An Introduction to the ANS and Higher-Order Functions

An Introduction to the ANS and Higher-Order Functions
Learning Outcomes 16-1 Compare the organization of the autonomic nervous system with that of the somatic nervous system. 16-2 Describe the structures and functions of the sympathetic and parasympathetic division of the autonomic nervous system. 16-3 Describe the mechanisms of sympathetic and parasympathetic neurotransmitter release and their effects on target organs and tissues.

Learning Outcomes. 16-4 Describe the hierarchy of interacting levels of control in the autonomic nervous system, including the significance of visceral reflexes. 16-5 Summarize the effects of aging on the nervous system and give examples of interactions between the nervous system and other organ systems.

Somatic Nervous System (SNS) Operates under conscious control Seldom affects long-term survival SNS controls skeletal muscles Autonomic Nervous System (ANS) Operates without conscious instruction ANS controls visceral effectors Coordinates vitals system functions Cardiovascular, respiratory, digestive, urinary, reproductive 5 year survival after heart attack: increased since 1960 Since 1960 the understanding of the ANS and how to imitate it to regulate blood pressure increased the survival rate after a Hear attack

16-1 Autonomic Nervous System
Organization of the ANS Integrative centers  ViscMotN (PreGN)  G  PostGN  Efec Integrative centers For autonomic activity in hypothalamus Neurons here are comparable to upper motor neurons in SNS Synapses with ganglionic neurons Centros integradores 0 Hipotalamo Neuronas motoras viscerales en CNS Neuronas pregangionares Ganglio Neuronas ganglionares Efectores

Organization of the ANS 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 Centros integradores 0 Hipotalamo Neuronas motoras viscerales en CNS Neuronas pregangionares Ganglio Neuronas ganglionares Efectores

Visceral Motor Neurons Autonomic ganglia Contain many ganglionic neurons Ganglionic neurons innervate visceral effectors Such as cardiac muscle, smooth muscle, glands, and adipose tissue Postganglionic fibers Axons of ganglionic neurons Centros integradores 0 Hipotalamo Neuronas motoras viscerales en CNS Neuronas pregangionares Ganglio Neuronas ganglionares Efectores

Motor neurons of the CNS exerts direct control over skeletal muscles
Figure 16-1a The Organization of the Somatic and Autonomic Nervous Systems. Upper motor neurons in primary motor cortex Brain Somatic motor nuclei of brain stem Skeletal muscle Lower motor neurons Spinal cord Neuronas motoras superior Neurona motora inferior Efector Somatic motor nuclei of spinal cord Motor neurons of the CNS exerts direct control over skeletal muscles Skeletal muscle a Somatic nervous system

visceral motor neurons in autonomic ganglia, and
Figure 16-1b The Organization of the Somatic and Autonomic Nervous Systems. Visceral motor nuclei in hypothalamus Brain Preganglionic neuron Visceral Effectors Smooth muscle Autonomic nuclei in brain stem Autonomic ganglia Glands Cardiac muscle Ganglionic neurons Spinal cord Adipocytes Centros integradores 0 Hipotalamo Neuronas motoras viscerales en CNS -Neuronas pregangionares Ganglio Neuronas ganglionares Efectores Autonomic nuclei in spinal cord Motor neurons of the CNS synapse on visceral motor neurons in autonomic ganglia, and these ganglionic neurons control visceral effectors Preganglionic neuron b Autonomic nervous system

16-1 Divisions of the ANS The Autonomic Nervous System
Operates largely outside our awareness Control activities of target organs Modify or alter some ongoing activity Two divisions Sympathetic division Increases alertness, metabolic rate, and muscular abilities Kicks in only during exertion, stress, or emergency (F or F) Parasympathetic division Reduces metabolic rate and promotes digestion Controls during resting conditions (R and D) Control del musculo erector del pili, en frios… Modifica frecuencia cardiaca y actividad digestiva al msmo momento que saltas de un susto

