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Chapter 16: Neural Integration II: The Autonomic Nervous System and Higher-Order Functions Somatic Nervous System (SNS) • Operates under conscious control • Seldom affects long-term survival Autonomic Nervous System (ANS) • Operates without conscious instruction • Coordinates systems functions: – cardiovascular – respiratory – digestive – urinary – reproductive Organization Similarities of SNS and ANS Figure 16–2 Organization Similarities of SNS and ANS • Are efferent divisions • Carry motor commands: – SNS controls skeletal muscles – ANS controls visceral effectors PLAY The Organization of the Somatic and Autonomic Nervous Systems The SNS Figure 16–2a The SNS • Motor neurons of central nervous system • Direct control over skeletal muscles The ANS Figure 16–2b The ANS • Motor neurons synapse on visceral motor neurons in autonomic ganglia • Ganglionic neurons control visceral effectors 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 • Part of visceral reflex arcs Preganglionic Fibers • Axons of preganglionic neurons • Leave CNS and synapse on ganglionic neurons Autonomic Ganglia • Peripheral ganglia • Contain many ganglionic neurons • Ganglionic neurons innervate visceral effectors: – cardiac muscle – smooth muscle – glands – adipose tissues Postganglionic Fibers • Axons of ganglionic neurons • Begin at autonomic ganglia: – extend to peripheral target organs Somatic or Visceral Sensory Information • Trigger visceral reflexes • Motor commands of reflexes distributed by ANS Motor Commands • May control activities of target organs • May alter ongoing activity • Changes in visceral activity: – postganglionic fibers release neurotransmitters Sympathetic Division • Does not “Kick in” only during exertion, stress, or emergency (common misconception) • Some aspects of the system are functioning in visceral reflexes for normal activity. (pupil dilation and water balance, for instance) Parasympathetic Division • Controls during resting conditions • Tends to conserve energy • Allows for “quiet functions” (e.g. digestion, defecation, etc.) Divisions of the ANS • 2 divisions may work independently: – some structures innervated by only 1 division • 2 divisions may work together: – each controlling one stage of a complex process Sympathetic Division • Preganglionic fibers (thoracic and superior lumbar) synapse in ganglia near spinal cord • Preganglionic fibers are short • Postganglionic fibers are long ANS: Sympathetic Division Figure 16–3 Fight or Flight • Sympathetic division readies body for crisis • Increase in sympathetic activity: – stimulates tissue metabolism – increases alertness 7 Responses to Increased Sympathetic Activity 1. 2. 3. 4. 5. Heightened mental alertness Increased metabolic rate Reduced digestive and urinary functions Energy reserves activated Increased respiratory rate and respiratory passageways dilate 6. Increased heart rate and blood pressure 7. Sweat glands activated Structure of the Sympathetic Division • Preganglionic neurons located between segments T1 and L2 of spinal cord • Ganglionic neurons in ganglia near vertebral column • Cell bodies of preganglionic neurons in lateral gray horns • Axons enter ventral roots of segments Ganglionic Neurons • Occur in 3 locations: – sympathetic chain ganglia – collateral ganglia – adrenal medullae Figure 16–4 Sympathetic Chain Ganglia • Are on both sides of vertebral column • Control effectors: – in body wall – inside thoracic cavity – in head – in limbs Sympathetic Chain Ganglia Figure 16–4a Collateral Ganglia • Are anterior to vertebral bodies • Contain ganglionic neurons that innervate tissues and organs in abdominopelvic cavity Collateral Ganglia Figure 16–4b 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 Pattern of Responses to Increased Levels of Parasympathetic Activity • Decreased: – metabolic rate – heart rate and blood pressure • Increased: – salivary and digestive glands secretion – 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 The Adrenal Medullae Figure 16–4c Modified Sympathetic Ganglion • At the center of each adrenal gland in area known as adrenal medulla • Very short axons • When stimulated, release neurotransmitters into bloodstream (not at synapse) • Functions as hormones affect target cells throughout body Fibers in Sympathetic Division • Preganglionic fibers: – are relatively short – ganglia located near spinal cord • Postganglionic fibers: – are relatively long, except at adrenal medullae • Ventral roots of spinal segments T1–L2 contain sympathetic preganglionic fibers Ventral Roots • Give rise to myelinated white ramus • Carry myelinated preganglionic fibers into sympathetic chain ganglion • May synapse at collateral ganglia or in adrenal medullae Preganglionic Fibers • 1 preganglionic fiber synapses on many ganglionic neurons • Fibers interconnect sympathetic chain ganglia • Each ganglion innervates particular body segment(s) Postganglionic Fibers • Paths of unmyelinated postganglionic fibers depend on targets Sympathetic Innervation PLAY Figure 16–5 The Distribution of Sympathetic Innervation Sympathetic Chain • • • • • 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) – gray rami (unmyelinated postganglionic fibers) Rami • Only spinal nerves T1–L2 have white rami • Every spinal nerve has gray ramus: – that carries sympathetic postganglionic fibers for distribution in body wall Postganglionic Sympathetic Fibers • In head and neck leave superior cervical sympathetic ganglia • Supply the regions and structures innervated by cranial nerves III, VII, IX, X Abdominopelvic Viscera • Receive sympathetic innervation via sympathetic preganglionic fibers • Synapse in separate collateral ganglia 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 Postganglionic Fibers • Leave collateral ganglia • Extend throughout abdominopelvic cavity • Innervate variety of visceral tissues and organs Preganglionic Fibers • From 7 inferior thoracic segments: – end at celiac ganglion or superior mesenteric ganglion • Ganglia embedded in network of autonomic nerves • From lumbar segments: – form splanchnic nerves – end at inferior mesenteric ganglion Celiac Ganglion • Pair of interconnected masses of gray matter • May form single mass or many interwoven masses • Postganglionic fibers innervate stomach, liver, gallbladder, pancreas, and spleen Superior Mesenteric Ganglion • Near base of superior mesenteric artery • Postganglionic fibers innervate small intestine and proximal 2/3 of large intestine Inferior Mesenteric Ganglion • Near base of inferior mesenteric artery • Postganglionic fibers provide sympathetic innervation to portions of large intestine, kidney, urinary bladder, and sex organs Neurotransmitters of the sympathetic division Neuroendocrine Cells of Adrenal Medullae • Secrete neurotransmitters epinephrine (E) and norepinephrine (NE) • Since they are carried in the blood they are actually considered hormones Epinephrine • Also called adrenaline • Is 75–80% of secretory output • Remaining is noradrenaline (NE) Sympathetic Division • Can change activities of tissues and organs by: – releasing NE at peripheral synapses – distributing E and NE throughout body in bloodstream Crisis Mode • Entire division responds (sympathetic activation) • Are controlled by sympathetic centers in hypothalamus • Effects are not limited to peripheral tissues • Alters CNS activity 5 Effects of Sympathetic Activation 1. 2. 3. 4. 5. 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 Cholinergic Synapses • Use ACh as transmitter • Excitatory effect on ganglionic neurons Stimulation of Ganglionic Neurons • Releases neurotransmitters at specific target organs from telodendria • Form branching network instead of synaptic knobs Sympathetic Varicosities • Resemble string of pearls • Packed with neurotransmitter vesicles Figure 16–6 Chains of Varicosities • • • • Formed from postganglionic neurons Pass along or near surface of effector cells No specialized postsynaptic membranes Membrane receptors on surfaces of target cells • Release NE Adrenergic Neurons • Use NE as neurotransmitter Varicosities and ACh • Some ganglionic neurons release ACh instead of NE • Are located in body wall, skin, brain, and skeletal muscles NE Released by Varicosities • Affects targets until reabsorbed or inactivated • 50–80% of NE is reabsorbed by varicosities: – is reused or broken down by MAO • The rest diffuses out or is broken down by enzymes Duration of Effects on Postsynaptic Membrane • NE persist for a few seconds • ACh only for 20 msec Effects of NE or E Released by Adrenal Medullae Last longer because: – bloodstream does not contain MAO or COMT – most tissues contain low concentrations 2 Classes of Sympathetic Receptors • Alpha receptors • Beta receptors Norepinephrine • Stimulates alpha receptors to greater degree than beta receptors Epinephrine • Stimulates both classes of receptors Localized Sympathetic Activity • Involves release of NE at varicosities • Primarily affects alpha receptors near active varicosities Generalized Sympathetic Activation • Release of E by adrenal medulla • Affect alpha and beta receptors throughout body Stimulation of Alpha (a) Receptors • Activates enzymes on inside of cell membrane • Alpha-1 (a1) • Alpha-2 (a2) Alpha-1 (a1) • More common type of alpha receptor • Releases intracellular calcium ions from reserves in endoplasmic reticulum • Has excitatory effect on target cell Alpha-2 (a2) • Lowers cAMP levels in cytoplasm • Has inhibitory effect on the cell • Helps coordinate sympathetic and parasympathetic activities Beta () Receptors • Affect membranes in many organs (skeletal muscles, lungs, heart, and liver) • Trigger metabolic changes in target cell • Changes occur indirectly • Each is a G protein • Stimulation increases intracellular cAMP levels Beta Receptors • Two types: – Beta-1 (1) Increases metabolic activity – Beta-2 (2) • Causes inhibition • Triggers relaxation of smooth muscles along respiratory tract Beta-3 (3) • Found in adipose tissue • Leads to lipolysis, the breakdown of triglycerides in adipocytes • Releases fatty acids into circulation Sympathetic Postganglionic Fibers • Mostly adrenergic (release NE) • A few cholinergic (release ACh) • Innervate sweat glands of skin and blood vessels of skeletal muscles and brain • Stimulate sweat gland secretion and dilates blood vessels ACh • Released by parasympathetic division • Body wall and skeletal muscles are not innervated by parasympathetic division • Both NE and ACh needed to regulate visceral functions Nitroxidergic Synapses • Release nitric oxide (NO) as neurotransmitter • Neurons innervate smooth muscles in walls of blood vessels in skeletal muscles and the brain • Produces vasodilation and increased blood flow Summary of Sympathetic Division (1 of 3) • Includes 2 sets of sympathetic chain ganglia, 1 on each side of vertebral column • 3 collateral ganglia anterior to vertebral column • 2 adrenal medullae • Preganglionic fibers are short because ganglia are close to spinal cord Summary of Sympathetic Division (2 of 3) • Postganglionic fibers are longer and stretch to reach target organs • Single preganglionic fiber may innervate 2 dozen or more ganglionic neurons in different ganglia Summary of Sympathetic Division (3 of 3) • Preganglionic neurons release ACh; most postganglionic fibers release NE, few release ACh or NO • Effector response depends on second messengers activated when NE or E binds to alpha or beta receptors ANS: The Parasympathetic Division Autonomic Nuclei • Are contained in the mesencephalon, pons, and medulla oblongata: – associated with cranial nerves III, VII, IX, X • In lateral gray horns of spinal segments S2–S4 Ganglionic Neurons in Peripheral Ganglia • Preganglionic fiber synapses on 6–8 ganglionic neurons: – terminal ganglion: • near target organ • usually paired – intramural ganglion: • embedded in tissues of target organ • interconnected masses • clusters of ganglion cells Pattern of Parasympathetic Division • All ganglionic neurons in same ganglion • Postganglionic fibers influence same target organ • Effects of parasympathetic stimulation more specific and localized What are the mechanisms of neurotransmitter release in the parasympathetic division? Parasympathetic Preganglionic Fibers • Leave brain as components of cranial nerves: – III (oculomotor) – VII (facial) – IX (glossopharyngeal) – X (vagus) PLAY The Distribution of Parasympathetic Innervation 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 Vagus Nerve • Preganglionic parasympathetic innervation to structures in: – neck – thoracic and abdominopelvic cavity – distal portion of large intestine • Provides 75% of all parasympathetic outflow • Branches intermingle with fibers of sympathetic division Sacral Segments of Spinal Cord • Preganglionic fibers carry sacral parasympathetic output • Do not join ventral roots of spinal nerves Pelvic Nerves • Innervate intramural ganglia in walls of: – kidneys – urinary bladder – portions of large intestine – sex organs Parasympathetic Activation • Centers on relaxation, food processing, and energy absorption • Localized effects, last a few seconds at most 10 Effects of Parasympathetic Activation 1. Constriction of pupils: – restricts light entering eyes 2. Secretion by digestive glands: – exocrine and endocrine 3. Secretion of hormones 4. Changes in blood flow and glandular activity: – associated with sexual arousal 5. Increases smooth muscle activity: – along digestive tract 6. Defecation: – stimulation and coordination 7. Contraction of urinary bladder: – during urination 8. Constriction of respiratory passageways 9. Reduction in heart rate: – and force of contraction 10. Sexual arousal: – stimulation of sexual glandsSexual arousal: – stimulation of sexual