Anatomy and Physiology
Chapter 16The Autonomic Nervous System and Higher-Order FunctionsAn Introduction to the ANS and Higher-Order FunctionsLearning Outcomes16-1Compare the organization of the autonomic nervous system with that of the somatic nervous system.16-2Describe the structures and functions of the sympathetic division of the autonomic nervous system.16-3Describe the mechanisms of sympathetic neurotransmitter release and their effects on target organs and tissues.An Introduction to the ANS and Higher-Order FunctionsLearning Outcomes16-4Describe the structures and functions of the parasympathetic division of the autonomic nervous system.16-5Describe the mechanisms of parasympathetic neurotransmitter release and their effects on target organs and tissues.16-6Discuss the functional significance of dual innervation and autonomic tone.16-7Describe the hierarchy of interacting levels of control in the autonomic nervous system, including the significance of visceral reflexes.An Introduction to the ANS and Higher-Order FunctionsLearning Outcomes16-8Explain how memories are created, stored, and recalled, and distinguish among the levels of consciousness and unconsciousness.16-9Describe some of the ways in which the interactions of neurotransmitters influence brain function.16-10Summarize the effects of aging on the nervous system and give examples of interactions between the nervous system and other organ systems.An Introduction to the ANS and Higher-Order FunctionsSomatic Nervous System (SNS) Operates under conscious controlSeldom affects long-term survivalSNS controls skeletal musclesAutonomic Nervous System (ANS)Operates without conscious instructionANS controls visceral effectorsCoordinates system functionsCardiovascular, respiratory, digestive, urinary, reproductive16-1 Autonomic Nervous SystemOrganization of the ANSIntegrative centersFor autonomic activity in hypothalamusNeurons comparable to upper motor neurons in SNS16-1 Autonomic Nervous SystemOrganization of the ANSVisceral motor neuronsIn brain stem and spinal cord, are known as preganglionic neurons Preganglionic fibersAxons of preganglionic neurons Leave CNS and synapse on ganglionic neurons16-1 Autonomic Nervous SystemVisceral Motor NeuronsAutonomic gangliaContain many ganglionic neuronsGanglionic neurons innervate visceral effectors Such as cardiac muscle, smooth muscle, glands, and adipose tissuePostganglionic fibersAxons of ganglionic neurons16-1 Divisions of the ANSThe Autonomic Nervous System Operates largely outside our awarenessHas two divisions Sympathetic divisionIncreases alertness, metabolic rate, and muscular abilities Parasympathetic divisionReduces metabolic rate and promotes digestion16-1 Divisions of the ANSSympathetic DivisionKicks in only during exertion, stress, or emergency“Fight or flight”Parasympathetic DivisionControls during resting conditions“Rest and digest”16-1 Divisions of the ANSSympathetic and Parasympathetic DivisionMost often, these two divisions have opposing effectsIf the sympathetic division causes excitation, the parasympathetic causes inhibitionThe two divisions may also work independentlyOnly one division innervates some structuresThe two divisions may work together, with each controlling one stage of a complex process16-1 Divisions of the ANSSympathetic Division Preganglionic fibers (thoracic and superior lumbar; thoracolumbar) synapse in ganglia near spinal cordPreganglionic fibers are shortPostganglionic fibers are longPrepares body for crisis, producing a “fight or flight” responseStimulates tissue metabolismIncreases alertness16-1 Divisions of the ANSSeven Responses to Increased Sympathetic Activity Heightened mental alertnessIncreased metabolic rateReduced digestive and urinary functionsEnergy reserves activatedIncreased respiratory rate and respiratory passageways dilateIncreased heart rate and blood pressureSweat glands activated16-1 Divisions of the ANSParasympathetic Division Preganglionic fibers originate in brain stem and sacral segments of spinal cord; craniosacralSynapse in ganglia close to (or within) target organsPreganglionic fibers are longPostganglionic fibers are shortParasympathetic division stimulates visceral activityConserves energy and promotes sedentary activities16-1 Divisions of the ANSFive Responses to Increased Parasympathetic Activity Decreased metabolic rateDecreased heart rate and blood pressureIncreased secretion by salivary and digestive glandsIncreased motility and blood flow in digestive tractUrination and defecation