1. Chapter 15 Lecture Outline
15-1
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2. Autonomic Nervous System and Visceral Reflexes
Autonomic Nervous System (ANS)
general properties
Autonomic Effects on Target Organs
Central Control of Autonomic Function

3. Autonomic Nervous System
portion of the nervous system that operates in comparative secrecy
it manages a multitude of unconscious processes responsible for the body’s homeostasis
homeostasis cannot be maintained without the ANS

4. General Properties of ANS
autonomic nervous system (ANS) – a motor nervous system that controls glands, cardiac muscle, and smooth muscle
also called visceral motor system
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

5. Visceral Reflexes
visceral reflexes - unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors
visceral reflex arc
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

6. Visceral Reflex to High BP
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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 blood pressure
homeostatic negative feedback loop
Glossopharyngeal
nerve transmits signals
to medulla oblongata 2
Baroreceptors sense increased blood pressure 1 3
Vagus nerve
transmits
inhibitory
signals
to cardiac
pacemaker
Common carotid
artery
Terminal
ganglion 4
Heart rate
decreases
Figure 15.1

7. Divisions of ANS two divisions innervate same target organs
may have cooperative or contrasting effects
sympathetic division
prepares body for physical activity – exercise, trauma, arousal, competition, anger, or fear
heart rate, BP, airflow, blood glucose levels, etc.
reduces blood flow to the skin and digestive tract
parasympathetic division
calms many body functions reducing energy expenditure and assists in bodily maintenance
digestion and waste elimination
“resting and digesting” state

8. Divisions of ANS
autonomic tone - normal background rate of activity that represents the balance of the two systems
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
sympathetic division excites the heart but inhibits digestive and urinary function, while parasympathetic has the opposite effect

9. Neural Pathways
ANS components are in both the central and peripheral nervous systems
control nucleus in hypothalamus and other brainstem areas
motor neurons in the spinal cord and peripheral ganglia
nerve fibers that travel through the cranial and spinal nerves
autonomic pathway
signal must travel across two neurons to get to the target organ
must cross a synapse where these two neurons meet in an autonomic ganglion
presynaptic neuron – first neuron (soma in the brainstem or spinal cord)
postganglionic neuron – second neuron (axon extends the rest of the way to the target cell)

10. Somatic versus Autonomic Pathways
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Somatic efferent innervation
ACh
Myelinated
fiber
Somatic effectors
(skeletal muscles)
Autonomic efferent innervation
ACh
ACh or NE
Myelinated
preganglionic fiber
Unmyelinated
postganglionic fiber
Visceral effectors
(cardiac muscle,
smooth muscle,
glands)
Figure 15.2
Autonomic
ganglion
ANS – two neurons from CNS to effectors
presynaptic neuron whose cell body is in CNS
postsynaptic neuron cell body in peripheral ganglion

11. Sympathetic Division: Efferent Pathways
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Eye
Pons
Salivary glands
Preganglionic neurons
Postganglionic neurons
Regions of spinal cord
Cardiac and
pulmonary plexuses
Heart
Cervical
Thoracic
Lumbar
Sacral
Celiac
ganglion
Lung
Liver and
gallbladder
Superior
mesenteric
ganglion
Stomach
Spleen
Pancreas
Postganglionic fibers to
skin, blood vessels,
adipose tissue
Inferior
mesenteric
ganglion
Small intestine
Large intestine
Sympathetic chain
ganglia
Rectum
Adrenal medulla
Kidney
Figure 15.4
Ovary
Penis
Scrotum
Uterus
Bladder

12. Preganglionic Pathways
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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 sweat glands,
piloerector muscles,
and blood vessels
of skin and
skeletal muscles
To somatic effector
(skeletal muscle) 1
Soma of
somatic motor
neuron 3
White ramus
Communicating
rami
Splanchnic nerve
Gray ramus
Preganglionic neuron
Soma of
postganglionic
neuron
Postganglionic neuron
Collateral ganglion
Somatic neuron
Postganglionic
sympathetic fibers
Sympathetic
trunk
To liver, spleen, adrenal glands,
stomach, intestines, kidneys,
urinary bladder, reproductive organs
Sympathetic
ganglion
Figure 15.5 2

