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Neural Integration II: The Autonomic Nervous
System and Higher-Order Functions
 Operates under conscious control  Seldom affects long-term survival  SNS controls skeletal muscles  Operates without conscious instruction  ANS controls visceral effectors  Coordinates system functions: cardiovascular, respiratory, digestive, urinary, reproductive  Integrative centers
 For autonomic activity in hypothalamus  Neurons comparable to upper motor neurons in SNS  Visceral motor neurons
 In brain stem and spinal cord, are known as preganglionic neurons
 Preganglionic fibers:
– axons of preganglionic neurons
– leave CNS and synapse on ganglionic neurons
 Contain many ganglionic neurons  Ganglionic neurons innervate visceral effectors: – such as cardiac muscle, smooth muscle, glands, and adipose tissue  Operates largely outside our awareness  Has two divisions  Sympathetic division
– increases alertness, metabolic rate, and muscular abilities  Parasympathetic division
– reduces metabolic rate and promotes digestion  “Kicks in” only during exertion, stress, or emergency  Parasympathetic Division
 Controls during resting conditions  “Rest and digest”  Two divisions may work independently
 Some structures innervated by only one division  Two divisions may work together
 Each controlling one stage of a complex process  Sympathetic Division
 Preganglionic fibers (thoracic and superior lumbar; thoracolumbar) synapse in  Preganglionic fibers are short  Postganglionic fibers are long  Prepares body for crisis, producing a “fight or flight” response  Stimulates tissue metabolism  Increases alertness  Seven Responses to Increased Sympathetic Activity  Heightened mental alertness  Increased metabolic rate  Reduced digestive and urinary functions  Energy reserves activated  Increased respiratory rate and respiratory passageways dilate  Increased heart rate and blood pressure  Sweat glands activated  Parasympathetic Division
 Preganglionic fibers originate in brain stem and sacral segments of spinal cord;  Synapse in ganglia close to (or within) target organs  Preganglionic fibers are long  Postganglionic fibers are short  Rest and repose  Parasympathetic division stimulates visceral activity  Conserves energy and promotes sedentary activities  Decreased metabolic rate, heart rate, and blood pressure  Increased salivary and digestive glands secretion  Increased motility and blood flow in digestive tract  Urination and defecation stimulation  Enteric Nervous System (ENS)
 Third division of ANS  Extensive network in digestive tract walls  Complex visceral reflexes coordinated locally  Roughly 100 million neurons  All neurotransmitters are found in the brain  Preganglionic neurons located between segments T1 and L2 of spinal  Ganglionic neurons in ganglia near vertebral column  Cell bodies of preganglionic neurons in lateral gray horns  Axons enter ventral roots of segments  Ganglionic Neurons  Sympathetic chain ganglia  Collateral ganglia  Suprarenal medullae  Sympathetic chain ganglia
 Are on both sides of vertebral column  Control effectors: – in body wall – inside thoracic cavity – in head – in limbs  Collateral ganglia
 Are anterior to vertebral bodies  Contain ganglionic neurons that innervate tissues and organs in  Suprarenal (adrenal) medullae
 Very short axons
 When stimulated, release neurotransmitters into bloodstream (not at synapse)
 Function as hormones to affect target cells throughout body
 Are relatively short  Ganglia located near spinal cord  Are relatively long, except at suprarenal medullae Organization and Anatomy of the Sympathetic Division  Ventral roots of spinal segments T1–L2 contain sympathetic preganglionic  Give rise to myelinated white ramus
 Carry myelinated preganglionic fibers into sympathetic chain ganglion
 May synapse at collateral ganglia or in suprarenal medullae
 One preganglionic fiber synapses on many ganglionic neurons  Fibers interconnect sympathetic chain ganglia  Each ganglion innervates particular body segment(s)  Paths of unmyelinated postganglionic fibers depend on targets  Postganglionic fibers control visceral effectors  In body wall, head, neck, or limbs
 Enter gray ramus
 Return to spinal nerve for distribution
