Sympathetic Nervous System

Aka: Sympathetic Nervous System, Sympathetic System, Sympathetic Nerve

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II. Definitions

  1. Sympathetic Nervous System
    1. Part of Autonomic Nervous System with activity that typically counters the Parasympathetic Nervous System
    2. Energy expending (catabolic) system, activated in stressful situations (e.g. emergency fight or flight)
      1. Contrast with the Parasympathetic Nervous System, an energy conserving system activated at times of rest

III. Physiology: Activity

  1. See Adrenergic Receptor
  2. See Alpha Adrenergic Receptor (alpha 1 and alpha 2)
  3. See Beta Adrenergic Receptor (beta 1 and beta 2)
  4. Increases Heart Rate (chronotropic), heart contraction strength (ionotropic), Blood Pressure
  5. Increases Respiratory Rate and bronchodilation
  6. Increases pupil size or Mydriasis (contrast with Miosis and accommodation by the Parasympathetic System)
  7. Stimulates Salivary VISCOUS secretion (contrast with watery secretion by Parasympathetic System)
  8. Stimulates sweat secretion (via Cholinergic postganglionic fibers)
  9. Decreases gastrointestinal activity and secretion, and contracts gastrointestinal sphincters
  10. Stimulates liver Gluconeogenesis and glycogenesis and fat lipolysis
  11. Stimulates Kidney renin release and Adrenal MedullaEpinephrine release (Cholinergic postganglionic fibers)
  12. Mediates ejaculation (contrast with Erection mediated by Parasympathetic System)
  13. Shunts Blood Flow to critical organs
    1. Cardiac Muscle and skeletal Muscle vasodilation (beta-2 receptor)
    2. Skin and gastrointestinal Vasoconstriction (alpha-1 receptor)

IV. Anatomy

  1. Thoracolumbar division of the Autonomic Nervous System
  2. Signals originate in the spinal cord intermediolateral column (T1 to L2)
    1. Sympathetic Ganglionic chain extends from the foramen magnum to the low Sacrum
    2. Preganglionic nerves enter the paravertebral sympathetic Ganglionic chain
    3. Preganglionic nerves may traverse the chain several levels up or down before synapsing
    4. Preganglionic nerves Synapse at paravertebral or prevertebral ganglia
      1. Trigger postganglionic nerves via NeurotransmitterAcetylcholine
  3. Postganglionic Neuron (autonomic Ganglion to target organ)
    1. Norepinephrine mediated (with exceptions, such as Acetylcholine for sweating)
    2. Contrast with parasympathetic postganglionic fibers which release Acetylcholine
  4. Images
    1. sympatheticNervousSystem.jpg
    2. autonomicSynapse.png

V. Pathophysiology

  1. See Sympathomimetic Toxicity

VI. 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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