16-1 Divisions of the ANS Sympathetic and Parasympathetic Division
Most often, these two divisions have opposing effects (antagonist) If the sympathetic division causes excitation, the parasympathetic causes inhibition The two divisions may also work independently Only one division innervates some structures The two divisions may work together, with each controlling one stage of a complex process

16-1 Divisions of the ANS Sympathetic Division –Preganglionic fibers originates in thoracic and superior lumbar; (thoracolumbar, between T1 – L2 segments) Synapse in ganglia near spinal cord Preganglionic fibers are short Postganglionic fibers are long Prepares body for crisis, producing a “fight or flight” response Stimulates tissue metabolism Increases alertness

16-1 Divisions of the ANS 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

16-1 Divisions of the ANS Parasympathetic Division
Preganglionic fibers originate in brain stem and sacral segments of spinal cord; craniosacral Synapse in ganglia close to (or within) target organs Preganglionic fibers are long Postganglionic fibers are short Parasympathetic division stimulates visceral activity Conserves energy and promotes sedentary activities

16-1 Divisions of the ANS Five Responses to Increased Parasympathetic Activity Decreased metabolic rate Decreased heart rate and blood pressure Increased secretion by salivary and digestive glands Increased motility and blood flow in digestive tract Urination and defecation stimulation

Figure 16-2 Overview of the Autonomic Nervous System (Part 1 of 2).
Sympathetic Division (Thoracolumbar) Preganglionic Neurons Preganglionic neurons are located in the lateral gray horns of spinal segments T1–L2. Ganglia Ganglia are located near the spinal cord. Preganglionic fibers release acetylcholine (Ach), stimulating ganglionic neurons. Target Organs Most postganglionic fibers release norepinephrine (NE) at neuroeffector junctions. Sympathetic activation “Fight or flight” response KEY Preganglionic fibers Postganglionic fibers

Figure 16-2 Overview of the Autonomic Nervous System (Part 2 of 2).
Parasympathetic Division (Craniosacral) Preganglionic Neurons Preganglionic neurons in brain stem and in lateral portion of anterior gray horns of S2–S4. Ganglia Ganglia are in or near the target organ. Preganglionic fibers release acetylcholine (Ach), stimulating ganglionic neurons. Target Organs All postganglionic fibers release Ach at neuroeffector junctions. Parasympathetic stimulation “Rest and digest” response KEY Preganglionic fibers Postganglionic fibers

16-1 Divisions of the ANS Enteric Nervous System (ENS)
Third division of ANS Extensive network in digestive tract walls Complex visceral reflexes coordinated locally plus influence of sympathetic and parasympathethic divisions Neurotransmitters are the same found in the brain

16-2 The Sympathetic Division
Ganglionic Neurons Occur in three locations Sympathetic chain ganglia On both sides of vertebral column (paravertebral) Control effectors: In body wall Inside thoracic cavity In head, and limbs Collateral ganglia Are anterior to vertebral bodies (prevertebral) Innervate tissues and organs in abdominopelvic cavity

Figure 16-3a Sites of Ganglia in Sympathetic Pathways.
SYMPATHETIC CHAIN GANGLIA Spinal nerve Preganglionic neuron Autonomic ganglion of right sympathetic chain Autonomic ganglion of left sympathetic chain Innervates visceral effectors by spinal nerves White ramus Sympathetic nerve (postganglionic fibers) Ganglionic neuron Gray ramus Innervates visceral organs in thoracic cavity by sympathetic nerves KEY Preganglionic neurons Note: Both innervation patterns occur on each side of the body. Ganglionic neurons

Figure 16-3b Sites of Ganglia in Sympathetic Pathways.
COLLATERAL GANGLIA Lateral gray horn Splanchnic nerve (preganglionic fibers) White ramus Innervates visceral organs in abdominopelvic cavity Collateral ganglion Postganglionic fibers

