End of Chapter
At the end of the chapters you will
fi nd:
Test Questions that are
designed to test student
comprehension of key concepts.
Quantitative and Thought
Questions that challenge the
student to go beyond the
memorization of facts, to solve
problems and to encourage
thinking about the meaning or
broader signifi cance of what has
just been read.
End of Section
At the end of sections throughout the book
you will fi nd a summary, key terms, clinical
terms, and review questions.
294
Chapter 9
an isotonic twitch of a
ore slowly when the fi ber is
ired to activate the entire
es to
reater than
se isotonic twitches only
co
m
pleted.
b. ADP is rapidly converted bac
k
to ATP by creatine
phosphate.
c. Gl
u
cose is
m
etabolized in
g
lycolysis, prod
u
cin
g
lar
g
e
q
u
antities of ATP.
d. The
m
itochondria i
mm
ediately be
g
in oxidative
phosphorylation.
e. Fatty acids are rapidly converted to ATP by oxidative
g
lycolysis.
7. Which correctly characterizes a “fast-oxidative” type of
s
k
eletal
mu
scle fi ber?
a. few
m
itochondria and hi
g
h
g
lyco
g
en content
b. low
m
yosin ATPase rate and few s
u
rro
u
ndin
g
capillaries
c. low
g
lycolytic enzy
m
e activity and inter
m
ediate contraction
velocity
d. hi
g
h
m
yo
g
lobin content and inter
m
ediate
g
lycolytic enzy
m
e
activity
e. s
m
al fi ber dia
m
eter and fast onset of fati
gu
e
8. Which is
false
re
g
ardin
g
the str
u
ct
u
re of s
m
ooth
mu
scle?
a. The thin fi la
m
ent does not incl
u
de the re
gu
latory protein
troponin.
b. The thic
k
and thin fi la
m
ents are not or
g
anized in sarco
m
eres.
c. Thic
k
fi l a
m
ents are anchored to dense bodies instead of Z
lines.
d. The cel s have a sin
g
le n
u
cle
u
s.
e. Sin
g
le-
u
nit s
m
ooth
mu
scles have
g
ap j
u
nctions connectin
g
individ
u
al cel s.
9. The role of
m
yosin li
g
ht-chain
k
inase in s
m
ooth
mu
scle is to
a. bind to calci
um
ions to initiate excitation-contraction
co
u
plin
g
.
b. phosphorylate cross-brid
g
es, th
u
s drivin
g
the
m
to bind with
the thin fi la
m
ent.
c. split ATP to provide the ener
g
y for the power stro
k
e of the
cross-brid
g
e cycle.
d. dephosphorylate
m
yosin li
g
ht chains of the cross-brid
g
e,
th
u
s relaxin
g
the
mu
scle.
e. p
um
p calci
um
fro
m
the cytosol bac
k
into the sarcoplas
m
ic
retic
u
l
um
.
10. Sin
g
le-
u
nit s
m
ooth
mu
scle differs fro
m
mu
lti
u
nit s
m
ooth
mu
scle beca
u
se
a. sin
g
le-
u
nit
mu
scle contraction speed is slow, while
mu
lti
u
nit
is fast.
b. sin
g
le-
u
nit
mu
scle has T-t
u
b
u
les,
mu
lti
u
nit
mu
scle
does not.
c. sin
g
le-
u
nit
mu
scles are not innervated by a
u
tono
m
ic nerves.
d. sin
g
le-
u
nit
mu
scle contracts when stretched, whereas
mu
lti
u
nit
mu
scle does not.
e. sin
g
le-
u
nit
mu
scle does not prod
u
ce action potentials
spontaneo
u
sly, b
u
t
mu
lti
u
nit
mu
scle does.
11. Which of the fol owin
g
describes a si
m
ilarity between cardiac
and s
m
ooth
mu
scle cel s?
a. An action potential always precedes contraction.
b. The
m
ajority of the calci
um
that activates contraction co
m
es
fro
m
the extracel
u
lar fl
u
id.
c. Action potentials are
g
enerated by pace
m
a
k
er potentials.
d. An extensive syste
m
of T-t
u
b
u
les is present.
e. Calci
um
release and contraction stren
g
th are
g
raded.
Chapter 9 Q
u
antitative and Tho
ug
ht Q
u
estions
(
A
nswers appear in
A
ppendix
A
.)
1. Which of the fol owin
g
corresponds to the state of
m
yosin (M)
u
nder restin
g
conditions and in ri
g
or
m
ortis? (a) M · ATP
(b) M · ADP · P
i
(c) A · M · ADP · P
i
(d) A · M
2. If the transverse t
u
b
u
les of a s
k
eletal
mu
scle are disconnected
fro
m
the plas
m
a
m
e
m
brane, wil action potentials tri
gg
er a
contraction? Give reasons.
3. When a s
m
al load is attached to a s
k
eletal
mu
scle that is then
tetanical y sti
mu
lated, the
mu
scle lifts the load in an isotonic
contraction over a certain distance, b
u
t then stops shortenin
g
and enters a state of iso
m
etric contraction. With a heavier
load, the distance shortened before enterin
g
an iso
m
etric
contraction is shorter. Explain these shortenin
g
li
m
its in ter
m
s
of the len
g
th-tension relation of
mu
scle.
4. What conditions wil prod
u
ce the
m
axi
mum
tension in a
s
k
eletal
mu
scle fi ber?
5. A s
k
eletal
mu
scle can often
m
aintain a
m
oderate level of active
tension for lon
g
periods of ti
m
e, even tho
ug
h
m
any of its fi bers
beco
m
e fati
gu
ed. Explain.
