General physiology

1. AUTONOMIC NERVOUS
SYSTEM
Dr. E. Ramnath,
I yr Post Graduate,
Department of Periodontology.

2. CONTENTS
 INTRODUCTION
 GENERAL ORGANIZATION OF AUTONOMIC NERVOUS SYSTEM
 PHYSIOLOGIC ANATOMY OF SYMPATHETIC NERVOUS SYSTEM
 PHYSIOLOGIC ANATOMY OF PARASYMPATHETIC NERVOUS SYSTEM
 BASIC CHARACTERISTICS OF SYMPATHETIC AND PARASYMPATHETIC
FUNCTION
 RECEPTORS ON EFFECTOR ORGANS
 EXCITATORY AND INHIBITORY ACTIONS OF SYMPATHETIC AND
PARASYMPATHETIC STIMULATION
 ALARM REACTION
 PHARMACOLOGY OF AUTONOMIC NERVOUS SYSTEM
 TESTS OF AUTONOMIC NERVOUS SYSTEM

3. INTRODUCTION

4. AUTONOMIC NERVOUS SYSTEM
 “auto” – Self, “nomous” - Control
 AUTONOMOUS NERVOUS SYSTEM Controls most visceral functions of the body.
 Controls, ARTERIAL PRESSURE, GI MOTILITY, GI SECRETION, URINARY
BLADDER EMPTYING, SWEATING, BODY TEMPERATURE.
 RAPID AND INSTENSE ACTIVITY

5. IMPORTANCE
The ANS is most important in two situations:
1- In emergencies that cause stress and require us to "fight" or take "flight" (run
away).
2- In no emergencies that allow us to "rest" and "digest".

6. GENERAL ORGANIZATION OF
AUTONOMIC NERVOUS SYSTEM
 ACTIVATION: Centers located in spinal cord, brain stem, hypothalamus, portions
of cerebral cortex, esp. limbic cortex.
 Operates through VISCERAL REFLEXES
 Autonomic signal transmission through two subdivisions:
 SYMPATHEIC NERVOUS SYSTEM
 PARASYMPATHETIC NERVOUS SYSTEM
Chain of two neurons
 Preganglionic neuron
 Postganglionic neuron

7. Visceral Reflex Arc

8. PHYSIOLOGIC ANATOMY OF SYMPATHETIC
NERVOUS SYSTEM
- Nerve fibers Originates from
cord segments T-1 to L-2.
- Pass into sympathetic chain
- Then to organs.

9. somatic tissues
(body wall, limbs)
visceral tissues
(organs)
Sympathetic System: Preganglionic Cell Bodies
• Preganglionic cell bodies in
intermediolateral gray
• T1 — L2/L3
intermediolateral
gray columns
lateral
horn
T1 –
L2/L3

10. spinal
nerve
dorsal
ramus
ventral
ramus
gray ramus
communicans white ramus
communicans
sympathetic
ganglion
intermediolateral
gray column
Structure of spinal nerves: Sympathetic pathways

11.  From sympathetic chain course of the fibers can be of three types:
 Synapse with post ganglionic neuron of ganglion it enters
 Pass upward or downward in chain and synapse with one other ganglia
 Pass variable distance through chain and synapse with peripheral ganglia ( celiac and
hypogastric plexus)

12. Sympathetic System: Postganglionic Cell Bodies
Paravertebral
ganglia
Prevertebral
ganglia
• celiac ganglion
• sup. mesent. g.
• inf. mesent. g.
aorta
sympathetic
trunk (chain)
1. Paravertebral ganglia
• Located along sides of vertebrae
• United by preganglionics into Sympathetic Trunk
• Preganglionic neurons are thoracolumbar (T1–L2/L3)
but postganglionic neurons are cervical to coccyx
• Some preganglionics ascend or descend in trunk
synapse at
same level
ascend to
synapse at
higher level
descend to
synapse at
lower level

13. Sympathetic System: Postganglionic Cell Bodies
Paravertebral
ganglia
Prevertebral
ganglia
• celiac ganglion
• sup. mesent. g.
• inf. mesent. g.
aorta
sympathetic
trunk (chain)
2. Prevertebral (preaortic) ganglia
• Located anterior to abdominal aorta, in plexuses
surrounding its major branches
• Preganglionics reach prevertebral ganglia via
abdominopelvic splanchnic nerves
abdominopelvic
splanchnic
nerve

14. spinal
nerve
dorsal
ramus
ventral
ramus
gray ramus
communicans white ramus
communicans
sympathetic
ganglion
intermediolateral
gray column
SYMPATHETIC NERVE FIBERS IN SKELETAL NERVES:
Post ganglionic
fibers from
sympathetic
chain -> spinal
nerve through
grey ramus
Sweat
glands,
blood
vessels,
piloerector
muscles of
hairs.