3. Adrenal Medullae (Suprarenal Medullae) Modified sympathetic ganglia Center suprarenal medulla Very short axons When stimulated, release neurotransmitters into bloodstream (not at synapse) Neurotransmitters then function as hormones to affect target cells throughout body

Figure 16-3c Sites of Ganglia in Sympathetic Pathways.
THE ADRENAL MEDULLAE Preganglionic fibers Adrenal medullae Secretes neurotransmitters into general circulation Endocrine cells (specialized ganglionic neurons)

Fibers in Sympathetic Division Preganglionic fibers Are relatively short Ganglia located near spinal cord Postganglionic fibers Are relatively long Except at adrenal medullae

Organization and Anatomy of the Sympathetic Division Ventral roots of spinal segments T1–L2 contain sympathetic preganglionic fibers Carry myelinated preganglionic fibers into sympathetic chain ganglion May synapse at collateral ganglia or in adrenal medullae

Sympathetic Chain Ganglia Preganglionic fibers One preganglionic fiber synapses on many ganglionic neurons Fibers interconnect sympathetic chain ganglia Each ganglion innervates particular body segment(s) 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

Sympathetic Chain Ganglia Postganglionic fibers control visceral effectors In body wall, head, neck, or limbs Postganglionic fibers innervate effectors Sweat glands of skin Smooth muscles in superficial blood vessels Postganglionic fibers innervating structures in thoracic cavity form bundles Sympathetic nerves

Sympathetic Chain Ganglia 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

Figure 16-4 The Distribution of Sympathetic Innervation (Part 2 of 4).
Eye Pons Salivary glands Sympathetic nerves Heart Cardiac and pulmonary plexuses T1 T2 T3 Lung KEY T4 Preganglionic fibers Postganglionic fibers

Figure 16-4 The Distribution of Sympathetic Innervation (Part 3 of 4).
Greater splanchnic nerve KEY T2 Preganglionic fibers T3 Postganglionic fibers Celiac ganglion T4 T5 Superior mesenteric ganglion T6 Liver and gallbladder T7 T8 Stomach T9 Lesser splanchnic nerve Spleen T10 Pancreas T11 T12 Large intestine L1 L2 Lumbar splanchnic nerves Inferior mesenteric ganglion Small intestine L3 L4 L5 Adrenal medulla S1 S2 Sacral splanchnic nerves S3 S4 Kidney S5 Coccygeal ganglia (Co1) fused together (ganglion impar) Uterus Ovary Penis Scrotum Urinary bladder

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

Collateral Ganglia Postganglionic fibers 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

Collateral Ganglia Preganglionic fibers from inferior thoracic segments End at celiac ganglion or superior mesenteric ganglion Preganglionic fibers from lumbar segments Form splanchnic nerves End at inferior mesenteric ganglion

Collateral Ganglia Celiac ganglion Postganglionic fibers innervate stomach, liver, gallbladder, pancreas, and spleen Superior mesenteric ganglion Postganglionic fibers innervate small intestine and proximal 2/3 of large intestine Inferior mesenteric ganglion Postganglionic fibers provide sympathetic innervation to portions of: Large intestine Kidney Urinary bladder Sex organs

Adrenal Medullae Preganglionic fibers entering adrenal gland proceed to center (adrenal medulla) Modified sympathetic ganglion Preganglionic fibers synapse on neuroendocrine cells Specialized neurons secrete hormones into bloodstream

Adrenal Medullae Neuroendocrine cells Secrete neurotransmitters epinephrine (E) and norepinephrine (NE) Epinephrine Also called adrenaline Is 75–80 percent of secretory output Remaining is norepinephrine (NE) Noradrenaline

Adrenal Medullae Bloodstream carries neurotransmitters through body Causing changes in metabolic activities of different cells Including cells NOT innervated by sympathetic postganglionic fibers Effects last longer Hormones continue to diffuse out of bloodstream