stimulation16-1 Divisions of the ANSEnteric Nervous System (ENS) Third division of ANSExtensive network in digestive tract wallsComplex visceral reflexes coordinated locallyRoughly 100 million neuronsAll neurotransmitters are found in the brain16-2 The Sympathetic DivisionThe Sympathetic DivisionPreganglionic neurons located between segments T1 and L2 of spinal cordGanglionic neurons in ganglia near vertebral columnCell bodies of preganglionic neurons in lateral gray hornsAxons enter ventral roots of segments16-2 The Sympathetic DivisionGanglionic Neurons Occur in three locations Sympathetic chain ganglia Collateral ganglia Adrenal medullae 16-2 The Sympathetic DivisionSympathetic Chain Ganglia On both sides of vertebral columnControl effectors:In body wall Inside thoracic cavity In head In limbs16-2 The Sympathetic DivisionCollateral GangliaAre anterior to vertebral bodiesContain ganglionic neurons that innervate tissues and organs in abdominopelvic cavity16-2 The Sympathetic DivisionAdrenal Medullae (Suprarenal Medullae) Very short axonsWhen stimulated, release neurotransmitters into bloodstream (not at synapse)Function as hormones to affect target cells throughout body16-2 The Sympathetic DivisionFibers in Sympathetic Division Preganglionic fibersAre relatively shortGanglia located near spinal cordPostganglionic fibersAre relatively long, except at adrenal medullae16-2 The Sympathetic DivisionOrganization and Anatomy of the Sympathetic DivisionVentral roots of spinal segments T1–L2 contain sympathetic preganglionic fibersGive rise to myelinated white ramusCarry myelinated preganglionic fibers into sympathetic chain ganglionMay synapse at collateral ganglia or in adrenal medullae16-2 The Sympathetic DivisionSympathetic Chain GangliaPreganglionic fibersOne preganglionic fiber synapses on many ganglionic neuronsFibers interconnect sympathetic chain gangliaEach ganglion innervates particular body segment(s)16-2 The Sympathetic DivisionSympathetic Chain GangliaPostganglionic FibersPaths of unmyelinated postganglionic fibers depend on targets16-2 The Sympathetic DivisionSympathetic Chain Ganglia Postganglionic fibers control visceral effectorsIn body wall, head, neck, or limbs Enter gray ramusReturn to spinal nerve for distributionPostganglionic fibers innervate effectors Sweat glands of skinSmooth muscles in superficial blood vessels16-2 The Sympathetic DivisionSympathetic Chain Ganglia Postganglionic fibers innervating structures in thoracic cavity form bundlesSympathetic nerves16-2 The Sympathetic DivisionSympathetic Chain Ganglia Each sympathetic chain ganglia contains: 3 cervical ganglia10–12 thoracic ganglia4–5 lumbar ganglia4–5 sacral ganglia1 coccygeal ganglion 16-2 The Sympathetic DivisionSympathetic Chain Ganglia Preganglionic neuronsLimited to spinal cord segments T1–L2White rami (myelinated preganglionic fibers)Innervate neurons in:Cervical, inferior lumbar, and sacral sympathetic chain ganglia16-2 The Sympathetic DivisionSympathetic Chain Ganglia Chain ganglia provide postganglionic fibersThrough gray rami (unmyelinated postganglionic fibers)To cervical, lumbar, and sacral spinal nerves16-2 The Sympathetic DivisionSympathetic Chain Ganglia Only spinal nerves T1–L2 have white ramiEvery spinal nerve has gray ramusThat carries sympathetic postganglionic fibers for distribution in body wall16-2 The Sympathetic DivisionSympathetic Chain Ganglia Postganglionic sympathetic fibersIn head and neck leave superior cervical sympathetic gangliaSupply the regions and structures innervated by cranial nerves III, VII, IX, X16-2 The Sympathetic DivisionCollateral GangliaReceive sympathetic innervation via sympathetic preganglionic fibersSplanchnic nervesFormed by preganglionic fibers that innervate collateral gangliaIn dorsal wall of abdominal cavityOriginate as paired ganglia (left and right)Usually fuse together in adults16-2 The Sympathetic DivisionCollateral Ganglia Postganglionic fibers Leave collateral ganglia Extend throughout abdominopelvic cavityInnervate variety of visceral tissues and organsReduction of blood flow and energy by organs not vital to short-term survivalRelease of stored energy reserves16-2 The Sympathetic DivisionCollateral Ganglia Preganglionic fibers from seven inferior thoracic segmentsEnd at celiac ganglion or superior mesenteric ganglion Ganglia embedded in network of autonomic nervesPreganglionic fibers from lumbar segmentsForm splanchnic nerves End at inferior mesenteric ganglion16-2 The Sympathetic DivisionCollateral Ganglia