General Properties of ANS
Autonomic Nervous System
and Visceral Reflexes
• autonomic nervous system (ANS) – a motor nervous
system that controls glands, cardiac muscle, and smooth
muscle
• Maintains homeostasis
• Autonomic Nervous System (ANS)
– general properties
– anatomy
• Autonomic Effects on Target Organs
• Central Control of Autonomic Function
•
Primary organs of the ANS
• viscera of thoracic and abdominal cavities
• some structures of the body wall
– cutaneous blood vessels
– sweat glands
– piloerector muscles
• carries out actions involuntarily – no intent/awareness
• visceral effectors do not depend on the ANS to function
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15-2
Divisions of ANS
Divisions of ANS
•
sympathetic division (Fight or Flight)
– prepares body for physical activity – exercise, trauma,
arousal, competition, anger, or fear
• increases heart rate, BP, airflow, blood glucose
levels, etc.
• reduces blood flow to the skin and digestive tract
parasympathetic division (Rest and digest)
– calms many body functions reducing energy
expenditure and assists in bodily maintenance
• digestion and waste elimination
autonomic tone - balance of the two systems according to
the body’s changing needs
–
parasympathetic tone
• maintains smooth muscle tone in intestines
• holds resting heart rate down to about 70 – 80 beats
per minute
–
sympathetic tone
• keeps most blood vessels partially constricted and
maintains blood pressure
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Somatic versus Autonomic Pathways
Neural Pathways
Somatic efferent innervation
•
ANS has components in both the central and peripheral
nervous systems
– nuclei in the hypothalamus and other brainstem
regions
– motor neurons in the spinal cord and peripheral ganglia
– nerve fibers that travel through the cranial and spinal
nerves
ACh
Myelinated
fiber
Somatic effectors
(skeletal muscles)
Autonomic efferent innervation
ACh
Myelinated
preganglionic fiber
ACh or NE
Unmyelinated
postganglionic fiber
Visceral effectors
(cardiac muscle,
smooth muscle,
glands)
Autonomic
ganglion
Preganglionic cell bodies in grey matter
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15-6
1
Sympathetic Nervous System
•
Aka thoracolumbar division (T1 – L2)
•
relatively short preganglionic and long postganglionic
fibers
•
preganglionic cell bodies in lateral horns and nearby
regions of the gray matter of spinal cord
–
Sympathetic Nervous System
lead to sympathetic chain of ganglia (paravertebral ganglia)
–
each paravertebral ganglion is connected to a spinal nerve by
two branches – communicating rami (rami communicants)
–
preganglionic fibers are small myelinated fibers that travel
form spinal nerve to the ganglion via white communicating
ramus (myelinated)
–
postganglionic fibers leave the ganglion by via gray
communicating ramus (unmyelinated)
•
–
forms a bridge back to the spinal nerve
postganglionic fibers extend to target organ
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15-8
Preganglionic Pathways
Sympathetic Chain Ganglia
3 pathways of preganglionic neurons
entering sympathetic chain
Soma of
preganglionic
neuron
To iris, salivary glands,
lungs, heart, thoracic
blood vessels, esophagus
Sympathetic nerve
2
Spinal nerve
Somatic
motor fiber
Preganglionic
sympathetic fiber
Postganglionic
sympathetic fiber
To somatic effector
(skeletal muscle)
To sweat glands,
piloerector muscles,
and blood vessels
of skin and
skeletal muscles
1
Soma of
somatic motor
neuron
3
White ramus
Gray ramus
Splanchnic nerve
Preganglionic neuron
Postganglionic neuron
Somatic neuron
3 pathways of leaving
sympathetic chain No.s 1,
2, & 3
Communicating
rami
Collateral ganglion
Soma of
postganglionic
neuron
Postganglionic
sympathetic fibers
Sympathetic
trunk
To liver, spleen, adrenal glands,
