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ANSC WEEK 6 - Nervous & Endocrine Systems.pdf - LECTURE 16...

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LECTURE 16 & 17- Feb 14 - 16thMaster Notes DocTextbook: p. 226 - 247BIOL 1050 notes on nervous systemNeuronsNeurons- basic functional units of nervous system, responsible forresponding to stimuli and conduction of electrical impulses from body toeffectorsNeurons cannot reproduce (mitosis) but can regenerate cell processes if cellbody remains intactLack of reproductive ability is why damage to nervous system is so seriousand debilitatingGlial cells- provide support to neurons, 10 glia : 1 neuronNeurons are divided into cell body (soma),dendritesandaxonsDendritesreceive stimuli from other neurons and conduct it to somaReception of stimulus =afferent processDendrites can besensory receptorsthat receive/sensestimuli such as heat, cold, touch, pressure, stretch, etcAxons- conduct nerve impulses away from soma toward anotherneuron/effector, these areefferentprocessesAxons, unlike branching dendrites, arevery longAxons are sometimes referred to asnerve fibersNerve tract- bundle of axonsMyelin sheath- fatty tissue surrounding axon that helps with conduction ofelectrical impulses, wrapped around axon like a crepeMyelinated nervous tissue is referred to aswhite matter,unmyelinated nervous tissue isgray matterMyelin sheath is composed ofoligodendrocytes(specialized glialcells) in the CNS andSchwann cellsin the PNSSpaces between sheath are thenodes of RanvierOrganization of Nervous SystemCentral nervous system(CNS) - brain and spinal cordPeripheral nervous system(PNS) - any other nerves, includingcranialandspinalnervesAfferent/sensory nerve fibers- conduct impulsestowardtheCNSEfferent/motor nerve fibers- conduct impulsesawayfrom theCNSMixed nerve fibers- nerve tracts that contain both afferent and efferent nerve fibersSomatic/voluntary NS- regulated by voluntary actions, acts throughskeletal muscleAutonomic/involuntary NS- self regulated, acts throughsmooth & cardiac muscleand regulatesheartbeat, digestive muscle contractions, blood pressure, etcAutonomic NS can be further classified into thesympathetic(fight-or-flight) andparasympathetic(return to rest) systemsNeuron FunctionWhen a neuron is not being stimulated it is in itsresting statebut still has aresting potentialSodium-potassium pump- Na+ cannot diffuse through cell membrane on its own, Na-K pump causesNa+ to accumulateoutsidethe cell and K+ to accumulateinsidethe cell
Na-K pump brings2 K+into the cell and releases3 Na+, causing agreaterpositivecharge outside the cell and creating anelectrochemical gradientResting membrane potential- difference in electrical charges acrossmembrane, usually–70mVStimulus activates a neuron and results infiring(depolarization) of nerveDepolarization-Na+ channels OPENand allow Na+ to floodintothe cell,resulting in balance of Na+ and charge and causing loss ofpolesof cellAction potential- another term used to refer to nerve impulsesRepolarization-Na+ channels CLOSEand halt influx, K+ channelsOPENand K+ floods out of cellCell isrepolarizedbut ions are on the wrong sides of the membraneTo restore this, theNa-K pumppumps the ions back to theirrespective sidesStimulus must reachthresholdto cause depolarizationIf it does not, only a few Na+ channels will open and then close, K+ channelswill not open, and Na-K pump will quickly return Na+Sensory information would not be transmitted to the brainAll-or-nothing principle- ether neuron completely depolarizes or not at all,

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Term
Winter
Professor
IraMandell
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