Key Terms
Also called
Craniosacral system Origin: brain stem nuclei + lateral horn of sacral spinal cord (S2-S4)
Two-neuron pathway
Same concept as sympathetic, different anatomy.
Three junction types in the chain
1. Synapse at same level as target 2.
White rami communicantes
Myelinated; carry preganglionic sympathetic fibers from spinal cord to chain ganglion
Vagus nerve reaches
Heart, bronchi, esophagus, stomach, liver, pancreas, gallbladder, small intestine The postganglionic fibers are often em
Picks up where the vagus leaves off
Majority of large intestine, urinary bladder, reproductive organs.
Two chemical systems
Cholinergic (releases ACh) and adrenergic (releases norepinephrine)
UNIVERSAL RULE
ALL preganglionic fibers — sympathetic AND parasympathetic — release acetylcholine (ACh). No exceptions.
Somatic efferent
One neuron from spinal cord directly to skeletal muscle Visceral efferent: preganglionic neuron to ganglion; ganglionic
Classic example
Heart attack pain felt in the left shoulder and arm. Why?
Long reflex
Involves the CNS; afferent signal goes to spinal cord or brain stem; efferent comes back out
Short reflex
Completely peripheral; no CNS involvement; sensory neuron activates postganglionic fiber directly
Example of short reflex
Stretch receptors in stomach wall activate smooth muscle directly via enteric neurons when the stomach is full. No CNS n
Heart rate
Parasympathetic tone. The heart's intrinsic rate is ~100 bpm.
Blood pressure
Sympathetic tone. Smooth muscle in blood vessel walls has adrenergic receptors.