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Physiology of autonomic nervous system

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									    Physiology of autonomic nervous system
              Learning objectives
•   Divisions of ANS.
•   Pre-ganglionic and Post ganglionic fibers.
•   Receptors types in the ANS.
•   Functions of sympathetic and parasympathetic system.
•   Role of adrenal glands in ANS.

              Autonomic nervous system
The autonomic nervous system is the subdivision of the
 peripheral nervous system that regulates body activities
 that are generally not under conscious control


         Divisions of the autonomic nervous system
• Parasympathetic division
• Sympathetic division

    Serve most of the same organs but cause opposing or
    antagonistic effects

             Parasympathetic nervous system
                            “rest & digest”
• Also called the craniosacral system because all its
  preganglionic neurons are in the brain stem or sacral
  levels of the spinal cord
    – Cranial nerves III,VII, IX and X
    – In lateral horn of gray matter from S2-S4
• Only innervate internal organs (not skin)

         Cranial outflow
    – III - pupils constrict
    – VII - tears, nasal mucus, saliva
  – IX – parotid salivary gland
  – X (Vagus n) – visceral organs of thorax & abdomen:
     • Stimulates digestive glands
     • Increases motility of smooth muscle of digestive tract
     • Decreases heart rate
     • Causes bronchial constriction
• Sacral outflow (S2-4): form pelvic splanchnic nerves
             nd
  – Supply 2 half of large intestine
  –   Supply all the pelvic (genitourinary) organs
              Sympathetic nervous system
                         “fight, flight or fright”
• Also called thoracolumbar system: all its neurons are in lateral
  horn of gray matter from T1-L2

• Lead to every part of the body (unlike parasymp.)
  – Easy to remember that when nervous, you sweat; when
    afraid, hair stands on end; when excited blood pressure
    rises (vasoconstriction): these sympathetic only
  – Also causes: dry mouth, pupils to dilate, increased heart
    & respiratory rates to increase O2 to skeletal muscles,
    and liver to release glucose
  Regardless of target, all begin same




• Preganglionic axons exit spinal cord through ventral root
  and enter spinal nerve
• Exit spinal nerve via communicating ramus
• Enter sympathetic trunk/chain where postganglionic
 neurons are


               Organization of ANS
• Autonomic nervous system
  – Chain of two motor neurons
     • Preganglionic neuron
     • Postganglionic neuron
  – Conduction is slower due to thinly or unmyelinated
    axons

• Axon of 1st (preganglionic) neuron leaves CNS to synapse
  with the 2nd (ganglionic) neuron
• Axon of 2nd (ganglionic) neuron extends to the organ it
serves.
General nerve pathway
  A. Sympathetic
           Preganglionic cell body
           Axons move through ventral root of spinal nerve.
           Synapses w/postganglionic at sympathetic chain
             ganglion
           Axons of post ganglions exit via spinal nerve and
             sympathetic nerve.
Exceptions: some preganglionic fibers do not synapse at symp
chain i.e Splanchnic nerve and Adrenal gland

        Options of preganglionic axons in
               sympathetic trunk
  Synapse on postganglionic neuron in chain ganglion
   then return to spinal nerve and follow its branch to the
   skin
 Ascend or descend within sympathetic trunk, synapse
   with a posganglionic neuron within a chain ganglion, and
   return to spinal nerve at that level and follow branches to
   skin
 Enter sympathetic chain, pass through without
   synapsing, form a splanchnic nerve that passes toward
   thoracic or abdominal organs
  – These synapse in prevertebral ganglion in front of
     aorta
  – Postganglionic axons follow arteries to organs
b. Parasympathetic nervous
   Cell bodies of preganglionic – brainstem( nuclei) and sacral
    region of spinal cord.
   Axons moves through cranial nerves and spinal nerves
   Synapses with post ganglion at ganglia or in the target system
system




 Anatomical Differences in Sympathetic
    and Parasympathetic Divisions
• Length of postganglionic fibers
   – Sympathetic – long postganglionic fibers
   – Parasympathetic – short postganglionic fibers
• Branching of axons
– Sympathetic axons – highly branched
  •  Influences many organs
– Parasympathetic axons – few branches
   • Localized effect


        Anatomical Differences in
              Sympathetic
      and Parasympathetic Divisions




                                         Figure 15.4a
       Anatomical Differences in
             Sympathetic
     and Parasympathetic Divisions




                                               Figure 15.4b




             Signal transmission
A. Parasympathetic

       Preganglionic fibers secretes acetylcholine
       Post ganglionic receptor = nicotinic
       Post ganglionic secretes acetylcholine.
       Target are smooth muscles ,heart and glands
       Receptor = muscranic

B .Sympathetic
        Preganglionic fibers secretes acetylcholine
      Post ganglionic receptor = nicotinic
      Post ganglionic secretes NE
      Target are smooth muscles ,heart and glands
      Receptor = Adrenergic and beta
          Adrenal gland is exception
    On top of kidneys

    Adrenal medulla (inside part) is a major organ of the
      sympathetic nervous system
• Synapse in gland
• Can cause body-wide release of epinephrine aka
  adrenaline and norepinephrine in an extreme emergency
  (adrenaline “rush” or surge)




         Receptors types in the ANS
Adrenergic receptors
  a .alpha 1 Receptors
    - Location : vascular smooth muscle of the skin and
 splanchnic regions ,GIT and urinary bladder sphincters
 and the radial muscle of the iris.
    - Produce :excitation(contraction or constriction)
  - Equally sensitive to nor-epinephrine and epinephrine.
 - Mechanism of action : Formation of inositol triphosphate
  and increase in intracellular ca.

b .Alpha 2 Receptors.

 - Location : in pre-synaptic nerve terminals,platelets ,fat
 cells and the walls of GIT.
  - Produces: inhibition.(relaxation or dilatation)
  - MOA :Inhibition of adenylate cyclase and decreases
 cAMP

C .Beta 1 Receptor
    - Location: SA Node ,AV node and ventricular muscle
 wall.
  - Produces :excitation.
  - Sensitive to both epinephrine and norephinephrine and
 are more sensitive than the alpha 1 receptors.
  - MOA: Excitation of adenylate cyclase and increases
 cAMP

D .Beta 2 Receptor
    - Location: Vascular smooth muscle,bronchial smooth
 muscle and wall of GIT bladder.
  - Produces: relaxation.
  - More Sensitive to epinephrine than NE - More
 Sensitive to epinephrine than the alpha 1 receptors.
  - MOA: Excitation of adenylate cyclase and increases
 cAMP

              Cholinergic receptors
a .Nicotinic Receptor
    - Location: Autonomic ganglia of sympathetic and
 parasympathetic nervous system, at neuromuscular
 junction and in the adrenal medulla.
  - Produces :Excitation.
  - Activated : By Ach Or nicotine.
  - MOA: Ach binds to nicotinic Ach receptor .The nicotinic
 Ach Receptors are also ion channels for Na+ and K+

b .Muscarinic Receptor
    - Location:Heart, smooth muscle and glands.
  - Produces : inhibitory in the heart
            excitatory in smooth muscle and glands
  - Activated : By Ach Or muscarine.
  - MOA: Heart SA Node : Inhibition of adenylate cyclase .
    Smooth muscle and glands: Formation of inositol
 triphosphate and increase in intracellular ca.

								
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