 Postganglionic fibers innervate effectors  Sweat glands of skin  Smooth muscles in superficial blood vessels  Postganglionic fibers innervating structures in thoracic cavity form bundles  Each sympathetic chain ganglia contains  3 cervical ganglia  10–12 thoracic ganglia  4–5 lumbar ganglia  4–5 sacral ganglia  1 coccygeal ganglion  Preganglionic neurons  Limited to spinal cord segments T1–L2  White rami (myelinated preganglionic fibers)  Innervate neurons in – cervical, inferior lumbar, and sacral sympathetic chain ganglia
 Chain ganglia provide postganglionic fibers  Through gray rami (unmyelinated postganglionic fibers)  To cervical, lumbar, and sacral spinal nerves  Only spinal nerves T1–L2 have white rami  That carries sympathetic postganglionic fibers for distribution in body wall  In head and neck leave superior cervical sympathetic ganglia  Supply the regions and structures innervated by cranial nerves III, VII, IX, X  Collateral Ganglia
 Receive sympathetic innervation via sympathetic preganglionic fibers  Splanchnic nerves  Formed by preganglionic fibers that innervate collateral ganglia  In dorsal wall of abdominal cavity  Originate as paired ganglia (left and right)  Usually fuse together in adults  Leave collateral ganglia  Extend throughout abdominopelvic cavity  Innervate variety of visceral tissues and organs: – reduction of blood flow and energy by organs not vital to short-term survival – release of stored energy reserves  Preganglionic fibers from seven inferior thoracic segments  End at celiac ganglion or superior mesenteric ganglion
 Ganglia embedded in network of autonomic nerves
 Preganglionic fibers from lumbar segments  Form splanchnic nerves
 End at inferior mesenteric ganglion
 Pair of interconnected masses of gray matter  May form single mass or many interwoven masses  Postganglionic fibers innervate stomach, liver, gallbladder, pancreas, and  Near base of superior mesenteric artery  Postganglionic fibers innervate small intestine and proximal 2/3 of large  Near base of inferior mesenteric artery  Postganglionic fibers provide sympathetic innervation to portions of large intestine, kidney, urinary bladder, and sex organs  Suprarenal Medullae
 Preganglionic fibers entering suprarenal gland proceed to center (suprarenal  Modified sympathetic ganglion  Preganglionic fibers synapse on neuroendocrine cells  Specialized neurons secrete hormones into bloodstream  Neuroendocrine cells of suprarenal medullae  Secrete neurotransmitters epinephrine (E) and norepinephrine (NE)
 Epinephrine:
– also called adrenaline
– is 75–80% of secretory output
 Bloodstream carries neurotransmitters through body  Causing changes in metabolic activities of different cells including cells not innervated by sympathetic postganglionic fibers  Hormones continue to diffuse out of bloodstream  Change activities of tissues and organs by  Releasing NE at peripheral synapses: – target specific effectors: smooth muscle fibers in blood vessels of skin – are activated in reflexes – do not involve other visceral effectors  Distributing E and NE throughout body in bloodstream: – entire division responds (sympathetic activation) – are controlled by sympathetic centers in hypothalamus – effects are not limited to peripheral tissues – alters CNS activity  Increased alertness  Feelings of energy and euphoria  Change in breathing  Elevation in muscle tone  Mobilization of energy reserves  Stimulation of Sympathetic Preganglionic Neurons  Releases ACh at synapses with ganglionic neurons  Excitatory effect on ganglionic neurons  Release neurotransmitters at specific target organs  Form branching networks of telodendria instead of synaptic knobs
 Telodendria form sympathetic varicosities:
– resemble string of pearls
– swollen segment packed with neurotransmitter vesicles
– pass along or near surface of effector cells
– no specialized postsynaptic membranes
– membrane receptors on surfaces of target cells
 Some ganglionic neurons release ACh instead:
– are located in body wall, skin, brain, and skeletal muscles – called cholinergic neurons  Sympathetic Stimulation and the Release of NE and E  Primarily from interactions of NE and E with two types of adrenergic membrane  Alpha receptors (NE more potent)  Beta receptors  Activates enzymes on inside of cell membrane via G proteins
 Alpha-1 (α1)
 More common type of alpha receptor  Releases intracellular calcium ions from reserves in endoplasmic reticulum  Has excitatory effect on target cell  Alpha-2 (α2)
 Lowers cAMP levels in cytoplasm  Has inhibitory effect on the cell  Helps coordinate sympathetic and parasympathetic activities  Beta (β) receptors