Sympathetic Activation Change activities of tissues and organs by: Releasing NT at peripheral synapses Distributing E and NE throughout body in bloodstream Target specific effectors, smooth muscle fibers in blood vessels of skin Are activated in reflexes Do not involve other visceral effectors

Changes Caused by Sympathetic Activation Increased alertness Feelings of energy and euphoria Change in breathing Elevation in muscle tone Mobilization of energy reserves

16-3 Various Sympathetic Neurotransmitters
Stimulation of Sympathetic Preganglionic Neurons Releases ACh at synapses with ganglionic neurons Excitatory effect on ganglionic neurons Ganglionic Neurons Release neurotransmitters (NE, ACh) at specific target organs

Ganglionic Neurons Axon terminals Release NE at most varicosities Called adrenergic neuron Monoamine oxidase (MAO) Catechol O methyltransferase (COMT) Some ganglionic neurons release ACh instead Are located in body wall, skin, brain, and skeletal muscles Called cholinergic neurons AChe NE dura mas porque en la sangre no hay MAO ni COMT En los tejoidos hay bajos niveles de ellas Hasta 30 seg Vs 20 msec de Ach

Figure 16-5 Sympathetic Varicosities.
Preganglionic fiber (myelinated) Ganglionic neuron Postganglionic fiber (unmyelinated) Ganglion Varicosities Vesicles containing norepinephrine (NE) Mitochondrion Schwann cell cytoplasm Varicosities es para SNA lo que union neuromuscular es para SNS 5 μm Smooth muscle cells Varicosities

Sympathetic Stimulation and the Release of NE and E Effects occurs primarily from interactions of NE and E with: Alpha receptors NE more potent E same potency Beta receptors NE less potent Two types of adrenergic membrane receptors Activates enzymes on inside of cell membrane via G proteins (2nd messengers) PLT – estimulacion simpatica localizada que provoca liberacion de NE afecta mas receptores alfa - estimulacion generalizada que provoca liberacion de E por las suprarenales afecta todos los receptores por todo el cuerpo

Alpha receptors Alpha-1 (1) More common type of alpha receptor Releases intracellular calcium ions from reserves in endoplasmic reticulum Has excitatory effect on target cell In smooth muscles Vessels constriction Closing sphincters

Alpha receptors Alpha-2 (2) Lowers cAMP levels in cytoplasm Has inhibitory effect on the cell Helps coordinate sympathetic and parasympathetic activities When sympathetic division is active: NE is released Binds to 2, on parasympathetic efectors (neuromuscular and neuroglandular) and inhibits their activity

Beta () receptors Affect membranes in many organs (skeletal muscles, lungs, heart, and liver) Trigger metabolic changes in target cell via G proteins Stimulation increases intracellular cAMP levels Three Main Types of Beta Receptors Beta-1 (1) Beta-2 (2) Beta-3 (3)

Three Main Types of Beta Receptors Beta-1 (1) Increases metabolic activity, skeletal muscle Heart, increase heart rate and force of contraction Beta-2 (2) (inhibition) Triggers relaxation of smooth muscles along respiratory tract Easier breathing, respiratory therapy Beta-3 (3) Leads to lipolysis, the breakdown of triglycerides in adipocytes Make fatty acids available for other tissues

Sympathetic Stimulation and the Release of Ach 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 La mayoria de fibras simpaticas liberan NE Las menos liberan Ach

Sympathetic Stimulation and the Release of NO Nitroxidergic synapses Release nitric oxide (NO) as neurotransmitter Neurons innervate smooth muscles in walls of blood vessels in skeletal muscles and the brain Produce vasodilation and increased blood flow

Summary: Sympathetic Division
Includes: 2 sets of chain ganglia 3 collateral ganglia two adrenal ganglia Preganglionic fibers shorts, post ganglionic are long ganglia are near spinal cord Adrenal: very short fibers direct to bloodstream Extensive divergence: a single sympathetic motor neuron can control a variety of visceral effectors producing a complex and coordinated response.