15. SEGMENTAL DISTRIBUTION
 T1  terminates in head
 T2  terminates in neck
 T3 to T6  terminates in thorax
 T7 to T11 terminates in abdomen
 T12, L1 & L2  terminates in legs
 Approx and overlaps
greatly.
 Distribution to each
organ dertermined partly
by locus In the embryo.
 Eg: heart

16. PHYSIOLOGIC ANATOMY OF
PARASYMPATHETIC NERVOUS
SYSTEM

Cranial outflow
• CN III, VII, IX, X
• Four ganglia in head
• Vagus nerve (CN X) is major
preganglionic parasymp.
supply to thorax & abdomen
• Synapse in ganglia within
wall of the target organs (e.g.,
enteric plexus of GI tract)
Sacral outflow
• S1–S4 via pelvic splanchnics
• Hindgut, pelvic viscera, and
external genitalia

17. CN III: Oculomotor Nerve
Innervates four of the extrinsic eye muscles
Pupillary
sphincter
ciliary
muscles

18. CN VII: Facial Nerve
 Innervates muscles of facial expression
 Sensory innervation of face
Lacrimal, nasal,
submandibular salaivary
gland.

19. CN IX: Glossopharyngeal Nerve
Sensory and motor innervation of structures of
the tongue and pharynx
Taste
Parotid gland

20. CN X: Vagus Nerve
 A mixed sensory and motor nerve
 Main parasympathetic nerve
 “Wanders” into thorax and abdomen
75% of parasympathetic fibers.
Heart, lungs, esophagus, stomach, small
intestine, proximal half of colon, liver gall
bladder, pancreas, kidneys and upper
portions of ureters.

21. Pre ganglionic and post ganglionic
neurons
 Long pre ganglionic fibers
 Short post ganglionic fibers located in the walls of the organs
 Post ganglionic fibers extremely short fraction of mm to centimeters.

22. BASIC CHARACTERISTICS OF
SYMPATHETIC AND PARASYMPATHETIC
FUNCTION
 Two synaptic transmitter
 Acetyle choline (cholinergic)
 Norepinephrine ( adrenergic)
 Pre ganglionic neurons( sympathetic and parasympathetic)  cholinergic
 Post ganglionic neurons ( parasympathetic  cholinergic)
 Post ganglionic neurons (sympatheic  adrenergic) except (sweat glands, pilo erector
muscles and few blood vessels)

23. SECRETION OF ACETYL CHOLINE AND
NOR EPINEPHRINE
 Both sympathetic and para sympathetic post ganglionic fibers merely touch the
effector cells  innervate ->terminate at connective tissue  adjacent to cells to
be stimulated.
 Interface has bulbous enlargements called “ varicosities”
 It is where neurotransmitters are secreted.

24. Secretion of ACETYL CHOLINE
Acetyl CoA + choline  Acetyl choline (choline acetyl transferase)
Acetyl choline  Acetate + choline (acetyl choline esterase)

25. Tyrosine L-Dopa
H2OO2
Tyrosine hydroxylase
(rate-determining step)
Dopa
decarboxylase
CO2
Dopamine
pyridoxal
phosphate
2
Dopamine hydroxylase
ascorbate
H2O
Norepinephrine
O2
3
methylation
Epinephrine
Adrenal medulla
Secretion of Norepinephrine
Destroyed : Mono amine oxidase and catechol – O – methyl
transferase

26. RECEPTORS ON EFFECTOR ORGANS
 Neuro transmitters  bind  specific receptors stimulation of effector organs.
 Specific receptors located outside cell membrane( prosthetic protein molecule)
 Neuro transmitters  binds to receptors  change in structure of protein molecule
 Excites or inhibits cell.
 Excitation or Inhibition of cell is by:
 Change in cell membrane permeability to one or more ions
 Activating or inactivating an enzyme attached to other end of receptor protein(adenylyl
cyclase  cAMP)

27. CHOLENERGIC RECEPTORS
 TWO TYPES OF RECEPTOR;
 Muscarinic  Activated by muscarine a poison.
 Nicotinic  Activated by nicotine.
 Both receptors are activated by acetyl choline
 Muscarinic recpetors  M1  gastric glands, autonomic ganglia, CNS
M2  heart
M3  smooth muscles, exocrine glands, endothelial
cells.
 Nicotinic receptors  Nn  autonomic ganglia, Adrenal Medulla
Nm  Neuromuscular junction

28. ADRENERGIC RECEPTORS
 Two major types of adrenergic receptors:
 Alpha (alpha1 and alpha2)
 Beta ( beta1, beta2 and beta3)
 Norepinephrine excites mainly alpha receptors but excites beta receptors to lesser
extent
 Epinephrine excites both types of receptors equally
 Synthetic hormone chemically similar to epinephrine and norepinephrine
 Isopropyl norepinephrine  strong action on beta and no action on alpha

29. EXCITATORY AND INHIBITORY ACTIONS OF
SYMPATHETIC AND PARASYMPATHETIC
STIMULATION
 GIT: ( intramural plexus or intestinal enteric nervous system)
Sympathetic system  not very dependent, strong stimulation causes inhibition of
peristalsis, increased tone of sphincters, decreased secretion
parasympathetic system  increases activity, promotes peristalsis, relaxes sphincters,
increased rate of secretion.
 HEART:
Sympathetic system  increases heart rate and force of contraction
Parasympathetic system  decreases heart rate and strength of contraction.

