Parasympathetic division

The craniosacral division and parasympathetic division are one in the same. The term was deemed due to the production of preganglionic neurons origination in the brain as well as in the 2nd through 4th sacral sections of the spinal column. The brain is responsible for the bulk of the production and the neurons originate from the pons, midbrain, and the medulla oblongata. The organs which are innervated are also the location of the preganglionic parasympathetic neurons in ganglia. These ganglia are known as the terminal ganglia. The terminal ganglia are the direct supplier of the postganglionic neurons that conjoin in synapse with the cells of the effector organs. Parasympathetic neurons are unique to the sympathetic neurons especially in their lack of necessity to traverse through the spinal nerves.

The coetaneous effectors, which includes functions such as sweating and crying and effectors such as blood vessels and arrector pili muscles, as well as the blood vessels within the skeletal muscles, only receive sympathetic innervation and are denied parasympathetic innervation.

Out of the 12 pairs of cranial nerves, only 4 are allotted preganglionic parasympathetic neurons. These 4 preganglionic supplied cranial nerves include the vagus, the facial nerve, the oculomotor nerve, and the glossopharyngeal nerve. The parasympathetic neurons that arise from the first 3 cranial nerves conjoin in synaptic activity with the ganglia positioned in the head. The parasympathetic neurons which arise from the vagus nerve conjoin in synaptic activity with the terminal ganglia positioned throughout the body in many locations. The oculomotor nerve houses both somatic motor and parasympathetic neurons which stem from the midbrain in the oculomotor nuclei. The oculomotor neurons conjoin in synaptic activity with the ciliary ganglion. The ciliary ganglion branch off innervations to the eye’s iris and constrictor muscles as well as the ciliary muscle. In continuation, the facial nerve’s parasympathetic neurons conjoin in synaptic activity with pterygopalatine ganglion from their origin in the pons. From here they proceed to send appropriate postganglionic neurons to the palate, pharynx, nasal mucosa, and the lacrimal glands.

The facial nerve also responds to another set of neurons which in fact terminate in the submandibular ganglion. This set of parasympathetic neurons is responsible for synaptic activity for the submandibular gland and the sublingual glands.

The otic ganglion receives the pregnaglionic neurons from the glossopharyngeal nerve which acts in synaptic activity with and the execution of postganglionic neurons to innervate the parotid gland.

Parasympathetic division

The most extensive and intricate innervation process in the body occurs from the synaptic activity of the extremely long vagus nerve. The nuclei arising from the medulla oblongata are responsible for the origination of this process. The preganglionic neurons begin their journey from the medulla oblongata and continue throughout the length of the vagus nerve and then initially pass through the thorax where they innervate in part the cardiac plexus and the pulmonary plexuses. The process of innervation continues well into the pulmonary plexuses as the branches from the vagus nerves then follow the blood vessels into the lungs along the course of the bronchi.

Continuing from the pulmonary plexuses, the vagus nerves temporarily meet with the esophageal plexus. The nerves follow the esophageal plexus along the esophagus and innervate appropriately along the way. When the esophagus terminates, the vagus nerves then draw into the vagal neurons which are responsible for the collection of more vagal neurons to create the formation of the anterior and posterior vagal trunk. Both the anterior and posterior portions of the vagal trunk are composites derived from both vagus nerves. The vagal trunks then continue the original journey as they pass through the abdominal cavity, making their entrance through the esophageal hiatus, which can be located in the diaphragm. The vagal trunks send out neurons which are responsible for the innervation of the anterior and posterior sides of the stomach.

The vagus nerves once again branch out to cover the regions within the abdominal cavity. They are responsible for the process of innervation of the celiac plexus as well as the plexuses of the abdominal aorta, at least in part. Postganglionic neurons are positioned inside the organs and the preganglionic neurons are responsible for adjoining with these postganglionic neurons for the purpose of synaptic activity. The length of the preganglionic neurons is extreme, and they deliver parasympathetic innervation to various organs, including the liver, heart, stomach, esophagus, small intestine, lungs, pancreas, and the upper portion of the large intestine. Within each of these organs is the terminal ganglia which is necessary for synaptic activity to innervate each organ. From these terminal ganglia the postganglionic parasympathetic neurons are diverged and the smooth muscle tissue and glandular epithelium has achieved innervation.

The sacral levels of the spinal column release preganglionic neurons which are responsible for the innervation and synaptic activity necessary for the lower half of the large intestine as well as the rectum. This same process applies to the urinary system and the reproductive system as well. Just like the vagus nerves, the terminal ganglia for the necessary processes are positioned within each organ and the postganglionic neurons must provide synaptic activity inside the effector organs. Preganglionic neurons serve the parasympathetic nerves which serve the visceral organs. The postganglionic neurons thus come from the sympathetic nerves.