Anatomy

Autonomic Nervous System

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Autonomic Nervous System, Autonomic System, Autonomic Pathway, Postganglionic Autonomic Fibers, Preganglionic Autonomic Fibers

  • Definitions
  1. Autonomic Nervous System
    1. System of internal regulation for times of both rest (parasympathetic) and stress (sympathetic)
  1. Central control (especially Hypothalamus and solitary nucleus) based on peripheral visceral afferent signals
  2. Primarily two Neuron pathway
    1. See Preganglionic and Postganglionic Fibers as below
  3. Regulates involuntary actions
    1. Internal organs (e.g. cardiopulmonary and Gastrointestinal Systems)
    2. Glands (e.g. lacrimal, Salivary, sweat)
  1. Parasympathetic and Sympathetic Systems typically counter one another with opposing actions
  2. Parasympathetic Nervous System
    1. Signals originate in the Sacral spinal cord (S2 to S4) and Brain Stem nucleii (CN 3, CN 7, CN 9, CN 10)
    2. Energy conserving (anabolic) system activated in rest and relaxation situations
      1. Decreases Heart Rate, Blood Pressure and pupil size (Miosis)
      2. Stimulates gastrointestinal activity, Salivary secretion and urinary contraction
  3. Sympathetic Nervous System
    1. Signals originate in the spinal cord intermediolateral column (T1 to L2)
    2. Energy expending (catabolic) system, activated in stressful situations (e.g. emergency fight or flight)
      1. Increases Heart Rate, Blood Pressure, Respiratory Rate and pupil size
      2. Shunts blood flow to critical organs (cardiac and skeletal muscle) from gastrointestinal tract
  • Anatomy
  • Preganglionic and Postganglionic Fibers
  1. Preganglionic Neuron (CNS to autonomic Ganglion)
    1. Acetylcholine mediated (Cholinergic) in both sympathetic and Parasympathetic Systems
  2. Postganglionic Neuron (autonomic Ganglion to target organ)
    1. Parasympathetic System: Acetylcholine mediated (Cholinergic) as with preganglionic fibers
    2. Sympathetic System: Norepinephrine mediated (with exceptions, such as acetylcholine for sweating)
  • Pathophysiology
  • References
  1. Goldberg (2014) Clinical Neuroanatomy, Medmaster, p. 54-60
  2. Netter (1997) Atlas Human Anatomy, ICON Learning, p. 152-4