Sultan Ayoub Meo, MBBS, PGCMed Ed, M.Phil, Ph.D

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AUTONOMIC NERVOUS SYSTEM

• Sultan Ayoub Meo, MBBS, PGCMed Ed, M.Phil, Ph.D
  
• Professor, Department of Physiology, College of
  Medicine King Khalid University Hospital, Riyadh,
  Saudi Arabia

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THE NERVOUS SYSTEM

• Central Nervous System
• Peripheral Nervous System
• 1. Central Nervous System
• A. Brain
• Fore brain Cerebrum, Diencephalon (Thalamus,
  Metathalamus, Epithalamus, Hypothalamus and
  subthalamus
• Mid brain
• Hind brain Pons, Medulla oblongata, Cerebellum
• Spinal cord

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THE NERVOUS SYSTEM

2. Peripheral nervous system a) Somatic Nervous
System b) Autonomic Nervous System i.
Sympathetic nervous system ii. Para sympathetic
nervous system
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THE NERVOUS SYSTEM
The nervous system monitors and controls almost
every organ / system through a series of positive
and negative feedback loops. The Central Nervous
System (CNS) Includes the brain and spinal cord.
The Peripheral Nervous System (PNS) Formed by
neurons their process present in all the
regions of the body. It consists of cranial
nerves arises from the brain spinal nerves
arising from the spinal cord. This again divided
into Somatic Nervous system Autonomic nervous
system

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THE PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system is divided
into Somatic nervous system which controls
organs under voluntary control (mainly
muscles) Autonomic Nervous System (ANS) It
regulates individual organ function and
homeostasis and for the most part is not subject
to voluntary control. It is also known as the
visceral or automatic system.
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CHEMICAL DIVISION OF THE ANS

• Cholinergic
• Nor Adrenergic
• The neurons that are cholinergic are
• Are pre ganglionic neurons
• Anatomicallt para syampatheic post ganglionic
  neuron
• Anatomicallt syampatheic post ganglionic neuron
  ineervate sweet glands
• Anatomically syampatheic neurons that end on
  blood vessels in skeletal muscles produce
  vasodilatation
• The remaining post ganglionic sympathetic
  neurons are nor adrenergic

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SOMATIC NERVOUS SYSTEM

• The somatic nervous system includes the nerves
  supplying the skeletal muscles.
• Thus the somatic nervous system controls the
  movements of the body by acting on skeletal
  muscles.

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THE AUTONOMIC NERVOUS SYSTEM

Autonomic nervous system (ANS) Innervates organs
whose functions are not usually under voluntary
control. Effectors include cardiac and smooth
muscles and glands. Effectors are part of
visceral organs and blood vessels
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THE AUTONOMIC NERVOUS SYSTEM

• The Autonomic nervous system is concerned with
  regulation of visceral or vegetative function.
  Therefore also called vegetative or involuntary
  nervous system
• The autonomic nervous system (ANS) is a
  regulatory structure that helps people adapt to
  changes in their environment.
• It adjusts or modifies some functions in
  response to stress.

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THE AUTONOMIC NERVOUS SYSTEM

• Anatomical functional basis ANS is divided into
  two separate divisions
• Sympathetic systems
• Parasympathetic system
• Both of these systems consist of myelinated
  preganglionic fibres which make synaptic
  connections with unmyelinated postganglionic
  fibres, and then innervate the effector organ
• These synapses usually occur in clusters called
  ganglia.

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DIVISION OF THE AUTONOMIC NERVOUS SYSTEM
Subdivision Nerves Employed Location of Ganglia Chemical Messenger General Function
Sympathetic Thoracolumbar Alongside vertebral column Norepinephrine Fight or flight
Parasympathetic Craniosacral On or near an effector organ Acetylcholine Conservation of body energy

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BASIC ANATOMY OF ANS

• Preganglionic neuron
• Cell body in brain or spinal cord
• Axon is myelinated type fiber that extends to
  autonomic ganglion
• Postganglionic neuron
• Cell body lies outside the CNS in an autonomic
  ganglion
• Axon is unmyelinated type fiber that terminates
  in a visceral effector

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BASIC ANATOMY OF ANS

• 2 neurons in the efferent pathway.
• 1st neuron has its cell body in gray matter of
  brain or spinal cord.
• Preganglionic neuron.
• Synapses with 2nd neuron within an autonomic
  ganglion.
• Postganglionic neuron.
• Autonomic ganglion has axon which extends to
  synapse with target tissue.

