part3BME314finalreview2010

part3BME314finalreview2010 - Lecture 13 Membrane Potential...

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Lecture 13 Membrane Potential: created by separation of charged ions across a cells external membrane regulated by: ion pumps/channels critical in: muscle cells/nerve cells Resting Potential: vm = vi - vo where vo = 0(ground) for convention; potential difference across a membrane at rest key exterior ions: salty out (Na+) key interior ions: salty - K in (Na+ and K+) ion conc of cell: in out Na+ 12 120. K+ 125 5 Cl- 5 125 ion gradients are used to: *make ATP *drive transport processes *generate electrical signals hyperpolarization: makes the inside more negative depolarization: makes the inside more neutral how do ions move across memb? active-regulated by ATP, opened or closed in response to stimulus, selective and allows only specific ions to pass passive - open channels allow ions to flow through, ion specific, only one type of ion can pass Rest memb controlled by?Cl-, K+, Na+ channels Passive channels are responsible for resting membrane potential Active channels are responsible for action potentials Ficks Law J = D d [ I ] dx Ohms Law J = μ Z [ I ] dv dx J = flow of ions due to drift in E field mu = ion mobility (L 2 /sV) Z = ionic valence dv/dx = voltage gradient [i] = ion concentration
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Einsteins: D = KT μ q relationship of diffusivity and mobility; drift of particles in an E field under osmotic pressure k = 1.38 E-23 J/K q = 1.61E-19 C = magnitude of electric charge Nerst Equation: v m = v i - v o = KT Zq ln( [ K o ] [ K i ] ) Assume only permeability to: one ion species Nerst Equation: Fundamental biophysical description of: membrane pot. arising due to charge separation; only separation of one ionic species Derivation of Nerst Equation using Ficks ʼ Law: J(diff) and Ohm ʼ s Law: J(drift) J k ( diff ) = D d [ K + ] dx J k ( drift ) = μ Z [ K + ] dv dx D = KT μ q J k ( drift ) + J k ( diff ) = 0( equilibrium ) KT μ q d [ K + ] dx = μ Z [ K + ] dv dx dv = KT Zq d [ K + ] [ K + ] dv Vo Vi = KT Zq d [ K + ] [ K + ] Ko Ki V i V o = KT Zq ln( [ K o ] [ K i ] )
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Lecture 14 Donnan Equilibrium: membrane potential of a cell is due to the presence of all ions At equilibrium the Nerst potentials for K+ and Cl- must be equal. Ek =Ecl faster 0 < # slower 0 > # Goldman Hodgkin Katz Equation: P is the permeability find J then use space charge neutrality when perm. of one ion is high compared to others, Vm predicted by Goldman equation Electrical components of cell: concentration gradient across a channel for an ion gives rise to an emf that drives ions across the channel (modeled as a battery) R = 1/G : resistance given in conductance G (conductance) measured in Siemens G measure of ease of flow of ions through channel Lecture 15 Biomedical Instrumentation: Measurand: variable you measure examples: blood glucose, blood flow, blood pressure, pH, respiratory rate, temperature Instrumentation systems consist of: a sensor that measures a desired property, components that convert the analog output signal from the sensor into an electrical signal.
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