19.8:
Cranial Part of Parasympathetic Division
The cranial part of the ANS parasympathetic division consists of preganglionic fibers that originate in the brainstem and innervate various structures in the head, neck, thorax, and abdomen.
These preganglionic fibers leave the brainstem as parts of cranial nerves III, VII, IX, and X.
The parasympathetic fibers of cranial nerve III or the oculomotor nerve enter the ciliary ganglia, which sends postganglionic fibers to smooth muscles in the eye.
The parasympathetic fibers of cranial nerve VII, known as the facial nerve, extend to the pterygopalatine ganglia and the submandibular ganglia.
The pterygopalatine ganglia stimulate tear and mucus production in the lacrimal and nasal glands.
The submandibular ganglia stimulate saliva production by innervating the submandibular and sublingual salivary glands.
The parasympathetic fibers of cranial nerve IX, or the glossopharyngeal nerve, send parasympathetic signals to the parotid salivary gland through the otic ganglia.
The parasympathetic fibers of cranial nerve X, or the vagus nerve, reach the terminal ganglia in the thorax and abdomen, supplying parasympathetic signals to the heart, lungs, and abdominal organs.
19.8:
Cranial Part of Parasympathetic Division
The cranial part of the parasympathetic division plays a crucial role in regulating the visceral functions of the head and specific structures in the neck, thoracic, and abdominopelvic cavities. Preganglionic fibers of the parasympathetic division exit the brain through cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal), and X (vagus), delivering parasympathetic output to the respective visceral structures.
The vagus nerve (cranial nerve X) alone accounts for approximately 75 percent of all parasympathetic outflow from the central nervous system (CNS). It provides preganglionic parasympathetic innervation to structures in the neck, thoracic cavity, and abdominopelvic cavity, extending as far as the distal portion of the large intestine. The cranial parasympathetic ganglia associated with these cranial nerves are located close to the organs they innervate.
The ciliary ganglia are situated laterally to each optic (II) nerve. Preganglionic axons travel alongside the oculomotor (III) nerves to reach the ciliary ganglia. Postganglionic axons originating from these ganglia innervate the smooth muscle fibers within the eyeball.
The pterygopalatine ganglia are found laterally to the sphenopalatine foramen. They receive preganglionic axons from the facial (VII) nerve and send postganglionic axons to the nasal mucosa, palate, pharynx, and lacrimal glands.
The submandibular ganglia are located near the ducts of the submandibular salivary glands. They also receive preganglionic axons from the facial nerves and send postganglionic axons to the submandibular and sublingual salivary glands.
The otic ganglia are situated just inferior to each foramen ovale. Preganglionic axons from the glossopharyngeal (IX) nerves reach the otic ganglia, sending postganglionic axons to the parotid salivary glands.