Transcript Chapter 15 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. 15-1 Copyright (c) The McGraw-Hill Companies, Inc.

Chapter 15
Lecture Outline
See PowerPoint Image Slides
for all figures and tables pre-inserted into
PowerPoint without notes.
15-1
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Subdivisions of the Nervous System
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Autonomic Nervous System
and Visceral Reflexes
• Autonomic nervous system (ANS)
– general properties
– anatomy
• Autonomic effects on target organs
• Central control of autonomic function
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ANS - General Properties
• Motor nervous system controls glands, cardiac and
smooth muscle
– also called visceral motor system
• Regulates unconscious processes that maintain
homeostasis
– BP, body temperature, respiratory airflow
• ANS actions are automatic
– biofeedback techniques
• train people to control hypertension, stress and migraine
headaches
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Visceral Reflexes
•
Unconscious, automatic responses to stimulation of
glands, cardiac or smooth muscle
1. Receptors
– detect internal stimuli -- stretch, blood chemicals, etc.
2. Afferent neurons
– connect to interneurons in the CNS
3. Efferent neurons
– carry motor signals to effectors
– ANS is the efferent neurons of these reflex arcs
4. Effectors
– glands, smooth or cardiac muscle
•
ANS modifies effector activity
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Visceral Reflex to High BP
• High blood pressure
detected by arterial
stretch receptors (1),
afferent neuron (2)
carries signal to CNS,
efferent (3) signals
travel to the heart (4),
heart slows reducing
BP
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Divisions of ANS
•
Two divisions innervate same target organs
–
may have cooperative or contrasting effects
1. Sympathetic division
–
prepares body for physical activity
•
increases heart rate, BP, airflow, blood glucose levels, etc
2. Parasympathetic division
–
–
•
•
calms many body functions and assists in bodily maintenance
digestion and waste elimination
Autonomic tone is the normal rate of activity that
represents the balance of the two systems
Effects of each depend upon neurotransmitters released
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Somatic versus Autonomic Pathways
ANS = 2 neurons from CNS to effectors
• presynaptic neuron cell body in CNS
• postsynaptic neuron cell body in peripheral ganglion
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Sympathetic Nervous System
• Origin of presynaptic neurons
– lateral horns of spinal cord (T1-L2)
• Sympathetic chain ganglia (paravertebral)
– 3 cervical, 11 thoracic, 4 lumbar, 4 sacral and 1
coccygeal ganglia
– white and gray communicating rami suspend ganglia
from spinal nerve
– pathways of preganglionic fibers
1. enter ganglia and synapse on postganglionic cell
2. travel to higher or lower ganglia and synapse
3. pass through chain without synapsing to reach collateral
ganglia via splanchnic nerves
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Sympathetic Nervous System
• Neuronal divergence predominates
– each preganglionic cell branches and synapses on
multiple postganglionic cells
– produces widespread effects on multiple organs
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Efferent Pathways
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Preganglionic Pathways
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Ganglia and Abdominal Aortic Plexus
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Sympathetic Innervation
• Effectors in body wall are innervated by
sympathetic fibers in spinal nerves
• Effectors in head and thoracic cavity are innervated
by fibers in sympathetic nerves
• Effectors in abdominal cavity are innervated by
sympathetic fibers in splanchnic nerves
– celiac, superior and inferior mesenteric ganglion
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Adrenal Glands
• Paired glands sit on superior pole of each kidney
• Cortex (outer layer)
– secretes steroid hormones
• Medulla (inner core)
– a modified sympathetic ganglion
• stimulated by preganglionic sympathetic neurons
– secretes neurotransmitters (hormones) into blood
• catecholamines (85% epinephrine and 15% norepinephrine)
• Sympathoadrenal system is the closely related
functioning adrenal medulla and symphathetic nervous
system
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Parasympathetic Nervous System
• Origin of preganglionic fibers
– pons and medulla (for cranial nerve nuclei)
– sacral spinal cord segments S2-S4
• Pathways of preganglionic fibers
– cranial nerves III, VII, IX and X
– arising from sacral spinal cord
• pelvic splanchnic nerves and inferior hypogastric plexus
• Terminal ganglia in/near target organs
– long preganglionic, short postganglionic fibers
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Efferent Pathways
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Parasympathetic Cranial Nerves
• Oculomotor nerve (III)
– narrows pupil and focuses lens
• Facial nerve (VII)
– tear, nasal and salivary glands
• Glossopharyngeal (IX)
– parotid salivary gland
• Vagus nerve (X)
– viscera as far as proximal half of
colon
– Cardiac, pulmonary, and
esophageal plexus
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Enteric Nervous System
• Nervous system of the digestive tract
• Composed of 100 million neurons found in the
walls of the digestive tract (no components in
CNS)
• Has its own reflex arcs
• Regulates motility of viscera and secretion of
digestive enzymes and acid in concert with the
ANS
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In Class Exercise
• You are hiking in the woods when suddenly you come face to
face with a bear. Which division of the ANS will be activated?
