Parasympathetic Nervous System: Animated Scheme (Craniosacral Outflow)

Content:
0:00 Introduction
01:35 Ganglion and Nucleus
02:06 General Structure
02:55 Sympathetic vs Parasympathetic
06:10 Neurotransmitters
07:35 Craniosacral Outflow
08:55 Cranial Part
17:42 Sacral Part
19:19 Ending

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Parasympathetic nervous system is a part of the autonomic nervous system, which is under the motor division of the peripheral nervous system. Neuroanatomy

General Structures and Terms:
Group of cell bodies in CNS - Nucleus
Group of cell bodies outside CNS - Ganglion
Presynaptic neuron is a cholinergic neuron (Ach binds to nicotinic receptors, allowing an influx of cations)
Postganglionic neurons are also cholinergic neurons (Acetylcholine binds to muscarinic receptors of the target organ, activating a g-protein)

General Functional Aspects of the Sympathetic and Parasympathetic Divisions:
Antagonistic Systems:
Territory:
Sympathetic: All areas of the body
Parasympathetic: Not all areas, no innervation in the body wall and limbs
Activity:
Sympathetic: More generalized and indirect. Ratio of pre- to postganglionic neurons is 1:15 or more.
E.g., accelerated heart rate, bronchodilation, decreased peristalsis in the gut tube, closing of the sphincters, relaxation of the general bladder wall, and dilation of the pupils.
Parasympathetic: More specific and direct, Ratio of pre- to postganglionic neurons is 1:2
Decelerated heart rate, bronchoconstriction, increased gut peristalsis, opening of sphincters, contraction of the bladder wall, and constriction of the pupils.

Functions:
Sympathetic: Classic ''Fight-or-Flight''. Increase levels of activity and assistance in coping with stress and physical exertion
Parasympathetic: Classic ''Rest-and-Digest''. Homeostasis, restoration, recuperation, and relaxation

Complementary (Synergistic) Systems:
Parasympathetic activity produces erection, and sympathetic activity results in ejaculation.
Independent function:
Sympathetic activates sweat gland secretion, but parasympathetics play no role in sweat gland activity.

Cranial Outflow:
Oculomotor nerve (nervus oculomotorius)
Nucleus: Edinger-Westphal nucleus, accessory oculomotor nucleus (nucleus accessorii nervi oculomotorii)
Synapse with Ciliary ganglion (ganglion ciliare), and innervates the ciliary body and sphincter pupillae

Facial nerve (nervus facialis)
Nucleus: Superior salivatory nucleus (nucleus salivatorius superior)
Greater petrosal nerve synapse with Pterygopalatine ganglion (ganglion pterygopalatinum) to innervate the lacrimal, palatine, nasal and nasopharyngeal glands.
Chorda tympani synapse with Submandibular ganglion (ganglion submandibulare) to innervate submandibular and sublingual glands

Glossopharyngeal nerve (nervus glossopharyngeus)
Nucleus: Inferior salivatory nucleus (nucleus salivatorius inferior)
Lesser petrosal nerve synapse with otic ganglion (ganglion oticum), then innervates the parotid gland

Vagus nerve (nervus vagus)
Nucleus: Posterior nucleus of the vagus nerve (nucleus posterior nervi vagi)
Innervates smooth muscle, glands, internal organs

Sacral Outflow:
Sacral parasympathetic nuclei in the lateral horns of the spinal cord as Intermediolateral nucleus (nucleus intermediolateralis) S2, S2, and S4
Sacral splanchnic nerves (nervi splanchnici sacrales)
Preganglionic fibers going into the inferior hypogastric plexus (plexus hypogastricus inferior) and through organs of the lesser pelvis and synapse with purely parasympathetic ganglia.

Sources:
Singh, I. (2017). Human Neuroanatomy (10th ed.).
Wineski, L. E. (2019). Snell’s Clinical Anatomy by Regions (10th ed.). Pearson.
Kozlowski, T. (2017). *Memorix Anatomy: The Complete Study Guide*. 2nd ed. Thieme Medical Publishers.
Fryer, A. D., & Jacoby, D. B. (1998). Muscarinic Receptors and Control of Airway Smooth Muscle. *American Journal of Respiratory and Critical Care Medicine, 158*(Supplement 2), 13tac120. https://doi.org/10.1164/ajrccm.158.su...
Pterygopalatine Ganglion. (n.d.). *ScienceDirect*. Retrieved 20.01.2024.
Selective Serotonin Reuptake Inhibitors for Premature Ejaculation: Review of Erectile and Ejaculatory Side Effects - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/F... [accessed 23 Jan, 2024]
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