Parasympathetic Nervous System


Parasympathetic Nervous System, Parasympathetic System, Parasympathetic Nerve

  • Definitions
  1. Parasympathetic Nervous System
    1. Part of Autonomic Nervous System with activity that typically counters the Sympathetic Nervous System
    2. Energy conserving (anabolic) system activated in rest and relaxation situations
      1. Contrast with the Sympathetic Nervous System, an energy expending system activated in times of stress
  • Physiology
  • Activity
  1. Decreases pupil size (Miosis) and contracts ciliary Muscle (accommodation)
  2. Stimulates Salivary WATERY secretion (contrast with viscous secretion by the Sympathetic System)
  3. Decreases Heart Rate and Blood Pressure
  4. Stimulates bronchoconstriction and Bronchial gland secretion
  5. Increases gastrointestinal activity (peristalsis) and secretion
  6. Relaxes gastrointestinal sphincters (e.g. anal sphincter in Defecation)
  7. Stimulates Urethral relaxation and Bladder contraction
  8. Mediates Erection (contrast with ejaculation mediated by the Sympathetic System)
  • Anatomy
  1. Craniosacral division of the Autonomic Nervous System
  2. Signals originate
    1. Sacral spinal cord (S2 to S4) supplies urinary and Gastrointestinal Systems
    2. Brain Stem nucleii (CN 3, CN 7, CN 9, CN 10)
      1. Vagus Nerve (CN 10) has broad, far ranging activity (lungs, heart, gastrointestinal)
      2. Limited roles by CN 3 (pupil/ciliary constriction), CN 7 (tears/Saliva) and CN 9 (Saliva)
  3. Preganglion Neurons Synapse at cranial autonomic ganglia or in terminal ganglia near target organs
    1. Transmitted to target organ
  4. Images
    1. parasympatheticNervousSystem.jpg
  • References
  1. Goldberg (2014) Clinical Neuroanatomy, Medmaster, p. 54-60
  2. Netter (1997) Atlas Human Anatomy, ICON Learning, p. 152-4