 Affect membranes in many organs (skeletal muscles, lungs, heart, and liver)  Trigger metabolic changes in target cell  Stimulation increases intracellular cAMP levels  Beta-1 (β1)
 Beta-2 (β2)
 Triggers relaxation of smooth muscles along respiratory tract  Beta-3 (β3)
 Leads to lipolysis, the breakdown of triglycerides in adipocytes
 Sympathetic Stimulation and the Release of ACh and NO  Cholinergic (ACh) sympathetic terminals  Innervate sweat glands of skin and blood vessels of skeletal muscles and brain  Stimulate sweat gland secretion and dilate blood vessels  Release nitric oxide (NO) as neurotransmitter
 Neurons innervate smooth muscles in walls of blood vessels in skeletal
 Produce vasodilation and increased blood flow  Are contained in the mesencephalon, pons, and medulla oblongata  associated with cranial nerves III, VII, IX, X In lateral gray horns of spinal segments S  Ganglionic Neurons in Peripheral Ganglia  Terminal ganglion
 Near target organ  Usually paired  Intramural ganglion
 Embedded in tissues of target organ  Interconnected masses  Clusters of ganglion cells Organization and Anatomy of the Parasympathetic  Parasympathetic preganglionic fibers leave brain as components of cranial nerves  III (oculomotor)  VII (facial)  IX (glossopharyngeal)  X (vagus)  Parasympathetic preganglionic fibers leave spinal cord at sacral level  Oculomotor, Facial, and Glossopharyngeal Nerves  Control visceral structures in head
 Synapse in ciliary, pterygopalatine, submandibular, and otic ganglia
 Short postganglionic fibers continue to their peripheral targets
 Provides preganglionic parasympathetic innervation to structures in  Neck  Thoracic and abdominopelvic cavity as distant as a distal portion of large intestine  Provides 75% of all parasympathetic outflow  Branches intermingle with fibers of sympathetic division  Preganglionic fibers carry sacral parasympathetic output  Do not join ventral roots of spinal nerves, instead form pelvic nerves  Pelvic nerves innervate intramural ganglia in walls of kidneys, urinary bladder, portions of
 Centers on relaxation, food processing, and energy absorption  Localized effects, last a few seconds at most  Major effects of parasympathetic division include  Constriction of pupils
 Secretion by digestive glands
 Secretion of hormones
 Changes in blood flow and glandular activity
 Major effects of parasympathetic division include  Increase in smooth muscle activity along digestive tract
 Defecation: stimulation and coordination
 Contraction of urinary bladder during urination
 Constriction of respiratory passageways
 Reduction in heart rate and force of contraction

 Stimulation increases nutrient content of blood  Cells absorb nutrients  Neuromuscular and Neuroglandular Junctions  All release ACh as neurotransmitter  Small, with narrow synaptic clefts  Effects of stimulation are short lived  Inactivated by AChE at synapse
 ACh is also inactivated by pseudocholinesterase (tissue cholinesterase) in surrounding
 Nicotinic receptors
 On surfaces of ganglion cells (sympathetic and parasympathetic): – exposure to ACh causes excitation of ganglionic neuron or muscle fiber  Muscarinic receptors
 At cholinergic neuromuscular or neuroglandular junctions (parasympathetic)  At few cholinergic junctions (sympathetic)  G proteins: – effects are longer lasting than nicotinic receptors – response reflects activation or inactivation of specific enzymes – can be excitatory or inhibitory  Dangerous environmental toxins
 Produce exaggerated, uncontrolled responses  Nicotine: – binds to nicotinic receptors – targets autonomic ganglia and skeletal neuromuscular junctions – 50 mg ingested or absorbed through skin – signs: ª vomiting, diarrhea, high blood pressure, rapid heart rate, sweating, profuse salivation,  Dangerous Environmental Toxins (cont’d)  Produce exaggerated, uncontrolled responses  Muscarine  Binds to muscarinic receptors  Targets parasympathetic neuromuscular or neuroglandular junctions  Signs and symptoms: – salivation, nausea, vomiting, diarrhea, constriction of respiratory passages, low blood pressure, slow  Widespread impact  Reaches organs and tissues throughout body  Innervates only specific visceral structures  Most vital organs receive instructions from both sympathetic and parasympathetic  Two divisions commonly have opposing effects  Parasympathetic postganglionic fibers accompany cranial nerves to  Sympathetic innervation reaches same structures by traveling directly from superior cervical ganglia of sympathetic chain  Nerve networks in the thoracic and abdominopelvic