glands Parasympathetic Neurons • • • • All release ACh as neurotransmitter Effects vary widely Inactivated by AChE at synapse Ach is also inactivated by pseudocholinesterase in surrounding tissues 2 Types of ACh Receptors on Postsynaptic Membranes • Nicotinic receptors • Muscarinic receptors Nicotinic Receptors • On surfaces of ganglion cells (sympathetic and parasympathetic) • At neuromuscular junctions of somatic nervous system Action of Nicotinic Receptors • Exposure to ACh causes excitation of ganglionic neuron or muscle fiber • Open chemically gated channels in postsynaptic membrane Muscarinic Receptors • At cholinergic neuromuscular or neuroglandular junctions (parasympathetic) • At few cholinergic junctions (sympathetic) • G proteins Action of Muscarinic Receptors • Effects are longer lasting than nicotinic receptors • Response reflects activation or inactivation of specific enzymes • Can be excitatory or inhibitory Toxins • Produce exaggerated, uncontrolled responses • Nicotine: – binds to nicotinic receptors – targets autonomic ganglia and skeletal neuromuscular junctions • Muscarine: – binds to muscarinic receptors – targets parasympathetic neuromuscular or neuroglandular junctions Nicotine Poisoning • 50 mg ingested or absorbed through skin • Symptoms: – vomiting, diarrhea, high blood pressure, rapid heart rate, sweating, profuse salivation, convulsions • May result in coma or death Muscarine Poisoning • Symptoms: – salivation, nausea, vomiting, diarrhea, constriction of respiratory passages, low blood pressure, slow heart rate (bradycardia) ANS: Adrenergic and Cholinergic Receptors Comparing Sympathetic and Parasympathetic Divisions • Sympathetic: – widespread impact – reaches organs and tissues throughout body • Parasympathetic: – innervates only specific visceral structures Differences between Sympathetic and Parasympathetic Divisions Figure 16–9 Summary: Sympathetic and Parasympathetic Divisions Table 16-2 Dual Innervation • Most vital organs receive instructions from both sympathetic and parasympathetic divisions • 2 divisions commonly have opposing effects Summary: Comparing Sympathetic and Parasympathetic Divisions Table 16-3 (1 of 2) Summary: Comparing Sympathetic and Parasympathetic Divisions Table 16-3 (2 of 2) Anatomy of Dual Innervation • Parasympathetic postganglionic fibers accompany cranial nerves to peripheral destinations • Sympathetic innervation reaches same structures by traveling directly from superior cervical ganglia of sympathetic chain Structure: Autonomic Plexuses • Nerve networks in the thoracic and abdominopelvic cavities: – are formed by mingled sympathetic postganglionic fibers and parasympathetic preganglionic fibers • Travel with blood and lymphatic vessels that supply visceral organs 6 Autonomic Plexuses 1. 2. 3. 4. 5. 6. Cardiac plexus Pulmonary plexus Esophageal plexus Celiac plexus Inferior mesenteric plexus Hypogastric plexus The Autonomic Plexuses Figure 16–10 Autonomic Motor Neurons • Maintains resting level of spontaneous activity • Background level of activation determines autonomic tone 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 activity Autonomic Tone and Dual Innervation • Significant where dual innervation occurs: – 2 divisions have opposing effects • More important when dual innervation does not occur Visceral Reflexes ANS • Simple reflexes from spinal cord provide rapid and automatic responses • Complex reflexes coordinated in medulla oblongata Medulla Oblongata • Contains centers and nuclei involved in: – salivation – swallowing – digestive secretions – peristalsis – urinary function • Regulated by hypothalamus Hypothalamus • Interacts with all other portions of brain Enteric Nervous System • 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 Characteristics of Higher-Order Functions • Require cerebral cortex • Involve conscious and unconscious information processing • Not part of programmed “wiring” of brain • Can adjust over time Memories Stored bits of information gathered through experience • Declarative memory – Facts • Skill Memory – Learned motor behaviors – Incorporated at unconscious level with repetition – Programmed behaviors stored in appropriate area of brain stem Short & Long Term Memories Short Term • Information that can be recalled immediately • Contain small bits of information Long Term • Can last a life time 2 Types of Long-Term Memory • Secondary memories fade and require effort to recall • Tertiary memories are with you for life Long-Term Memories • Most stored in cerebral cortex • Conscious motor and sensory memories referred to