13. Adrenal Glands paired adrenal glands on superior poles of the kidneys
each is two organs with different functions
adrenal cortex (outer layer)
secretes steroid hormones
adrenal medulla (inner core)
essentially a sympathetic ganglion
secretes a mixture of hormones into bloodstream
catecholamines - 85% epinephrine (adrenaline) and 15% norepinephrine (noradrenaline)
also function as neurotransmitters
sympathoadrenal system is the closely related functioning adrenal medulla and sympathetic nervous system

14. Parasympathetic Division: Efferent Pathways
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Parasympathetic Division: Efferent Pathways
Pterygopalatine
ganglion
Preganglionic neurons
Postganglionic neurons
Oculomotor n.
(CN III)
Ciliary ganglion
Lacrimal gland
Eye
Facial n.
(CN VII)
Submandibular
ganglion
Submandibular
salivary gland
Otic ganglion
Glossopharyngeal n.
(CN IX)
Parotid
salivary gland
Vagus n.
(CN X)
Cardiac plexus
Heart
Pulmonary
plexus
Regions of
spinal cord
Esophageal
plexus
Cervical
Lung
Thoracic
Lumbar
Celiac
ganglion
Stomach
Sacral
Liver and
gallbladder
Abdominal
aortic plexus
Spleen
Pelvic
splanchnic
nerves
Pancreas
Kidney and
ureter
Inferior
hypogastric
plexus
Descending
colon
Small intestine
Rectum
Figure 15.7
Pelvic
nerves
Ovary
Penis
Bladder
Uterus
Scrotum

15. Enteric Nervous System
enteric nervous system – the nervous system of the digestive tract
does not arise from the brainstem or spinal cord
innervates smooth muscle and glands
100 million neurons found in walls of the digestive tract
no components in CNS
has its own reflex arcs
regulates motility of esophagus, stomach, and intestines and secretion of digestive enzymes and acid
normal digestive function also requires regulation by sympathetic and parasympathetic systems

16. Megacolon
Hirschsprung disease – hereditary defect causing absence of enteric nervous system
no innervation in sigmoid colon and rectum
constricts permanently and will not allow passage of feces
feces becomes impacted above constriction
megacolon – massive dilation of bowel accompanied by abdominal distension and chronic constipation
maybe colonic gangrene, perforation of bowel, and peritonitis
usually evident in newborns who fail to have their first bowel movement

17. Neurotransmitters and Receptors
how can different autonomic neurons have different effects? constricting some vessels but dilating others
2 fundamental reasons:
sympathetic and parasympathetic fibers secrete different neurotransmitters
target cells respond to the same neurotransmitter differently depending upon the type of receptor they have
all autonomic fibers secrete either acetylcholine or norepinephrine
there are 2 classes of receptors for each of these neurotransmitters

18. Acetylcholine (ACh)
ACh is secreted by all preganglionic neurons in both divisions and the postganglionic parasympathetic neurons
any receptor that binds it is called cholinergic receptor
2 types of cholinergic receptors
muscarinic receptors
Found in all cardiac muscle, smooth muscle, and gland cells
excitatory or inhibitory due to subclasses of muscarinic receptors
nicotinic receptors
on all ANS postganglionic neurons, in the adrenal medulla, and at neuromuscular junctions of skeletal muscle
excitatory when ACh binding occurs

19. Norepinephrine (NE)
NE is secreted by nearly all sympathetic postganglionic neurons
receptors for it called adrenergic receptors
alpha-adrenergic receptors
usually excitatory
2 subclasses (α1 & α2)
beta-adrenergic receptors
usually inhibitory
2 subclasses with different effects (β1 & β2)