Summary: Sympathetic Division
All preG neurons release ACh at synapses with ganglionic neurons Most postG neurons release NE a few release Ach or NO The effector response depends on the 2nd messenger triggered by activation of G proteins by NE o E to α or β receptors.

16-4 The Parasympathetic Division
Autonomic Nuclei Preganglionics neurons 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 Terminal ganglion Near target organ Usually paired Intramural ganglion Embedded in or within tissues of target organ

Organization and Anatomy of the Parasympathetic Division 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 S2-S4

Oculomotor(III), Facial(VII), and Glossopharyngeal Nerves(IX) Control visceral structures in head Synapse in ganglia; ciliary pterygopalatine, submandibular otic ganglia Short postganglionic fibers continue to their peripheral targets

Vagus Nerve(X) Provides preganglionic parasympathetic innervation to structures in: Neck Thoracic and abdominopelvic cavities as distant as a distal portion of large intestine Provides 75 percent of all parasympathetic outflow

Submandibular ganglion
Figure 16-6 The Distribution of Parasympathetic Innervation (Part 1 of 2). Pterygopalatine ganglion N III Lacrimal gland Eye Pons Ciliary ganglion N VII Salivary glands Submandibular ganglion N IX Otic ganglion N X (Vagus) Heart Lungs Oculomotor(III) Facial(VII) Glossopharyngeal Nerves(IX) Vagus (X)

Sacral Segments of Spinal Cord 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 large intestine sex organs

Autonomic plexuses (see Figure 16-8) Liver and gallbladder
Figure 16-6 The Distribution of Parasympathetic Innervation (Part 2 of 2). Lungs Autonomic plexuses (see Figure 16-8) Liver and gallbladder Stomach Spleen Pancreas Large intestine Pelvic nerves Small intestine Rectum Spinal cord S2 Kidney S3 S4 KEY Preganglionic fibers Postganglionic fibers Uterus Ovary Penis Scrotum Urinary bladder

Parasympathetic Activation centers on relaxation food processing energy absorption localized effects last a few seconds at most Anabolic system Raisin up nutrient content in the blood

Major Effects of Parasympathetic Division Constriction of the pupils To restrict the amount of light that enters the eyes Focusing of the lenses of the eyes on nearby objects Secretion by digestive glands Salivary, gastric glands, intestinal glands the pancreas (exocrine and endocrine) the liver

Major Effects of Parasympathetic Division Secretion of hormones Promote the absorption and utilization of nutrients by peripheral cells Changes in blood flow and glandular activity Associated with sexual arousal Increase in smooth muscle activity Along the digestive tract, peristalsis

Major Effects of Parasympathetic Division Stimulation and coordination of defecation Contraction of the urinary bladder during urination Constriction of the respiratory passageways Reduction in heart rate and in the force of contraction

16-5 Parasympathetic Neurons Release ACh
Neuromuscular and Neuroglandular Junctions All PS fibers release ACh as neurotransmitter Effects of stimulation are short lived Inactivated by acetylcholinesterase (AChE) at synapse ACh is also inactivated by tissue cholinesterase in surrounding tissues

Two Types of Membrane Receptors and Responses Nicotinic receptors On surfaces of ganglion cells (sympathetic and parasympathetic) On neuromuscular junction of Somatic Nervous System Exposure to ACh causes excitation of ganglionic neuron or muscle fiber Open Na+ channels in post sinaptic membrane

Muscarinic receptors At cholinergic neuromuscular or neuroglandular junctions (parasympathetic) At few cholinergic junctions (sympathetic) G proteins Effects are longer lasting than nicotinic receptors Can be excitatory or inhibitory Response reflects activation or inactivation of specific enzymes