Celiac ganglionPair of interconnected masses of gray matter May form single mass or many interwoven massesPostganglionic fibers innervate stomach, liver, gallbladder, pancreas, and spleen16-2 The Sympathetic DivisionCollateral GangliaSuperior mesenteric ganglion Near base of superior mesenteric arteryPostganglionic fibers innervate small intestine and proximal 2/3 of large intestine16-2 The Sympathetic DivisionCollateral GangliaInferior mesenteric ganglion Near base of inferior mesenteric arteryPostganglionic fibers provide sympathetic innervation to portions of: Large intestine Kidney Urinary bladder Sex organs16-2 The Sympathetic DivisionAdrenal Medullae Preganglionic fibers entering adrenal gland proceed to center (adrenal medulla)Modified sympathetic ganglionPreganglionic fibers synapse on neuroendocrine cellsSpecialized neurons secrete hormones into bloodstream16-2 The Sympathetic DivisionAdrenal MedullaeNeuroendocrine cells Secrete neurotransmitters epinephrine (E) and norepinephrine (NE)EpinephrineAlso called adrenaline Is 75–80 percent of secretory outputRemaining is norepinephrine (NE)Noradrenaline16-2 The Sympathetic DivisionAdrenal MedullaeBloodstream carries neurotransmitters through bodyCausing changes in metabolic activities of different cells including cells not innervated by sympathetic postganglionic fibersEffects last longer Hormones continue to diffuse out of bloodstream16-2 The Sympathetic DivisionSympathetic ActivationChange activities of tissues and organs by:Releasing NE at peripheral synapsesTarget specific effectors, smooth muscle fibers in blood vessels of skinAre activated in reflexes Do not involve other visceral effectors16-2 The Sympathetic DivisionSympathetic ActivationChanges activities of tissues and organs by:Distributing E and NE throughout body in bloodstreamEntire division responds (sympathetic activation) Are controlled by sympathetic centers in hypothalamusEffects are not limited to peripheral tissuesAlters CNS activity16-2 The Sympathetic DivisionChanges Caused by Sympathetic ActivationIncreased alertnessFeelings of energy and euphoriaChange in breathingElevation in muscle tone Mobilization of energy reserves16-3 Various Sympathetic NeurotransmittersStimulation of Sympathetic Preganglionic Neurons Releases ACh at synapses with ganglionic neurons Excitatory effect on ganglionic neurons Ganglionic NeuronsRelease neurotransmitters at specific target organs16-3 Various Sympathetic NeurotransmittersGanglionic Neurons Axon terminalsForm branching networks of telodendria instead of synaptic terminalsTelodendria form sympathetic varicositiesResemble string of pearlsSwollen segment packed with neurotransmitter vesiclesPass along or near surface of effector cellsNo specialized postsynaptic membranesMembrane receptors on surfaces of target cells16-3 Various Sympathetic NeurotransmittersGanglionic Neurons Axon terminals Release NE at most varicositiesCalled adrenergic neuronSome ganglionic neurons release ACh insteadAre located in body wall, skin, brain, and skeletal musclesCalled cholinergic neurons16-3 Various Sympathetic NeurotransmittersSympathetic Stimulation and the Release of NE and EPrimarily from interactions of NE and E with two types of adrenergic membrane receptors Alpha receptors (NE more potent) Beta receptorsActivates enzymes on inside of cell membrane via G proteins16-3 Various Sympathetic NeurotransmittersSympathetic Stimulation and the Release of NE and EAlpha-1 (1)More common type of alpha receptorReleases intracellular calcium ions from reserves in endoplasmic reticulumHas excitatory effect on target cell16-3 Various Sympathetic NeurotransmittersSympathetic Stimulation and the Release of NE and EAlpha-2 (2)Lowers cAMP levels in cytoplasmHas inhibitory effect on the cellHelps coordinate sympathetic and parasympathetic activities16-3 Various Sympathetic NeurotransmittersSympathetic Stimulation and the Release of NE and EBeta () receptorsAffect membranes in many organs (skeletal muscles, lungs, heart, and liver)Trigger metabolic changes in target cellStimulation increases intracellular cAMP levels16-3 Various Sympathetic NeurotransmittersThree Main Types of Beta ReceptorsBeta-1 (1) Increases metabolic activityBeta-2 (2) Triggers relaxation of smooth muscles along respiratory tractBeta-3 (3) Leads to lipolysis, the breakdown of triglycerides in adipocytes16-3 Various Sympathetic NeurotransmittersSympathetic Stimulation and the Release of ACh and NOCholinergic (ACh) sympathetic terminalsInnervate sweat glands of