The parasympathetic system is responsible for stimulation of "rest-and-digest" or "feed-and-breed"[3] activities that occur when the body is at rest, especially after eating, including sexual arousal, salivation, lacrimation (tears), urination, digestion, and defecation.
The axons of presynaptic parasympathetic neurons are usually long, extending from the CNS into a ganglion that is either very close to or embedded in their target organ.
The greater palatine parasympathetic synapse on the hard palate and regulate mucous glands located there.
The lesser palatine nerve synapses at the soft palate and controls sparse taste receptors and mucous glands.
The chorda tympani travels through the middle ear and attaches to the lingual nerve (mandibular division of trigeminal, CN V3).
From the otic ganglion postganglionic parasympathetic fibers travel with the auriculotemporal nerve (mandibular branch of trigeminal, CN V3) to the parotid salivary gland.
This is very efficient as the major function of the vagus nerve from there on will be control of the gut smooth muscles and glands.
The extent of the parasympathetic in the abdomen include the pancreas, kidneys, liver, gall bladder, stomach and gut tube.
The preganglionic neurons in the pathway do not synapse in a ganglion as in the cranium but rather in the walls of the tissues or organs that they innervate.
There are other skeletal muscles involved with these processes but the parasympathetic plays a huge role in continence and bowel retention.
This suggestion is based on detailed analysis of 15 phenotypic and ontogenetic factors differentiating sympathetic from parasympathetic neurons in the mouse.
If the peritoneal cavity becomes inflamed or if the bowel is suddenly distended, the body will interpret the afferent pain stimulus as somatic in origin.
Considering a healthy heart, the main pacemaker is a collection of cells on the border of the atria and vena cava called the sinoatrial node.
In absence of any external stimuli, sinoatrial pacing contributes to maintain the heart rate in the range of 60-100 beats per minute (bpm).
[16] At the same time, the two branches of the autonomic nervous system act in a complementary way increasing or slowing the heart rate.
In this context, the vagus nerve acts on sinoatrial node slowing its conduction thus actively modulating vagal tone accordingly.
[18][19] The main mechanism by which the parasympathetic nervous system acts on vascular and cardiac control is the so-called respiratory sinus arrhythmia (RSA).
In males, the cavernous nerves from the prostatic plexus stimulate smooth muscles in the fibrous trabeculae of the coiled helicine arteries of penis to relax and allow blood to fill the two corpora cavernosa and the corpus spongiosum of the penis, making it rigid to prepare for sexual activity.
Upon emission of ejaculate, the sympathetics participate and cause peristalsis of the ductus deferens and closure of the internal urethral sphincter to prevent semen from entering the bladder.
In the female, there is erectile tissue analogous to the male yet less substantial that plays a large role in sexual stimulation.
Also in the female, the parasympathetics innervate the fallopian tubes, which helps peristaltic contractions and movement of the oocyte to the uterus for implantation.
A mnemonic to summarize the functions of the parasympathetic nervous system is SSLUDD (sexual arousal, salivation, lacrimation, urination, digestion and defecation).
The parasympathetic nervous system promotes digestion and the synthesis of glycogen, and allows for normal function and behavior.