association areas Memory Storage Brain Structures and Memory • Amygdaloid body and hippocampus: – are essential to memory consolidation Damage to the Hippocampus • Inability to convert short-term memories to new long-term memories • Existing long-term memories remain intact and accessible Occipital and Temporal Lobes • Special portions crucial to memories of faces, voices, and words “Grandmother cells” • Specific neuron activated by combination of sensory stimuli associated with particular individual (grandmother) Memories Stored In • • • • • 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 Memory Consolidation at Cellular Level • Involves anatomical, physiological changes in neurons, synapses Increased Neurotransmitter Release • Frequently active synapse increases the amount of neurotransmitter it stores • Releases more on each stimulation • The more neurotransmitter released, the greater effect on postsynaptic neuron Facilitation at Synapses (1 of 2) • Neural circuit repeatedly activated • Synaptic terminals begin continuously releasing neurotransmitter • Neurotransmitter binds to receptors on postsynaptic membrane Facilitation at Synapses (2 of 2) • Produce 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 neuron Memory Engram • Single circuit corresponds to single memory • Form as result of experience and repetition Factors of Conversion of short to long term memory • Nature, intensity, and frequency of original stimulus • Strong, repeated, and exceedingly pleasant or unpleasant events likely converted to long-term memories 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 States of Consciousness • Many gradations of both states • Degree of wakefulness indicates level of ongoing CNS activity • When abnormal or depressed, state of wakefulness is affected 2 types of Sleep • Characteristic patterns of brain wave activity – deep sleep – REM Figure 16–14a 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 30% 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 Significance of Sleep • Has important impact on CNS • 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 Arousal • Awakening from sleep • Function of reticular formation Reticular Activating System (RAS) • Important brain stem component • Diffuse network in reticular formation • Extends from medulla oblongata to mesencephalon Reticular Activating System (RAS) Figure 16–15 Ending Sleep • Any stimulus activates reticular formation and RAS • Arousal occurs rapidly • Effects of single stimulation of RAS last less than a minute Regulation of Awake–Asleep Cycles • 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 Drugs and Clinical Considerations Lysergic Acid Diethylamide (LSD) • Powerful hallucinogenic drug • Activates serotonin receptors in brain stem, hypothalamus, and limbic system Serotonin • Compounds that enhance effects also produce hallucinations • Compounds that inhibit or block action cause severe depression and anxiety • 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: – Celexa, Luvox, Paxil, and Zoloft Parkinson’s Disease • Inadequate dopamine production causes motor problems Huntington’s Disease • Destruction of ACh-secreting and GABAsecreting neurons in basal nuclei • Symptoms appear as basal nuclei and frontal lobes slowly degenerate • Difficulty controlling movements • Intellectual abilities gradually decline 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 Aging • Anatomical and physiological changes begin after maturity (age 30) • Accumulate over time • 85% of people over age 65 have changes in mental performance and CNS function Reduction in Brain Size and Weight • Decrease in volume of cerebral cortex • Narrower gyri and wider sulci • Larger subarachnoid space Reduction in Number of Neurons • Brain shrinkage linked to loss of cortical neurons • No neuronal loss in brain stem nuclei Decrease in Blood Flow to Brain • Arteriosclerosis: – fatty deposits in walls of blood vessels – reduce blood flow through arteries – increase chances of rupture • Cerebrovascular accident (CVA), or stroke: – may damage surrounding neural tissue Intracellular and Extracellular Changes in CNS Neurons • Neurons in brain accumulate abnormal intracellular deposits • Including lipofuscin and neurofibrillary tangles Incapacitation • 85% of elderly population develops changes that do not interfere with abilities • Some individuals become incapacitated by progressive CNS changes Senility • Also called senile dementia • Degenerative changes: – memory loss – anterograde amnesia – emotional disturbances • Alzheimer’s disease is most common That’s it (phew!)