Chapter 8 - Muscle

Question 1

Which of the following is true for mammalian skeletal muscle?
(A) T tubules are located at the Z disk.
(B) T tubules are absent.
(C) Troponin is absent.
(D) It possesses triads.
(E) It possesses caveolae.

Answer 1

D. The T tubules of skeletal muscle cells are positioned so that they form triads with the termi­nal cisternae of the SR at the interface of the A and I bands (see Chapter 8 II C).

Question 2

Which of the following is true for cardiac
muscle?
(A) T tubules are located at the Z disk.
(B) T tubules have a smaller diameter than
those of skeletal muscle.
(C) Troponin is absent.
(D) It possesses triads.
(E) Oxytocin triggers contraction.

Answer 2

A. The T tubules of cardiac muscle cells are wider than those of skeletal muscle cells and are lined by external lamina (a basal lamina-like material). In contrast to skeletal muscle, the
T tubules are located at the Z disk, where they often form dyads, not triads (see Chapter 8 V B 6).

Question 3

Which of the following is true for smooth muscle?
(A) T tubules are located at the Z disk.
(B) It possesses dyads.
(C) Caveolae store and release calcium ions.
(D) It possesses triads.
(E) T tubules are located at the A-I interface.

Answer 3

C. Smooth muscle cells do not have T tubules. Contraction may be initiated by stretching, neural impulses, the intercellular passage of small molecules via gap junctions, or the action of hormones such as oxytocin. Contraction is not dependent on troponin, which is absent from the thin filament of smooth muscle. Instead, Ca2+ controlled by sarcolemmal vesicles known as caveolae is released into the cytosol, where it binds with calmodulin. The calcium-calmodulin complex activates myosin light-chain kinase, which participates in the contraction process (see Chapter 8 VI A 2).

Question 4

Contraction in all types of muscle requires calcium ions. Which of the following muscle components can bind or sequester calcium ions?
(A) Rough endoplasmic reticulum
(B) Tropomyosin
(C) Troponin
(D) Active sites on actin
(E) Titin

Answer 4

C. Binding of Ca2+ to the TnC subunit of troponin leads to the uncovering of myosin-binding sites on actin (thin filaments) (see Chapter 8 II F l c).

Question 5

Each smooth muscle cell:
(A) has triads associated with its contraction
(B) has dyads associated with its contraction
(C) possesses a single central nucleus
(D) is characterized by the absence of sarcolemmal vesicles
(E) contains troponin

Answer 5

C. Smooth muscle cells contain one centrally located nucleus (see Chapter 8 VI A l).

Question 6

Thick filaments are anchored to Z disks by:
(A) C protein
(B) nebulin
(C) titin
(D) myomesin
(E) alpha-actinin

Answer 6

C. Titin forms an elastic lattice that anchors thick filaments to Z disks (see Chapter 8 II F 2 c).

Question 7

The endomysium is a connective tissue investment that surrounds:
(A) individual muscle fibers
(B) muscle fascicles
(C) individual myofibrils
(D) an entire muscle
(E) small bundles of muscle cells

Answer 7

A. The endomysium is a thin connective tissue layer composed of reticular fibers and an ex­ternal lamina that invests individual muscle fibers (cells). The epimysium surrounds the entire muscle, and the perimysium surrounds bundles (fascicles) of muscle fibers (see Chapter 8 II A 3).

Question 8

Which of the following statements concern­ ing triads in mammalian skeletal muscle is true?
(A) They are located in the Z disk
(B) They consist of two terminal cisternae of the SR separated by a T tubule
(C) They can be observed with the light microscope
(D) They are characterized by a T tubule that sequesters calcium ions
(E) They consist of two T tubules separated by a central terminal cisterna

Answer 8

B. A triad in skeletal muscle is composed of three components: a T tubule and two terminal cisternae of the SR that flank it. The SR, not the T tubules, sequesters Ca2+ (see Chapter 8 II C 4).

Question 9

Which one of the following statements concerning cardiac muscle cells is true?
(A) They are spindle shaped.
(B) They require an external stimulus to
undergo contraction.
(C) They are multinuclear cells.
(D) They are joined together end to end by
intercalated disks.
(E) They possess numerous caveolae.

Answer 9

D. Cardiac muscle cells are joined together end to end by a unique junctional specialization called the intercalated disk (see Chapter 8 V B 6).

Question 10

A 19-year-old male patient and his mother
arrive in the emergency department, both with nausea, vomiting, and visual disorders. The physician taking their history notes that they both had canned green beans that tasted funny. Which of the following possibilities should the physician consider?
(A) Duchenne muscular dystrophy
(B) Amyotrophic lateral sclerosis
(C) Botulism
(D) Myasthenia gravis
(E) Myocardial infarct

Answer 10

C. Botulism is the only possible consideration, especially since they both had canned food. Duchenne muscular dystrophy is most common in young men but very rare in older women. It would be highly unlikely that both mother and son would show symptoms of amyotrophic lateral sclerosis or myasthenia gravis or have myocardial infarct at the same time (see Chapter 8 II E Clinical Considerations).