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BASIC ANATOMY OF ANS

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ANS Neurotransmitters  Classified as either
cholinergic or adrenergic neurons based upon the
neurotransmitter released
Adrenergic

Cholinergic
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ANS
Preganglionic autonomic fibers originate in
midbrain, hindbrain, and upper thoracic to 4th
sacral levels of the spinal cord. Autonomic
ganglia are located in the head, neck, and
abdomen Presynaptic neuron is myelinated and
postsynaptic neuron is unmyelinated Autonomic
nerves release NT that may be stimulatory or
inhibitory.

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Overview of actions
LOCATIONS OF AUTONOMIC GANGLIA

• Sympathetic Ganglia
• Trunk (chain) ganglia near vertebral bodies
• Prevertebral ganglia near large blood vessel in
  gut
• celiac superior mesenteric
• inferior mesenteric
• Parasympathetic Ganglia
• Terminal ganglia in the wall of organ

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Overview of actions
AUTONOMIC PLEXUSES

• Cardiac plexus
• Pulmonary plexus
• Celiac plexus
• Superior mesenteric
• Inferior mesenteric
• Hypogastric

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SYMPATHETIC PARASYMPATHETIC NERVOUS SYSTEM

Blue Para symp Red symp
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The Sympathetic Nervous System
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The Parasympathetic Nervous System
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THE AUTONOMIC NERVOUS SYSTEM

• The ANS is predominantly an efferent system
  transmitting impulses from the Central Nervous
  System (CNS) to peripheral organ systems.
• Its effects include
• Control of heart rate and force of contraction
• Constriction and dilatation of blood vessels
• Contraction and relaxation of smooth muscle
• Visual accommodation
• Pupillary size and secretions from exocrine and
  endocrine glands.

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The Autonomic Nervous System The Autonomic Nervous System The Autonomic Nervous System
Structure Sympathetic Stimulation Parasympathetic Stimulation
Iris (eye muscle) Pupil dilation Pupil constriction
Salivary Glands Saliva production reduced Saliva production increased
Oral/Nasal Mucosa Mucus production reduced Mucus production increased
Heart Heart rate and force increased Heart rate and force decreased
Lung Bronchial muscle relaxed Bronchial muscle contracted
Stomach Peristalsis reduced Gastric juice secreted motility increased
Small Intes Motility reduced Digestion increased
Large Intes Motility reduced Secretions and motility increased
Liver Increased conversion ofglycogen to glucose     
Kidney Decreased urine secretion Increased urine secretion
Adrenal medulla Norepinephrine andepinephrine secreted     
Bladder Wall relaxedSphincter closed Wall contractedSphincter relaxed

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Sympathetic (adrenergic, with exceptions) Parasympathetic (muscarinic)
circulatory system
cardiac output increases M2 decreases
SA node heart rate (chronotropic) ß1, ß2 increases M2 decreases
cardiac muscle contractility (inotropic) ß1, ß2 increases M2 decreases (atria only)
conduction at AV node ß1 increases M2 decreases
vascular smooth muscle M3 contracts a contracts ß2 relaxes ---
platelets a2 aggregates ---
mast cells - histamine ß2 inhibits ---

