1. The Autonomic System Ching-Liang Lu, M.D. Professor
Institute of Brain Science
National Yang-Ming
University

2. Autonomic Nervous System (ANS)
Innervate smooth and cardiac muscle and glands
Make adjustments to ensure optimal support for body activities
Operate via subconscious control
Have viscera as most of their effectors

3. Somatic vs. Visceral attribute Somatic System Visceral System
embryological origin of tissue
“body wall:” somatic (parietal) mesoderm (dermatome, myotome)
“organs:” splanchnic (visceral) mesoderm, endoderm
examples of adult tissues
dermis of skin, skeletal muscles, connective tissues
glands, cardiac muscle, smooth muscle
perception
conscious, voluntary
unconscious, involuntary

4. Sensory/Motor + Somatic/Visceral
(Afferent)
somatic sensory
[General Somatic Afferent (GSA)]
visceral sensory
[General Visceral Afferent (GVA)]
Motor
(Efferent)
somatic motor
[General Somatic Efferent (GSE)]
visceral motor
[General Visceral Efferent (GVE)]
Somatic
Nervous
System
Autonomic
Nervous
System

5. Divisions of the ANS
Sympathetic division (thoracolumbar,“fight or flight”)
Thoracic and lumbar segments
Parasympathetic division
(craniosacral, “rest and repose”)
Preganglionic fibers leaving the brain and sacral segments
Enteric nervous system (ENS)
May work independently

6. Sympathetic and Parasympathetic
Often they have opposing effects
May work independently
May work together each one controlling one stage of the process

7. Functional Differences
Overview of ANS
Functional Differences
Sympathetic
• “Fight or flight”
• Catabolic (expend energy)
Parasympathetic
• “Feed & breed”, “rest & digest”
• Homeostasis
» Dual innervation of many organs — having a brake and an accelerator provides more control

8. Somatic vs. Autonomic Nervous Systems
The ANS differs from the SNS in the following three areas
Effectors
Efferent pathways
Target organ responses

9. Somatic vs. Autonomic Systems: Effector
The effectors of the SNS are skeletal muscles
The effectors of the ANS are cardiac muscle, smooth muscle, and glands

10. Somatic vs. Autonomic Systems: Efferent Pathways
Heavily myelinated axons of the somatic motor neurons extend from the CNS to the effector
Axons of the ANS are a two-neuron chain
The preganglionic (first) neuron has a lightly myelinated axon
The ganglionic (second) neuron extends to an effector organ

11. Somatic vs. Autonomic Systems

12. Overview of the Autonomic Nervous System
Similarities between Sympathetic & Parasympathetic
• Both are efferent (motor) systems: “visceromotor”
• Both involve regulation of the“internal”environment generally outside of our conscious control: “autonomous”
• Both involve 2 neurons that synapse in a peripheral ganglion
• Innervate glands, smooth muscle, cardiac muscle
glands
ganglion
CNS
smooth
muscle
cardiac
muscle
preganglionic
neuron
postganglionic
neuron

13. Location of Preganglionic Cell Bodies
Overview of the Autonomic Nervous System
Differences between Sympathetic & Parasympathetic
Location of Preganglionic Cell Bodies
Sympathetic
Parasympathetic
Thoracolumbar
T1 – L2/L3 levels of the spinal cord
Craniosacral
Brain: CN III, VII, IX, X
Spinal cord: S2 – S4

14. Relative Lengths of Neurons
Overview of the Autonomic Nervous System
Differences between Sympathetic & Parasympathetic
Relative Lengths of Neurons
Sympathetic
target
ganglion
CNS
short preganglionic
neuron
long postganglionic
neuron
Parasympathetic
target
ganglion
CNS
long preganglionic
neuron
short postganglionic
neuron