stomach, intestines, kidneys,
urinary bladder, reproductive organs
Sympathetic
ganglion
2
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Other ganglia of Sympathetic Nervous System
•
•
Efferent Pathways of
sympathetic division
collateral ganglia (prevertebral ganglia)
Some preganglionic fibers pass thru sympathetic
chain
- form splancic nerves
- synapse in collateral (prevertebral ganglia)
Eye
Pons
Salivary glands
Preganglionic neurons
Postganglionic neurons
Heart
Cardiac and
pulmonary plexuses
Regions of spinal cord
Cervical
Thoracic
Lumbar
Sacral
–
three major collateral ganglia in this plexus
•
•
–
Liver and
gallbladder
Stomach
Superior
mesenteric
ganglion
celiac, superior mesenteric, and inferior mesenteric
postganglionic fibers accompany these arteries and their branches to
their target organs
Spleen
Pancreas
Postganglionic fibers to
skin, blood vessels,
adipose tissue
solar plexus – collective name for the celiac and superior
mesenteric ganglia
•
Lung
Celiac
ganglion
contribute to a network called the abdominal aortic plexus
Inferior
mesenteric
ganglion
Small intestine
Large intestine
nerves radiate from ganglia like rays of the sun
Rectum
Sympathetic chain
ganglia
Adrenal medulla
Kidney
15-11
Ovary
Penis
Uterus
Scrotum
Bladder
2
Ganglia and Abdominal Aortic Plexus
Summary of Sympathetic Innervation
• effectors in body wall are innervated by sympathetic
fibers in spinal nerves
Diaphragm
Esophagus
Adrenal medulla
Adrenal cortex
(b)
Celiac ganglia
• effectors in head and thoracic cavity are innervated by
fibers in sympathetic nerves
Adrenal gland
Celiac trunk
Superior mesenteric
ganglion
Renal plexus
First lumbar
sympathetic
ganglion
Superior mesenteric artery
Kidney
Inferior mesenteric artery
Aortic plexus
• effectors in abdominal cavity are innervated by
sympathetic fibers in splanchnic nerves
Inferior mesenteric
ganglion
Aorta
Figure 15.6
Pelvic
sympathetic
chain
15-13
(a)
15-14
Adrenal Glands
Parasympathetic Division
• parasympathetic division (aka craniosacral division)
• two glands with different functions
• origin of long preganglionic neurons
– adrenal cortex (outer layer)
• secretes steroid hormones
– adrenal medulla (inner core)
• essentially a sympathetic ganglion
– stimulated by preganglionic sympathetic neurons that
terminate on these cells
• secretes a mixture of hormones into bloodstream
– catecholamines - 85% epinephrine (adrenaline) and 15%
norepinephrine (noradrenaline)
» also function as neurotransmitters
– midbrain, pons, and medulla (III, VII, IX, X)
– sacral spinal cord segments S2-S4
• terminal ganglia in or near target organs
– long preganglionic, short postganglionic fibers
• sympathoadrenal system is adrenal medulla and
sympathetic nervous system
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Parasympathetic Cranial Nerves
•
Preganglionic neurons
Pterygopalatine
ganglion
Oculomotor n.
(CN III)
Facial n.
(CN VII)
Submandibular
ganglion
Submandibular
salivary gland
•
Heart
Cardiac plexus
Lumbar
Sacral
Facial n.
(CN VII)
Facial nerve (VII)
– tear, nasal and salivary glands
Pulmonary
plexus
Esophageal
plexus
Glossopharyngeal nerve (IX)
– parotid salivary gland
•
Lung
Celiac
ganglion
Stomach
Liver and
gallbladder
Abdominal
aortic
plexus
Spleen
Pancreas
Pelvic
splanchnic
nerves
Kidney and
ureter
Transverse
colon
Descending
colon
Inferior
hypogastric
plexus
Small intestine
Rectum
•
Vagus nerve (X)
– viscera as far as proximal half of
colon
– cardiac, pulmonary, and
esophageal plexus
form pelvic splanchnic
nerves that lead to the
inferior hypogastric
plexus
most form pelvic nerves to
their terminal ganglion on
the target organs
– distal half of colon, rectum,
urinary bladder, and
reproductive organs
Lacrimal gland
Eye
Submandibular
ganglion
Submandibular
salivary gland
Otic ganglion
Parotid
salivary gland
Vagus n.