Dangerous Environmental Toxins Produce exaggerated, uncontrolled responses Nicotine 3mg/g on tobacco Binds to nicotinic receptors Targets autonomic ganglia and skeletal neuromuscular junctions Poisoning with 50 mg ingested or absorbed through skin Signs and symptoms: Vomiting, diarrhea, high blood pressure, rapid heart rate, sweating, profuse salivation, convulsions May result in coma or death

Dangerous Environmental Toxins 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 heart rate (bradycardia) Sweating Amanita muscaria

Amanita muscaria

Table 16-1 Adrenergic and Cholinergic Receptors of the ANS.
Summary of details of Adrenergic and Cholinergic Receptors in ANS

16-6 Dual Innervation: S y PS interaction
Sympathetic Division Widespread impact Reaches organs and tissues throughout body Parasympathetic Division Innervates only specific visceral structures Sympathetic and Parasympathetic Division Most vital organs receive instructions from both sympathetic and parasympathetic divisions Dual innervation Two divisions commonly have opposing effects

Sympathetic Parasympathetic
Figure 16-7 Summary: The Anatomical Differences between the Sympathetic and Parasympathetic Divisions. Sympathetic Parasympathetic CNS Preganglionic neuron PNS Preganglionic fiber KEY Sympathetic ganglion Neurotransmitters Acetylcholine Norepinephrine or Epinephrine Ganglionic neurons Bloodstream Postganglionic fiber Parasympathetic ganglion TARGET

Table 16-2 A Structural Comparison of the Sympathetic and Parasympathetic Divisions of the ANS.

16-6 Dual Innervation 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

Table 16-3 A Functional Comparison of the Sympathetic and Parasympathetic Divisions of the ANS (Part 1-2 of 4).

Table 16-3 A Functional Comparison of the Sympathetic and Parasympathetic Divisions of the ANS (Part 3-4 of 4).

16-6 Dual Innervation Anatomy of Dual Innervation 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

16-6 Dual Innervation Anatomy of Dual Innervation Cardiac plexus
Pulmonary plexus Esophageal plexus Celiac plexus Inferior mesenteric plexus Hypogastric plexus

Figure 16-8 The Autonomic Plexuses and Ganglia (Part 1 of 2).
Aortic arch Right vagus nerve Autonomic Plexuses and Ganglia Cardiac plexus Pulmonary plexus Thoracic sympathetic chain ganglia Esophageal plexus Celiac plexus and ganglion Superior mesenteric ganglion Inferior mesenteric plexus and ganglia Hypogastric plexus Pelvic sympathetic chain

Figure 16-8 The Autonomic Plexuses and Ganglia (Part 1 of 2).
Aortic arch Right vagus nerve Trachea Autonomic Plexuses and Ganglia Left vagus nerve Cardiac plexus Thoracic spinal nerves Pulmonary plexus Esophagus Thoracic sympathetic chain ganglia Esophageal plexus Splanchnic nerves Celiac plexus and ganglion Superior mesenteric ganglion Diaphragm Superior mesenteric artery Inferior mesenteric plexus and ganglia Inferior mesenteric artery Hypogastric plexus Pelvic sympathetic chain

16-6 Dual Innervation 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 Significant where dual innervation occurs Two divisions have opposing effects Heart More important when dual innervation does not occur Blood vessels

16-6 Dual Innervation The Heart Receives Dual Innervation
Two divisions have opposing effects on heart function Parasympathetic division Acetylcholine released by postganglionic fibers slows heart rate Sympathetic division NE released by varicosities accelerates heart rate Balance between two divisions Autonomic tone is present Releases small amounts of both neurotransmitters continuously

16-6 Dual Innervation 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

16-7 Visceral Reflexes Regulate the ANS
Provide automatic motor responses Can be modified, facilitated, or inhibited by higher centers, especially hypothalamus Visceral reflex arc Receptor Sensory neuron Processing center (one or more interneurons) All polysynaptic Two visceral motor neurons

