Parasympathetic Division

The preganglionic fibers of the parasympathetic division (craniosacral division) arise from neurons in the mid-brain, pons, and medulla oblongata of the brain stem and from the sacral region of the spinal cord (fig. 11.40). From there, they lead outward on cranial or sacral nerves to ganglia located near or within various organs (terminal ganglia). The short postganglionic fibers continue from the ganglia to specific muscles or glands within these organs (fig. 11.41). Parasympathetic preganglionic axons are usually myelinated, and the parasympathetic post-ganglionic fibers are unmyelinated.

The parasympathetic preganglionic fibers associated with parts of the head are included in the oculomotor, facial, and glossopharyngeal nerves. Those fibers that innervate organs of the thorax and upper abdomen are parts of the vagus nerves. (The vagus nerves carry about

75% of all parasympathetic fibers.) Preganglionic fibers arising from the sacral region of the spinal cord lie within the branches of the second through the fourth sacral spinal nerves, and they carry impulses to viscera within the pelvic cavity (see fig. 11.40).

99 What is the general function of the autonomic nervous system?

^9 How are the divisions of the autonomic system distinguished?

^9 Describe a sympathetic nerve pathway and a parasympathetic nerve pathway.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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