm’s Law For current flowing during the charging or discharging of a capacitor I C = C d V /d t
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Electrical units used in physiology Units of current are Amperes (A). In physiology we normally use nA or pA py g y Units of voltage are Volts (V). In physiology we normally use mV Units of resistance are Ohms ( Ω ). In physiology we normally use M Ω Units of conductance are Siemens (S). In physiology we normally use pS nits of capacitance are Farads (F) physiology we normally use F Units of capacitance are Farads (F). In physiology we normally use pF Units of charge are Coulombs (C) (= the charge of 6.24×10 18 protons) Alessandro Volta, Professor of Physics and Physiology, University of Pavia, Italy from 1779 1804
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It is possible to relate electrical charges (in Coulombs) to the number of ions in terms of chemical concentration. he charge of one mole of protons (or electrons) is ~ 96 485 coulombs The charge of one mole of protons (or electrons) is 96,485 coulombs. This number is known as the Faraday constant ( F ) Recall that one mole is ~6.022×10 23 (or Avogadro's number) A current of 1 A = 1 C/sec is equivalent to 6.24×10 18 electrons/sec
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lectrodiffusion fers to the diffusion of Electrodiffusion refers to the diffusion of charged particles in a solution All particles in solution (including ions) diffuse according to J dif = D d c /d x (first law of diffusion). Charged particles in solution also influenced by electric fields. For example, negatively charged ions will move towards an positively charged electrode. The later process is described by J drift = ucz d V /d x where u is the mobility constant, c is the concentration of the charged particle, z is the charge on the particle, and d V /d x is the electric field (change of voltage with distance).
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Na + (at high concentration) Na + (at low concentration) Imagine that the membrane is completely impermeable to Na + .
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This note was uploaded on 01/26/2012 for the course BIOL 3324 taught by Professor Ziburkus during the Spring '07 term at University of Houston.

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human phys lec 3 - Biophysical...

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