126.The sarcoplasmic reticulum of skeletal muscle functions in which of
the following?
a. Cellular Ca^2 +storage
b. Cellular glycogen storage
c. Glycogen degradation
d. Transport of Ca^2 +into the terminal cisternae during muscle contraction
e. Ca^2 +release from the transverse tubules during muscle relaxation
127.Observation of a histologic preparation of muscle reveals cross-
striationsand peripherally located nuclei. The use of histochemistry shows
a strong staining reaction for succinic dehydrogenase. The same tissue pre-
pared for electron microscopy shows many mitochondria in rows between
myofibrils and underneath the sarcolemma. Which of the following is the
best description of this tissue?
a. White muscle fibers
b. Fibers that contract rapidly but are incapable of sustaining continuous heavy
work
c. Red muscle fibers
d. Cardiac muscle
e. Smooth muscle
128.In skeletal muscle contraction, the “powerstroke” is initiated by
which of the following?
a. The initial binding of ATP to the myosin heads
b. Release of Pi from the myosin heads
c. Release of ADP and subsequent addition of an ATP molecule
d. Detachment of the myosin head from the actin
e. Phosphorylation of the myosin light chains
129.In muscular dystrophy, the actin-binding protein dystrophin is
absent or defective. Dystrophin contains similar actin-binding domains to
the spectrins (I and II) and α-actinin and has a similar structure. Which of
the following is most likely to occur as a result of this deficiency?
a. Enhanced smooth-muscle contractility
b. Deficiency in skeletal muscle actin synthesis
c. Loss of binding of the I and M bands to the cell membrane
d. Loss of organelle and vesicle transport throughout the muscle cell
e. Loss of integrity of the desmosomal components of the intercalated discs of
cardiac muscle
218 Anatomy, Histology, and Cell Biology