Autonomic Nervous System

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

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II. Definitions

  1. Autonomic Nervous System
    1. System of internal regulation for times of both rest (parasympathetic) and stress (sympathetic)
    2. Coordinates organ function (e.g. Heart Rate, Respiratory Rate, sweating and crying, urination and stooling)
    3. Hypothalamus regulates the Autonomic System via both direct Neuron connections, as well as hormonal release

III. Anatomy: General

  1. Autonomic System operates in parallel to the somatic system (motor, sensory)
  2. Central control (especially Hypothalamus and solitary nucleus) based on peripheral visceral afferent signals
  3. Autonomic Pathways are primarily two Neuron (preganglionic, postganglionic)
    1. See Preganglionic and Postganglionic Fibers as below
    2. Involves a CNS Neuron (preganglionic), a Ganglion, and a peripheral Neuron (postganglionic) before terminating at target organ
  4. Regulates involuntary actions
    1. Smooth Muscle and cardiac Muscle
      1. Cardiopulmonary system
      2. Gastrointestinal System
    2. Glands (e.g. lacrimal, Salivary, sweat)

IV. Anatomy: Parasympathetic and Sympathetic Systems

  1. Parasympathetic and Sympathetic Systems typically counter one another with opposing actions
    1. Some activities (e.g. sexual arousal) involve both systems (Erection is parasympathetic, ejaculation sympathetic)
  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)
      1. Parasympathetic Ganglions are close to the organs and glands they innervate
    2. Energy conserving (anabolic) system activated in rest and relaxation situations ("housekeeping" functions)
      1. Decreases Heart Rate, Blood Pressure and pupil size (Miosis)
      2. Stimulates gastrointestinal activity, Salivary secretion and urinary contraction
    3. Images
      1. parasympatheticNervousSystem.jpg
  3. Sympathetic Nervous System
    1. Signals originate in the spinal cord intermediolateral column (T1 to L2)
      1. Preganglionic nerves enter the paravertebral sympathetic Ganglionic chain
      2. Preganglionic nerves may traverse the chain several levels up or down before synapsing
        1. Sympathetic Ganglionic chain extends from the foramen magnum to the low Sacrum
    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
    3. Images
      1. sympatheticNervousSystem.jpg

V. 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)
  3. Images
    1. autonomicSynapse.png

VI. Pathophysiology

  1. See Autonomic Dysfunction

VII. References

  1. Goldberg (2014) Clinical Neuroanatomy, Medmaster, p. 54-60
  2. Netter (1997) Atlas Human Anatomy, ICON Learning, p. 152-4

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