Autonomic Neurotransmitters

The preganglionic fibers of the sympathetic and parasympathetic divisions all secrete acetylcholine, and for this reason they are called cholinergic (ko"lin-er'jik) fibers. The parasympathetic postganglionic fibers are also cholinergic fibers. Most sympathetic postganglionic fibers, however, secrete norepinephrine (noradrenalin) and are called adrenergic (ad"ren-er'jik) fibers (see fig. 11.41). Exceptions to this include the sympathetic postganglionic fibers that stimulate sweat glands and a few sympathetic fibers to blood vessels in skin (which cause vasodilation); these fibers secrete acetylcholine and therefore are cholinergic (adrenergic sympathetic fibers to blood vessels cause vasoconstriction).

Viscera

Dorsal root ganglion

Sensory neuron

Sensory neuron

Preganglionic fiber

Spinal cord

Dorsal root ganglion

- Autonomic ganglion Interneurons -Postganglionic fiber

Dorsal root ganglion

- Autonomic ganglion Interneurons -Postganglionic fiber

Skeletal muscle

(b) Somatic pathway

(a) Autonomic pathway

Figure 11.36

(a) Autonomic pathways include two neurons between the central nervous system and an effector. (b) Somatic pathways usually have a single neuron between the central nervous system and an effector.

Ventral root

Sympathetic trunk

Paravertebral sympathetic ganglion

Spinal nerves

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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