Transcript Document 7193522
Chapter 15
The Autonomic Nervous System
Principles of Human Anatomy and Physiology, 11e 1
INTRODUCTION
• The
autonomic nervous system
arcs.
(
ANS
) operates via reflex • Operation of the ANS to maintain homeostasis, however, depends on a continual flow of sensory afferent input, from receptors in organs, and efferent motor output to the same effector organs.
• Structurally, the ANS includes autonomic sensory neurons, integrating centers in the CNS, and autonomic motor neurons.
• Functionally, the ANS usually operates without conscious control.
• The ANS is regulated by the hypothalamus and brain stem.
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Chapter 15 The Autonomic Nervous System
• Regulate activity of smooth muscle, cardiac muscle & certain glands • Structures involved – general visceral afferent neurons – general visceral efferent neurons – integration center within the brain • Receives input from limbic system and other regions of the cerebrum
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SOMATIC
AND AUTONOMIC NERVOUS SYSTEMS
• The
somatic nervous system
motor neurons.
contains both sensory and • The somatic sensory neurons receive input from receptors of the special and somatic senses.
• These sensations are consciously perceived.
• Somatic motor neurons innervate skeletal muscle to produce conscious, voluntary movements.
• The effect of a motor neuron is always excitation.
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SOMATIC AND
AUTONOMIC
NERVOUS SYSTEMS
• The
autonomic nervous system
sensory and motor neurons.
contains both autonomic – Autonomic sensory input is not consciously perceived.
• The autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities of cardiac muscle, smooth muscle, and glands.
– Most autonomic responses can not be consciously altered or suppressed.
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SOMATIC vs AUTONOMIC NERVOUS SYSTEMS
• All somatic motor pathways consist of a
single
motor neuron • Autonomic motor pathways consists of
two
motor neurons in series – The first autonomic neuron motor has its cell body in the CNS and its myelinated axon extends to an autonomic ganglion.
• It may extend to the adrenal medullae rather than an autonomic ganglion – The second autonomic motor neuron has its cell body in an autonomic ganglion; its nonmyelinated axon extends to an effector.
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Somatic versus Autonomic NS
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Basic Anatomy of ANS
• Preganglionic neuron – cell body in brain or spinal cord – axon is myelinated fiber that extends to autonomic ganglion • Postganglionic neuron – cell body lies outside the CNS in an autonomic ganglion – axon is unmyelinated fiber that terminates in a visceral effector
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Sympathetic vs. Parasympathetic NS
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AUTONOMIC NERVOUS SYSTEM
• The output (efferent) part of the ANS is divided into two principal parts: – the
sympathetic division
– the
parasympathetic division
– Organs that receive impulses from both sympathetic and parasympathetic fibers are said to have
dual innervation.
• Table 15.1 summarizes the similarities and differences between the somatic and autonomic nervous systems.
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Sympathetic ANS vs. Parasympathetic ANS
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Principles of Human Anatomy and Physiology, 11e
Divisions of the ANS
• 2 major divisions – –
parasympathetic sympathetic
• Dual innervation –
one speeds up organ
–
one slows down organ
–
Sympathetic NS increases heart rate
–
Parasympathetic NS decreases heart rate
12
Principles of Human Anatomy and Physiology, 11e
Divisions of the ANS
• 2 major divisions – –
parasympathetic sympathetic
• Dual innervation –
one speeds up organ
–
one slows down organ
–
Sympathetic NS increases heart rate
–
Parasympathetic NS decreases heart rate
13
Sympathetic Ganglia
• These ganglia include the
sympathetic trunk
or
vertebral chain
or
paravertebral ganglia
that lie in a vertical row on either side of the vertebral column (Figures 15.2).
• Other sympathetic ganglia are the
prevertebral
or
collateral ganglia
that lie anterior to the spinal column and close to large abdominal arteries. – –
celiac superior mesenteric
–
inferior mesenteric ganglia
– (Figures 15.2 and 15.4).
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Parasympathetic Ganglia
• Parasympathetic ganglia are the
terminal
or
intramural ganglia
that are located very close to or actually within the wall of a visceral organ.
