Download Sympathetic Trunk Ganglia

15 PART 1
The Autonomic Nervous System and Visceral Sensory Neurons
The ANS and Visceral Sensory Neurons
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The ANS—a system of motor neurons
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Innervates
• Smooth muscle
• Cardiac muscle
• Glands
The ANS and Visceral Sensory Neurons
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The ANS—a system of motor neurons
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Regulates visceral functions
• Heart rate
• Blood pressure
• Digestion
• Urination
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The ANS is the
• General visceral motor division of the PNS
Comparison of Autonomic and Somatic Motor Systems
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Somatic motor system
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One motor neuron extends from the CNS to skeletal muscle
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Axons are well myelinated, conduct impulses rapidly
Comparison of Autonomic and Somatic Motor Systems
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Autonomic nervous system
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Chain of two motor neurons
• Preganglionic neuron
• Postganglionic neuron
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Conduction is slower than somatic nervous system because
• Axons are thinly myelinated or nonmyelinated
• Motor neuron synapses in a ganglion
Divisions of the Autonomic Nervous System
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Sympathetic and parasympathetic divisions
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Chains of two motor neurons
• Innervate mostly the same structures
• Cause opposite effects
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Sympathetic division mobilizes the body during extreme situations
• Fear, rage, exercise
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Parasympathetic division controls routine maintenance functions
Divisions of the Autonomic Nervous System
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Sympathetic—“fight or flight”
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Activated during EXTREME situations
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Exercise
Excitement
Emergencies
Divisions of the Autonomic Nervous System
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All sympathetic responses help us respond to dangerous situations
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Increase heart rate and breathing rate
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Increase blood and oxygen to skeletal muscles
• Vasoconstriction of other blood vessels
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Dilate pupils and bronchioles
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Inhibit motility of the digestive tract and urinary tracts
Divisions of the Autonomic Nervous System
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Parasympathetic division
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Active when the body is at rest
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Concerned with conserving energy
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Directs “housekeeping” activities
• Digestion
• Elimination of feces and urine
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Buzzwords for parasympathetic division: “rest and digest”
• Heart rate, blood pressure, respiration at low-normal levels
Divisions of the ANS
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Issue from different regions of the CNS
• Sympathetic
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Also called the thoracolumbar division
• Parasympathetic
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Also called the craniosacral division
Divisions of the ANS
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Length of postganglionic fibers
• Sympathetic—long postganglionic fibers
• Parasympathetic—short postganglionic fibers
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Branching of fibers
• Sympathetic fibers—highly branched
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Influence many organs at once
• Parasympathetic fibers —few branches
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Localized effect
Divisions of the ANS
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Neurotransmitter released by postganglionic axons
• Sympathetic
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Most release norepinephrine (adrenergic)
• Parasympathetic
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Release acetylcholine (cholinergic)
The Parasympathetic Division
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Cranial outflow
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Originates from the brain
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Innervates
• Organs of the head, neck, thorax, and abdomen
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Sacral outflow
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Innervation supplies
• Remaining abdominal and pelvic organs
Cranial Outflow (Parasympathetic)
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Preganglionic fibers run via
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Oculomotor nerve (III)
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Facial nerve (VII)
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Glossopharyngeal nerve (IX)
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Vagus nerve (X)
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Cell bodies of preganglionic neurons located in motor cranial nerve nuclei in gray
matter of the brain stem
Outflow via the Oculomotor Nerve (III)
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Parasympathetic fibers innervate smooth muscles in the eye
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Cause pupil constriction
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Preganglionic cell bodies
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Located in the oculomotor nucleus in the midbrain
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Postganglionic cell bodies
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Lie in the ciliary ganglion
Outflow via the Facial Nerve (VII)
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Parasympathetic fibers stimulate secretion of glands in the head
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Lacrimal nucleus
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Located in the pons
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Synapse in the pterygopalatine ganglion
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Superior salivatory nucleus
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Located in the pons
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Synapse in the submandibular ganglion
Outflow via the Glossopharyngeal Nerve (IX)
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Parasympathetic fibers
