LECTURE 16 & 17- Feb 14 - 16thMaster Notes DocTextbook: p. 226 - 247BIOL 1050 notes on nervous systemNeurons●Neurons- basic functional units of nervous system, responsible forresponding to stimuli and conduction of electrical impulses from body toeffectors●Neurons cannot reproduce (mitosis) but can regenerate cell processes if cellbody remains intact●Lack of reproductive ability is why damage to nervous system is so seriousand debilitating●Glial cells- provide support to neurons, 10 glia : 1 neuron●Neurons are divided into cell body (soma),dendritesandaxons○Dendritesreceive stimuli from other neurons and conduct it to soma■Reception of stimulus =afferent process■Dendrites can besensory receptorsthat receive/sensestimuli such as heat, cold, touch, pressure, stretch, etc○Axons- conduct nerve impulses away from soma toward anotherneuron/effector, these areefferentprocesses■Axons, unlike branching dendrites, arevery long■Axons are sometimes referred to asnerve fibers■Nerve tract- bundle of axons●Myelin sheath- fatty tissue surrounding axon that helps with conduction ofelectrical impulses, wrapped around axon like a crepe○Myelinated nervous tissue is referred to aswhite matter,unmyelinated nervous tissue isgray matter○Myelin sheath is composed ofoligodendrocytes(specialized glialcells) in the CNS andSchwann cellsin the PNS○Spaces between sheath are thenodes of RanvierOrganization of Nervous System●Central nervous system(CNS) - brain and spinal cord●Peripheral nervous system(PNS) - any other nerves, includingcranialandspinalnerves●Afferent/sensory nerve fibers- conduct impulsestowardtheCNS●Efferent/motor nerve fibers- conduct impulsesawayfrom theCNS●Mixed nerve fibers- nerve tracts that contain both afferent and efferent nerve fibers●Somatic/voluntary NS- regulated by voluntary actions, acts throughskeletal muscle●Autonomic/involuntary NS- self regulated, acts throughsmooth & cardiac muscleand regulatesheartbeat, digestive muscle contractions, blood pressure, etc○Autonomic NS can be further classified into thesympathetic(fight-or-flight) andparasympathetic(return to rest) systemsNeuron Function●When a neuron is not being stimulated it is in itsresting statebut still has aresting potential●Sodium-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 gradient●Resting membrane potential- difference in electrical charges acrossmembrane, usually–70mV●Stimulus activates a neuron and results infiring(depolarization) of nerve●Depolarization-Na+ channels OPENand allow Na+ to floodintothe cell,resulting in balance of Na+ and charge and causing loss ofpolesof cell○Action potential- another term used to refer to nerve impulses●Repolarization-Na+ channels CLOSEand halt influx, K+ channelsOPENand K+ floods out of cell○Cell isrepolarizedbut ions are on the wrong sides of the membrane○To restore this, theNa-K pumppumps the ions back to theirrespective sides●Stimulus must reachthresholdto cause depolarization●If 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 brain●All-or-nothing principle- ether neuron completely depolarizes or not at all,
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Term
Winter
Professor
IraMandell
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