• Examples of terminal ganglia include (Figure 15.3) –
ciliary,
– –
submandibular otic ganglia
,
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Sympathetic ANS vs. Parasympathetic ANS
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Dual Innervation, Autonomic Ganglia
• Sympathetic (thoracolumbar) division – preganglionic cell bodies in thoracic and first 2 lumbar segments of spinal cord • Ganglia – trunk (chain) ganglia near vertebral bodies – prevertebral ganglia near large blood vessel in gut (celiac, superior mesenteric, inferior mesenteric) • Parasympathetic (craniosacral) division – preganglionic cell bodies in nuclei of 4 cranial nerves and the sacral spinal cord • Ganglia – terminal ganglia in wall of organ
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Structures of Sympathetic NS
• Preganglionic cell bodies at T1 to L2 • Postganglionic cell bodies – sympathetic chain ganglia along the spinal column – prevertebral ganglia at a distance from spinal cord •
celiac ganglion
• •
superior mesenteric ganglion inferior mesenteric ganglion
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Postganglionic Neurons: Sympathetic vs. Parasympathetic
• Sympathetic preganglionic neurons pass to the sympathetic trunk. They may connect to postganglionic neurons in the following ways. (Figure 17.5).
– May synapse with postganglionic neurons in the ganglion it first reaches.
– May ascend or descend to a higher of lower ganglion before synapsing with postganglionic neurons.
– May continue, without synapsing, through the sympathetic trunk ganglion to a prevertebral ganglion where it synapses with the postganglionic neuron.
• Parasympathetic preganglionic neurons synapse with postganglionic neurons in terminal ganglia (Figure 17.3).
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Pathways of Sympathetic Fibers
• Spinal nerve route –
out same level
• Sympathetic chain route –
up chain & out spinal nerve
• Collateral ganglion route –
out splanchnic nerve to collateral ganglion
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Organs Innervated by Sympathetic NS
• Structures innervated by each spinal nerve – sweat glands, arrector pili mm., blood vessels to skin & skeletal mm.
• Thoracic & cranial plexuses supply: – heart, lungs, esophagus & thoracic blood vessels – plexus around carotid artery to head structures • Splanchnic nerves to prevertebral ganglia supply: – GI tract from stomach to rectum, urinary & reproductive organs
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Ganglia & Plexuses of Sympathetic NS
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Structure of the Parasympathetic Division
• Preganglionic axons extend from the brain stem in four cranial nerves. (Figure 15.3). – The cranial outflow consists of four pairs of ganglia and the plexuses associated with the vagus (X) nerve.
• The sacral parasympathetic outflow consists of preganglionic axons in the anterior roots of the second through fourth sacral nerves and they form the pelvic splanchnic nerve. (Figure15.3)
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Anatomy of Parasympathetic NS
• Preganglionic cell bodies found in – 4 cranial nerve nuclei in brainstem – S2 to S4 spinal cord • Postganglionic cell bodies very near or in the wall of the target organ in a terminal ganglia
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Parasympathetic Cranial Nerves
• Oculomotor nerve – –
ciliary ganglion in orbit ciliary muscle & pupillary constrictor muscle inside eyeball
• Facial nerve –
pterygopalatine and submandibular ganglions
–
supply tears, salivary & nasal secretions
• Glossopharyngeal –
otic ganglion supplies parotid salivary gland
• Vagus nerve –
supply heart, pulmonary and GI tract as far as the midpoint of the colon
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Parasympathetic Sacral Nerve Fibers
• Form pelvic splanchnic nerves • Preganglionic fibers end on terminal ganglia in walls of target organs • Innervate smooth muscle and glands in colon, ureters, bladder & reproductive organs
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ANS Neurotransmitters
• Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released • Adrenergic • Cholinergic
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Cholinergic Neurons and Receptors
• Cholinergic neurons release acetylcholine – all preganglionic neurons – all parasympathetic postganglionic neurons – few sympathetic postganglionic neurons (to most sweat glands) • Excitation or inhibition depending upon receptor subtype and organ involved.