(CN X)
Heart
Cardiac plexus
Regions of
spinal cord
Cervical
Pulmonary
plexus
Esophageal
plexus
Lung
Thoracic
Lumbar
Sacral
Celiac
ganglion
Stomach
Liver and
gallbladder
Abdominal
aortic
plexus
Spleen
Pancreas
Pelvic
splanchnic
nerves
Kidney and
ureter
Transverse
colon
Descending
colon
Inferior
hypogastric
plexus
Small intestine
Rectum
Pelvic
nerves
Penis
Uterus
Postganglionic neurons
Ciliary ganglion
Glossopharyngeal n.
(CN IX)
Pelvic
nerves
Ovary
Preganglionic neurons
Pterygopalatine
ganglion
Oculomotor n.
(CN III)
Parotid
salivary gland
Glossopharynge
al n.
(CN IX)
Vagus n.
(CN X)
Thoracic
•
Lacrimal gland
Eye
Efferent Pathways
•
Postganglionic neurons
Ciliary ganglion
Otic ganglion
Regions of
spinal cord
Cervical
Oculomotor nerve (III)
– narrows pupil and focuses lens
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Bladder
Scrotum
15-17
Penis
Ovary
Uterus
Bladder
Scrotum
3
Enteric Nervous System
Neurotransmitters and Receptors
• enteric nervous system – nervous system of the
digestive tract
• how can different autonomic neurons have different effects?
constricting some vessels but dilating others
– does not arise from the brainstem or spinal cord
– innervates smooth muscle and glands
– effects determined by types of neurotransmitters released and types
of receptors found on target cells
• semiautonomous
• 2 fundamental reasons:
• has its own reflex arcs
– sympathetic and parasympathetic fibers secrete different
neurotransmitters
• regulates motility of esophagus, stomach, and
intestines and secretion of digestive enzymes and acid
– target cells respond to the same neurotransmitter differently
depending upon the type of receptor they have for it
• normal digestive function also requires regulation by
sympathetic and parasympathetic systems
• all autonomic fibers secrete either acetylcholine or norepinephrine
• there are 2 classes of receptors for each of these neurotransmitters
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Acetylcholine (ACh)
• ACh is secreted by all preganglionic neurons in both divisions
and the postganglionic parasympathetic neurons
– cholinergic fibers
– any receptor that binds it is called cholinergic receptor
• 2 types of cholinergic receptors
– muscarinic receptors
• all cardiac muscle, smooth muscle, and gland cells have
muscarinic receptors
• excitatory or inhibitory due to subclasses of muscarinic
receptors
– nicotinic receptors
• on all ANS postganglionic neurons, and at
neuromuscular junctions of skeletal muscle
• excitatory when ACh binding occurs
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15-20
Norepinephrine (NE)
• NE is secreted by nearly all sympathetic postganglionic
neurons
– called adrenergic fibers
– receptors for it called adrenergic receptors
• alpha-adrenergic receptors
– usually excitatory
– 2 subclasses use different second messengers
(α1 & α2)
• beta-adrenergic receptors
– usually inhibitory
– 2 subclasses with different effects, but both act
through cAMP as a second messenger (β1 & β2)
Neurotransmitters and Receptors
Overview
(a) Parasympathetic fiber
•
Nicotinic
receptor
autonomic effects on glandular secretion are often an indirect
result of their effect on blood vessels
ACh
Target
cell
– vasodilation – increased blood flow – increased secretion
– vasoconstriction – decreased blood flow – decreased secretion
•
ACh
Preganglionic
neuron
sympathetic effects tend to last longer than parasympathetic effects
ACh
Target
cell
Preganglionic
neuron
Postganglionic
neuron
many substances released as neurotransmitters that modulate ACh
and NE function
NE
Adrenergic receptor
(c) Sympathetic cholinergic fiber
– sympathetic fibers also secrete enkephalin, substance P, neuropeptide Y,
somatostatin, neurotensin, or gonadotropin-releasing hormone
– parasympathetic fibers stimulate endothelial cells to release the gas, nitric
oxide – causes vasodilation by inhibiting smooth muscle tone
• function is crucial to penile erection - means of action of Viagra
Muscarinic
receptor
Nicotinic
receptor
– ACh released by parasympathetics is broken down quickly at synapse
– NE by sympathetics is reabsorbed by nerve, diffuses to adjacent tissues,
and much passes into bloodstream
•
Postganglionic
neuron
(b) Sympathetic adrenergic fiber
15-23
Nicotinic
receptor