skin and blood vessels of skeletal muscles and brainStimulate sweat gland secretion and dilate blood vessels16-3 Various Sympathetic NeurotransmittersSympathetic Stimulation and the Release of ACh and NONitroxidergic synapses Release nitric oxide (NO) as neurotransmitterNeurons innervate smooth muscles in walls of blood vessels in skeletal muscles and the brainProduce vasodilation and increased blood flow16-4 The Parasympathetic DivisionAutonomic Nuclei Are contained in the mesencephalon, pons, and medulla oblongataAssociated with cranial nerves III, VII, IX, XIn lateral gray horns of spinal segments S2–S416-4 The Parasympathetic DivisionGanglionic Neurons in Peripheral GangliaTerminal ganglionNear target organUsually pairedIntramural ganglion Embedded in tissues of target organInterconnected massesClusters of ganglion cells16-4 The Parasympathetic DivisionOrganization and Anatomy of the Parasympathetic DivisionParasympathetic preganglionic fibers leave brain as components of cranial nervesIII (oculomotor)VII (facial)IX (glossopharyngeal)X (vagus)Parasympathetic preganglionic fibers leave spinal cord at sacral level16-4 The Parasympathetic DivisionOculomotor, Facial, and Glossopharyngeal NervesControl visceral structures in headSynapse in ciliary, pterygopalatine, submandibular, and otic gangliaShort postganglionic fibers continue to their peripheral targets16-4 The Parasympathetic DivisionVagus NerveProvides preganglionic parasympathetic innervation to structures in:NeckThoracic and abdominopelvic cavities as distant as a distal portion of large intestineProvides 75 percent of all parasympathetic outflowBranches intermingle with fibers of sympathetic division16-4 The Parasympathetic DivisionSacral Segments of Spinal CordPreganglionic fibers carry sacral parasympathetic outputDo not join ventral roots of spinal nerves, instead form pelvic nervesPelvic nerves innervate intramural ganglia in walls of kidneys, urinary bladder, portions of large intestine, and the sex organs16-4 The Parasympathetic DivisionParasympathetic Activation Centers on relaxation, food processing, and energy absorptionLocalized effects, last a few seconds at most16-4 The Parasympathetic DivisionMajor Effects of Parasympathetic Division Constriction of the pupils To restrict the amount of light that enters the eyes And focusing of the lenses of the eyes on nearby objectsSecretion by digestive glands Including salivary glands, gastric glands, duodenal glands, intestinal glands, the pancreas (exocrine and endocrine), and the liver16-4 The Parasympathetic DivisionMajor Effects of Parasympathetic DivisionSecretion of hormones That promote the absorption and utilization of nutrients by peripheral cellsChanges in blood flow and glandular activity Associated with sexual arousalIncrease in smooth muscle activity Along the digestive tract16-4 The Parasympathetic DivisionMajor Effects of Parasympathetic Division Stimulation and coordination of defecationContraction of the urinary bladder during urinationConstriction of the respiratory passagewaysReduction in heart rate and in the force of contraction16-5 Parasympathetic Neurons Release AChNeuromuscular and Neuroglandular Junctions All release ACh as neurotransmitterSmall, with narrow synaptic cleftsEffects of stimulation are short livedInactivated by acetylcholinesterase (AChE) at synapse ACh is also inactivated by tissue cholinesterase in surrounding tissues16-5 Parasympathetic Neurons Release AChMembrane Receptors and ResponsesNicotinic receptorsOn surfaces of ganglion cells (sympathetic and parasympathetic)Exposure to ACh causes excitation of ganglionic neuron or muscle fiber16-5 Parasympathetic Neurons Release AChMembrane Receptors and ResponsesMuscarinic receptorsAt cholinergic neuromuscular or neuroglandular junctions (parasympathetic)At few cholinergic junctions (sympathetic)G proteinsEffects are longer lasting than nicotinic receptorsResponse reflects activation or inactivation of specific enzymesCan be excitatory or inhibitory16-5 Parasympathetic Neurons Release AChDangerous Environmental ToxinsProduce exaggerated, uncontrolled responsesNicotineBinds to nicotinic receptorsTargets autonomic ganglia and skeletal neuromuscular junctions 50 mg ingested or absorbed through skinSigns and symptoms: Vomiting, diarrhea, high blood pressure, rapid heart rate, sweating, profuse salivation, convulsionsMay result in coma or death16-5 Parasympathetic Neurons Release AChDangerous Environmental Toxins Produce exaggerated, uncontrolled responsesMuscarineBinds