A. The involuntary effectors are somewhat independent of their innervation and become hypersensitive when their innervation is removed.
B. Autonomic nerves can have either excitatory or inhibitory effects on their target organs.
Divisions of the Autonomic Nervous System 222
II. Preganglionic parasympathetic fibers originate in the brain and in the sacral levels of the spinal cord. A. Preganglionic parasympathetic fibers contribute to cranial nerves III, VII, IX, and X.
B. The long preganglionic fibers of the vagus (X) nerve synapse in terminal ganglia located next to or within the innervated organ. Short postganglionic fibers then innervate the effector cells.
D. Parasympathetic outflow from the sacral levels of the spinal cord innervates terminal ganglia in the lower half of the large intestine, in the rectum, and in the urinary and reproductive systems.
I. The sympathetic division of the autonomic system activates the body to "fight or flight" through adrenergic effects. The parasympathetic division often exerts antagonistic actions through cholinergic effects.
A. All postganglionic parasympathetic fibers are cholinergic.
B. Most postganglionic sympathetic fibers are adrenergic (use norepinephrine as a neurotransmitter).
C. Sympathetic fibers that innervate sweat glands and those that innervate blood vessels in skeletal muscles are cholinergic.
A. The two main classes of adrenergic receptor proteins are alpha and beta.
B. Some organs have only alpha or only beta receptors; other organs (such as the heart) have both types of receptors.
C. There are two subtypes of alpha receptors (aj and a2) and two subtypes of beta receptors (Pj and P2). These subtypes can be selectively stimulated or blocked by therapeutic drugs.
IV. Cholinergic effects of parasympathetic nerves are promoted by the drug muscarine and inhibited by atropine.
V. In organs with dual innervation, the effects of the sympathetic and parasympathetic divisions can be antagonistic, complementary, or cooperative.
A. The effects are antagonistic in the heart and pupils of the eyes.
A. The medulla oblongata is in turn influenced by sensory input and by input from the hypothalamus.
B. The hypothalamus is influenced by input from the limbic system, cerebellum, and cerebrum. These interconnections provide an autonomic component to some of the visceral responses that accompany emotions.
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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.