Parasympathetic Nervous System
parasympathetic nervous system
Overview
- The parasympathetic nervous system comprises a cranial component and a sacral component.
- The cranial component comprises cranial nerves 3, 7, 9, and 10.
- The sacral component comprises spinal cord intermediolateral cell column from S2 - S4.
Cranial Component
- CN 3 emerges from the Edinger-Westphal nucleus (in the midbrain) and innervates the ciliary ganglion, which innervates the ciliary body and pupillary constrictor muscles.
- CN 7 emerges from the superior salivatory nucleus (in the pons) and innervates both the pterygopalatine ganglion and also the submandibular ganglion, which innervate the majority of the major glands of the face.
- The pterygopalatine ganglion innervates the nasal, lacrimal, pharyngeal, and palatine glands; these constitute the major glands of the upper face except for the parotid gland (which the otic ganglion innervates).
- The submandibular ganglion innervates the submandibular and sublingual glands.
- CN 9 emerges from the inferior salivatory nucleus of cranial nerve 9 (in the medulla) and innervates the otic ganglion, which, as mentioned, innervates the parotid gland.
- CN 10 emerges from the dorsal motor nucleus of the vagus nerve and innervates:
- Lower respiratory system
- Abdominal organs (represented by the liver)
- GI tract from esophagus to proximal 2/3 transverse colon (the foregut and midgut derivatives).
- Upper urinary system: the kidneys and upper portion of the ureters
It induces bronchoconstriction and increases gut peristalsis.
- CNs 9 and 10 both also emerge from nucleus ambiguus (in the medulla).
- Via its CN 9 fibers, nucleus ambiguus innervates ganglia that lie within and act on the carotid body and carotid sinus.
- Via its CN 10 fibers, nucleus ambiguus innervates cardiac ganglia, which act on the heart (they produce heart rate deceleration).
sacral component
- Resides within the nuclei of the intermediolateral cell column for sacral levels 2 – 4.
- These nuclei reside in lamina 7 in the intermediate gray matter horn of the spinal cord.
- The visceromotor axons from sacral levels 2 – 4 travel as pelvic splanchnic nerves, pass through the inferior hypogastric (pelvic) plexus to innervate:
- GI tract from distal 1/3 transverse colon to anal canal (the hindgut derivatives).
- Lower urinary system – the bladder with lower portion of the ureters.
- Reproductive organs (represented by the uterus and fallopian tubes).
Key Physiologic Functions
From superior to inferior along the human axis:
- Pupillary constriction (miosis)
- Lacrimation
- Salivation
- Heart rate slowing
- Bronchoconstriction
- Digestion
- Urination
- Defecation
- Genital engorgement
Mneomnics for Autonomic Physiology
- Reproductive physiology (penile function):
- Parasympathetic: Point
- Sympathetic: Shoot
- Acetylcholine stimulates all of these functions and cholinergic crisis presents with the oft-used (although variable) mnemonics: SLUDS
- Salivation, Lacrimation, Urination, Defecation, and Sweating (which is a sympathetic nervous system response to acetylcholine).
Pharmacologic Correlations
- We use atropine (a cholinergic antagonist) for life-threatening bradycardia.
- We use glycopyrrolate (another cholinergic antagonist) to reduce pulmonary secretions and bronchoconstriction in patient's being terminally weaned from a ventilator to reduce the "death rattle" that labors their breathing.