NPB+112+11+membrane%2C+action+potential+lecture+notes

NPB+112+11+membrane%2C+action+potential+lecture+notes - NPB...

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NPB 112, Jan. 4-6, 2011 OUTLINE I. The neuron (pp. 4-9) II. Resting membrane potential (Ch. 2,4) A. due mainly to K+ efflux: Nernst (Fig. 2.6.b) B. influenced by Na+ : GHK Equation C. Na+/K+ exchange pump (Fig. 4.13a) III. Action potential (Ch. 3) I. The neuron: dendrites ("antennae" to receive signals), cell body with nucleus; axon to transmit signals over sometimes long distances; presynaptic terminal to release neurotransmitter to communicate with another neuron. Fig. 1.2. II. Resting membrane potential. Ch. 2 A. Neurons have lipid bilayer which surrounds cytoplasm, intracellular organelles to isolate them from the extracellular environment. B. Neurons are electrically polarized, inside negative relative to the outside. 1. When a thin glass micropipette is inserted into a neuron one can record the electrical potential difference across the cell membrane (Fig. 2.2) 2. Voltage difference between the inside and outside is about -65 mV. This is the cell's resting membrane potential. Animation : http://www.sinauer.com/neuroscience4e/animations2.1.html 3. By convention, changes in the membrane potential toward zero are DEPOLARIZING. Changes in a more negative direction are HYPERPOLARIZING. C. Interior of cell: high concentration of K+ and organic anions, low concentrations of Na+ and Cl-. D. Extracellular fluid, like sea water, contains high Na+ and Cl-. E. Cell membrane is SELECTIVELY PERMEABLE to K+ ions, and much less permeable to other ions. F. Strong chemical driving force on K+ to DIFFUSE out of the cell into the extracellular region of lower concentration. G. As K+ ions leave the cell, the interior layer of membrane becomes progressively more negative and the exterior layer more positive.
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H. ELECTROSTATIC force develops, since negative charges accumulating inside the cell tend to pull K+ back inside (opposite charges attract). I. Chemical and electrical forces eventually balance each other to achieve a steady state- the resting potential. J. K+ ion channel: 1. 4 membrane-spanning subunits with a hole, or channel, between them through the membrane (Fig. 4.8). 2. Channel diameter is just large enough for hydrated K+ to pass, but excludes Na+ which has a larger cloud of hydration due to its stronger electric field 3. Negative charge at the mouth of K+ channel repels anions III. Nernst equation: A. Equilibrium potential. The balance between chemical and electrical forces on an ion is described by the Nernst equation: E = RT ln [K+]out This translates to 58 log [K+]out mv zF [K+] in [K+] in (R= gas constant; F= Faraday's constant; T= temperature; z= valence). 1. For [K+] in is 400 mM and [K+] out is 20 mM, we have 58 log 20/400 = 58 log 1/20 = 58 (-1.3) = -75 mV. 2.
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NPB+112+11+membrane%2C+action+potential+lecture+notes - NPB...

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