Lecture_28_Dec5_2011

Lecture_28_Dec5_2011 - Introduction to Biophysics Lecture...

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Introduction to Biophysics Lecture 28 Neuronal signal transduction
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Human brain consists of 10 11 neurons, 10000 different types of neurons Axon (d=0.2-20 μ m) propagates all-or-none transient electrical signal, called action potential. Myelen is essential for high speed conduction of action potential. The branches of one axon (can be up to 1 meter long) may form synapses with as many as 1000 other neurons.
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Purkinje cell in cerebellum makes about 150000 contacts.
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Cell membrane is an electrical structure. Examples of trans membrane potentials. Which factors control transmembrane potential?
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Differences in ion concentration create Nernst potential: Resting state of neuron: Outside, 0 (+) Inside, -65 mV (-) Experiment can be done in “giant” axon (d=1mm) of squid
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KCl on both sides of the membrane. What of one ion (K + ) is more permeable than the other (Cl - )? The layer of net positive charge (excess of K + ) will form just outside of the membrane. λ -Debye screening length V = ψ K Nernst = -(k B T/ez)*ln(c 2 /c 1 ) gives the potential arising when permeant species reach equilibrium By analogy with chemical potential (which should be everywhere the same for molecular species equilibrium), the electrochemical potential of permeable ion should be everywhere the same in the equilibrium µ i (electrochem) = µ i + z i FV F- Faraday constant
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Lecture_28_Dec5_2011 - Introduction to Biophysics Lecture...

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