to muscarinic receptorsTargets parasympathetic neuromuscular or neuroglandular junctionsSigns and symptoms: Salivation, nausea, vomiting, diarrhea, constriction of respiratory passages, low blood pressure, slow heart rate (bradycardia)16-6 Dual InnervationSympathetic DivisionWidespread impactReaches organs and tissues throughout bodyParasympathetic DivisionInnervates only specific visceral structuresSympathetic and Parasympathetic DivisionMost vital organs receive instructions from both sympathetic and parasympathetic divisionsTwo divisions commonly have opposing effects16-6 Dual InnervationAnatomy of Dual Innervation Parasympathetic postganglionic fibers accompany cranial nerves to peripheral destinationsSympathetic innervation reaches same structures By traveling directly from superior cervical ganglia of sympathetic chain16-6 Dual InnervationAnatomy of Dual InnervationAutonomic plexuses Nerve networks in the thoracic and abdominopelvic cavitiesAre formed by mingled sympathetic postganglionic fibers and parasympathetic preganglionic fibers Travel with blood and lymphatic vessels that supply visceral organs16-6 Dual InnervationAnatomy of Dual InnervationCardiac plexusPulmonary plexusEsophageal plexusCeliac plexusInferior mesenteric plexusHypogastric plexus16-6 Dual InnervationCardiac and Pulmonary PlexusesAutonomic fibers entering thoracic cavity intersectContain: Sympathetic and parasympathetic fibers for heart and lungsParasympathetic ganglia whose output affects those organs16-6 Dual InnervationEsophageal PlexusContains:Descending branches of vagus nervesSplanchnic nerves leaving sympathetic chainParasympathetic preganglionic fibers of vagus nerve enter abdominopelvic cavity with esophagusFibers enter celiac plexus (solar plexus)16-6 Dual InnervationCeliac PlexusAssociated with smaller plexuses, such as inferior mesenteric plexus Innervates viscera within abdominal cavity16-6 Dual InnervationHypogastric PlexusContains:Parasympathetic outflow of pelvic nervesSympathetic postganglionic fibers from inferior mesenteric ganglionSplanchnic nerves from sacral sympathetic chainInnervates digestive, urinary, and reproductive organs of pelvic cavity16-6 Dual InnervationAutonomic Tone Is an important aspect of ANS functionIf nerve is inactive under normal conditions, can only increase activityIf nerve maintains background level of activity, can increase or decrease activity16-6 Dual InnervationAutonomic Tone Autonomic motor neurons Maintain resting level of spontaneous activityBackground level of activation determines autonomic tone16-6 Dual InnervationAutonomic Tone Significant where dual innervation occursTwo divisions have opposing effects More important when dual innervation does not occur16-6 Dual InnervationThe Heart Receives Dual InnervationTwo divisions have opposing effects on heart functionParasympathetic divisionAcetylcholine released by postganglionic fibers slows heart rateSympathetic divisionNE released by varicosities accelerates heart rateBalance between two divisionsAutonomic tone is presentReleases small amounts of both neurotransmitters continuously16-6 Dual InnervationThe Heart Receives Dual Innervation Parasympathetic innervation dominates under resting conditionsCrisis accelerates heart rate by:Stimulation of sympathetic innervationInhibition of parasympathetic innervation 16-6 Dual InnervationAutonomic Tone Blood vessel dilates and blood flow increasesBlood vessel constricts and blood flow is reducedSympathetic postganglionic fibers release NEInnervate smooth muscle cells in walls of peripheral vessels16-6 Dual InnervationAutonomic Tone Background sympathetic tone keeps muscles partially contractedTo increase blood flow:Rate of NE release decreasesSympathetic cholinergic fibers are stimulatedSmooth muscle cells relaxVessels dilate and blood flow increases16-7 Visceral Reflexes Regulate the ANSSomatic Motor Control Centers in all portions of CNSLowest level regulatory control Lower motor neurons of cranial and spinal visceral reflex arcsHighest level Pyramidal motor neurons of primary motor cortexOperating with feedback from cerebellum and basal nuclei16-7 Visceral Reflexes Regulate the ANSVisceral ReflexesProvide automatic motor responsesCan be modified, facilitated, or inhibited by higher centers, especially hypothalamusVisceral reflex arc ReceptorSensory neuronProcessing center (one or more interneurons)All polysynapticTwo visceral motor neurons16-7 Visceral Reflexes Regulate the ANSVisceral ReflexesLong reflexes Autonomic