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Overview of actions
Sympathetic (adrenergic, with exceptions) Parasympathetic (muscarinic)
respiratory system
smooth muscles of bronchioles ß2 relaxes (major contribution) a1 contracts (minor contribution) M3 contracts
nervous system
pupil of eye a1 relaxes M3 contracts
ciliary muscle ß2 relaxes M3 contracts
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Overview of actions
Sympathetic (adrenergic, with exceptions) Parasympathetic (muscarinic)
digestive system
salivary glands secretions ß stimulates viscous, amylase secretions a1 stimulates potassium cation stimulates watery secretions
lacrimal glands (tears) decreases M3 increases
kidney (renin) secretes ---
parietal cells --- M1 secretion
liver a1, ß2 glycogenolysis, gluconeogenesis ---
adipose cells ß3 stimulates lipolysis ---
GI tract motility decreases M1, M3 increases
smooth muscles of GI tract a, ß2 relaxes M3 contracts
sphincters of GI tract a1 contracts M3 relaxes
glands of GI tract inhibits M3 secretes
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Overview of actions
Sympathetic (adrenergic, with exceptions) Parasympathetic (muscarinic)
ENDOCRINE
pancreas (islets) a2 decreases secretion ---
adrenal medulla N secretes epinephrine ---
urinary system
bladder wall ß2 relaxes contracts
ureter a1 contracts relaxes
sphincter a1 contracts ß2 relaxes relaxes
reproductive system
uterus a1 contracts ß2 relaxes ---
genitalia a contracts M3 erection
integument
sweat gland secretions M stimulates (major contribution) a1 stimulates (minor contribution) ---
arrector pili a1 stimulates ---
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PARASYMPATHETIC NERVOUS SYSTEM

• The preganglionic outflow of the parasympathetic
  nervous system arises from
• Cell bodies of the motor nuclei of the cranial
  nerves III, VII, IX and X in the brain stem
• Second, third and fourth S2-S4 sacral segments
  of the spinal cord. It is therefore also known as
  the cranio-sacral outflow

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PARASYMPATHETIC NERVOUS SYSTEM

• The cranial nerves III, VII and IX affect the
  pupil and salivary gland secretion
• Vagus nerve (X) carries fibres to the heart,
  lungs, stomach, upper intestine and ureter
• The sacral fibres form pelvic plexuses which
  innervate the distal colon, rectum, bladder and
  reproductive organs.

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PARASYMPATHETIC NERVOUS SYSTEM

• The parasympathetic nervous system has "rest and
  digest" activity.
• In physiological terms, the parasympathetic
  system is concerned with conservation and
  restoration of energy, as it causes a reduction
  in heart rate and blood pressure, and facilitates
  digestion and absorption of nutrients, and
  consequently the excretion of waste products
• The chemical transmitter at both pre and
  postganglionic synapses in the parasympathetic
  system is Acetylcholine (Ach).

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Overview of actions
PARASYMPATHETIC RESPONSE
Enhance rest-and-digest activities Mechanisms
that help conserve and restore body energy during
times of rest Normally dominate over
sympathetic impulses SLUDD type responses
salivation, lacrimation, urination, digestion
defecation 3 Decreases decreased HR, diameter
of airways and diameter of pupil Paradoxical
fear when there is no escape route or no way to
win causes massive activation of parasympathetic
division loss of control over urination and
defecation
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Overview of actions
ORGANS INNERVATED BY SYMPATHETIC NS
Structures innervated by each spinal nerve
Sweat glands, arrector pili, blood vessels to
skin skeletal mm. Thoracic cranial plexuses
supply Heart, lungs, esophagus thoracic blood
vessels Plexus around carotid artery to head
structures Splanchnic nerves to prevertebral
ganglia supply GIT from stomach to rectum,
urinary reproductive organs
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SYMPATHETIC NERVOUS SYSTEM

• Cell bodies of the sympathetic preganglionic
  fibres are in the lateral horns of the spinal
  segments T1-L2, called thoraco-lumbar outflow.
• The preganglionic fibres travel a short distance
  in the mixed spinal nerve and then branch off as
  white rami (myelinated) to enter the sympathetic
  ganglia.
• These are mainly arranged in two paravertebral
  chains which lie anterolateral to the vertebral
  bodies and extend from the cervical to the sacral
  region. They are called the sympathetic
  ganglionic chains.

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SYMPATHETIC NERVOUS SYSTEM

• The short preganglionic fibres which enter the
  chain make a synapse with a postsynaptic fibre
  either at the same dermatomal level, or at a
  higher or lower level
• The longer postganglionic fibres usually return
  to the adjacent spinal nerve via grey rami
  (unmyelinated) and are conveyed to the effector
  organ.

