1. Learning Objectives: Describe the anatomical differences between
the sympathetic and parasympathetic nervous systems
Describe the differences in the neurotransmitters and their
receptors between the two systems
Describe how the sympathetic and parasympathetic systems
differ in their regulation of the major organ systems
Understand the nature of sympathetic and parasympathetic tone

2. Autonomic Nervous System
(Involuntary or Visceral Nervous System)
I Function --Overview
II. Anatomy
III. Neurotransmitters and receptors
IV. Specific Organ Effects

3. I. Function-- Overview Autonomic nervous system controls
involuntary functions:
arterial pressure
gastrointestinal motility
gastrointestinal secretion
urinary bladder emptying
sweating
body temperature
pupilary dilation and constriction
Striking feature of the ANS is the rapidity and
intensity with which it can change visceral functions
(3-5 seconds)

4. nervous system Peripheral nervous system Central nervous system
Autonomic
nervous system
Somatic
nervous system
Parasympathetic
nervous system
Sympathetic
nervous system

5. Peripheral nervous system
Autonomic
nervous system
Somatic
nervous system
Innervates heart, blood vessels, visceral organs, glands,
and virtually all other organs with smooth muscle;
regulates function of these organs in a
manner beyond conscious (involuntary or automatic) control
Nerves innervating the skeletal muscles;
activity is under conscious (voluntary) control

6. Autonomic nervous system
Parasympathetic
nervous system
Sympathetic
nervous system
“rest and digest”
“Fight or flight”

7. ANATOMY ANS is activated by centers located in spinal cord
brain stem and hypothalamus
ANS often operates by visceral reflexes:
subconscious sensory signals from visceral organs
can enter the spinal cord, brainstem or
hypothalamus and then return subconscious
reflex responses directly back to the visceral
organ to control its activities

8. ANATOMY Autonomic nerves are composed of two neuron relays.
Preganglionic neurons have their cell bodies in the spinal cord
and their activity is controlled by higher brain centers
and spinal reflexes.
Postganglionic neurons send their axons directly to the
effector organ.
Spinal cord
ganglia
Preganglionic neuron
Postganglionic neuron
organ

10. Sympathetic Nervous System
1) preganglionic nerves leave spinal cord at the
thoracic and lumbar levels
2) preganglionic axons are short and myelinated
3) postganglionic axons are long and unmyelinated
4) ganglia are located near the spinal cord

11. Sympathetic nervous system.

12. Parasympathetic Nervous System
1) Nerves leave spinal cord at cranial and sacral levels
cranial nerves innervate head, neck, thorax,
and abdomen
sacral division forms the pelvic nerve and innervates the
remainder of the intestines, bladder and
reproductive organs
2) Preganglionic axons are myelinated and extremely long
3) Postganglionic axons are unmyelinated and short
4) Postsynaptic ganglia located near the effector organ

13. Parasympathetic nervous system
cranial
sacral

14. Next…………...
Neurotransmitters and receptors

15. ALL PREGANGLIONC AXONS USE ACETYLCHOLINE AS THEIR NEUROTRANSMITTER
BUT…………….
Parasympathetic Postganglionic axons
release acetylcholine
Sympathetic Postganglionic axons
release norepinephrine
accept axons on sweat glands, piloerector muscles of the hairs, and some blood vessels which release acetylcholine

16. Adrenal medulla
Stimulation of sympathetic innervation of adrenal medulla
causes release of large quantities of epinephrine (80%)
and norepinephrine (20%)

18. Cholinergic receptors
Nicotinic
Muscarinic
Ganglionic
Skeletal
muscle
Neuronal
CNS M1 M3 M5 M2 M4
Adrenergic receptors a1 a2 b
a1A
a1B
a1D
a2A
a2B
a2C b1 b2 b3

19. Receptors in the parasympathetic system
Nicotinic receptor
Muscarinic receptor
Neuroscience, Sinauer Asssoc., Inc

20. Adrenergic receptors in the sympathetic system
Neuroscience, Sinauer Asssoc., Inc

21. List of relevant receptors and their messengers
Cholinergic receptors:
nicotinic receptor--- ligand-gated ion channel
muscarinic receptor--- G-protein coupled receptor
Adrenergic receptors:
alpha (a1 and a2) receptors
a1: Gq increase in PI turnover
a2: Gi inhibition of adenylate cyclase
beta (b1 and b2) receptors
b1 b2: Gs stimulation of adenylate cyclase

