Notes

• Preganglionic fibers originate in brain stem and sacral segments of spinal cord.
• Synapse in ganglia close to (or within) target organs.
• Preganglionic fibers are long (they go all the way to the organs).
• Postganglionic fibers are short.

Rest and Repose Parasympathetic division stimulates visceral activity. It conserves energy and promotes sedentary activities.

What are the structures and functions of the parasympathetic division of the ANS?

The Parasympathetic Division Autonomic Nuclei

• Are contained in the mesencephalon, pons, and medulla oblongata: in lateral gray horns of spinal segments S2 -- S4.

Ganglionic Neurons in Peripheral Ganglia Preganglionic fiber synapses on 6-8 ganglionic neurons:

• Terminal ganglion (near target organ)
• Intramural ganglion (embedded in tissues of target organ).

Parasympathetic Innervation

Vagus Nerve Often mentioned because of the vagus reflex, when you have a long sustained activation of the sympathetic division, then the vagus nerve is activated to bring back the body to a state of rest, reduce heartbeat (e.g., runners at the end of the marathon collapse because blood misses in the brain due to the vagus nerve reflex).

• It provides 75% of all parasympathetic outflow.
• Branches intermingle with fibers of sympathetic division.

What are the effects of parasympathetic neurotransmitters on target organs and tissues? Parasympathetic Activation

• Centers on relaxation, food processing and energy absorption.
• Localized effects last a few seconds at most.

Parasympathetic Neurons

• All release ACh as neurotransmitter.
• Effects vary widely.