30.  SYSTEMIC BLOOD VESSELS:
Sympathetic system  Constricted in abdominal viscera, muscle and skin
Parasympathetic system  No effects
 ARTERIAL PRESSURE:
Sympathetic system  increases propulsion of blood and peripheral resistance
Parasympathetic system decrease in pumping of heart by vagus  mild decrease in arterial
pressure stong vagal stimulation can stop heart and contemporary loss of all or most arterial
pressure.
 GLANDS:
Sympathetic system  GIT concentrated and high percentage of mucus secretion and enzymes
 sometimes reduces by causing vasoconstriction of blood vessels to glands
Increased sweat glands secretion  hypothalamus  parasympathetic function though governed
by sympathetic system.
Apocrine glands  thick odiferous secretions
Parasympathetic system  copious quantities of watery secretion, increases gastric secretions.

31. Other
functions

32. AUTONOMIC REFLEXES
 SYMPATHETIC AND PARASYMPATHETIC TONE
 CARDIOVASCULAR AUTONOMIC REFLEX:
Baroreceptor Reflex ( carotid body and aortic arch)
 Gastrointestinal Autonomic Reflex
Upper GI tract secretion of digestive juices on visualizing food
Lower GI tract inducing strong peristaltic waves for defecation on filing of rectum.
 Other reflexes:
Emptying of urinary bladder.
Sexual reflex
Regulation of pancreatic secretion, excretion of urine, sweating, blood glucose
concentration.

33. The Adrenal Medulla

34. “ALARM” or “STRESS” Response
 Mass discharge of sympathetic system.
 Activated in emotional stress and in danger  stimulating hypothalamus  signals
transmitted through reticular formation of brain to spinal cord  massive sympathetic
discharge fight, flight and fright reaction  “ALARM” reaction
 ALARM REACTION:
 Increased arterial pressure
 Increased blood flow to muscles and decreased blood flow to GIT and Kidneys
 Increased cellular metabolism
 Increased blood glucose concentration
 Increased glycolysis in liver and muscles
 Increased muscle strength and muscle activity
 Increased rate of blood coagulation.

35. Fig. 45.34(TE Art)Hypothalamus activates
sympathetic division of
nervous system
Heart rate, blood pressure,
and respiration increase
Blood flow to
skeletal muscles
increases
Stomach
contractions
are inhibited
Adrenal medulla
secretes
epinephrine and
norepinephrine
EXAMS

36. PHARMACOLOGY OF AUTONOMIC
NERVOUS SYSTEM
 SYMPATHOMIMETICS: Epinephrine, nor epinephrine and methoxamine.
Adrenergic stimulators : phenylephrine (alpha), isoproterenol (beta) and albuterol (beta
2)
 Indirect sympathomimetic effect: ephedrine, tyramine, amphetamine.
Adrenergic blockers:
 Reserpine ( blocks synthesis and storage of norepinephrine in nerve endings)
 Guanethidine ( blocks release of nor epinephrine)
 Phenoxybenzamine and phentolamine
 Beta1 and beta 2 receptors blocked by propranolol.
 Beta 1 blocker metoprolol

37.  Parasympathomimetic : pilocarpine and methacholine ( act on muscarinic
receptor )
Indirect parasympathomimetic effect: neostigmine, pyridostigmine, ambenonium. (
inhibit acetylcholine esterase preventing rapid destruction of acetylcholine)
Drugs blocking cholinergic activity:
Atropine, homatropine and scopolamine ( block ACH in muscarinic receptors)

38. GANGLIONIC BLOCKING DRUGS
 Block impulse transmission from preganglionic fiber to post ganglionic fibers
 Tetra ethyl ammonium ions, hexamethonuim ion, pentolinium
 They reduce arterial pressure.
 Not clinically usefull as their effects are difficult to control.

39. TESTS OF AUTONOMIC NERVOUS
SYSTEM
 Principle stimulus provided in easily measurable physiologic parameters
 The tests for autonomic reflexes:
 Valsalva maneuver
 Postural stress (lying to standing)
 Timed deep breathing
 Inspiratory gasp
Biochemical tests include measuring neurotransmitter levels or its metabolites in
plasma/urine (acetyl choline is not measured as it is rapidly broken down)

40. REFERENCES:
 Text book of Medical Physiology – GUYTON & HALL
 Text book of Medical Physiology – INDU KHURANA
 Text book of Medical Physiology – Dr. G.K. PAL
 Text book of Medical Pharmacology - TRIPATI