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SYMPATHETIC NERVOUS SYSTEM
FEAR, FLIGHT OR FIGHT

• The sympathetic system enables the body to be
  prepared for fear, flight or fight
• Sympathetic responses include an increase in
  heart rate, blood pressure and cardiac output
• Diversion of blood flow from the skin and
  splanchnic vessels to those supplying skeletal
  muscle
• Increased pupil size, bronchiolar dilation,
  contraction of sphincters and metabolic changes
  such as the mobilisation of fat and glycogen.

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FUNCTIONS OF SYMPATHETIC NERVOUS SYSTEM
Frequently referred to as the fear, flight or
fight system It has a stimulatory effect on
organs and physiological systems, responsible for
rapid sensory activity (pupils in the eye) and
movement (skeletal muscle). It diverts blood
flow away from the GIT and skin via
vasoconstriction. Blood flow to skeletal
muscles, lungs is not only maintained, but
enhanced (by as much as 1200), in case of
skeletal muscles.

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FUNCTIONS OF SYMPATHETIC NERVOUS SYSTEM

Bronchioles dilate, which allows for greater
alveolar oxygen exchange. It increases heart rate
and the contractility of cardiac cells
(myocytes), thereby providing a mechanism for the
enhanced blood flow to skeletal muscles.
Sympathetic nerves dilate the pupil and relax
the lens, allowing more light to enter the eye.
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Overview of actions
SYMPATHETIC RESPONSE
Dominance by the sympathetic system is caused by
physical or emotional stress E
situations Emergency, Embarrassment, Excitement,
Exercise
Alarm reaction flight or fight response

• Dilation of pupils
• Increase heart rate, force of contraction BP
• Decrease in blood flow to nonessential organs
• Increase in blood flow to skeletal cardiac
  muscle
• Airways dilate respiratory rate increases
• Blood glucose level increase

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ADRENALINE NOR ADRENALINE

• Adrenaline and noradrenaline are both
  cate-cholamines
• Both synthesized from the essential amino acid
  phenylalanine by a series of steps, which
  includes the production of dopamine.
• The terminal branches of the sympathetic
  postganglionic fibres have varicosities or
  swellings, giving them the appearance of a string
  of beads.
• These swellings form the synaptic contact with
  the effector organ, and are also the site of
  synthesis and storage of noradrenaline.

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ADRENALINE NOR ADRENALINE

• On the arrival of a nerve impulse, noradrenaline
  is released from granules in the presynaptic
  terminal into the synaptic cleft.
• The action of noradrenaline is terminated by
  diffusion from the site of action, re-uptake back
  into the presynaptic nerve ending where it is
  inactivated by the enzyme Monoamine Oxidase in
  mitochondria or metabolism locally by the enzyme
  Catechol-O-Methyl-Transferase.

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Overview of actions
RECEPTORS

• The parasympathetic nervous system uses only
  acetylcholine (ACh) as its neurotransmitter.
• The ACh acts on two types of receptors, the
  muscarinic and nicotonic choloinergic receptors.
• Most transmissions occur in two stages When
  stimulated, the preganglionic nerve releases ACh
  at the ganglion, which acts on nicotinic
  receptors of the postganglionic nerve.
• The postganglionic nerve then releases ACh to
  stimulate the muscarinic receptors of the target
  organ.

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Overview of actions
TYPES OF MUSCARINIC RECEPTORS
The three main types of muscarinic receptors M1
muscarinic receptors located in the neural
system. M2 muscarinic receptors located in the
heart, and act to bring the heart back to normal
after the actions of the sympathetic nervous
system slowing down the heart rate, reducing
contractile forces of the atrial cardiac muscle,
and reducing conduction velocity of the SA and
AV node. Note, they have no effect on the
contractile forces of the ventricular muscle.
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Overview of actions
TYPES OF MUSCARINIC RECEPTORS
M3 muscarinic receptors located at many places
in the body, such as the smooth muscles of the
blood vessels, as well as the lungs, which means
that they cause vasoconstriction
bronchioconstriction and. They are also in the
smooth muscles of the GIT, which help in
increasing intestinal motility and dilating
sphincters. M3 receptors are also located in
many glands that help to stimulate secretion in
salivary glands and other glands of the body.
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