cavities: – are formed by mingled sympathetic postganglionic fibers and parasympathetic  Travel with blood and lymphatic vessels that supply visceral organs  Cardiac plexus  Pulmonary plexus  Esophageal plexus  Celiac plexus  Inferior mesenteric plexus  Hypogastric plexus  Autonomic fibers entering thoracic cavity intersect  Contain  Sympathetic and parasympathetic fibers for heart and lungs  Parasympathetic ganglia whose output affects those organs  Descending branches of vagus nerve  Splanchnic nerves leaving sympathetic chain  Parasympathetic preganglionic fibers of vagus nerve enter abdominopelvic cavity  Fibers enter celiac plexus (solar plexus)  Associated with smaller plexuses, such as inferior mesenteric
 Innervates viscera within abdominal cavity  Parasympathetic outflow of pelvic nerves  Sympathetic postganglionic fibers from inferior mesenteric ganglion  Splanchnic nerves from sacral sympathetic chain  Innervates digestive, urinary, and reproductive organs of pelvic cavity  Autonomic Tone
 Is an important aspect of ANS function  If nerve is inactive under normal conditions, can only increase activity  If nerve maintains background level of activity, can increase or decrease  Maintain resting level of spontaneous activity  Background level of activation determines autonomic tone  Significant where dual innervation occurs  More important when dual innervation does not occur  The heart receives dual innervation
 Two divisions have opposing effects
 Acetylcholine released by postganglionic fibers slows heart rate  NE released by varicosities accelerates heart rate  Autonomic tone is present  Releases small amounts of both neurotransmitters continuously  The heart receives dual innervation
 Parasympathetic innervation dominates under resting conditions  Crisis accelerates heart rate by  Stimulation of sympathetic innervation  Inhibition of parasympathetic innervation  Blood vessel dilates and blood flow increases  Blood vessel constricts and blood flow is reduced  Sympathetic postganglionic fibers release NE  Innervate smooth muscle cells in walls of peripheral vessels  Background sympathetic tone keeps muscles partially contracted  To increase blood flow  Rate of NE release decreases  Sympathetic cholinergic fibers are stimulated  Smooth muscle cells relax  Vessels dilate and blood flow increases Visceral Reflexes Regulate Autonomic Function  Centers in all portions of CNS  Lowest level regulatory control  Lower motor neurons of cranial and spinal visceral reflex arcs  Pyramidal motor neurons of primary motor cortex  Operating with feedback from cerebellum and basal nuclei  Provide automatic motor responses
 Can be modified, facilitated, or inhibited by higher centers, especially
 Receptor  Sensory neuron  Processing center (one or more interneurons):  Autonomic equivalents of polysynaptic reflexes  Visceral sensory neurons deliver information to CNS along dorsal roots of spinal nerves: – within sensory branches of cranial nerves – within autonomic nerves that innervate visceral effectors  ANS carries motor commands to visceral effectors  Coordinate activities of entire organ  Bypass CNS  Involve sensory neurons and interneurons located within autonomic ganglia  Interneurons synapse on ganglionic neurons  Motor commands distributed by postganglionic fibers  Control simple motor responses with localized effects  One small part of target organ – short reflexes provide most control and coordination  Ganglia in the walls of digestive tract contain cell bodies of: – visceral sensory neurons – interneurons – visceral motor neurons  Axons form extensive nerve nets  Control digestive functions independent of CNS  Simple reflexes from spinal cord provide rapid and automatic responses
 Complex reflexes coordinated in medulla oblongata
 Contains centers and nuclei involved in: – salivation – swallowing – digestive secretions – peristalsis – urinary function  The Integration of SNS and ANS Activities  Many parallels in organization and function
 Integration at brain stem
 Both systems under control of higher centers  Require the cerebral cortex
 Involve conscious and unconscious information processing
 Not part of programmed “wiring” of brain
 Can adjust over time
 Memory
 Fact memories
 Skill memories
 Learned motor behaviors  Incorporated at unconscious level with repetition  Programmed behaviors stored in appropriate area of brain stem  Complex are stored and involve motor patterns in the basal nuclei, cerebral cortex, and  Short–term memories