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Stimulate secretion of glands in the head
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Lacrimal nucleus—located in the pons
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Synapse in the pterygopalatine ganglion
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Superior salivatory nucleus—located in the pons
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Synapse in the submandibular ganglion
Outflow via the Vagus Nerve (X)
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Fibers innervate visceral organs of the thorax and most of the abdomen
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Stimulates:
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Digestion, reduction in heart rate, and reduction in blood pressure
Preganglionic cell bodies
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Located in dorsal motor nucleus in the medulla
Postganglionic neurons
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Confined within the walls of organs being innervated
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Cell bodies form intramural ganglia
Path of the Vagus Nerve
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Sends branches through
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Autonomic nerve plexuses
• Cardiac plexus
• Pulmonary plexus
• Esophageal plexus
• Celiac plexus
• Superior mesenteric plexus
15 PART 2
The Autonomic
Nervous System and Visceral Sensory Neurons
Sacral Outflow
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Emerges from S2 to S4
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Innervates organs of the pelvis and lower abdomen
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Preganglionic cell bodies
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Located in visceral motor region of spinal gray matter
Sacral Outflow
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Axons run in ventral roots to ventral rami
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Form pelvic splanchnic nerves
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Run through the inferior hypogastric plexus
The Sympathetic Division
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Basic organization
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Issues from T1 to L2
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Preganglionic fibers form the lateral gray horn
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Supplies visceral organs in internal body cavities and structures of superficial body
regions
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Contains more ganglia than the parasympathetic division
Sympathetic Trunk Ganglia
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Located on both sides of the vertebral column
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Linked by short nerves into sympathetic trunks
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Sympathetic trunk ganglia are also called
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Chain ganglia
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Paravertebral ganglia
Sympathetic Trunk Ganglia
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Joined to ventral rami by white and gray rami communicantes
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Fusion of ganglia  fewer ganglia than spinal nerves
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Fusion of ganglia most apparent in the cervical region
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Superior, middle, and inferior cervical ganglia
Collateral Ganglia
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Differ from sympathetic trunk ganglia in three ways
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Unpaired, not segmentally arranged
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Occur only in abdomen and pelvis
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Lie anterior to the vertebral column
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Main ganglia
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Celiac, superior mesenteric, inferior mesenteric, and inferior hypogastric ganglia
Sympathetic Pathways
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Preganglionic neurons in the thoracolumbar spinal cord send motor axons through
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Adjacent ventral root into
• Spinal nerve, then the
• White ramus communicans
• And to the associated sympathetic trunk ganglion
Sympathetic Pathways
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Preganglionic axons follow one of three pathways
• Synapses with a postganglionic neuron at the same level and exit on a spinal nerve at
that level
Sympathetic Pathways
• Axon ascends or descends in the sympathetic trunk to synapse in another ganglion
• Axon passes through the sympathetic trunk
and exits on a splanchnic nerve
Sympathetic Pathways to the Body Periphery
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Innervate
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Sweat glands
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Arrector pili muscles
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Peripheral blood vessels
Pathways to the Body Periphery
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Preganglionic fibers enter the sympathetic trunk ganglia and synapse there
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Some preganglionic fibers travel superiorly or inferiorly on the sympathetic trunk
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Postganglionic axons travel in gray rami communicantes
Pathways to the Body Periphery
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Gray and white rami communicantes
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Gray rami—contain only postganglionic fibers traveling to peripheral structures
• Fibers are nonmyelinated
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White rami—contain preganglionic fibers traveling to sympathetic trunk ganglia
• Fibers are myelinated
Sympathetic Pathways to the Head
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Preganglionic fibers originate in spinal cord at T1–T4
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Fibers ascend in the sympathetic trunk
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Synapse in superior cervical ganglion
Pathways to the Head
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Postganglionic fibers associate with large arteries
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Carried by these structures to
• Glands
• Smooth muscle
• Vessels throughout the head
Pathways to Thoracic Organs
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Preganglionic fibers originate at spinal levels T1–T6
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Some fibers synapse in nearest sympathetic trunk ganglion
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Postganglionic fibers run directly to the
