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This 3 page Class Notes was uploaded by jaaibirdd on Sunday January 24, 2016. The Class Notes belongs to BIO 467 at Arizona State University taught by Dr. Newbern in Fall 2016. Since its upload, it has received 23 views. For similar materials see Neurobiology in Biology at Arizona State University.
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Date Created: 01/24/16
Week 2- Lecture 1/20: Wed. ▯ Neurons sit around in slightly hyperpolarized state ▯ receptor potential (i.e. touch) moves up sensory nerves to NS ▯ synaptic potential- usually chemical neurotransmitter ▯ action potential- wave of electrical signal usually moving down axon receptor & synaptic --> graded ▯ ▯ Ohm's Law V= IR o V-voltage, I-current, R-resistance ▯ graded potentials summate to action potential ▯ passive response goes away when microelectrode is removed ▯ ▯ axons- poor conductors of electricity weak stimulation at a single point in axon will not travel very far ▯ action potentials not passive response reaches a threshold potential independent of magnitude of stimulus current o a stronger current won't generate a larger action potential all-or-none rule o information in the brain usually encoded by action potential frequency ▯ action potentials- self-sustaining; doesn't decay with distance slide questions: o action potential is a brief change in membrane potential from negative to positive o if triggered, action potential amplitude is independent of the magnitude of stimulation current o if amp. or duration of stimulus current is increased, multiple action potentials may occur o intensity of synaptic input is usually encoded in frequency of action potentials not amplitude ▯ ▯ Lipid bilayer doesn't normally let ions cross ▯ Electrical signals driven by ion concentration differences across membrane ion selective permeability ▯ K+, Na+, Cl-, Ca2+ only have to worry about these ions ▯ Table 2.1- ion concentrations ▯ differential concentrations form concentration gradient performed by active transporters ▯ ions move "down" gradient--> from high conc. to low conc. ▯ ▯ membranes are somewhat charged; negative ions tend to be on inner cytoplasmic membrane ▯ electrical potential across membrane created from separation of charge ▯ chemical force offset by electrical force, or charge distribution chemical force- pushes ion down concentration gradient electrical force- resists movement of chemical force o creates balance o Electrochemical equilibrium (Ex): when exact balance occurs ▯ not much of an alteration in concentration takes place during action potentials only small number of ions needed ▯ ▯ ion movement determines membrane potential but, electrical potential can drive ion flow o i.e. use electrode to make inside of cell more negative. K flow will stop, b/c electrical potential will resist chemical force that pushes K to the outside of the membrane if electrical potential is strong enough, K will rather flow into the cell and won't be affected by the chemical force ▯ Nernst- only one ion present; only one ion channel open calculates electrochemical equilibrium and membrane potential E= 61.5 log [ion]outside/ [ion] inside ▯ but membrane potential (Vm) is determined by the overall contribution of many ions ▯ Goldman- multiple ions; multiple ion channels open equation on lecture slides dependent on membrane permeability to each ion o typical neuron at rest: highly permeable to K compared to others Pk : Pna : Pcl = 1: .05 : .45 o during action potential, membrane much more permeable to Na Pk : Pna : Pcl = 1: 12 : .45 membrane potential becomes closer to equilibrium potential of Na (Ena) happens during action potential, when permeability to Na increases The negative resting membrane potential due to selective permeability to K ▯ ▯ ▯ ▯ ▯
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