Autonomic Nervous System (ANS)

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Autonomic Nervous System (ANS)
CHAPTER 9

• Divisions of ANS
• Sympathetic
• Parasympatheitc
• Functions of ANS
• Control of ANS

Dr. Hameed Al-Sarraf Dept. Physiology hameed_at_hsc.e
du.kw
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Autonomic Nervous System

• Nervous system that controls many involuntary
  functions of the body.
• ANS effects (controls) organs which are under
  involuntary control.
• Effectors of ANS usually are
• Cardiac Muscle
• Smooth Muscle
• Glands

HEART
Many internal Organs
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Divisions of ANS

• 1- Sympathetic (Thoracolumbar) Division
• 2- Parasympathetic (Craniosacral) Division.

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Sympathetic
Thoracolumbar
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Sympathetic Chain
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Sympathetic Chain
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Parasympathetic
Vagus
Craniosacral
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Parasympathetic
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Innervation of Body Organs

• In the body there are organs which are
  innervated by both sympathetic and
• parasympathetic systems
• - Heart
• - Digestive tract
• - Pupil of the eye
• - Salivary glands, etc
• There are organs with only sympathetic
  innervation
• - Adrenal medulla
• - Sweat glands
• - Most blood vessels

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Functions of ANS

• 1- Sympathetic system
• Mass discharge of sympatheic system prepares the
  body for
• activity (Fight/Flight).
• Excitation of sympathetic centers will cause
• - Increase in heart rate.
• - increase in blood pressure,
• - blood glucose is elevated
• - increase in the rate of metabolism
• - mental activity is also raised,
• - blood is diverted to skeletal muscle.
• 2- parasympathetic system usually has opposite
  effects to those of sympathetic
• system. Excitation of parasympathetic causes
• - decrease in heart rate,
• - increase blood flow to the digestive system,
• - increase activity of the digestive system.

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Sympathetic Tone

• Fast rate of action potentials

• Slow rate of action potentials

Vasoconstriction
Vessel diameter at rest
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Sympathetic Tone

• Stop sending action potentials

• Slow rate of action potentials

Vasodilatation
Vessel diameter at rest
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Sympathetic and Prasympathetic Tone
- Normally both symathetic and parasympathetic
systems continuously transmit action potentials
(signals) at low rate throughout their nerve
fibers. - By doing this the ANS can have both
positive and negative effects on its effector
organs
e.g control of blood vessel diameter by
sympathetics,
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Examples of Sympathetic System in Action
Mass discharge (activation) of sympathetic system
prepares the body for activity
Example 1 Blood flow to muscle in
exercise Sympathetic nervous system causes
blood shift to muscle during exercise by
vasoconstriction of blood vessels of all other
organs except heart and brain.
Example 2 Liver Stimulation of
glycogenolysis to produce glucose which will be
release into blood to provide muscle with fuel.
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Examples of Parasympathetic System in Action
Activation of parasympathetics usually has
opposite effects to the sympathetics.
Example 1 on gastrointestinal
tract Parasympathetic system causes increased
blood flow, motility and secretion of
gastrointestinal tract (e.g. stomach, small
intestine)
Example 2 Heart and lungs Reduced heart rate
and constriction of air tubes (bronchioles) in
the lung.
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Neurotransmitters of the ANS
1- Acetylcholine (ACh)- the transmission is said
to be cholinergic. - ACh is the transmitter
released by - all preganglionic fibers - most
parasympathetic postganglionic fibers - some
sympathetic postganglionic fibers
(in both sympathetic and parasympathetic)
2- Norepinephrine (noradrenaline)- the
transmission is said to be adernergic. -
Norepinephrine is the transmitter released by -
most postganglionic sympathetic fibers,
3- Non-adernergic non-cholinergic (NANC)- -
the transmitter is neither ACh nor NE -
proposed candidates are ATP, VIP, and NO.
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Some sympathetics that innervate blood vessels
and all sympathetics that supply sweat glands
release acetylcholine (ACh) as their
neurotransmitter.
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Receptors
- NE causes excitation to some tissues while it
inhibits others. This is due to the presence
of different receptors on the target cells.
- There are two types of adernergic
receptors - a-adernergic receptors -
b-adernergic receptors
- ACh also has two types of receptors -
Nicotinic - Muscarinic
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Adernergic Stimulation
1- Binding of epinephrine or norepinephrine (NE)
to a-receptor causes increase in
cytoplasmic Ca levels
NE
Membrane
a-receptor
Phospholipase C
Increase cytoplasmic Ca
Inositol triphosphate (IP3)
receptor
Endoplasmic Reticulum
Opening Ca channels
Closed Ca channels
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Adernergic Stimulation
2- Binding of epinephrine or norepinephrine to
b-receptor stimulates the production of
cyclic adonesine monophosphate (cAMP).
NE
Membrane
b-receptor
Adenylate cyclase (inactive)
Adenylate cyclase (active)
ATP
cAMP
Cytoplasm
Catalyse many Reactions in the cell
Protein kinase (inactive)
Protein kinase (active)
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Cholinergic Stimulation
Nicotinic receptors n Muscarinic receptors m
n
Brain
m
Parasympathetic
ACh
ACh
n
somatic
ACh
n
Adernal Medulla
ACh
Sympathetic
n
NE
ACh
m
n
ACh
ACh
Parasympathetic
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Control of the ANS by Higher Brain Centers
Higher Brain Centers
Hypothalamus
Medulla Oblongata
Preganglionic
Sensory Inputs
Postganglionic
Effector Organs
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Control of ANS by Centers in Brain

• Brain stem mainly controls vascular system and
  respiration.
• Hypothalamus-
• Cardiovascular system stimulation of
• - posterior hypothalamus causes increase in
  blood pressure and heart rate,
• - anterior hypothalamus causes decrease in blood
  pressure and heart rate.
• Body temperature
• changes in blood temperature in anterior
  hypothalamus causes several
• mechanisms to operate for temperature
  regulation.
• - Body water- secretion of ADH and signals to
  initiate thirst
• Feeding hunger and satiety centers
• Excitement and rage- perifornical nucleus in
  hypothalamus
• Endocrine function neurosecretory substances
  secretion to anterior pituatory.

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Reflex Effects of Sensory Inputsto Brain Centers
Organ Type of Receptor Reflex Effect
Lung Stretch receptor inhalation
is inhibited and heart rate
increase
Aorta Chemoreceptor
increase breathing and heart
rate Baroreceptor
decrease in heart rate
Heart Stretch receptor
increase volume of urine excreted
and decrease in heart rate
G.I. Tract Stretch receptor
feeling of satiety