equivalents of polysynaptic reflexesVisceral sensory neurons deliver information to CNS along dorsal roots of spinal nervesWithin sensory branches of cranial nervesWithin autonomic nerves that innervate visceral effectorsANS carries motor commands to visceral effectorsCoordinate activities of entire organ16-7 Visceral Reflexes Regulate the ANSVisceral ReflexesShort reflexes Bypass CNSInvolve sensory neurons and interneurons located within autonomic gangliaInterneurons synapse on ganglionic neuronsMotor commands distributed by postganglionic fibersControl simple motor responses with localized effectsOne small part of target organ16-7 Visceral Reflexes Regulate the ANSVisceral ReflexesRegulating visceral activityMost organs Long reflexes most importantDigestive tract Short reflexes provide most control and coordination16-7 Visceral Reflexes Regulate the ANSVisceral ReflexesEnteric nervous system Ganglia in the walls of digestive tract contain cell bodies of:Visceral sensory neuronsInterneuronsVisceral motor neuronsAxons form extensive nerve netsControl digestive functions independent of CNS16-7 Visceral Reflexes Regulate the ANSHigher Levels of Autonomic ControlSimple reflexes from spinal cord provide rapid and automatic responsesComplex reflexes coordinated in medulla oblongataContains centers and nuclei involved in:SalivationSwallowingDigestive secretionsPeristalsisUrinary functionRegulated by hypothalamus16-7 Visceral Reflexes Regulate the ANSThe Integration of SNS and ANS ActivitiesMany parallels in organization and functionIntegration at brain stemBoth systems under control of higher centers16-8 Higher-Order FunctionsHigher-Order Functions Share Three CharacteristicsRequire the cerebral cortexInvolve conscious and unconscious information processingAre not part of programmed “wiring” of brain Can adjust over time16-8 Higher-Order FunctionsMemoryFact memoriesAre specific bits of informationSkill memoriesLearned motor behaviorsIncorporated at unconscious level with repetitionProgrammed behaviors stored in appropriate area of brain stemComplex skill memories are stored and involve motor patterns in the basal nuclei, cerebral cortex, and cerebellum16-8 Higher-Order FunctionsMemory Short-term memoriesInformation that can be recalled immediatelyContain small bits of informationPrimary memories16-8 Higher-Order FunctionsMemory Long-term memoriesMemory consolidation – conversion from short-term to long-term memoryTwo types of long-term memory Secondary memories fade and require effort to recall Tertiary memories are with you for life16-8 Higher-Order FunctionsBrain Regions Involved in Memory Consolidation and AccessAmygdaloid body and hippocampusNucleus basalisCerebral cortex16-8 Higher-Order FunctionsAmygdaloid Body and HippocampusAre essential to memory consolidationDamage may cause:Inability to convert short-term memories to new long-term memoriesExisting long-term memories remain intact and accessible16-8 Higher-Order FunctionsNucleus Basalis Cerebral nucleus near diencephalonPlays uncertain role in memory storage and retrievalTracts connect with hippocampus, amygdaloid body, and cerebral cortexDamage changes emotional states, memory, and intellectual functions16-8 Higher-Order FunctionsCerebral CortexStores long-term memoriesConscious motor and sensory memories referred to association areasOccipital and temporal lobesSpecial portions crucial to memories of faces, voices, and wordsA specific neuron may be activated by combination of sensory stimuli associated with particular individual; called “grandmother cells”16-8 Higher-Order FunctionsCerebral Cortex Visual association areaAuditory association areaSpeech centerFrontal lobesRelated information stored in other locationsIf storage area is damaged, memory will be incomplete16-8 Higher-Order FunctionsCellular Mechanisms of Memory Formation and StorageInvolves anatomical and physiological changes in neurons and synapsesIncreased neurotransmitter releaseFacilitation at synapsesFormation of additional synaptic connections16-8 Higher-Order FunctionsIncreased Neurotransmitter Release Frequently active synapse increases the amount of neurotransmitter it storesReleases more on each stimulationThe more neurotransmitter released, the greater effect on postsynaptic neuron16-8 Higher-Order FunctionsFacilitation at Synapses Neural circuit repeatedly activatedSynaptic terminals begin continuously releasing neurotransmitterNeurotransmitter binds to receptors on postsynaptic membraneProduces graded depolarization Brings