Autonomic Nervous System ( ANS) Part 1

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Autonomic Nervous System ( ANS)Part 1

• Dr Taha Sadig Ahmed
• Physiology Department , College of Medicine ,
  King Saud University , Riyadh

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• Nervous System
• Central Nervous System (II) Peripheral
  Nervous
• 
  System
• (I) Central Nervous System (CNS)
• Consists of Brain Spinal Cord
• Brain
• (1)Forebrain Cerebrum, Diencephalon (Thalamus,
  Metathalamus, Epithalamus, Hypothalamus and
  subthalamus
• (2)Mid brain
• (3) Hind brain Pons, Medulla , Cerebellum
• B/Spinal cord

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• (II) Peripheral Nervous System
• Consists of cranial nerves (arising from brain)
  and spinal nerves (arising from spinal cord)
• The Nervous System can also be classified into
• Somatic ( voluntary) Nervous System For organs
• under voluntary control (namely skeletal muscles)
• (II) Autonomic (involuntary,visceral) Nervous
  System
• Not under voluntary control.
• It regulates internal organs visceral functions
  and homeostasis
• Effectors include cardiac muscles , smooth
  muscles and glands
• The Autonomic Nervous System ( ANS) helps to
  adjust
• maintain the internal environment ( homeostasis)
  and helps the
• body to adapt to to changes in the external
  environment ,

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• ANS is controlled activated by centers located
  in the spinal cord, brain stem, hypothalamus and
  also cerebral cortex especially the limbic cortex
• The hypothalamus is very important in this
  regard
• Posterior hypothalamus controls Sympathetic NS
  ,
• Anterior hypothalamus controls Parasympathetic
  NS

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Parasympathetic NS
Sympathetic NS

• Parasympathetic system activities is related to
  the relaxed state , rest and anabolism ?
• It promotes vegetative functions ( nutritive ,
  body-building , restorative functions tissue
  repair )
• Increased secretion of endocrine exocrine
  glands .

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COMPARISON OF AUTONOMIC AND SOMATIC SYSTEMS

• Somatic system
• One motor neuron extends from the CNS to skeletal
  muscle
• Axons are well myelinated
• Conduct impulses rapidly

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THE AUTONOMIC NERVOUS SYSTEM
Sympathetic and parasympathetic systems are
consists of myelinated pre-ganglionic fibers
which make synaptic connections with
un-myelinated postganglionic fibers and then
innervate the effector organ These synapses
usually occur in clusters called ganglia.
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COMPARISON OF AUTONOMIC AND SOMATIC MOTOR SYSTEMS

• Autonomic nervous system
• Chain of two motor neurons in series
• Preganglionic neuron ( have myelinated axons)
• Postganglionic neuron ( have unmyelinated , thin
  axons )
• Conduction is slower than in Somatic due to
  presence of thin , un-myelinated postganglionic
  axons

Pre-ganglionic
Post-ganglionic
Ganglion
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The Autonomic Outflow consists 2 Neurons neurons
arranged in series

• (A) Preganglionic nerves
• (1) Are myelinated
• (2) In case of sympathetic NS ? arise from spinal
  cord
• In case of Parasympathetic NS ? arise from
  Brainstem spinal cord

• .(B) Postganglionic nerves arise from ganglia .
• (1) Are unmywelinated
• (2) arise from ganglia .

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COMPARISON OF AUTONOMIC AND SOMATIC MOTOR SYSTEMS
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THE AUTONOMIC NERVOUS SYSTEM

• 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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THE AUTONOMIC NERVOUS SYSTEM
Sympathetic and parasympathetic systems are
consists of myelinated pre-ganglionic fibers
which make synaptic connections with
un-myelinated postganglionic fibers and then
innervate the effector organ These synapses
usually occur in clusters called ganglia.
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• 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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DIFFERENCES IN SYMPATHETIC AND PARASYMPATHETIC
DIVISIONS

• Length of postganglionic fibers
• Sympathetic ? long postganglionic fibers
• Parasympathetic ? short postganglionic fibers
• Therefore , in sympathetic Preganglionic fibers
  are shorter than Postganglionic ones
• And in parasympathetic Preganglionic fibers are
  longer than Postganglionic ones .
• Branching of axons
• Sympathetic axons highly branched
• Parasympathetic axons few branches

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DIFFERENCES IN SYMPATHETIC AND PARASYMPATHETIC
DIVISIONS
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Subdivision of ANS Location of soma ( cell-body ) of preganglionic nerve Location of Ganglia Transmitter at Ganglia Chemical secreted by Postganglionic Fiber General Function
Sympathetic Thoracolumbar Segments of spinal cord Alongside vertebral column ACh is transmitter Norepinephrine except? Vasodilator postganglionic sympathetic fibers in Skeletal Muscle Postganglionic sympathetic fibers to Sweat Glands Fight or flight
Parasympathetic Cranium ( in side skull , in Brain ) and Sacral Segments of Spinal Cord On or near the effector organ ACh is transmitter Acetylcholine Conservation of body energy
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• Preganglionic Sympathetic nerves
• exit the CNS from the thoracic lumbar
• segments of the spinal cord
• ?Therefore , the sympathetic system is
• also called Thoraco-lumbar Outflow
• Preganglionic Parasympathetic nerves
• exit the CNS from the Cranium ( skull ) sacral
• segments of the spinal cord
• ?Therefore , the Parasympathetic system
• is called Craniosacral Outflow
• Hence , in the Sympathtic system ,
• Preganglionic fibers are myelinated and
• shorter than the unmyelinated Postganglionic
• fibers
• In Parasympathetic system , Preganglionic
• fibers are also myelinated but longer than the
• unmyelinated Postganglionic fibers .

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Origin of ANS fibers
Sympathetic Originate in the thoracic and
lumbar regions of the spinal cord
(Thoracolumbar) Parasympathetic Originate from
cranial nerves (3rd, 7th, 9th, 10th), and sacral
spinal nerves (craniosacral)
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• In the Parasympathetic NS , there is little
  divergence ? the ratio of pre- to postgaglionic
  fibers is 1/3 .
• This little divergence implies more specific ,
  localized actions .
• On the other hand , in the Sympathetic NS there
  is greater divergence . The ratio (pre/post)
  being 1/10
• This divergence implies diffuse ( generalized )
  actions .

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THE AUTONOMIC NERVOUS SYSTEM