Autonomic Nervous System

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The classic definition of the ANS is the preganglionic and postganglionic neurons within the sympathetic and parasympathetic divisions. A modern definition of the ANS takes into account the descending pathways from several forebrain and brainstem regions as well as visceral afferent pathways that set the level of activity in sympathetic and parasympathetic nerves.

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Parasympathetic

Level 3 - stop at this level

longer pre-, shorter post- ganglionic neuron

AKA craniosacral division

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because of the location of its preganglionic neurons; preganglionic neurons are located in several cranial nerve nuclei (III, VII, IX, and X) and in the IML of the sacral spinal cord

Edinger–Westphal nucleus

superior salivatory nucleus

sphenopalatine ganglia

submandibular ganglia

submandibular (also called submaxillary) and sublingual glands

inferior salivatory nucleus

otic ganglion

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parotid salivary gland

ciliary ganglia

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 innervate the sphincter (constrictor) muscle of the iris and the ciliary muscle.

nucleus ambiguus

sinoatrial (SA) and atrioventricular (AV) nodes in the heart

dorsal motor vagal nucleus

esophagus, trachea, lungs, and gastrointestinal tract

pelvic nerve

pelvic viscera via branches of the second to fourth sacral spinal nerves

Sympathetic

shorter pre-, longer post-ganglionic neuron

aka " thoracolumbar division of the ANS"

ventral root

white rami communicantans

sympathetic paravertebral ganglion

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 Paravertebral ganglia are located adjacent to each thoracic and upper lumbar spinal segment; in addition, there are a few ganglia adjacent to the cervical and sacral spinal segments. The ganglia are connected to each other via the axons of preganglionic neurons that travel rostrally or caudally to terminate on postganglionic neurons located at some distance. Together these ganglia and axons form the sympathetic chain bilaterally. This arrangement is seen inFigure 13–2 and Figure 13–3.

SYMPATHETIC CHAIN*

gray rami communicans

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The axons of some of the postganglionic neurons leave the chain ganglia and reenter the spinal nerves via the gray rami communicans and are distributed to autonomic effectors in the areas supplied by these spinal nerves (Figure 13–2). These postganglionic sympathetic nerves terminate mainly on smooth muscle (eg, blood vessels and hair follicles) and on sweat glands in the limbs. Other postganglionic fibers leave the chain ganglia to enter the thoracic cavity to terminate in visceral organs. Postganglionic fibers from prevertebral ganglia also terminate in visceral targets.

PRE-VERTEBRAL GANGLIA

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Some preganglionic neurons pass through the paravertebral ganglion chain and end on postganglionic neurons located in prevertebral (orcollateral) ganglia close to the viscera, including the celiac, superior mesenteric, and inferior mesenteric ganglia (Figure 13–3). There are also preganglionic neurons whose axons terminate directly on the effector organ, the adrenal gland.

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