15. NE (ACh at sweat glands),
Overview of the Autonomic Nervous System
Differences between Sympathetic & Parasympathetic
Neurotransmitters
Sympathetic
NE (ACh at sweat glands),
+ / -, α & ß receptors
ACh, +
• All preganglionics release acetylcholine (ACh) & are excitatory (+)
• Symp. postgangl. — norepinephrine (NE) & are excitatory (+) or inhibitory (-)
• Parasymp. postgangl. — ACh & are excitatory (+) or inhibitory (-)
• Excitation or inhibition is a receptor-dependent & receptor-mediated response
ACh, +
Parasympathetic
Potential for pharmacologic
modulation of autonomic responses
ACh, + / -
muscarinic receptors

16. Overview of the Autonomic Nervous System
Differences between Sympathetic & Parasympathetic
Target Tissues
Sympathetic
Parasympathetic
• Organs of head, neck, trunk, & external genitalia
• Organs of head, neck, trunk, & external genitalia
• Adrenal medulla
• Sweat glands in skin
• Arrector muscles of hair
• ALL vascular smooth muscle
» Sympathetic system is distributed to essentially all tissues (because of vascular smooth muscle)
» Parasympathetic system never reaches limbs or body wall (except for external genitalia)

17. Sympathetic division anatomy
Preganglionic neurons between segments T1 and L2 – lateral gray horn of spinal cord
Preganglionic fibers
Short
Travel in the ventral root and spinal nerve
Ganglionic neurons in ganglia near vertebral column
Specialized neurons in adrenal glands
Postganglionic fibers
Long fibers

18. Sympathetic ganglia Sympathetic chain ganglia (paravertebral ganglia)
Typically there are 23 ganglia – 3 cervical, 11 thoracic, 4 lumbar, 4 sacral, and 1 coccygeal
Collateral ganglia (prevertebral ganglia)
Adrenal medulla

19. Structure of spinal nerves: Somatic pathways
dorsal
ramus
dorsal root
ganglion
dorsal root
spinal
nerve
somatic
sensory
nerve
(GSA)
dorsal
horn
CNS
inter-
neuron
somatic
motor
nerve
(GSE)
ventral
horn
ventral
ramus
gray ramus
communicans
ventral root
white ramus
communicans
Mixed Spinal
Nerve
sympathetic
ganglion

20. Structure of spinal nerves: Sympathetic pathways
dorsal
ramus
intermediolateral
gray column
spinal
nerve
ventral
ramus
gray ramus
communicans
white ramus
communicans
sympathetic
ganglion

21. Organization and anatomy of the sympathetic division
Segments T1-L2, ventral roots give rise to myelinated white ramus
Leads to sympathetic chain ganglia

22. Postganglionic fibers of the sympathetic ganglia
Some fibers will return to the spinal nerve through a gray ramus and will innervate skin, blood vessels, sweat glands, adipose tissue, arrector pili muscle
Some fibers will form sympathetic nerves that will innervate thoracic organs
Go directly to innervate the thoracic organs

23. Sympathetic System: Postganglionic Cell Bodies
1. Paravertebral ganglia
• Located along sides of vertebrae
• United by preganglionics into Sympathetic Trunk
• Preganglionic neurons are thoracolumbar (T1–L2/L3) but postganglionic neurons are cervical to coccyx
• Some preganglionics ascend or descend in trunk
Paravertebral
ganglia
sympathetic
trunk (chain)
synapse at
same level
Prevertebral ganglia
• celiac ganglion
• sup. mesent. g.
• inf. mesent. g.
ascend to
synapse at
higher level
descend to
synapse at
lower level
aorta
Moore’s COA5 2006

24. Collateral (prevertebra) ganglia
Preganglionic fibers will pass through the sympathetic chain without synapsing
Preganglionic fibers will synapse within collateral ganglia (prevertebra ganglia)
Splanchnic nerves will synapse on one of the 4 collateral ganglions

25. Collateral (prevertebra) ganglia
Celiac ganglion
Postganglionic fibers innervates stomach, liver, gall bladder, pancreas, spleen
Superior mesenteric ganglion
Posganglinic fibers innervates small intestine and initial portion of large intestine
Inferior mesenteric ganglion
Postganglionic fibers innervate the final portion of large intestine
Inferior hypogastric
Posganglionic fibers innervates urinary bladder , sex organs

