The autonomic nervous system consists of the sympathetic and parasympathetic divisions. The sympathetic division uses norepinephrine as its neurotransmitter and is active during stress responses, while the parasympathetic division uses acetylcholine and is active at rest. Together they control functions like heart rate, digestion, and gland secretion through complementary actions on target organs like the heart and intestines. Pharmacological agents can either mimic or block the neurotransmitters of each division to modulate autonomic functions.

1. 1
The Autonomic Nervous System
Def: The ANS consists of all visceral motor
neurons innervating smooth muscle, cardiac
muscle and glands.
Chapter 60

2. 2

3. 3
Sympathetic and Parasympathetic
Divisions of the ANS
• How they are similar:
– Both divisions are part of
the ANS
– Both have effects on
smooth muscle, cardiac
muscle and glands
• How they differ:
– Stimulation of effectors by
each system vary from one
body system to another.
Effects may be stimulatory
or inhibitory.
– Location
– Length of pre and
postganglionic fiber
– Neurotransmitters used

4. 4
Comparison of ANS and Somatic Motor
Pathways
• Somatics
– Single neuron from spinal
cord to effector
– One neuron innervates the
effector cell
– NTS is acetylcholine (ACh)
• Autonomics
– Two neurons relay
(ganglion) to effector
– Dual innervation of
effectors
– NTS at ganglia (ACh); NTS
at effector can be ACh or
norepinephrine

5. Location and neurotransmitters
used by Sympathetic/Parasymp
sympathetic
parasympathetic
preganglionic neuron
postganglionic neuron
nicotinic receptors muscarinic receptors
adrenergic receptors

6. Characteristics of Sympathetic and
Parasympathetic Function
• Post-ganglionic sympathetic nerves release
norepinephrine at their nerve endings
– these nerves are called adrenergic nerves
• Pre and post-ganglionic parasympathetic
nerves release acetylcholine at their nerve
endings (Nitric oxide- corpora cavernosa)
– these nerves are called cholinergic nerves
• EXCEPTION FOR SYMPATHETIC:
– Cholinergic: mACH; used in body wall.
– Vasodilation of vessels in brain and
skeletal muscle
– Piloerector muscles
– Sweat glands
– Nitric oxide: vasodilation of vessels in
brain, skeletal muscle

7. 7
Sympathetic
Nervous System
“Thoracolumbar”
Figure 60-1;
Guyton & Hall

When active?

Length of pre and
postganglionic
nerve?

Location of cell
bodies of
preganglionic nerve?

Location of cell
bodies of
postganglionic
nerve?

Neurotransmitters
released?

Adrenal medulla

8. 8
Lipolysis and thermogenesisAdipose tissue
β 3
Inhibitory, relaxation of resp. tract to
get dilation
Respiratory tract, GI,
glands, hepatocytes
β 2
Increased heart rate and inotropyHEART, kidney,
adipocytes
β 1
Presynaptic control/ release of NTVascular endothelium
α 2c
Increase vasoconstriction (increased
MI mortality w/polymorphism)
Vascular endothelium
α 2b
Lipid metabolismVascular endothelium
and adipocytes
α 2a
Increased BP, vasoconstrictionArteries, heart
α 1B
Increased inotropy, closure of GI
sphincters, vasoconstriction, pupil
dilation
Iris, intestine, heart and
arteries
α 1a
ActionsWhere found?Receptor

9. 9
Parasympathetic
Nervous System
“cranio-sacral”
Parasympathetic nerves originate
from cranial nerves III, VII, IX, and X
and the sacral spinal cord.
occulomotor nerve - fibers to
the pupillary sphincters and
ciliary muscle
facial nerve - fibers to lacrimal
and submandibular gland
glossopharyngeal nerve - fibers
to parotid gland
vagus nerve - motor inputs to
visceral organs
sacral segments - fibers to
descending colon, rectum,
bladder and genitalia
Figure 60-3;
Guyton & Hall

10. Effects of the ANS on the Organs
• eye
– sympathetic --pupillary dilation
(alpha 1 receptor)
– parasympathetic--pupillary
constriction and
accommodation (focusing) of
the lens (mACh receptor)
• glands of the body
– parasympathetic stimulate the
nasal, lacrimal, salivary, and
G.I. glands (mACh receptor)
– sympathetic stimulates the
sweat glands (mACh receptor)

11. Effect of the Autonomic Nervous
System on the Organs
• G.I. tract
– parasympathetic stimulates overall
activity including G.I. smooth muscle
– sympathetic has very little effect
• heart
– sympathetic increases the rate and
contractility
– parasympathetic decreases heart rate
• blood vessels
– sympathetic causes vasoconstriction.
Reduced sympathetic response accounts
for most vasodilation.
– parasympathetic causes some
vasodilation (e.g., penis)

12. Sympathetic and Parasympathetic
“Tone”
• the basal rate of activity
of each system
• this background activity
allows for an increase or
decrease in activity by a
single system
– sympathetic tone
normally causes about a
50 % vasoconstriction
• increasing or decreasing
“tone” can change vessel
diameter
– parasympathetic tone
provides background
G.I. activity

13. adrenergic or sympathomimetic
drugs act like norepinephrine
• these drugs have an effect which is much more prolonged
than that of either norepinephrine
– phenylephrine stimulates alpha receptors
– isoproterenol stimulates both beta1 and beta2 receptors
– albuterol stimulates only beta2 receptors
• some drugs act indirectly by increasing the release of
norepi from its storage terminals
– ephedrine, amphetamine, pseudoephedrine,

14. Pharmacology of the Sympathetic
Nervous System
• drugs that block the
effect of
norepinephrine
• alpha blockers
– phentolamine
– Cheap Viagra!
• beta blockers
– beta1 and 2 -
propranolol

15. Pharmacology of the
Parasympathetic Nervous System
• parasympathomimetic drugs
– muscarine
– pilocarpine
• activates muscarinic
receptors, cause profuse
sweating (why if sweat
glands are controlled by
sympathetic system?)
• cholinesterase inhibitors
– neostigmine, potentiates the
effect of acetylcholine
• antimuscarinic drugs
– atropine blocks the effect of
acetylcholine on effector cells