Chapter 1 A Perspective on Human Genetics

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Autonomic Nervous System-I
Dr.Mohammed Sharique Ahmed Quadri Assistant prof.
Physiology Al Maarefa College
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PNS Efferent Division

• Communication link by which CNS controls
  activities of muscles and glands
• Two divisions of PNS
• Autonomic nervous system (ANS)
• Involuntary branch of PNS
• Innervates cardiac muscle, smooth muscle, most
  exocrine glands, some endocrine glands, and
  adipose tissue
• Somatic nervous system
• Subject to voluntary control
• Innervates skeletal muscle

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Autonomic Nervous System

• The portion of the nervous system which controls
  most visceral function of the body is called as
  autonomic nervous system.
• Arterial pressure
• heart rate
• GI motility
• GI secretion
• Urinary bladder emptying
• Sweating
• Body temperature

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• The efferent autonomic signals are transmitted to
  the various organs of the body through 2 major
  subdivision.
• Sympathetic nervous system
• Parasympathetic nervous system

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Physiologic anatomy of the ANS

• Sympathetic nerve fibers originate in the spinal
  cord along with the spinal nerve between T1-L2/L3
  ( thoraco lumbar ).
• Parasympathetic nerve fibers originate from brain
  stem (midbrain, pons, and medulla) or the sacral
  spinal cord ( craniosacral).
• The preganglionic fibers originates from nuclei
  of cranial nerves (CN) III, IV, IX and X or from
  sacral spinal segments S2-S4.

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ANS

• Autonomic nerve pathway
• Extends from CNS to an innervated organ
• Two-neuron chain
• Preganglionic fiber (synapses with cell body of
  second neuron)
• Postganglionic fiber (innervates effector organ)

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Physiologic anatomy of the sympathetic nervous
system

• Sympathetic nerve fibers originate in the spinal
  cord along with the spinal nerve between T1 L2.
  ( thoraco lumbar )
• Length of the pre postganglionic fibers
• Preganglionic fibers are shorter
• Post ganglionic fibers are longer

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sympathetic nervous system

• Pre ganglionic sympathetic fibers always
  cholinergic, i.e. secretes Ach. This activates
  nicotinic receptors in the post ganglionic
  fibers.
• Post ganglionic fibers are adrenergic. They act
  on adrenoreceptors (a1, a2, ß1, or ß2).
• Only exception is post ganglionic fibers
  supplying thermoregulatory sweat glands that is
  cholinergic that acts on muscarinic receptors.

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Functions of sympathetic nervous system

• Sympathetic system dominates in emergency or
  stressful (fight-or-flight) situations
• Promotes responses that prepare body for
  strenuous physical activity

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Parasympathetic nervous system

• Parasympathetic system originates from brain stem
  (midbrain, pons, and medulla) or the sacral
  spinal cord ( craniosacral).
• The preganglionic fibers originates from nuclei
  of cranial nerves (CN) III, IV, IX and X or from
  sacral spinal segments S2-S4.

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Parasympathetic nervous system

• Length of the pre postganglionic fibers
• Preganglionic fibers are longer
• Post ganglionic fibers are shorter
• Pre ganglionic para sympathetic fibers always
  cholinergic, ie secretes Ach. This activates
  nicotinic receptors in the post ganglionic
  fibers.
• Post ganglionic fibers are cholinergic.

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Parasympathetic nervous system

• e.g. parasympathetic innervation of eye muscles
  originates in the Edinger-Westphal nucleus in the
  midbarin.
• Like wise, X nerve (vagus) originates in the
  nuclei of the medulla.

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ANS

• Parasympathetic system dominates in quiet,
  relaxed (rest-and-digest) situations
• Promotes body-maintenance activities such as
  digestion
• It allows the body to recover from stress

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ANS
Sympathetic Nervous System Parasympathetic Nervous System
Fibers originate in thoracic and lumbar regions of spinal cord Fibers originate from cranial and sacral areas of CNS
Most preganglionic fibers are short Preganglionic fibers are longer
Long postganglionic fibers Very short postganglionic fibers
Preganglionic fibers release acetylcholine (Ach) Preganglionic fibers release acetylcholine (Ach)
Most postganglionic fibers release noradrenaline (norepinephrine), accept in sweat gland (Ach) Postganglionic fibers release acetylcholine
Autonomic ganglio is prevertebral paravertebral Autonomic ganglia is near effector organ
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ANS

• Most visceral organs innervated by both
  sympathetic and parasympathetic fibers
• In general produce opposite effects in a
  particular organ
• Dual innervation of organs by both branches of
  ANS allows precise control over organs activity

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EFFECTS OF ANS
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ANS

• Exceptions to general rule of dual reciprocal
  innervation by the two branches of autonomic
  nervous system
• Most arterioles and veins receive only
  sympathetic nerve fibers (arteries and
  capillaries are not innervated)
• Most sweat glands are innervated only by
  sympathetic nerves
• Salivary glands are innervated by both ANS
  divisions but activity is not antagonistic both
  stimulate salivary secretion

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Distinguishing Characteristics of Sympathetic and
Parasympathetic Nervous Systems
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References

• Human physiology by Lauralee Sherwood, seventh
  edition
• Text book physiology by Guyton Hall,11th edition
• Text book of physiology by Linda .s
  contanzo,third edition