26. Sympathetic System: Postganglionic Cell Bodies
2. Prevertebral (preaortic) ganglia
• Located anterior to abdominal aorta, in plexuses surrounding its major branches
• Preganglionics reach prevertebral ganglia via abdominopelvic splanchnic nerves
Paravertebral
ganglia
sympathetic
trunk (chain)
Prevertebral ganglia
• celiac ganglion
• sup. mesent. g.
• inf. mesent. g.
inf. hypogastric
abdominopelvic
splanchnic
nerve
aorta
Moore’s COA5 2006

27. Adrenal medulla
Preganglionic fibers will pass through sympathetic ganglia without synapsing
Preganglionic fibers will synapse on adrenal medulla
Adrenal medulla will secrete
Epinephrine
Norepinephrine

28. Adrenal medulla Neurotransmitter will go into general circulation
Their effects last longer than those produced by direct sympathetic innervation

29. Adrenal gland is exception
Synapse in gland
Can cause body-wide release of epinephrine (adernalin) and norepinephrine in an extreme emergency
(adrenaline “rush” or surge)

30. Sympathetic System: Summary
visceral tissues
(organs)
Cardiopulmonary Splanchnics: postganglionic fibers to thoracic viscera
somatic tissues
(body wall, limbs) T1
postganglionics
via 31 spinal nerves
to somatic tissues of neck, body wall, and limbs
Abdominopelvic Splanchnics: preganglionic fibers to prevertebral ganglia, postganglionic fibers to abdominopelvic viscera
sympathetic
trunk L2
prevertebral
ganglia
Moore’s COA5 2006

31. Role of the Sympathetic Division
The sympathetic division is the “fightor-flight” system
Involves E activities – exercise, excitement, emergency, and embarrassment
Promotes adjustments during exercise– blood flow to organs is reduced, flow to muscles is increased

32. Role of the Sympathetic Division
Its activity is illustrated by a person who is threatened
Heart rate increases, and breathing is rapid and deep
The skin is cold and sweaty, and the pupils dilate

33. Parasympathetic division (craniosacral division)
Preganglionic neurons in the brainstem(nuclei of cranial nerves III, VII, IX, X) and sacral segments of spinal cord (S2-S4)
Ganglionic neurons in peripheral ganglia located within or near target Organs
Terminal ganglion
Intramural ganglion

34. Parasympathetic Division Outflow

35. Parasympathetic Pathways Cranial outflow Sacral outflow
• CN III, VII, IX, X
• Four ganglia in head
• Vagus nerve (CN X) is major preganglionic parasymp. supply to thorax & abdomen
• Synapse in ganglia within wall of the target organs (e.g., enteric plexus of GI tract)
Sacral outflow
• S2–S4 via pelvic splanchnics
• Hindgut, pelvic viscera, and external genitalia
Clinical Relevance
» Surgery for colorectal cancer puts pelvic splanchnics at risk
» Damage causes bladder & sexual dysfunction
Moore’s COA5 2006

36. Parasympathetic activation
Effects produced by the parasympathetic division
Relaxation
food processing
energy absorption
Pupil constriction
Constriction of respiratory passageway
Decrease heart rate and blood pressure
Stimulates defecation and urination

37. Referred Pain
Pain stimuli arising from the viscera are perceived as somatic in origin
This may be due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers

38. Visceral Afferents and Referred Pain
dorsal root ganglion
Visceral sensory nerves [GVA]
• run with sympathetic nerves
• cell bodies in dorsal root ganglion
• nerve ending in viscera
Somatic sensation:
• conscious, sharp, well-localized
• touch, pain, temperature, pressure, proprioception
Visceral sensation:
• often unconscious; if conscious: dull, poorly-localized
• distension, blood gas, blood pressure, cramping, irritants