20. Neurotransmitters and Receptors
(b) Sympathetic adrenergic fiber
(c) Sympathetic cholinergic fiber
(a) Parasympathetic fiber NE
ACh
Adrenergic receptor
Muscarinic receptor
Nicotinic
receptor
Preganglionic
neuron
Postganglionic
Target
cell
Muscarinic
Neurotransmitters and Receptors
Figure 15.8

21. Overview
sympathetic effects tend to last longer than parasympathetic effects
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
many substances released as neurotransmitters that modulate ACh and NE function
various hormones, neurotransmitters, and the gas, nitric oxide

22. 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

23. Dual Innervation 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
pupillary dilator muscle (sympathetic) dilates pupil
constrictor pupillae (parasympathetic) constricts pupil

24. Dual Innervation of the Iris
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Brain
Parasympathetic fibers
of oculomotor nerve (III)
Sympathetic
fibers
Superior
cervical
ganglion
Ciliary
ganglion
Spinal cord
Cholinergic stimulation
of pupillary constrictor
Iris
Adrenergic
stimulation of
pupillary dilator
Pupil
Sympathetic
(adrenergic) effect
Parasympathetic
(cholinergic) effect
Figure 15.9
Pupil dilated
Pupil constricted

25. Dual Innervation
cooperative effects - when two divisions act on different effectors to produce a unified effect
parasympathetics increase salivary serous cell secretion
sympathetics increase salivary mucous cell secretion

26. Without Dual Innervation
some effectors receive only sympathetic fibers
adrenal medulla, piloerector muscles, sweat glands and many blood vessels
sympathetic vasomotor tone - baseline firing frequency
keeps vessels in state of partial constriction
increase in firing frequency - vasoconstriction
decrease in firing frequency - vasodilation
shifts blood flow from one organ to another as needed
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

27. Sympathetic and Vasomotor Tone
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Artery
sympathetic division prioritizes blood vessels to skeletal muscles and heart in times of emergency 1
Sympathetic
nerve fiber 1
Strong sympathetic
tone 2
Smooth muscle
contraction 2 3
Vasomotor
tone 3
Vasoconstriction
(a) Vasoconstriction
blood vessels to skin vasoconstrict to minimize bleeding if injury occurs during stress or exercise 1 1
Weaker sympathetic
tone 2
Smooth muscle
relaxation 2 3 3
Vasodilation
(b) Vasodilation
Figure 15.10

28. Control of Autonomic Function
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

29. Control of Autonomic Function
ANS regulated by several levels of CNS
midbrain, pons, and medulla oblongata contain:
nuclei for cardiac and vasomotor control, salivation, swallowing, sweating, bladder control, and pupillary changes
spinal cord reflexes
defecation and urination reflexes are integrated in spinal cord
we control these functions because of our control over skeletal muscle sphincters…but if the spinal cord is damaged, the reflexes will remain

30. Drugs and the Nervous System
neuropharmacology – study of effects of drugs on the nervous system
sympathomimetics enhance sympathetic activity
stimulate receptors or increase norepinephrine release
cold medicines that dilate the bronchioles or constrict nasal blood vessels
sympatholytics suppress sympathetic activity
block receptors or inhibit norepinephrine release
beta blockers reduce high BP by interfering with effects of epinephrine/norepinephrine on heart and blood vessels

31. Drugs and the Nervous System
parasympathomimetics enhance activity while parasympatholytics suppress activity
many drugs also act on neurotransmitters in CNS
Prozac blocks reuptake of serotonin to prolong its mood-elevating effect (SSRI: selective serotonin reuptake inhibitor)
MAOI’s (monoamine oxidase inhibitors) prevent MAO from breaking down neurotransmitters like NE
caffeine competes with adenosine (the presence of which causes sleepiness) by binding to its receptors

32. Adenosine and Caffeine
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NH2 N N O
CH3
H3C N N N N OH O O N N
CH3 OH OH
Figure 15.11
Adenosine
Caffeine