 Information that can be recalled immediately  Contain small bits of information  Long-term memories
 Memory consolidation: conversion from short-term to long-term memory: – secondary memories fade and require effort to recall – tertiary memories are with you for life  Brain Regions Involved in Memory Consolidation and Access  Amygdaloid body and hippocampus  Nucleus basalis  Cerebral cortex  Amygdaloid body and hippocampus
 Are essential to memory consolidation  Damage may cause  Inability to convert short-term memories to new long-term memories  Existing long-term memories remain intact and accessible  Nucleus Basalis
 Cerebral nucleus near diencephalon  Plays uncertain role in memory storage and retrieval  Tracts connect with hippocampus, amygdaloid body, and cerebral cortex  Damage changes emotional states, memory, and intellectual functions  Cerebral cortex
 Stores long-term memories  Conscious motor and sensory memories referred to association areas  Special portions crucial to memories of faces, voices, and words  A specific neuron may be activated by combination of sensory stimuli associated with particular individual; called “grandmother cells”  Visual association area  Auditory association area  Speech center  Frontal lobes  Related information stored in other locations  If storage area is damaged, memory will be incomplete  Cellular Mechanisms of Memory Formation and Storage  Involves anatomical and physiological changes in neurons and  Increased neurotransmitter release
 Facilitation at synapses
 Formation of additional synaptic connections
 Increased Neurotransmitter Release
 Frequently active synapse increases the amount of neurotransmitter it  Releases more on each stimulation  The more neurotransmitter released, the greater effect on postsynaptic  Facilitation at Synapses
 Neural circuit repeatedly activated  Synaptic terminals begin continuously releasing neurotransmitter  Neurotransmitter binds to receptors on postsynaptic membrane  Produces graded depolarization  Brings membrane closer to threshold  Facilitation results affect all neurons in circuit  Formation of Additional Synaptic Connections
 Neurons repeatedly communicating  Axon tip branches and forms additional synapses on postsynaptic neuron  Presynaptic neuron has greater effect on transmembrane potential of postsynaptic  Cellular Mechanisms of Memory Formation and Storage  Basis of memory storage
 Processes create anatomical changes  Facilitate communication along specific neural circuit  Memory Engram
 Single circuit corresponds to single memory  Forms as result of experience and repetition  Cellular Mechanisms of Memory Formation and Storage  Efficient conversion of short-term memory
 Takes at least 1 hour  Repetition crucial  Factors of conversion
 Nature, intensity, and frequency of original stimulus  Strong, repeated, and exceedingly pleasant or unpleasant events likely converted to long-term  Caffeine and nicotine are examples:
– enhance memory consolidation through facilitation  NMDA (N-methyl D-aspartate) Receptors: – linked to consolidation
– chemically gated calcium channels
– activated by neurotransmitter glycine
– gates open, calcium enters cell
– blocking NMDA receptors in hippocampus prevents long-term memory formation
 Many gradations of states
 Degree of wakefulness indicates level of ongoing CNS activity
 When abnormal or depressed, state of wakefulness is affected
 Deep sleep
 Also called slow-wave sleep  Entire body relaxes  Cerebral cortex activity minimal  Heart rate, blood pressure, respiratory rate, and energy utilization decline up to  Rapid eye movement (REM) sleep
 Active dreaming occurs  Changes in blood pressure and respiratory rate  Less receptive to outside stimuli than in deep sleep  Muscle tone decreases markedly  Intense inhibition of somatic motor neurons  Eyes move rapidly as dream events unfold  Nighttime sleep pattern
 Alternates between levels  Begins in deep sleep  REM periods average 5 minutes in length; increase to 20 minutes over 8 hours  Has important impact on CNS
 Produces only minor changes in physiological activities of organs and systems
 Protein synthesis in neurons increases during sleep
 Extended periods without sleep lead to disturbances in mental function
 25% of U.S. population experiences sleep disorders
 Arousal and the reticular activating system (RAS)