membrane closer to thresholdFacilitation results affect all neurons in circuit16-8 Higher-Order FunctionsFormation of Additional Synaptic Connections Neurons repeatedly communicatingAxon tip branches and forms additional synapses on postsynaptic neuronPresynaptic neuron has greater effect on transmembrane potential of postsynaptic neuron16-8 Higher-Order FunctionsCellular Mechanisms of Memory Formation and Storage Basis of memory storageProcesses create anatomical changesFacilitate communication along specific neural circuitMemory EngramSingle circuit corresponds to single memoryForms as result of experience and repetition16-8 Higher-Order FunctionsCellular Mechanisms of Memory Formation and Storage Efficient conversion of short-term memoryTakes at least 1 hourRepetition crucialFactors of conversion Nature, intensity, and frequency of original stimulusStrong, repeated, and exceedingly pleasant or unpleasant events likely converted to long-term memories16-8 Higher-Order FunctionsCellular Mechanisms of Memory Formation and StorageDrugs stimulate CNSCaffeine and nicotine are examplesEnhance memory consolidation through facilitation16-8 Higher-Order FunctionsCellular Mechanisms of Memory Formation and StorageDrugs stimulate CNSNMDA (N-methyl D-aspartate) ReceptorsLinked to consolidationChemically gated calcium channelsActivated by neurotransmitter glutamateGates open, calcium enters cellBlocking NMDA receptors in hippocampus prevents long-term memory formation16-8 Higher-Order FunctionsStates of Consciousness Many gradations of statesDegree of wakefulness indicates level of ongoing CNS activityWhen abnormal or depressed, state of wakefulness is affected16-8 Higher-Order FunctionsStates of Consciousness Deep sleepAlso called slow-wave or Non-REM (NREM) sleepEntire body relaxesCerebral cortex activity minimalHeart rate, blood pressure, respiratory rate, and energy utilization decline up to 30 percent16-8 Higher-Order FunctionsStates of Consciousness Rapid eye movement (REM) sleep Active dreaming occursChanges in blood pressure and respiratory rateLess receptive to outside stimuli than in deep sleepMuscle tone decreases markedlyIntense inhibition of somatic motor neuronsEyes move rapidly as dream events unfold16-8 Higher-Order FunctionsStates of Consciousness Nighttime sleep pattern Alternates between levelsBegins in deep sleepREM periods average 5 minutes in length; increase to 20 minutes over 8 hours16-8 Higher-Order FunctionsSleepHas important impact on CNSProduces only minor changes in physiological activities of organs and systemsProtein synthesis in neurons increases during sleepExtended periods without sleep lead to disturbances in mental function25 percent of the U.S. population experiences sleep disorders16-8 Higher-Order FunctionsStates of Consciousness Arousal and the reticular activating system (RAS)Awakening from sleepFunction of reticular formationExtensive interconnections with sensory, motor, integrative nuclei, and pathways along brain stemDetermined by complex interactions between reticular formation and cerebral cortex16-8 Higher-Order FunctionsReticular Activating System (RAS)Important brain stem componentDiffuse network in reticular formationExtends from medulla oblongata to midbrainOutput of RAS projects to thalamic nuclei that influence large areas of cerebral cortexWhen RAS inactive, so is cerebral cortexStimulation of RAS produces widespread activation of cerebral cortex16-8 Higher-Order FunctionsArousal and the Reticular Activating System Ending sleepAny stimulus activates reticular formation and RASArousal occurs rapidlyEffects of single stimulation of RAS last less than a minute16-8 Higher-Order FunctionsArousal and the Reticular Activating System Maintaining consciousness Activity in cerebral cortex, basal nuclei, and sensory and motor pathways continue to stimulate RASAfter many hours, reticular formation becomes less responsive to stimulationIndividual becomes less alert and more lethargicNeural fatigue reduces RAS activity16-8 Higher-Order FunctionsArousal and the Reticular Activating System Regulation of sleep–wake cyclesInvolves interplay between brain stem nuclei that use different neurotransmittersGroup of nuclei stimulates RAS with NE and maintains awake, alert stateOther group promotes deep sleep by depressing RAS activity with serotonin“Dueling” nuclei located in brain stem16-9 Brain ChemistryBrain ChemistryChanges in normal balance between two or more neurotransmitters can profoundly affect brain function16-9 Brain