Ch. 48 Questions

Question 1

The contraction of skeletal muscles is based on _____.

A) myosin filaments coiling up to become shorter
B) actin cross-bridges binding to myosin and transitioning from a high-energy to a low-energy state
C) myosin cross-bridges binding to actin and transitioning from a high-energy to a low-energy state
D) actin filaments coiling up to become shorter
E) actin and myosin filaments both coiling up to become shorter

Answer 1

C) myosin cross-bridges binding to actin and transitioning from a high-energy to a low-energy state

Question 2

Skeletal muscle contraction begins when calcium ions bind to _____.

A) acetylcholine receptors
B) troponin
C) energized cross-bridges
D) myosin
E) actin

Answer 2

B) troponin

Question 3

The hydrostatic skeleton of the earthworm allows it to move around in its environment by _____.

A) crawling with its feet
B) alternating contractions and relaxations of its flagella
C) using peristaltic contractions of its circular and longitudinal muscles
D) walking on its limbs
E) swimming with its setae

Answer 3

C) using peristaltic contractions of its circular and longitudinal muscles

Question 4

Which of the following is the correct sequence that describes the excitation and contraction of a skeletal
muscle fiber?

1. Tropomyosin shifts and unblocks the cross-bridge binding sites.
2. Calcium is released and binds to the troponin complex.
3. Transverse tubules depolarize the sarcoplasmic reticulum.
4. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using
   energy from ATP.
5. An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the
   muscle cell membrane.

Answer 4

5. An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the
   muscle cell membrane.
6. Transverse tubules depolarize the sarcoplasmic reticulum.
7. Calcium is released and binds to the troponin complex.
8. Tropomyosin shifts and unblocks the cross-bridge binding sites.
9. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using
   energy from ATP.

Question 5

Compared to oxidative skeletal muscle fibers, those classified as glycolytic typically have _____.

A) a higher density of mitochondria
B) a darker visual appearance
C) less resistance to fatigue
D) a higher concentration of myoglobin
E) a smaller diameter

Answer 5

C) less resistance to fatigue

Question 6

The “motor unit” in vertebrate skeletal muscle refers to _____.

A) one myofibril and all of its sarcomeres
B) one sarcomere and all of its actin and myosin filaments
C) an entire muscle
D) one actin binding site and its myosin partner
E) one motor neuron and all of the muscle fibers on which it has synapses

Answer 6

E) one motor neuron and all of the muscle fibers on which it has synapses

Question 7

Muscles are joined to bones by _____.

A) loose connective tissue
B) ligaments
C) spindle fibers
D) tendons
E) Haversian systems

Answer 7

D) tendons

Question 8

The muscles of a recently deceased human can remain in a contracted state, termed rigor mortis, for
several hours, due to the lack of _____.

A) oxygen supplies needed for myoglobin
B) ATP needed to break actin-myosin bonds
C) sodium ions needed to fire action potentials
D) phosphorylated myosin
E) calcium ions needed to bind to troponin

Answer 8

B) ATP needed to break actin-myosin bonds

Question 9

All skeletal muscle fibers are _____.

A) smooth and under involuntary control
B) smooth and under voluntary control
C) striated and electrically coupled to neighboring fibers
D) smooth and operate independently of other skeletal muscle fibers
E) striated and under voluntary control

Answer 9

E) striated and under voluntary control

Question 10

When an action potential from a motor neuron arrives at the neuromuscular junction (NMJ), a series
of events occurs that leads to muscle contraction. Which of the following events will occur last (that is,
after all of the others)?

A) conformational change in troponin
B) depolarization of the muscle cell
C) acetylcholine (ACh) release
D) release of Ca2+ from the sarcoplasmic reticulum
E) action potential propagation down the T-tubules

Answer 10

A) conformational change in troponin