Autonomic Nervous System Physiology

1. AUTONOMIC NERVOUS SYSTEM

3. Learning Objectives
• List the divisions of nervous system
• List the structural differences between
autonomic and somatic nervous system
• Describe the organisation of autonomic
nervous system
• Describe the origin and course of sympathetic
and parasympathetic fibres

4. Nervous
System
Central
Nervous
System
Brain Spinal Cord
Peripheral
Nervous
System

6. Autonomic = Free will
• Cardiovascular system
• Respiratory system
• Endocrine system
• Reproductive system
• Gastrointestinal system
• Renal system
• Musculoskeletal system
Autonomic Nervous System
Somatic Nervous System

7. ANS
• Homeostasis
• Coordinates responses to external stimuli
• Survival possible without ANS
• But ability to combat stress difficult

8. DIVISIONS OF ANS
1. Motor system – sympathetic & parasympathetic
2. Enteric nervous system of GIT
3. Visceral afferent pathways sensory
4. Descending pathways from forebrain, brainstem

9. Autonomic Motor System
Classical feature:
TWO MOTOR NEURON PATHWAY

12. • Preganglionic neurons:
B fibers – small diameter, myelinated , slow
conducting
• Postganglionic neurons:
C fibers – small, unmyelinated, slow
conducting

13. Erlanger and Gasser Classification
A and B fibers are Myelinated; C fibers are unmyelinated

15. Classification of Autonomic Motor System
Motor fibers of ANS are classified into
1. Sympathetic division
2. Parasympathetic division

18. Cranial
Outflow
Sacral
Outflow
Thoracolumbar
Outflow

22. The Sympathetic Nervous System

23. The Sympathetic Nervous System

27. Paravertebral Ganglion

28. Sympathetic Nervous System

29. Sympathetic Nervous System

30. The Adrenal Medulla
Similarities between adrenal medulla and
postganglionic sympathetic neurons
1. Both are excited by preganglionic
sympathetic fibres
2. Both respond to ACh
3. Both release catecholamines in response to
stimulation

31. Adrenal Medulla is a part of sympathetic nervous system

34. Oculomotor Nerve

35. Facial Nerve

36. Glossopharyngeal Nerve

37. Vagus Nerve

38. Sacral Outflow
S2, S3, S4 sacral spinal segments
supply,
• The distal colon
• Sex organs
• Organs within the pelvic cavity

40. Parasympathetic Nervous System

41. Impulse transmission
In ANS

43. Otto Loewi’s experiment – chemical
transmission of nerve impulses.

44. “Vagusstoff”

45. All preganglionic sympathetic neurons secrete ACh

46. Postganglionic parasympathetic neurons - Cholinergic
Acetylcholine

47. Postganglionic sympathetic neurons - Adrenergic
Norepinephrine is the
predominant
neurotransmitter
released by the
Postganglionic
sympathetic neurons
Exceptions – sweat
glands, blood vessels of
skeletal muscles ,
piloerector muscles –
Ach

48. Postganglionic sympathetic neurons - Adrenergic
Epinephrine constitutes
80% of catecholamines
secreted by the adrenal
medulla

49. Synthesis of Acetylcholine
Synthesized in the terminal endings of cholinergic
fibres

50. Termination of ACh action
• Acetylcholinesterase – split ACh into acetate
and choline
• Choline is taken up by the nerve terminal for
resynthesis of ACh.

51. Synthesis of epinephrine & norepinephrine
• Synthesis of epinephrine & norepinephrine
begins in the axoplasm and is completed
inside the vesicle

52. Termination of adrenergic action
1. Reuptake into nerve endings
2. Diffusion into blood
3. Degraded by enzymes Mono Amine
Oxidase(MAO), Catechol-O-Methyl
transferase(COMT).