39. Visceral Afferents and Referred Pain
• Pain originating in a visceral structure perceived as being from an area of skin innervated by the same segmental level as the visceral afferent
• Results from convergence of somatic & visceral afferents on the same segmental level of the spinal cord
• “Cross-talk” in the dorsal horn
convergence &
“cross-talk”
somatic afferent
visceral afferent
Kandel et al. 2000

40. Visceral Afferents and Referred Pain
Maps of Referred Pain
Grant’s Atlas

41. Interactions of the Autonomic Divisions
Most visceral organs are dual-innervated
both sympathetic and parasympathetic fibers
 dynamic antagonisms that precisely control visceral activity
Sympathetic fibers increase heart and respiratory rates, and inhibit digestion and elimination.
Parasympathetic fibers decrease heart and respiratory rates, and allow for digestion and the discarding of wastes

42. Cooperative Effects Example: control of external genitalia
Parasympathetic fibers:
vasodilation  erection of the penis and clitoris
Sympathetic fibers
cause ejaculation of semen in males and reflex contraction of a female vagina

43. Unique Roles of the Sympathetic Division
Regulates many functions not subject to parasympathetic influence
These include the activity of the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels
The sympathetic division controls:
Thermoregulatory responses to heat
Release of renin from the kidneys
Metabolic effects
Raises blood glucose levels
Mobilizes fat as a food source
Stimulates the reticular activating system (RAS) of the brain, increasing mental alertness

44. Localized Versus Diffuse Effects
The parasympathetic division exerts short-lived, highly localized control
The sympathetic division exerts long-lasting, diffuse effects

45. Central control of the Autonomic NS
Amygdala: main limbic region for emotions
-Stimulates sympathetic activity, especially previously learned fear-related behavior
-Can be voluntary when decide to recall frightful experience - cerebral cortex acts through amygdala
-Some people can regulate some autonomic activities by gaining extraordinary control over their emotions
Hypothalamus: main integration center
Reticular formation: most direct influence over autonomic function

46. Hypothalamic Control Centers of the hypothalamus control:
Heart activity and blood pressure
Body temperature, water balance,and endocrine activity
Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex)
Reactions to “fear” and the “fight or-flight” system

47. Neural innervation of bowel
Autonomic nervous system
Extrinsic set of nerves
Parasympathetic
Sympathetic
Enteric nervous system (ENS)
Intrinsic set of nerves
~108 neurons - similar to spinal cord  “brain of gut”
Neurons extending from esophagus to anus
2 plexuses
Myenteric plexus
Submucosal plexus

48. Neuroanatomy of ENS

49. Intrinsic Nervous System
Myenteric plexus (Auerbach)
Located between the longitudinal and circular layers of muscle in the tunica muscularis
Controls tonic and rhythmic contractions
Exerts control primarily over digestive tract motility
Submucosal plexus (Meissner)
Buried in the submucosa
Senses the environment within the lumen
Regulates GI blood flow
Controls epithelial cell function (local intestinal secretion and absorption)
May be sparse or missing in some parts of GI tract

50. Intrinsic Nervous System
3 types of neurons in enteric system
Sensory neurons (5 types)
Chemoreceptors sensitive to acid, glucose and amino acids have been demonstrated which, in essence, allows "tasting" of lumenal contents. Sensory receptors in muscle respond to stretch and tension
Motor neurons
Control GI motility and secretion, and possibly absorption
Interneurons
Largely responsible for integrating information from sensory neurons and providing it to motor neurons

51. Interstitial cell of Cajal (ICC) : Pacemaker cell of GI tract
Network within the muscularis propria
Specialized mesenchymal cells
Generate spontaneous electrical activity
Actually the slowwave of the smooth muscle in GI tract is controlled in a specilized cells, called interstitial cell of cajal. The ICC are found in the gut muscle wall. These cells are neither neuron nor muscle, but are a group of specilized mesenchmal cells. And GIST is the abnormal proliferation of ICC. ICC can generate the slow waves, so it can be called the pacemaker cells of the GI tract.
J Physiol 2001; 531: 827