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Cholinergic Neurons and Receptors
• The two types of cholinergic receptors are
nicotinic
and
muscarinic receptors
(Figure 15.6 a , b).
– Activation of nicotinic receptors causes excitation of the postsynaptic cell.
• Nicotinic receptors are found on dendrites & cell bodies of autonomic NS cells (and at NMJ.) – Activation of muscarinic receptors can cause either excitation or inhibition depending on the cell that bears the receptors.
• Muscarinic receptors are found on plasma membranes of all parasympathetic effectors
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Adrenergic Neurons and Receptors
• Adrenergic neurons release norepinephrine (NE) – from postganglionic sympathetic neurons only • Excites or inhibits organs depending on receptors • NE lingers at the synapse until enzymatically inactivated by monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT)
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Adrenergic Neurons and Receptors
• The main types of adrenergic receptors are
alpha
and
beta receptors
. These receptors are further classified into subtypes.
– Alpha1 and Beta1 receptors produce excitation – Alpha2 and Beta2 receptors cause inhibition – Beta3 receptors (brown fat) increase thermogenesis • Effects triggered by adrenergic neurons typically are longer lasting than those triggered by cholinergic neurons.
• Table 15.2 describes the location of the subtypes of cholinergic and adrenergic receptors and summarizes the responses that occur when each type of receptor is activated.
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Receptor Agonists and Antagonists
• An
agonist
is a substance that binds to and activates a receptor, mimicking the effect of a natural neurotransmitter or hormone.
• An
antagonist
is a substance that binds to and blocks a receptor, preventing a natural neurotransmitter or hormone from exerting its effect.
• Drugs can serve as agonists or antagonists to selectively activate or block ANS receptors.
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Physiological Effects of the ANS
• Most body organs receive dual innervation – innervation by both sympathetic & parasympathetic • Hypothalamus regulates balance (tone) between sympathetic and parasympathetic activity levels • Some organs have only sympathetic innervation – sweat glands, adrenal medulla, arrector pili mm & many blood vessels
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Sympathetic Responses
• Dominance by the sympathetic system is caused by physical or emotional stress - “E situations” – emergency, embarrassment, excitement, exercise • Alarm reaction = flight or fight response – dilation of pupils – increase of heart rate, force of contraction & BP – decrease in blood flow to nonessential organs – increase in blood flow to skeletal & cardiac muscle – airways dilate & respiratory rate increases – blood glucose level increase • Long lasting due to lingering of NE in synaptic gap and release of norepinephrine by the adrenal gland
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Parasympathetic Responses
• Enhance “rest-and-digest” activities • Mechanisms that help conserve and restore body energy during times of rest • Normally dominate over sympathetic impulses • SLUDD type responses = salivation, lacrimation, urination, digestion & defecation and 3 “decreases”--- decreased HR, diameter of airways and diameter of pupil • Paradoxical fear when there is no escape route or no way to win – causes massive activation of parasympathetic division – loss of control over urination and defecation
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Autonomic or Visceral Reflexes
• A visceral autonomic reflex adjusts the activity of a visceral effector, often unconsciously.
– changes in blood pressure, digestive functions etc – filling & emptying of bladder or defecation • Autonomic reflexes occur over autonomic reflex arcs. Components of that reflex arc: – sensory receptor – sensory neuron – integrating center – pre & postganglionic motor neurons – visceral effectors
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Control of Autonomic NS
• Not aware of autonomic responses because control center is in lower regions of the brain • Hypothalamus is major control center – input: emotions and visceral sensory information • smell, taste, temperature, osmolarity of blood, etc – output: to nuclei in brainstem and spinal cord – posterior & lateral portions control sympathetic NS • increase heart rate, inhibition GI tract, increase temperature – anterior & medial portions control parasympathetic NS • decrease in heart rate, lower blood pressure, increased GI tract secretion and mobility
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Autonomic versus Somatic NS - Review
• Somatic nervous system – consciously perceived sensations – excitation of skeletal muscle –
one
neuron connects CNS to organ • Autonomic nervous system – unconsciously perceived visceral sensations – involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion –
two
• neurons needed to connect CNS to organ
preganglionic and postganglionic neurons
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