organ supplied
Sympathetic Pathways to Thoracic Organs
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Sympathetic fibers to heart have a less direct route
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Functions
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Increase heart rate
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Dilate bronchioles
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Dilate blood vessels to the heart wall
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Inhibit muscles and glands in the esophagus and digestive system
Pathways to Abdominal Organs
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Preganglionic fibers originate in spinal cord (T5–L2)
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Pass through adjacent sympathetic trunk ganglia
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Then travel in thoracic splanchnic nerves
• Synapse in prevertebral ganglia on the abdominal aorta
• Celiac and superior mesenteric ganglia
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Inhibit activity of muscles and glands in visceral organs
Pathways to the Pelvic Organs
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Preganglionic fibers originate in the spinal cord from T10 to L2
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Fibers descend in the sympathetic trunk to lumbar and sacral ganglia
• Some postganglionic fibers run in lumbar and sacral splanchnic nerves to
plexuses
• Inferior mesenteric plexus, aortic plexus, or hypogastric plexus
Pathways to the Pelvic Organs
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Other preganglionic fibers pass directly to autonomic plexuses and synapse in collateral
ganglia
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Inferior mesenteric ganglia or inferior hypogastric ganglia
• Postganglionic fibers go from these plexuses to the
• Bladder, reproductive organs, and distal large intestine
The Role of the Adrenal Medulla in the Sympathetic Division
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Major organ of the sympathetic nervous system
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Constitutes largest sympathetic ganglia
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Secretes great quantities of norepinephrine and epinephrine (adrenaline)
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Stimulated to secrete by preganglionic sympathetic fibers
Visceral Sensory Neurons
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General visceral sensory neurons monitor these sensations within visceral organs
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Stretch
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Temperature
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Chemical changes
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Irritation
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Cell bodies are located in
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Dorsal root ganglion
Visceral Sensory Neurons
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Visceral pain
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No pain results when visceral organs are cut
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Visceral pain results from chemical irritation or inflammation
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Visceral pain often perceived to be of somatic origin
• Phenomenon of referred pain
Visceral Reflexes
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Visceral sensory and autonomic neurons
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Participate in visceral reflex arcs
• Defecation reflex
• Micturition reflex
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Some are simple spinal reflexes
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Others do not involve the CNS
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Strictly peripheral reflexes
Central Control of the ANS
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ANS is not under direct voluntary control
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Activities regulated by CNS
• Brain stem
• Spinal cord
• Hypothalamus
• Amygdaloid body
• Cerebral cortex
Control by the Brain Stem and Spinal Cord
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Control by the brain stem and spinal cord
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Reticular formation exerts most direct influence
• Medulla oblongata
• Periaqueductal gray matter
Control by the Hypothalamus and Amygdala
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Hypothalamus—the main integration center of the ANS
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Medial and anterior parts
• Direct parasympathetic functions
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Lateral and posterior parts
• Direct sympathetic functions
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Amygdaloid body
• Main limbic region for emotions
Control by the Cerebral Cortex
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People can exert some control over autonomic functions
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Feelings of calm during meditation
• Influence of cerebral cortex on parasympathetic centers in hypothalamus
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Voluntary sympathetic response
• Recalling scary event
Disorders of the Autonomic Nervous System
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Raynaud’s disease—characterized by constriction of blood vessels
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Provoked by exposure to cold or by emotional stress
Disorders of the Autonomic Nervous System
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Achalasia of the cardia
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Defect in the autonomic innervation of the esophagus
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Congenital megacolon (Hirschsprung’s disease)
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Birth defect
• Parasympathetic innervation of distal large intestine fails to develop correctly
• Feces and gas accumulate proximal to defect
The ANS Throughout Life
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Preganglionic neurons of the ANS develop from the neural tube
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Postganglionic neurons develop from the
neural crest
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Development of the sympathetic division
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Some cells migrate ventrally
• Form the sympathetic trunk ganglia
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Other cells migrate
• Form the prevertebral ganglia
The ANS Throughout Life
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Efficiency of the ANS declines with advancing age
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Constipation due to reduced mobility of gastrointestinal (GI) tract
Dry eyes due to reduced tear formation