THE AUTONOMIC NERVOUS SYSTEM

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THE AUTONOMIC NERVOUS SYSTEM
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INTRODUCTION
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ANS in the Structural Organization of the Nervous
System
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COMPARISON OF THE SOMATIC AND AUTONOMIC
NERVOUS SYSTEM

• The somatic nervous system stimulates skeletal
  muscles, while the ANS innervates cardiac and
  smooth muscle and glands
• In the somatic nervous system, the cell bodies of
  the neurons are in the spinal cord and their
  axons extend to the skeletal muscles they
  innervate
• The ANS consists of a two-neuron chain
• The neurotransmitter released by the somatic
  motor neurons is acetylcholine, which always has
  an excitatory effect the neurotransmitters
  released by the ANS are epinephrine and
  acetylcholine, and both may have either an
  excitatory or an inhibitory effect
• There is overlap between the somatic and
  autonomic nervous systems, and most body
  responses to changing internal and external
  stimuli involve both skeletal muscle activity and
  visceral organ responses

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SOMATIC VS AUTONOMIC
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DIVISIONS OF THE AUTONOMIC NERVOUS SYSTEM

• The parasympathetic division keeps body energy
  use as low as possible while directing digestion
  and elimination activities
• The sympathetic division prepares the body to
  respond to an emergency or threatening situation
  (or vigorous exercise)

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ANS ANATOMY
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ANS SUBDIVISIONS
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PARASYMPATHETIC (CRANIOSACRAL) DIVISION

• The preganglionic axons extend from the CNS
  nearly all the way to the structures to be
  innervated where they synapse with ganglionic
  neurons in the terminal ganglia
• The cranial outflow consists of preganglionic
  fibers that run in the oculomotor, facial,
  glossopharyngeal, and vagus cranial nerves
• The rest of the large intestine and the pelvic
  organs are served by the sacral outflow, which
  arises from neurons located in the lateral gray
  matter of spinal cord segments

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PARASYMPATHETIC NERVOUS SYSTEM
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SYMPATHETIC(THORACOLUMBAR)DIVISION

• The sympathetic division supplies the visceral
  organs in the internal body cavities but also all
  visceral structures in the somatic part of the
  body
• When synapses are made in chain ganglia, the
  postganglionic axons enter the ventral (or
  dorsal) ramus of the adjoining spinal nerves by
  way of communicating branches called gray rami
  communicates
• The preganglionic fibers from T5 down synapse in
  collateral ganglia thus these fibers enter and
  leave the sympathetic chains without synapsing
• Some fibers of the thoracic splanchnic nerves
  terminate by synapsing with the hormone producing
  medullary cells of the adrenal cortex

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SYMPATHETIC NERVOUS SYSTEM
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SYMPATHETIC PATHWAYS
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The visceral sensory neurons are the first link
in autonomic reflexes by sending information
concerning chemical changes, stretch, and
irritation of the viscera
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VISCERAL REFLEXES
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REFERRED PAIN
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ANS PHYSIOLOGY

• Neurotransmitters and Receptors
• Cholinergic receptors, such as nicotinic and
  muscarinic receptors, bind acetylcholine
• Adrenergic receptors alpha and beta bind to
  epinephrine
• Knowing the locations of the cholinergic and
  adrenergic receptor subtypes allows specific
  drugs to be prescribed to obtain desired
  inhibitory or stimulatory effects on target organs

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ANS PHYSIOLOGY

• Interactions of the autonomic divisions
• Most visceral organs receive dual innervations by
  both ANS divisions, allowing for a dynamic
  antagonism to exist between the divisions and
  precise control of visceral activity
• The sympathetic division will increase heart and
  respiratory rates during a fight-or-flight
  situation and decrease activity of digestive and
  elimination organs
• Sympathetic tone occurs in the vascular system,
  and parasympathetic tone occurs in the digestive
  and urinary tracts
• The parasympathetic and sympathetic divisions may
  work together to achieve a common purpose
• For example, the parasympathetic division
  controls erection while the sympathetic division
  controls ejaculation
• The sympathetic division mediates reflexes that
  regulate body temperature, release renin from the
  kidneys, and promote metabolic effects
• The parasympathetic division exerts short-live,
  localized control its effectors, while the
  sympathetic division responds in a diffuse and
  interconnected way to cause a body-wide
  mobilization

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ANS PHYSIOLOGY

• Control of Autonomic Functioning
• The brain stem appears to exert the most direct
  influence over autonomic functions
• The hypothalamus is the main integration center
  for the autonomic nervous system
• Cortical or voluntary control of the autonomic
  nervous system does appear to be possible

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LEVELS OF ANS CONTROL
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HOMEOSTATIC IMBALANCESOF THE ANS

• Hypertension, or high blood pressure, may result
  from an overactive sympathetic vasoconstrictor
  response due to continuous high levels of stress
• Raynauds disease is characterized by
  intermittent attacks causing the skin of the
  fingers and the toes to become pale, then
  cyanotic and painful
• Mass reflex reaction is a life-threatening
  condition involving uncontrolled activation of
  both somatic and autonomic motor neurons

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DEVELOPMENTAL ASPECTSOF THE ANS

• Embryonic and fetal development of the autonomic
  nervous system
• ANS preganglionic neurons and somatic motor
  neurons derive from the embryonic neural tube
• ANS structures found in the PNS (ganglionic
  neurons, adrenal medulla, and all autonomic
  ganglia) derive from the neural crest
• Nerve growth factor is a protein secreted by
  target cells of the postganglionic axons
• On old age the efficiency of the ANS begins to
  decline, partly due to structural changes of some
  preganglionic axonal terminals