Introduction to the autonomic nervous system

1. INTRODUCTION TO AUTONOMIC
NERVOUS SYSTEM
DR NASER ASHRAF TADVI

2. OBJECTIVES
• Describe distribution of ANS
• Enlist differences between ANS and PNS
• Describe Neurohumoral transmission
• Enlist main neurotransmitter for Sympathetic and
Parasympathetic NS
• Enlist receptors for Sympathetic and Parasympathetic nervous
system
• Briefly describe the synthesis of Acetyl choline and
Catecholamines

3. Introduction to ANS
• Peripheral nervous system is divided into
– Somatic nervous system (SNS)
– Autonomic nervous system (ANS)

4. Differences between Somatic and
autonomic nervous system
Somatic Autonomic
1 Organ supplied Skeletal Muscles All other organs
2 Distal most synapse Within CNS Outside CNS (in
ganglia)
3 Nerve fibers Myelinated Preganglionic
Myelinated
Post Ganglionic
Non myelinated
4 Peripheral plexus formation Absent Present
5 Primary efferent transmitter Acetylcholine(Ach) Ach, Noradrenaline
6 Effect of nerve section on
organ supplied
Paralysis &
atrophy
Activity maintained,
no atrophy

5. Autonomic innervation

6. Distribution of parasympathetic nervous system

7. Distribution of Sympathetic nervous system

8. ANS FIBRES
Afferents
Efferent
Sympathetic nervous system Para sympathetic nervous system
•Origin: thoraco lumbar (lateral
horns) outflow C8 to L2/L3
•Ganglia – paravertebral (22 pairs)
•Prevertebral (coeliac,
superior & inferior mesentric
& aortorenal)
•Adrenal medulla
•Terminal (u. bladder, rectum)
•Cranio sacral
•Midbrain – 3rd
•Medulla – 7,9,10
Sacral – 2,3,4, (nervi
erigentis)
• terminal near/with in
innervated tissue.

9. • Symp n. system
• Neurotansmitter
• PSNS
• Neurotansmitter
Nonadrenaline/
ADR
Acetyl
choline
•Function: prepare body
for fight
Acetyl choline
Acetyl choline
•Tissue building reaction

11. Differences between sympathetic &
parasympathetic
Features Sympathetic Parasympathetic
1 Origin From CNS Thoracolumbar
segments of spinal cord
(T1-T12, L1-L3)
Craniosacral regions (Cranial
nerves 3, 7,9,10 & sacral
segments of spinal cord S 2,3,4)
2 Preganglionic
fiber
Short Myelinated Long Myelinated
3 Ganglia Located away from the
organs of innervation
Located very close to organs of
innervation
4 Post ganglionic
Fiber
Long non myelinated Short non myelinated
5 Response to
stimulation
Diffused or generalized Localized reaction
6 Neurotransmitter
Preganglionic
Post Ganglionic
Acetylcholine
Noradrenaline
Acetylcholine
Acetylcholine
7 Important
function
Tackling stress and
Emergency
Assimilation of food and
conservation of energy

12. Neurohumoral transmission

13. Mechanisms of
termination of
neurotransmitter
action

14. Co-transmission
Examples of co-transmitters
• Purines : ATP, Adenosine
• VIP, NPY
• Substance P, enkephalins
• Somatostatin
• Nitric oxide

15. Synthesis of catechol amines

16. Synthesis of acetyl choline

17. Cholinergic receptors
Nicotinic Muscarinic
NM
(Skeletal
muscle)
NN
(Ganglia)
M1
•CNS
•GASTRIC
SECRETION
M2
Heart
M3
Smooth muscle
& Gland
secretion

18. Adrenergic receptors

19. Important terminology
• Sympathomimetic (Adrenergic)
• Sympatholytic (Antiadrenergic)
• Parasympathomimetic (Cholinergic)
• Parasympatholytic (Anticholinergic)

20. Summary
• Distribution
• Neurohumoral transmission
• Main neurotransmitters
• Main receptors

21. Which of the following is correct regarding the autonomic
nervous system (ANS)?
A. Afferent neurons carry signals from the CNS to the
effector organs.
B. The neurotransmitter at the parasympathetic ganglion is
norepinephrine (NE).
C. The neurotransmitter at the sympathetic ganglion is
acetylcholine (ACh).
D. Sympathetic neurons release ACh in the effector organs.
E. Parasympathetic neurons release NE in the effector
organs.

22. Which of the following is correct regarding
somatic motor neurons?
A. The neurotransmitter at the somatic motor
neuron ganglion is acetylcholine.
B. The neurotransmitter at the somatic motor
neuron ganglion is norepinephrine.
C. Somatic motor neurons innervate smooth
muscles.
D. Somatic motor neurons do not have ganglia.
E. Responses in the somatic motor neurons are
generally slower than in the autonomic nervous
system.

23. Which of the following physiological changes could happen
when a person is attacked by a dog?
A. Increase in heart rate.
B. Increase in lacrimation (tears).
C. Constriction of the pupil (miosis).
D. Increase in gastric motility.

24. A. Reduction in heart rate.
B. Constriction of the pupil (miosis).
C. Increase in gastric motility.
D. Dry mouth (xerostomia).
E. Contraction of detrusor muscle in the
bladder.
Which of the following changes could theoretically
happen in a person when the parasympathetic
system is inhibited using a pharmacological agent?

25. Which of the following is correct regarding
neurotransmitters and neurotransmission?
A. Neurotransmitters are released from the
presynaptic nerve terminals.
B. Neurotransmitter release is triggered by the
arrival of action potentials in the postsynaptic
cell.
C. Intracellular calcium levels drop in the neuron
before the neurotransmitter is released.
D. Serotonin and dopamine are the primary
neurotransmitters in the ANS.

26. All of the following statements regarding central
control of autonomic functions are correct except
A. Baroreceptors are pressure sensors located
at various cardiovascular sites.
B. The parasympathetic system is activated by
the CNS in response to a sudden drop in
blood pressure.
C. The parasympathetic system is activated by
the CNS in response to a sudden increase
in blood pressure.
D. The sympathetic system is activated by the
CNS in response to a sudden drop in blood
pressure.