Practice important
Myofibril Arrangement
MCQ questions and answers.
Page 1
of
1
|
10
MCQ Questions
1. A longitudinal section of a skeletal muscle fibre shows several myofibrils arranged side by side. Which feature most directly explains why the dark and light bands appear continuous across the entire fibre?
A.
The sarcomeres of adjacent myofibrils are aligned transversely with one another
B.
The actin filaments of adjacent myofibrils fuse at the centre of the fibre
C.
The myosin filaments extend continuously from one myofibril into the next
D.
The Z discs are absent at the lateral margins of neighbouring myofibrils
Correct Answer:
The sarcomeres of adjacent myofibrils are aligned transversely with one another
Explanation:
Myofibrils are arranged parallel to one another, and their sarcomeres are aligned at corresponding levels. This alignment places Z discs, A bands, and I bands in register, producing the regular striated appearance of the whole muscle fibre.
2. Which sequence correctly represents the arrangement of regions along one myofibril from the centre of one sarcomere to the centre of the next?
A.
M line → H zone → A band → I band → Z disc → I band → A band → H zone → M line
B.
Z disc → I band → H zone → A band → M line → A band → H zone → I band → Z disc
C.
M line → A band → H zone → I band → Z disc → I band → H zone → A band → M line
D.
Z disc → A band → I band → M line → H zone → M line → I band → A band → Z disc
Correct Answer:
M line → H zone → A band → I band → Z disc → I band → A band → H zone → M line
Explanation:
A sarcomere extends from one Z disc to the next, with the M line at its centre. Moving outward from the M line gives the H zone, the rest of the A band, the I band, and then the Z disc; the pattern repeats in the adjacent sarcomere.
3. If the Z discs of neighbouring myofibrils were not aligned transversely, what would be the most likely effect on the microscopic appearance of the muscle fibre?
A.
The fibre would show continuous transverse striations
B.
The fibre would lose the distinction between actin and myosin
C.
The transverse striations would appear irregular or staggered
D.
The A bands would disappear while the I bands remained unchanged
Correct Answer:
The transverse striations would appear irregular or staggered
Explanation:
The regular striated pattern depends on the transverse alignment of sarcomeres in adjacent myofibrils. If Z discs were staggered, corresponding bands would not lie at the same level, producing an irregular banding pattern.
4. Which statement best distinguishes the arrangement of a sarcomere from the arrangement of a myofibril within a skeletal muscle fibre?
A.
A sarcomere is a bundle of myofibrils, whereas a myofibril is a single contractile filament
B.
A sarcomere is a repeating segment of a myofibril, whereas many myofibrils lie parallel within a muscle fibre
C.
A sarcomere runs longitudinally across the entire muscle fibre, whereas myofibrils run transversely
D.
A sarcomere contains only thick filaments, whereas a myofibril contains only thin filaments
Correct Answer:
A sarcomere is a repeating segment of a myofibril, whereas many myofibrils lie parallel within a muscle fibre
Explanation:
A myofibril is a long cylindrical contractile structure composed of repeated sarcomeres arranged end to end. Numerous myofibrils are packed parallel to the long axis inside one skeletal muscle fibre.
5. A band is observed to retain approximately the same length during contraction, whereas the I band becomes narrower. Which arrangement of filaments explains this observation?
A.
Thin filaments are anchored to Z discs and slide further between thick filaments without shortening
B.
Thick filaments are anchored to Z discs and thin filaments dissolve during contraction
C.
Both thick and thin filaments shorten uniformly toward the M line
D.
The Z discs move apart while the thick filaments shorten within the H zone
Correct Answer:
Thin filaments are anchored to Z discs and slide further between thick filaments without shortening
Explanation:
The A band corresponds mainly to the length of the thick filaments, which does not change. During contraction, thin filaments attached to the Z discs slide toward the M line, increasing overlap and reducing the I band.
6. In a relaxed sarcomere, the H zone is visible because it represents a central region containing which arrangement?
A.
Thin filaments only, extending from the Z discs
B.
Thick filaments only, without overlap by thin filaments
C.
Both thick and thin filaments anchored directly to the M line
D.
Neither thick nor thin filaments, because it is an empty gap between Z discs
Correct Answer:
Thick filaments only, without overlap by thin filaments
Explanation:
The H zone is the central portion of the A band where only thick filaments are present. Thin filaments extend inward from the Z discs but do not reach this central region in a sufficiently relaxed sarcomere.
7. Which change in sarcomere arrangement would occur as a muscle fibre contracts, assuming the sliding-filament model?
A.
The Z discs move closer together, while the relative length of the A band remains essentially constant
B.
The Z discs move farther apart, while the H zone widens
C.
The thick filaments shorten, while the I band becomes longer
D.
The M line shifts to one end of the sarcomere, while the A band disappears
Correct Answer:
The Z discs move closer together, while the relative length of the A band remains essentially constant
Explanation:
Contraction involves increased sliding of thin filaments toward the M line. Consequently, the Z discs approach each other, the I band and H zone narrow, and the A band remains approximately constant because thick-filament length does not change.
8. A transverse section is taken through the H zone of a sarcomere. Which filament arrangement would be expected in the central region of the sarcomere?
A.
Only thin filaments arranged around each Z disc
B.
Only thick filaments arranged around the M line
C.
Equal numbers of thick and thin filaments directly overlapping
D.
No filaments, because the H zone is the gap between adjacent sarcomeres
Correct Answer:
Only thick filaments arranged around the M line
Explanation:
The H zone is the central, lighter part of the A band and contains thick filaments without overlapping thin filaments. The M line lies at its centre and helps organize the thick filaments.
9. Which structural relationship allows force generated in individual sarcomeres to contribute effectively to shortening of the whole muscle fibre?
A.
Sarcomeres are arranged end to end within each myofibril, while many myofibrils run parallel along the fibre
B.
Sarcomeres are arranged randomly, allowing contraction in different directions
C.
Myofibrils are arranged transversely so that their contractions oppose one another
D.
Thin filaments from one sarcomere are continuous with thick filaments of the next sarcomere
Correct Answer:
Sarcomeres are arranged end to end within each myofibril, while many myofibrils run parallel along the fibre
Explanation:
End-to-end repetition of sarcomeres allows shortening along the length of each myofibril. Parallel packing of many myofibrils enables their individual shortening forces to act together along the long axis of the muscle fibre.
10. Which pairing correctly identifies a region and its position relative to the sarcomere boundaries?
A.
I band: centred on the M line and containing only thick filaments
B.
A band: extends from one Z disc to the next and contains only thin filaments
C.
I band: lies on either side of a Z disc and contains thin filaments without the full length of thick-filament overlap
D.
H zone: lies between adjacent sarcomeres and contains the Z disc
Correct Answer:
I band: lies on either side of a Z disc and contains thin filaments without the full length of thick-filament overlap
Explanation:
Each I band is divided by a Z disc and contains portions of thin filaments that are not overlapped by thick filaments. The A band occupies the length of the thick filaments, while the H zone is central within the A band.
Short Questions and Answers
Practice short questions and answers related to
Myofibril Arrangement
.
Short questions are currently unavailable for this page.