264 Chapter 9
B. All preganglionic autonomic nerve fibers are cholinergic
(use ACh as a neurotransmitter).
- All postganglionic parasympathetic fibers are
cholinergic. - Most postganglionic sympathetic fibers are adrenergic
(use norepinephrine as a neurotransmitter). - Sympathetic fibers that innervate sweat glands and those
that innervate blood vessels in skeletal muscles are
cholinergic.
C. Adrenergic effects include stimulation of the heart, vasocon-
striction in the viscera and skin, bronchodilation, and glyco-
genolysis in the liver. - The two main classes of adrenergic receptor proteins are
alpha and beta. - Some organs have only alpha or only beta receptors; other
organs (such as the heart) have both types of receptors. - There are two subtypes of alpha receptors ( a 1 and a 2 )
and two subtypes of beta receptors ( b 1 and b 2 ). These
subtypes can be selectively stimulated or blocked by
therapeutic drugs.
D. Cholinergic effects of parasympathetic nerves are promoted
by the drug muscarine and inhibited by atropine.
E. In organs with dual innervation, the effects of the sympa-
thetic and parasympathetic divisions can be antagonistic,
complementary, or cooperative.
1. The effects are antagonistic in the heart and pupils of
the eyes.
2. The effects are complementary in the regulation of
salivary gland secretion and are cooperative in the
regulation of the reproductive and urinary systems.
F. In organs without dual innervation (such as most blood vessels),
regulation is achieved by variations in sympathetic nerve activity.
G. The medulla oblongata of the brain stem is the area that most
directly controls the activity of the autonomic system.
1. The medulla oblongata is, in turn, influenced by sensory
input and by input from the hypothalamus.
2. 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.Test Your Knowledge
- When a visceral organ is denervated,
a. it ceases to function.
b. it becomes less sensitive to subsequent stimulation by
neurotransmitters.
c. it becomes hypersensitive to subsequent stimulation.- Parasympathetic ganglia are located
a. in a chain parallel to the spinal cord.
b. in the dorsal roots of spinal nerves.
c. next to or within the organs innervated.
d. in the brain.- The neurotransmitter of preganglionic sympathetic
fibers is
a. norepinephrine. c. acetylcholine.
b. epinephrine. d. dopamine. - Which of these results from stimulation of alpha-adrenergic
receptors?
a. Constriction of blood vessels
b. Dilation of bronchioles
c. Decreased heart rate
d. Sweat gland secretion - Which of these fibers release norepinephrine?
a. Preganglionic parasympathetic fibers
b. Postganglionic parasympathetic fibers
c. Postganglionic sympathetic fibers in the heart
d. Postganglionic sympathetic fibers in sweat glands
e. All of theseReview Activities
- The effects of sympathetic and parasympathetic fibers are
cooperative in
a. the heart. c. the digestive system.
b. the reproductive system. d. the eyes. - Propranolol is a beta blocker. It would therefore cause
a. vasodilation.
b. slowing of the heart rate.
c. increased blood pressure.
d. secretion of saliva. - Atropine blocks parasympathetic nerve effects. It would
therefore cause
a. dilation of the pupils.
b. decreased mucous secretion.
c. decreased movements of the digestive tract.
d. increased heart rate.
e. all of these. - Which area of the brain is most directly involved in the
reflex control of the autonomic system?
a. Hypothalamus
b. Cerebral cortex
c. Medulla oblongata
d. Cerebellum - The two subtypes of cholinergic receptors are
a. adrenergic and nicotinic.
b. dopaminergic and muscarinic.
c. nicotinic and muscarinic.
d. nicotinic and dopaminergic.