ChemistryHuntington’s Disease Destruction of ACh-secreting and GABA-secreting neurons in basal nucleiSymptoms appear as basal nuclei and frontal lobes slowly degenerateDifficulty controlling movementsIntellectual abilities gradually decline16-9 Brain ChemistryLysergic Acid Diethylamide (LSD) Powerful hallucinogenic drug Activates serotonin receptors in brain stem, hypothalamus, and limbic system16-9 Brain ChemistrySerotoninCompounds that enhance effects also produce hallucinations (LSD)Compounds that inhibit or block action cause severe depression and anxietyVariations in levels affect sensory interpretation and emotional states16-9 Brain ChemistrySerotonin Fluoxetine (Prozac) Slows removal of serotonin at synapsesIncreases serotonin concentrations at postsynaptic membraneClassified as selective serotonin reuptake inhibitors (SSRIs)Other SSRIsCelexa, Luvox, Paxil, and Zoloft16-9 Brain ChemistryParkinson’s Disease Inadequate dopamine production causes motor problemsDopamineSecretion stimulated by amphetamines, or “speed” Large doses can produce symptoms resembling schizophrenia Important in nuclei that control intentional movementsImportant in other centers of diencephalon and cerebrum16-10 Effects of Aging on the Nervous SystemEffects of AgingAnatomical and physiological changes begin after maturity (age 30)Accumulate over time85 percent of people over age 65 have changes in mental performance and CNS function16-10 Effects of Aging on the Nervous SystemCommon Age-related Anatomical Changes in the Nervous SystemReduction in Brain Size and Weight Reduction in Number of NeuronsDecrease in Blood Flow to BrainChanges in Synaptic Organization of BrainIntracellular and Extracellular Changes in CNS Neurons16-10 Effects of Aging on the Nervous SystemReduction in Brain Size and Weight Decrease in volume of cerebral cortexNarrower gyri and wider sulci Larger subarachnoid spaceReduction in Number of NeuronsBrain shrinkage linked to loss of cortical neuronsNo neuronal loss in brain stem nuclei16-10 Effects of Aging on the Nervous SystemDecrease in Blood Flow to Brain ArteriosclerosisFatty deposits in walls of blood vesselsReduces blood flow through arteriesIncreases chances of ruptureCerebrovascular accident (CVA), or strokeMay damage surrounding neural tissue16-10 Effects of Aging on the Nervous SystemChanges in Synaptic Organization of Brain Number of dendritic branches, spines, and interconnections decreasesSynaptic connections lostRate of neurotransmitter production declines16-10 Effects of Aging on the Nervous SystemIntracellular and Extracellular Changes in CNS NeuronsNeurons in brain accumulate abnormal intracellular depositsLipofuscin Granular pigment with no known functionNeurofibrillary tanglesMasses of neurofibrils form dense mats inside cell body and axon16-10 Effects of Aging on the Nervous SystemIntracellular and Extracellular Changes in CNS Neurons Plaques Extracellular accumulations of fibrillar proteinsSurrounded by abnormal dendrites and axons16-10 Effects of Aging on the Nervous SystemIntracellular and Extracellular Changes in CNS Neurons Plaques and tangles Contain deposits of several peptidesPrimarily two forms of amyloid ? (A?) protein Appear in brain regions specifically associated with memory processing 16-10 Effects of Aging on the Nervous SystemAnatomical Changes Linked to functional changesNeural processing becomes less efficient with ageMemory consolidation more difficultSecondary memories harder to access16-10 Effects of Aging on the Nervous SystemSensory Systems Hearing, balance, vision, smell, and taste become less acuteReaction times slowedReflexes weaken or disappearMotor ControlPrecision decreasesTakes longer to perform16-10 Effects of Aging on the Nervous SystemIncapacitation 85 percent of elderly population develops changes that do not interfere with abilitiesSome individuals become incapacitated by progressive CNS changes16-10 Effects of Aging on the Nervous SystemSenility Also called senile dementiaDegenerative changes Memory lossAnterograde amnesia (lose ability to store new memories)Emotional disturbancesAlzheimer’s disease is most common16-10 Nervous System IntegrationThe Nervous SystemMonitors all other systemsIssues commands that adjust their activitiesLike conductor of orchestra16-10 Nervous System IntegrationNeural Tissue Extremely delicateExtracellular environment must maintain homeostatic limitsIf regulatory mechanisms break down, neurological disorders appear ................
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