ACh
Target
cell
Preganglionic
neuron
Postganglionic
neuron
ACh
Muscarinic receptor
Figure 15.8
15-24
4
Dual Innervation
Dual Innervation
• dual innervation - most viscera receive nerve fibers
from both parasympathetic and sympathetic
divisions
– antagonistic effect – oppose each other
– cooperative effects – two divisions act on different
effectors to produce a unified overall effect
• both divisions do not normally innervate an organ
equally
• digestion, heart rate
• antagonistic effects - oppose each other
– exerted through dual innervation of same effector cells
• heart rate decreases (parasympathetic)
• heart rate increases (sympathetic)
– exerted because each division innervates different
cells
• (sympathetic) dilates pupil
• (parasympathetic) constricts pupil
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15-26
Dual Innervation of the Iris
Dual Innervation
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Brain
Parasympathetic fibers
of oculomotor nerve (III)
Superior
cervical
ganglion
• cooperative effects - when two divisions act on
different effectors to produce a unified effect
Sympathetic
fibers
Ciliary
ganglion
– parasympathetics increase salivary serous cell
secretion
Spinal cord
Cholinergic stimulation
of pupillary constrictor
Iris
Adrenergic
stimulation of
pupillary dilator
– sympathetics increase salivary mucous cell
secretion
Pupil
Sympathetic
(adrenergic) effect
Parasympathetic
(cholinergic) effect
Figure 15.9
Pupil dilated
Pupil constricted
15-27
Without Dual Innervation
•
•
•
•
Sympathetic and Vasomotor Tone
some effectors receive only sympathetic fibers
– adrenal medulla, arrector pili muscles, sweat glands and many
blood vessels
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Artery
sympathetic division
prioritizes blood vessels to
skeletal muscles and heart
in times of emergency
control of blood pressure and routes of blood flow
sympathetic vasomotor tone - a baseline firing frequency of
sympathetics
•
•
•
•
keeps vessels in state of partial constriction
increase in firing frequency - vasoconstriction
decrease in firing frequency - vasodilation
can shift blood flow from one organ to another as needed
1
Sympathetic
nerve fiber
1 Strong
sympathetic
tone
2
2 Smooth muscle
contraction
3
Vasomotor
tone
3 Vasoconstriction
(a) Vasoconstriction
blood vessels to skin
vasoconstrict to
minimize bleeding if
injury occurs during
stress or exercise
sympathetic division acting alone can exert opposite effects on the
target organ through control of blood vessels
– during stress
• blood vessels to muscles and heart dilate
• blood vessels to skin constrict
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15-29
1
1 Weaker
sympathetic
tone
2
3
2 Smooth muscle
relaxation
3 Vasodilation
(b) Vasodilation
15-30
5
Control of Autonomic Function
Visceral Reflexes
• ANS regulated by several levels of CNS
– cerebral cortex has an influence – anger, fear, anxiety
•
• powerful emotions influence the ANS because of the connections
between our limbic system and the hypothalamus
– hypothalamus - major visceral motor control center
• nuclei for primitive functions – hunger, thirst, sex
•
– midbrain, pons, and medulla oblongata contain:
visceral reflexes - unconscious, automatic,
stereotyped responses to stimulation involving visceral
receptors and effectors and somewhat slower
responses
visceral reflex arc
–
• nuclei for cardiac and vasomotor control, salivation, swallowing,
sweating, bladder control, and pupillary changes
–
–
–
–
– spinal cord reflexes
• defecation and micturition reflexes are integrated in spinal cord
• we control these functions because of our control over skeletal
muscle sphincters…
•
15-31
receptors – nerve endings that detect stretch, tissue
damage, blood chemicals, body temperature, and other
internal stimuli
afferent neurons – leading to the CNS
interneurons – in the CNS
efferent neurons – carry motor signals away from the CNS
effectors – that make adjustments
ANS modifies effector activity
15-32
Visceral Reflex to High BP
2 Glossopharyngeal
nerve transmits signals
to medulla oblongata
3 Vagus nerve
transmits
inhibitory
signals
to cardiac
pacemaker
1 Baroreceptors
sense increased
blood pressure
Common carotid
artery
Terminal
ganglion
4 Heart rate
decreases
6