Long reflexes Visceral sensory neurons deliver information to CNS ANS carries motor commands to visceral effectors Coordinate activities of entire organ Short reflexes Bypass CNS Control simple motor responses with localized effects One small part of target organ Autonomic equivalents of polysynaptic reflexes

Figure 16-9 Visceral Reflexes.
Receptors in peripheral tissue Afferent (sensory) fibers CENTRAL NERVOUS SYSTEM Stimulus Long reflex Short reflex Processing center in spinal cord Peripheral effector Response Autonomic ganglion (sympathetic or parasympathetic) Postganglionic neuron Preganglionic neuron

Regulating visceral activity Most organs Long reflexes most important Digestive tract Short reflexes provide most control and coordination

Table 16-4 Representative Visceral Reflexes (Part 1 of 2).

The Integration of SNS and ANS Activities Many parallels in organization and function Integration at brain stem Both systems under control of higher centers

Table 16-5 A Comparison of the ANS and SNS.

16-10 Effects of Aging on the Nervous System
Anatomical and physiological changes begin after maturity (age 30) Accumulate over time 85 percent 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 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 Neurofibrillary tangles Masses of neurofibrils form dense mats inside cell body and axon

Intracellular and Extracellular Changes in CNS Neurons Plaques Extracellular accumulations of fibrillar proteins Surrounded by abnormal dendrites and axons

Intracellular and Extracellular Changes in CNS Neurons Plaques and tangles Contain deposits of several peptides Primarily two forms of amyloid ß (Aß) protein Appear in brain regions specifically associated with memory processing

Anatomical Changes Linked to functional changes Neural processing becomes less efficient with age Memory consolidation more difficult Secondary memories harder to access

Sensory Systems Hearing, balance, vision, smell, and taste become less acute Reaction times slowed Reflexes weaken or disappear Motor Control Precision decreases Takes longer to perform

Incapacitation 85 percent 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 (lose ability to store new memories) Emotional disturbances Alzheimer’s disease is most common

16-10 Nervous System Integration
The Nervous System Monitors all other systems Issues commands that adjust their activities Like conductor of orchestra

16-10 Nervous System Integration
Neural Tissue Extremely delicate Extracellular environment must maintain homeostatic limits If regulatory mechanisms break down, neurological disorders appear

Figure diagrams the functional relationships between the nervous system and other body systems we have studied so far. SYSTEM INTEGRATOR Body System Nervous System Nervous System Body System Provides sensations of touch, pressure, pain, vibration, and temperature; hair provides some protection and insulation for skull and brain; protects peripheral nerves Controls contraction of arrector pili muscles and secretion of sweat glands Integumentary Integumentary Page 174 Provides calcium ions for neural function; protects brain and spinal cord Controls skeletal muscle contractions that results in bone thickening and maintenance and determine bone position Skeletal Skeletal Page 285 Facial muscles express emotional state; intrinsic laryngeal muscles permit communication; muscle spindles provide proprioceptive sensations Controls skeletal muscle contractions; coordinates respiratory and cardiovascular activities Muscular Muscular Page 380 The Nervous System The nervous system is closely integrated with other body systems. Every moment of your life, billions of neurons in your nervous system are exchanging information across trillions of synapses and performing the most complex integrative functions in the body. As part of this process, the nervous system monitors all other systems and issues commands that adjust their activities. However, the significance and impact of these commands varies greatly from one system to another. The normal functions of the muscular system, for example, simply cannot be performed without instructions from the nervous system. By contrast, the cardiovascular system is relatively independent—the nervous system merely coordinates and adjusts cardiovascular activities to meet the circulatory demands of other systems. In the final analysis, the nervous system is like the conductor of an orchestra, directing the rhythm and balancing the performances of each section to produce a symphony, instead of simply a very loud noise. Endocrine Page 647 Cardiovascular Page 776 Lymphatic Page 824 Respiratory Page 874 Digestive Page 929 Urinary Page 1010 Reproductive Page 1090

An Introduction to the ANS and Higher-Order Functions

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