22. Adrenergic receptors:
alpha (a1 and a2) receptors
a1: Gq increase in PI turnover
a2: Gi inhibition of adenylate cyclase
beta (b1 and b2) receptors
b1 b2: Gs stimulation of adenylate cyclase
NE and Epi have same potency at a1 receptors
receptors are much more sensitive to catecholamines
than a1 receptors
NE and Epi are equipotent at b1 receptors
b2 receptors are preferentially activated by Epi

23. a1 receptors:
vascular smooth muscle, on GI and bladder sphincters, and radial muscle of the eye
cause excitation (contraction)
Gq IP3
a2 receptors
presynaptic nerve terminals, platelets, fat cells, walls of GI tract
cause inhibition (relation, dilitation)
inhibition of adenlyate cyclase and decrease in cAMP
b1 receptors
SA node, AV node, ventricular muscle of heart
produce excitation (increaes heart rate, contactility, increased conduction
velocity
stimulation of adenylate cyclase and increase in cAMP
b2 receptors
vascular smooth muscle of skeletal muscle, bronchioles, walls fo Gi tract and bladder
produce relaxation (dilation of vascular smooth muscle and bronchioles, relaxation of bladder wall)

25. Comparison of the Components of the Peripheral Nervous System
Parasympathetic Nervous System
Preganglionic
Neuron
Postganglionic
Synaptic connection
Ganglion near organ
At organ
Neuron length
Long
Short
Neurotransmitter
Acetylcholine
Sympathetic Nervous System
Ganglion near spinal cord
Norepinephrine
Somatic Motor Nervous System
At skeletal muscle

26. Organs are usually innervated by both systems
in opposing roles

28. Sympathetic Nervous System Receptors at Target Organs
Organ Action Receptor
Heart heart rate b1
contactility
AV node conduction
Vascular smooth constrict blood vessels a1
muscle dilates blood vessels
in skeletal muscles
Gastrointestinal motility a2, b2
Tract constricts sphincters
Bronchioles dilates bronchiolar b2
pupil dilation a1
smooth muscle
Bladder relaxes bladder wall b2
constricts sphincter a

29. Sympathetic Nervous Con’t
organ action receptor
sweat glands sweating muscarinic
goose bumps contracts a
kidney renin secretion b1
Male genitalia ejaculation a
fat cells lipolysis b1

30. Parasympathetic Action
Organ Action Receptor
Heart heart rate M
contractility
AV node conduction
Gastrointestinal motility M
Tract relaxes sphincters
Bronchioles constricts M
Male sex organs erection M
Bladder contracts wall M
relaxes sphincter
Pupil constriction M

31. Ganglionic blockers
These drugs block both divisions of the autonomic nervous system
equally.
However, the end-organ response may show a predominant adrenergic
or cholinergic. Therefore interruption of ganglionic transmission has
the effect of selectively eliminating the dominant component.

32. Sympathetic and Parasympathetic “tone”
Continual basal activity of the sympathetic
and parasympathetic systems allows either branch
of the ANS to increase or decrease its activity
of a stimulated organ
Sympathetic tone caused by basal secretion
from adrenal medulla

33. Denervation supersensitivity
Guyton and Hall fig 60-4

34. Increased arterial pressure
“Alarm” or “Stress” Response
Large portions of the sympathetic nervous system discharge simultaneously-----this increases the body’s ability to perform vigorous muscle activity
Increased arterial pressure
Increased blood flow to the skeletal muscles with concurrent decrease
blood flow to GI tract, kidneys
Increased metabolism
Increased blood glucose concentration
Increased glycoglysis in liver and muscle
Increased muscle strength
Increased mental activity
Increased rate of blood coagulation

35. Autonomic Reflexes cardiovascular reflexes gastrointestinal reflexes
bladder emptying
sweating
blood glucose concentration
sexual reflexes

36. Enteric Nervous System
Gastrointestinal tract nervous system
Myenteric plexus (auberbach’s)
meissner’s plexus (submucosal)
Sympathetic and Parasympathetic systems
interact with the Enteric System
Acetylcholine most often excites and
Norepinephrine inhibits