CHAPTER 6 • NEUROHUMORAL CONTROL OF THE HEART AND CIRCULATION
145
ANSWERS TO REVIEW QUESTIONS
1.
The correct answer is “c” because this
region of the brainstem contains cell
bodies for both sympathetic and para-
sympathetic neurons; choices “a” and
“b” are therefore incorrect. Choice “d”
is incorrect because the nucleus tractus
solitarius is the region in the medulla
that receives afferent fibers from periph-
eral sensors (e.g., baroreceptors) and
then sends excitatory or inhibitory fibers
to sympathetic and parasympathetic
neurons within the medulla.
2.
The correct answer is “b” because nor-
epinephrine binds to a i -adrenoceptors
located on vascular smooth muscle to
stimulate vasoconstriction. Choice “a”
is incorrect because norepinephrine
preferentially binds to (31
-adrenoceptors
in the heart. Choice “c” is incorrect
because prejunctional P2-adrenoceptors
facilitate norepinephrine release
(prejunctional a 2-adrenoceptors inhibit
release). Choice “d” is incorrect because
norepinephrine stimulates renin release
through P1
-adrenoceptors.
3.
The correct answer is “d” because the
vagus nerve is parasympathetic choliner-
gic and therefore releases acetylcholine.
Choice “a” is incorrect because efferent
right vagal stimulation primarily affects
the sinoatrial node and has no signifi-
cant direct effects on the systemic vas-
culature. Choice “b” is incorrect because
vagal stimulation decreases atrial
inotropy. Choice “c” is incorrect because
right vagal stimulation reduces heart
rate by decreasing the slope of Phase 4
of the pacemaker action potential.
4.
The correct answer is “c” because
increased carotid artery pressure stimu-
lates the firing of carotid sinus barore-
ceptors (therefore, choice “a” is incor-
rect), which leads to a reflex activation
of vagal efferents to slow the heart rate
(therefore, choice “d” is incorrect).
Choice “b” is incorrect because the baro-
receptor reflex would attempt to reduce
arterial pressure by withdrawing sympa-
thetic tone on the systemic vasculature.
5.
The correct answer is “b” because
increased blood PC02 stimulates chemo-
receptors, which activate the sympathetic
nervous system to constrict the systemic
vasculature and raise arterial pressure.
Choice “a” is incorrect because increased
arterial pulse pressure stimulates arterial
baroreceptors, which leads to vagal acti-
vation of the heart. Choice “c” is incor-
rect because increased carotid sinus firing
(usually caused by elevated arterial pres-
sure) causes a reflex decrease in heart
rate brought about by vagal activation
and sympathetic withdrawal. Choice “d”
is incorrect because the vasovagal reflex
causes vagal activation and bradycardia.
6.
The correct answer is “d” because a high
dose of epinephrine binds to both P2-
and a i-adrenoceptors on blood vessels.
Therefore, if the P2-adrenoceptors (which
produce vasodilation) are blocked, the
a i -adrenoceptors can produce vasocon-
striction unopposed by the P2-adreno-
ceptors. Choice “a” is incorrect because
the unopposed a-adrenoceptor activation
increases arterial pressure. Choice “b”
is incorrect because epinephrine binds
to oc as well as P-adrenoceptors. Choice
“c” is incorrect because epinephrine-
induced increased heart rate is mediated
primarily by P-adrenoceptors (which are
blocked), and systemic vasoconstriction
will increase arterial pressure and cause
a reflex decrease in heart rate.
7.
The correct answer is “c” because ace-
tylcholine dilates blood vessels, which
lowers arterial pressure and causes a
baroreceptor-mediated increase in heart
rate brought about by sympathetic acti-
vation. Choice “a” is incorrect because
stimulation of muscarinic receptors on
the sinoatrial node induces bradycar-
dia. Choice “b” is incorrect because the
hypotension causes decreased carotid
sinus firing. Choice “d” is incorrect
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