- Definition: That portion of the CNS and PNS that is
- responsible for unconscious control of visceral function, i.e. heart rate, respiratory rate, vascular diameter, gut motility, pupillary diameter, sexual preparedness, etc. This is accomplished through the direct innervation of cardiac muscle fibers, the smooth muscle fibers of bronchioles, arterioles and hollow organs (viscous) and the sudomotor cells (secretory) of glands.
a. Parasympathetic division (‘craniosacral’; cranial: motor nuclei of cranial nerves III, VII, IX, X and sacral: lateral horn *(I.M.L.C.C.) of spinal cord levels S2,3,4): Responsible for constant control of visceral function (vegetative state) i.e., decreased heart rate, decreased rate and depth of respiration, increased gut motility, shunting of blood toward the gut away from skeletal muscle, etc.
b. Sympathetic division (thoracolumbar: *(I.M.L.C.C.) lateral horn of spinal cord levels T1-L2): Responsible for control of visceral reaction in response to immediate stress (fight or flight), i.e. increased heart rate, increased rate and depth of respiration, decreased gut motility, shunting of blood from gut to skeletal muscle, etc.
- NOTE: Although the A.N.S. is classically described as a motor system (GVE),
- visceral afferents (GVA) parallel the course of the sympathetic subdivision, while
- visceral afferents can be found within branches of CNs VII, IX & X. In general,
- afferents paralleling sympathetic fibers carry visceral pain, while the para-
- sympathetic afferents (mostly vagal) are responsible for the modality of distention
- (feeling of fullness).