Human Physiology, 14th edition (2016)

250 Chapter 9

“vagrant” or “wandering” nerves), which provide the major

parasympathetic innervation in the body. These preganglionic

fibers travel through the neck to the thoracic cavity and through

the esophageal opening in the diaphragm to the abdominal

cavity ( fig.  9.6 ). In each region, some of these preganglionic

fibers branch from the main trunks of the vagus nerves and

synapse with postganglionic neurons located within the inner-

vated organs. The preganglionic vagus fibers are thus quite

long; they provide parasympathetic innervation to the heart,

lungs, esophagus, stomach, pancreas, liver, small intestine, and

the upper half of the large intestine. Postganglionic parasym-

pathetic fibers arise from terminal ganglia within these organs

and synapse with effector cells (smooth muscles and glands).

Preganglionic fibers from the sacral levels of the spinal

cord provide parasympathetic innervation to the lower half of

the large intestine, the rectum, and to the urinary and repro-

ductive systems. These fibers, like those of the vagus, synapse

with terminal ganglia located within the effector organs.

Parasympathetic nerves to the visceral organs thus consist

of preganglionic fibers, whereas sympathetic nerves to these

are mixed nerves. Visceral sensory information (from blood
pressure receptors in certain arteries, for example) evokes auto-
nomic reflex motor responses (of heart rate, for example). These
reflexes will be discussed in chapter 14.
The oculomotor nerve contains somatic motor and para-
sympathetic fibers that originate in the oculomotor nuclei of
the midbrain. These parasympathetic fibers synapse in the
ciliary ganglion, whose postganglionic fibers innervate the
ciliary muscle and constrictor fibers in the iris of the eye. Pre-
ganglionic fibers that originate in the pons travel in the facial
nerve to the pterygopalatine ganglion, which sends postgangli-
onic fibers to the nasal mucosa, pharynx, palate, and lacrimal
glands. Another group of fibers in the facial nerve terminates
in the submandibular ganglion, which sends postganglionic
fibers to the submandibular and sublingual salivary glands.
Preganglionic fibers of the glossopharyngeal nerve synapse in
the otic ganglion, which sends postganglionic fibers to inner-
vate the parotid salivary gland.
Nuclei in the medulla oblongata contribute preganglionic
fibers to the very long tenth cranial, or vagus, nerves (the

Figure 9.6 The path of the vagus nerves. The vagus nerves and their branches provide parasympathetic innervation to most
organs within the thoracic and abdominal cavities.

Left cardiac branch

Right Left pulmonary plexus

cardiac

branch

Hyoid bone

Thyroid cartilage

of larynx

Trachea

Right

pulmonary

plexus

Right

gastric nerve

Celiac plexus

Liver

Superior

mesenteric nerve

Vagus nerve

Left gastric nerve

Stomach