1. AUTONOMIC NERVOUS
SYSTEM
Prof. Vajira Weerasinghe
Professor of Physiology

4. 4
Autonomic nervous system
The autonomic nervous system is the
subdivision of the peripheral nervous system
that regulates body activities that are
generally not under conscious control

5. Autonomic (visceral motor)
autonomic
somatic
this dorsal
root ganglion
is sensory
Somatic motor

6. Difference between somatic
motor and autonomic motor
► Somatic motor:
 Cell bodies of motor neurons reside in CNS (brain or
spinal cord)
 Their axons (sheathed in spinal nerves) extend all the
way to their skeletal muscles
 Fast neural transmission
► Autonomic system: chains of two neurons
 1st = preganglionic neuron (in brain or cord)
 2nd = postgangionic neuron (cell body in ganglion
outside CNS)
 Slower because lightly or unmyelinated
6

7. 7
►Axon of 1st (preganglionic) neuron leaves
CNS to synapse with the 2nd
(postganglionic) neuron
►Axon of 2nd (postganglionic) neuron
extends to the organ it serves
Diagram contrasts somatic (lower) and autonomic:
autonomic
somatic
Note: the autonomic ganglion is motor
this dorsal
root ganglion
is sensory

8. Divisions of the autonomic nervous system
►Parasympathetic division
►Sympathetic division
Serve most of the same organs but
cause opposing or antagonistic
effects
cervical, thoracic, lumbar, sacral

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Where they come from
Parasympathetic:
craniosacral
Sympathetic:
thoracolumbar

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Sympathetic nervous system
“fight or flight”
► Also called thoracolumbar system: all its neurons
are in lateral horn of gray matter from T1-L2
► Lead to every part of the body (unlike parasymp.)
 Easy to remember that when nervous, you sweat; when
afraid, hair stands on end; when excited blood pressure
rises (vasoconstriction): these sympathetic only
 Also causes: dry mouth, pupils to dilate, increased heart
& respiratory rates to increase O2 to skeletal muscles,
and liver to release glucose
► Norepinephrine (noradrenaline) is
neurotransmitter released by most postganglionic
fibers (acetylcholine in preganglionic): “adrenergic”

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Sympathetic

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Parasympathetic nervous system
“rest & digest”
►Also called the craniosacral system
because all its preganglionic neurons are
in the brain stem or sacral levels of the
spinal cord
 Cranial nerves III,VII, IX and X
 In lateral horn of gray matter from S2-S4
►Only innervate internal organs (not skin)
►Acetylcholine is neurotransmitter at end
organ as well as at preganglionic synapse:
“cholinergic”

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Parasympathetic continued
► Cranial outflow
 III - pupils constrict
 VII - tears, nasal mucus, saliva
 IX – parotid salivary gland
 X (Vagus n) – visceral organs of thorax & abdomen:
►Stimulates digestive glands
►Increases motility of smooth muscle of digestive tract
►Decreases heart rate
►Causes bronchial constriction
► Sacral outflow (S2-4): form pelvic splanchnic nerves
 Supply 2nd half of large intestine
 Supply all the pelvic (genitourinary) organs

14. 14
Parasympathetic

15. Neurotransmitters
►Somatic = all motor neurons release ACH
which is always stimulatory
►Visceral = ACH & norepinephrine
 All preganglionic fibers release ACH
 All postganglionic PsNS fibers release ACH
 Most postganglionic SNS fibers release norepi
 Can be stimulatory or inhibitory based
on receptor types

16. Comparison of Sympathetic and
parasympathetic Systems

17. Divisions of the ANS
► Sympathetic NS
► Parasymathetic
NS
► Dual innervation
 Opposing effects on the
same organ
► SNS is usually stimulatory
(fight or flight)
► PsNS is usually inhibitory
(body maint. &
conservation of E

18. Sympathetic nervous system
► The sympathetic division is the “fight-or-flight” system
► Involves E activities – exercise, excitement, emergency,
and embarrassment
► Non-essential activities are dampened (GI/urinary)
► Promotes adjustments during exercise – blood flow to
organs is reduced, flow to muscles is increased
► 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
 Bronchioles dilate…increasing ventilation, delivering more oxygen
to cells
 Constriction of visceral & cutaneous bv’s (blood is shunted to
skeletal mm)
 Liver releases more glucose into blood to provide more readily
avail. E
 Targets adipocytes for lipolysis

19. Parasympathetic nervous system
► Salivation, Lacrimation, Urination, Digestion,
Defecation
► Most active in non-stressful situations
► Concerned with keeping body energy use low
► Lenses of eyes accommodated for near vision
► Its activity is illustrated in a person who relaxes
after a meal
 Blood pressure, heart rate, and respiratory rates are
low
 Gastrointestinal tract activity is high
 The skin is warm and the pupils are constricted

20. Differences
Ach (N)
Ach (N) Ach (M)
Nor
Sympathetic
Parasympathetic
Adre

21. Neurotransmitters and Receptors
► Acetylcholine (ACh) and norepinephrine (NE) are the
two major neurotransmitters of the ANS
► ACh is released by all preganglionic axons and all
parasympathetic postganglionic axons
► Cholinergic fibers – ACh-releasing fibers
► Adrenergic fibers – sympathetic postganglionic axons
that release NE
► Neurotransmitter effects can be excitatory or inhibitory
depending upon the receptor type