53. • Cholinergic – pertaining to Acetylcholine
• Adrenergic – pertaining to adrenaline &
noradrenaline

54. Cholinergic neurons in the ANS
1. All preganglionic neurons
2. All parasympathetic postganglionic neurons
3. Sympathetic postganglionic neurons that innervate
sweat glands
4. Sympathetic cholinergic fibres – sympathetic
postganglionic neurons that end on blood vessels in
some skeletal muscles and produce vasodilation when
stimulated (sympathetic vasodilator nerves)

55. Cholinergic Receptors

56. Nicotinic acetycholine receptors

57. Muscarinic acetylcholine receptors

58. Adrenergic receptors

59. Sympathetic & parasympathetic tone
The normal basal firing of sympathetic and
parasympathetic neurons is called the
‘sympathetic & parasympathetic tone’
eg: Blood vessels – sympathetic tone
GI tract – parasympathetic
Heart

60. Postganglionic sympathetic and
parasympathetic neurons have muscarinic
as well as nicotinic receptors
• Nicotinic receptor – Ionotropic (ligand gated)
• Muscarinic receptor – Metabotropic (GPCR)

62. Nonadrenergic, noncholinergic
transmitters can be released at each
level of ANS
• ATP
• Neuropeptide Y
• Vasoactive intestinal peptide (VIP)
• Sub P
• Encephalins
• Somatostatins.....

65. Effect of sympathetic and
parasympathetic stimulation on
different target organs

66. Responses of effector organs
1. Dual antagonistic control (Heart)
2. Complementary (Salivary glands)
3. Synergistic (Male sexual function)
4. Exclusively one innervation (Blood vessels,
sweat glands)

67. Effect on Eye
PARASYMPATHETIC SYMPATHETIC
Pupillary constriction
(Miosis)
Pupillary dilation
(Mydriasis)

68. Effect on Heart
PARASYMPATHETIC SYMPATHETIC
Decreases heart rate Increases heart rate
Decreases force of
contraction
Increases force of
contraction
Decreases conduction
velocity
Increases conduction
velocity

72. Parasympathetic nervous
system
Sympathetic nervous
system
Male Sex Organ Erection Ejaculation
Skin
Pilomotor muscle - Contraction
Sweat gland Secretion
Salivary Gland Profuse, watery secretion Thick, viscous secretion
Lacrimal Gland Secretion -

73. Enteric Nervous System

74. ENTERIC NERVOUS SYSTEM
• 3rd division of ANS
1. Myentric plexus – b/w longitudinal & circular M
control motility
2. Meissner’s plexus – b/w circular M & mucosa
control blood flow to GIT & secretions

75. ENS

76. ENTERIC NERVOUS SYSTEM
• MINIBRAIN
• Sensory N , interN, motor N
• Regulated by sympathetic and parasympathetic
nervous system
• But can also function autonomously

77. Higher centre inputs to autonomic
preganglionic neurons

78. HIGHER CONTROL:
• Greatest control by HYPOTHALAMUS
• Called as HEAD GANGLION of ANS – by
Sherrington
• HR, RR, temp, water & food intake

79. Applied Physiology and
Pharmacology of ANS

80. Horner’s Syndrome
Consists of a triad of signs,
• 1.Miosis
• 2.Anhydrosis (loss of sweating) of half the face
• 3.Ptosis (Drooping of eyelid)
Damage to the sympathetic supply to the face.
Causes:
• 1.Lesion in the brainstem
• 2.Lesion in the sympathetic ganglion
• 3.Damage to the nerves

81. Multiple system atrophy(MSA)/Shy-Dagger
syndrome

82. Mushroom poisoning

83. Autonomic Drugs

84. • Cholinoceptor activating drugs
Example: Carbachol, bethanachol
Uses:
1.Paralytic ileus
2.Urinary retention
• Cholinesterase inhibitors
Example: Physostigmine, neostigmine
Organophosphosphate insecticides Nerve gases
Uses:
1.Myasthenia gravis

85. Cholinoceptor blockers
Muscarinic blockers
Example: Atropine
Uses:
1.Pupillary dilation
2.Antidiarrheoal drugs
3.To relieve bladder spasm
Nicotinic blockers

86. Sympathomimetics

87. α and β-adrenergic blockers

88. Summary

89. Sympathetic & parasympathetic
nervous system

90. Effect on target organs