6. If the blood fl ow to a s
k
eletal
mu
scle were
m
ar
k
edly decreased,
which types of
m
otor
u
nits wo
u
ld
m
ost rapidly
u
nder
g
o a
severe red
u
ction in their ability to prod
u
ce ATP for
mu
scle
contraction? Why?
7. As a res
u
lt of an a
u
to
m
obile accident, 50 percent of the
mu
scle
fi bers in the biceps
mu
scle of a patient were destroyed. Ten
m
onths later, the biceps
mu
scle was able to
g
enerate 80 percent
of its ori
g
inal force. Describe the chan
g
es that too
k
place in the
da
m
a
g
ed
mu
scle that enabled it to recover.
Muscle
293
potential is due to the infl ux of calcium ions into the cel
through voltage-gated calcium channels.
VII. Some smooth muscles generate action potentials
spontaneously, in the absence of any external input, because
of pacemaker potentials in the plasma membrane that
repeatedly depolarize the membrane to threshold. Slow
waves are a pattern of spontaneous, periodic depolarization
of the membrane potential seen in some smooth muscle
pacemaker cel s.
VIII. Smooth muscle cel s do not have a specialized end-plate
region. A number of smooth muscle cel s may be infl uenced
by neurotransmitters released from the varicosities on a
single nerve ending, and a single smooth muscle cel may be
infl uenced by neurotransmitters from more than one neuron.
Neurotransmitters may have either excitatory or inhibitory
effects on smooth muscle contraction.
IX. Smooth muscles can be classifi ed broadly as single-unit or
multiunit smooth muscle.
Cardiac Muscle
I. Cardiac muscle combines features of skeletal and smooth
muscles. Like skeletal muscle, it is striated, is composed of
myofi brils with repeating sarcomeres, has troponin in its thin
fi laments, has T-tubules that conduct action potentials, and
has sarcoplasmic reticulum lateral sacs that store calcium.
Like smooth muscle, cardiac muscle cel s are smal and
single-nucleated, arranged in layers around hol ow cavities,
and connected by gap junctions.
II. Cardiac muscle excitation-contraction coupling involves
entry of a smal amount of calcium through L-type calcium
channels, which triggers opening of ryanodine receptors that
release a larger amount of calcium from the sarcoplasmic
reticulum. Calcium activates the thin fi lament and cross-
bridge cycling as in skeletal muscle.
III. Cardiac contractions and action potentials are prolonged,
tetany does not occur, and both the strength and
frequency of contraction are modulated by autonomic
neurotransmitters and hormones.
SECTION B REVIEW QUESTIONS
1. How does the organization of thick and thin fi laments in
smooth muscle fi bers differ from that in striated muscle fi bers?
2. Compare the mechanisms by which a rise in cytosolic calcium
concentration initiates contractile activity in skeletal, smooth,
and cardiac muscle cel s.
3. What are the two sources of calcium that lead to the increase in
cytosolic calcium that triggers contraction in smooth muscle?
4. What types of stimuli can trigger a rise in cytosolic calcium in
smooth muscle cel s?
5. What effect does a pacemaker potential have on a smooth
muscle cel ?
6. In what ways does the neural control of smooth muscle activity
differ from that of skeletal muscle?
7. Describe how a stimulus may lead to the contraction of a
smooth muscle cel without a change in the plasma membrane
potential.
8. Describe the differences between single-unit and multiunit
smooth muscles.
9. Compare and contrast the physiology of cardiac muscle with
that of skeletal and smooth muscles.
10. Explain why cardiac muscle cannot undergo tetanic
contractions.
dense body
284
intercalated disk
290
latch state
286
L-type calcium channel
290
multiunit smooth muscle
289
myosin light-chain kinase
285
myosin light-chain
phosphatase
286
pacemaker potential
287
single-unit smooth muscle
289
slow waves
287
smooth muscle tone
287
varicosity
288
IV. Table 9–6 summarizes and compares the features of skeletal,
smooth, and cardiac muscles.
SECTION B KEY TERMS
Chapter 9 Test Questions
(Answers appear in Appendix A.)
1. Which is a false statement about skeletal muscle structure?
a. A myofi bril is composed of multiple muscle fi bers.
b. Most skeletal muscles attach to bones by connective-tissue
tendons.
c. Each end of a thick fi lament is surrounded by six thin
fi l a m e n t s .
d. A cross-bridge is a portion of the myosin molecule.
e. Thin fi laments contain actin, tropomyosin, and troponin.
2. Which is correct regarding a skeletal muscle sarcomere?
a. M lines are found in the center of the I band.
b. The I band is the space between one Z line and the next.
c. The H zone is the region where thick and thin fi laments
overlap.
d. Z lines are found in the center of the A band.
e. The width of the A band is equal to the length of a thick
fi l a m e n t .
3. When a skeletal muscle fi ber undergoes a concentric isotonic
contraction:
a. M lines remain the same distance apart.
b. Z lines move closer to the ends of the A bands.
c. A bands become shorter.
d. I bands become wider.
e. M lines move closer to the end of the A band.
4. During excitation-contraction coupling in a skeletal muscle fi ber
a. the Ca
2+
-ATPase pumps calcium into the T-tubule.
b. action potentials propagate along the membrane of the
sarcoplasmic reticulum.
c. calcium fl oods the cytosol through the dihydropyridine
(DHP) receptors.
d. DHP receptors trigger the opening of lateral sac ryanodine
receptor calcium channels.
e. acetylcholine opens the DHP receptor channel.
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