22. Cholinergic Receptors
►The two types of receptors that bind
ACh are nicotinic and muscarinic
►These are named after drugs that bind
to them and mimic ACh effects

23. Nicotinic Receptors (cholinergic)
►Nicotinic receptors are found on:
 Motor end plates (somatic targets)
 All ganglionic neurons of both sympathetic
and parasympathetic divisions
 The hormone-producing cells of the
adrenal medulla
►The effect of ACh binding to nicotinic
receptors is always stimulatory

24. Muscarinic Receptors
(cholinergic)
►Muscarinic receptors occur on all effector
cells stimulated by postganglionic
cholinergic fibers
►The effect of ACh binding:
 Can be either inhibitory or excitatory
 Depends on the receptor type of the
target organ

25. Adrenergic Receptors
► The two types of adrenergic receptors are alpha
and beta
► Each type has two or three subclasses
( 1, 2, 1, 2 , 3)
► Effects of NE binding to:
 receptors is generally stimulatory
 receptors is generally inhibitory
► A notable exception – NE binding to receptors of
the heart is stimulatory

26. Adrenergic Receptors
►Norepinephrine produces its effects by
combining with adrenergic receptors
 Alpha
 Beta

27. Adrenergic Receptors
►Found in:
 Cardiovascular
 Endocrine
 Gastrointestinal
 Genitourinary
 Respiratory
 Ocular

28. Alpha Receptors
►Alpha 1: adrenergic receptors located on
postsynaptic effector cells.
 Smooth muscles of blood vessels: Constriction
►Arteriolar constriction
 Bladder sphincter
 Penis
 Uterus
 Pupillary muscles of iris

29. Alpha 2
►Same as the Alpha 1 but are located in the
presynaptic nerve terminals.

30. Adrenergic Receptor
►Beta 1
►Cardiovascular
 Cardiac muscle: increased contractility
increased force of contraction
 Atrioventricular node: increased heart rate
 Sinoatrial node: increase in heart rate
►Endocrine
 Pancreas

31. Beta 1 Drugs
►Predominately works on vascular smooth
muscle of the heart.

32. Adrenergic Receptor
►Beta 2
►Cardiovascular
 Dilation of blood vessels
►Endocrine
►Uterine relaxation
►Respiratory: dilation of bronchial muscles

33. Heart
►Direct stimulation of receptors
 Alpha 1 –
►Vasoconstriction of blood vessels which increases
blood pressure
►Pressor or vasopressor effect to maintain blood
pressure
 Beta 1
►Increased force of myocardial contraction
►Increased speed of electrical conduction in the heart.

34. Sympathetic vs parasympathetic
►Distribution on different organs
►Actions on different organs
►Drugs acting on receptors
►Reflexes in different systems

35. Sympathetic vs parasympathetic
►Distribution on different organs

36. Fig. 9.6

37. Sympathetic (Thoracolumbar)
Division
► Preganglionic cell bodies in lateral
horns of spinal cord T1-L2:
thoracolumbar
► Preganglionic axons pass through
ventral roots to white rami
communicantes to the
retroperitoneal sympathetic
chain ganglia

38. Parasympathetic (Craniosacral)
Division
► Preganglionic cell bodies in
nuclei of brainstem or lateral
parts of spinal cord gray matter
from S2-S4
 Preganglionic axons from
brain pass to terminal
ganglia through cranial
nerves III, VII, IX and X
 Preganglionic axons from
sacral region pass through
pelvic nerves to terminal
ganglia
► Terminal ganglia located
near organ innervated or
embedded in wall of organ

41. Sympathetic vs parasympathetic
►Actions on different organs

43. Sympathetic vs parasympathetic
►Drugs acting on receptors

44. Parasympathetic
Sympathetic

48. salbutamol

49. Sympathetic vs parasympathetic
►Reflexes in different systems

50. ANS reflexes
► CVS:
 baroreceptor reflex
 Control of heart rate
 chemoreceptor reflex
► GIT:
 GIT secretions and motility
► Other:
 Urinary bladder control
 Sexual reflexes
 Sweating
 Other visceral reflexes

51. Exception
–
adrenal medulla

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Adrenal glands
On top of kidneys
Adrenal medulla
(inside part) is a
major organ of
the sympathetic
nervous system

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

54. Innervation
Ach

55. Another exception - Sweat glands
► The sweat glands are innervated by the sympathetic
nervous system (part of the fight or flight response
system)
► Preganglionic neuron is short, originates from the
thoracolumbar region of the spinal cord, uses
acetylcholine as its neurotransmitter (nicotinic )
► Postganglionic neuron for sweat gland innervation
differs from other sympathetic postganglionic neurons
in that it releases acetylcholine to act on muscarinic
receptors

57. Another exception – skeletal
muscle blood vessels
►These are also innervated by sympathetic
cholinergic fibres

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Summary