 Awakening from sleep  Function of reticular formation: – extensive interconnections with sensory, motor, integrative nuclei, and pathways along brain stem  Determined by complex interactions between reticular formation and cerebral cortex  Reticular Activating System (RAS)
 Important brain stem component
 Diffuse network in reticular formation
 Extends from medulla oblongata to mesencephalon
 Output of RAS projects to thalamic nuclei that influence large areas of cerebral
 When RAS inactive, so is cerebral cortex  Stimulation of RAS produces widespread activation of cerebral cortex  Arousal and the Reticular Activating System  Any stimulus activates reticular formation and RAS  Arousal occurs rapidly  Effects of single stimulation of RAS last less than a minute  Activity in cerebral cortex, basal nuclei, and sensory and motor pathways continue to stimulate – after many hours, reticular formation becomes less responsive to stimulation – individual becomes less alert and more lethargic – neural fatigue reduces RAS activity  Involves interplay between brain stem nuclei that use different neurotransmitters  Group of nuclei stimulates RAS with NE and maintains awake, alert state  Other group promotes deep sleep by depressing RAS activity with serotonin  “Dueling” nuclei located in brain stem  Destruction of ACh-secreting and GABA-secreting neurons in basal nuclei  Symptoms appear as basal nuclei and frontal lobes slowly degenerate  Difficulty controlling movements  Intellectual abilities gradually decline  Powerful hallucinogenic drug
 Activates serotonin receptors in brain stem, hypothalamus, and limbic
 Compounds that enhance effects also produce hallucinations (LSD)  Compounds that inhibit or block action cause severe depression and  Variations in levels affect sensory interpretation and emotional states  Fluoxetine (Prozac)  Slows removal of serotonin at synapses  Increases serotonin concentrations at postsynaptic membrane  Classified as selective serotonin reuptake inhibitors (SSRIs)  Other SSRIs:  Inadequate dopamine production causes motor problems
 Dopamine
 Secretion stimulated by amphetamines, or “speed”  Large doses can produce symptoms resembling schizophrenia  Important in nuclei that control intentional movements  Important in other centers of diencephalon and cerebrum  Anatomical and physiological changes begin after maturity (age  Accumulate over time  85% of people over age 65 have changes in mental  Decrease in volume of cerebral cortex  Narrower gyri and wider sulci  Larger subarachnoid space  Brain shrinkage linked to loss of cortical neurons  No neuronal loss in brain stem nuclei  Fatty deposits in walls of blood vessels  Reduces blood flow through arteries  Increases chances of rupture  Cerebrovascular accident (CVA), or stroke  May damage surrounding neural tissue  Changes in Synaptic Organization of Brain  Number of dendritic branches, spines, and interconnections decreases  Synaptic connections lost  Rate of neurotransmitter production declines  Intracellular and Extracellular Changes in CNS Neurons  Neurons in brain accumulate abnormal intracellular deposits  Lipofuscin  Granular pigment with no known function  Masses of neurofibrils form dense mats inside cell body and axon  Intracellular and Extracellular Changes in CNS Neurons  Extracellular accumulations of fibrillar proteins  Surrounded by abnormal dendrites and axons  Contain deposits of several peptides  Primarily two forms of amyloid ß (Aß) protein  Appear in brain regions specifically associated with memory processing  Linked to functional changes  Neural processing becomes less efficient with age  Memory consolidation more difficult  Secondary memories harder to access  Hearing, balance, vision, smell, and taste become less acute  Reaction times slowed  Reflexes weaken or disappear  Precision decreases  Takes longer to perform  85% of elderly population develops changes that do not interfere with  Some individuals become incapacitated by progressive CNS changes  Also called senile dementia  Degenerative changes  Memory loss  Anterograde amnesia (lose ability to store new memories)  Emotional disturbances  Monitors all other systems  Issues commands that adjust their activities  Like conductor of orchestra  Neural Tissue  Extremely delicate  Extracellular environment must maintain homeostatic limits  If regulatory mechanisms break down, neurological disorders appear  Parkinson disease, Alzheimer disease  Physicians trace source of specific problem  Evaluate sensory, motor, behavioral, and cognitive functions of

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