• What will happen to your heart rate, blood flow to skeletal
muscles and heart, blood flow to skin and most other visceral
organs, airflow to bronchi and bronchioles, pupils, and
gastointestinal motility and secretion?
• Compare SNS and PSN in terms of origin of fibers, location of
ganglia, pre- and postganglionic fiber lengths, neural
divergence, and effects of system.
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Neurotransmitters and Receptors
• Effects of ANS
– determined by types of neurotransmitters released
and types of receptors on target cells
• Sympathetic has longer lasting effects
– neurotransmitters persist in synapse and some reach
the bloodstream
• Many substances released as neurotransmitters
– enkephalin, substance P, neuropeptide Y, neurotensin,
nitric oxide (NO)
• NO inhibits muscle tone in BV walls (vasodilation)
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Neurotransmitters and Receptors
Use diagram in textbook
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Cholinergic Receptors for ACh
•
Acetylcholine (Ach) binds to 2 classes of
receptors
1. nicotinic receptors
•
•
on all ANS postganglionic neurons, in the adrenal
medulla, and at neuromuscular junctions (skeletal
muscle)
excitatory when ACh binding occurs
2. muscarinic receptors
•
•
on all gland, smooth muscle and cardiac muscle cells
that receives cholinergic innervation
excitatory or inhibitory due to subclasses of
muscarinic receptors
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Adrenergic Receptors for NE
• Norepinephrine binds to 2 classes of receptors
– alpha adrenergic receptors (often excitatory)
– beta adrenergic receptors (often inhibitory)
• Exceptions
– existence of subclasses of each receptor type
• alpha 1 and 2; beta 1 and 2
• Function by means of 2nd messengers
– cyclic AMP and alpha 1 receptors
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Dual Innervation
• Most of viscera receive nerve fibers from both
parasympathetic and sympathetic divisions
• Both divisions do not normally innervate an organ
equally
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Dual Innervation
• Antagonistic effects
– oppose each other
– exerted through dual innervation of same effector
• heart rate decreases (parasympathetic)
• heart rate increases (sympathetic)
– exerted because each division innervates different cells
• pupillary dilator muscle (sympathetic) dilates pupil
• constrictor pupillae (parasympathetic) constricts pupil
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Dual Innervation
• Cooperative effects seen when 2 divisions act on
different effectors to produce a unified effect
– parasympathetics increase salivary serous cell secretion
– sympathetics increase salivary mucous cell secretion
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Dual Innervation of the Iris
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Without Dual Innervation
• Some effectors receive only sympathetic
– adrenal medulla, arrector pili muscles, sweat glands
and many blood vessels
• Sympathetic tone
– a baseline firing frequency
– vasomotor tone provides partial constriction
• increase in firing frequency = vasoconstriction
• decrease in firing frequency = vasodilation
• can shift blood flow from one organ to another as needed
– sympathetic stimulation increases blood to skeletal and cardiac
muscles -- reduced blood to skin
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Sympathetic and Vasomotor Tone
Sympathetic division
prioritizes blood vessels
to skeletal muscles and
heart in times of
emergency.
Blood vessels to skin
vasoconstrict to
minimize bleeding if
injury occurs during
stress or exercise.
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Control of Autonomic Function
• ANS regulated by several levels of CNS
– cerebral cortex has an influence
– hypothalamus (major visceral motor control center)
• nuclei for primitive functions – hunger, thirst
– midbrain, pons, and medulla oblongata
• nuclei for cardiac and vasomotor control, salivation,
swallowing, sweating, bladder control, and pupillary changes
– spinal cord reflexes
• defecation and micturition reflexes integrated in cord
• brain can inhibit these responses consciously
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Drugs
• Sympathomimetics enhance sympathetic activity
– stimulate receptors or norepinephrine release
• Sympatholytics suppress sympathetic activity
– block receptors or inhibit norepinephrine release
• Parasympathomimetics enhance activity while
parasympatholytics suppress activity
• Management of clinical depression
– Prozac blocks reuptake of serotonin to prolong its moodelevating effect
– MAO inhibitors interfere with breakdown of monoamine
neurotransmitters
• Caffeine competes with adenosine (inhibitory; causes
sleepiness) by binding to its receptors
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