1. What is the H zone in a skeletal muscle sarcomere?
A.
The region containing only thin filaments
B.
The central region containing only thick filaments
C.
The boundary between two sarcomeres
D.
The region containing only actin and no myosin
Correct Answer:
The central region containing only thick filaments
Explanation:
The H zone is the central part of the A band where only thick myosin filaments are present.
2. Where is the H zone located within a sarcomere?
A.
At the center of the A band
B.
At the edge of the I band
C.
At the Z line
D.
Between two muscle fibres
Correct Answer:
At the center of the A band
Explanation:
The H zone lies in the middle of the A band and contains the portion of thick filaments that does not overlap thin filaments.
3. Which contractile filament is present in the H zone?
A.
Only actin
B.
Only myosin
C.
Actin and tropomyosin only
D.
Only troponin
Correct Answer:
Only myosin
Explanation:
The H zone contains only thick myosin filaments, while thin actin filaments do not extend into its central region.
4. What happens to the H zone when a skeletal muscle contracts?
A.
It becomes wider
B.
It remains unchanged in width
C.
It becomes narrower
D.
It moves to the Z line
Correct Answer:
It becomes narrower
Explanation:
During contraction, thin filaments slide toward the center of the sarcomere, reducing the width of the H zone.
5. The H zone is a part of which band of a sarcomere?
A.
I band
B.
A band
C.
Z line
D.
M line only
Correct Answer:
A band
Explanation:
The H zone is the central region of the A band where the thick filaments are not overlapped by thin filaments.
6. In a relaxed skeletal muscle, the H zone is generally:
A.
Clearly visible
B.
Absent in every sarcomere
C.
Made only of thin filaments
D.
Located outside the A band
Correct Answer:
Clearly visible
Explanation:
In a relaxed sarcomere, the thin filaments overlap the thick filaments less, so the central H zone can be observed.
7. Why does the H zone decrease during muscle contraction?
A.
Thick filaments become shorter
B.
Thin filaments slide toward the center
C.
The Z lines disappear
D.
Thin filaments break apart
Correct Answer:
Thin filaments slide toward the center
Explanation:
The H zone narrows because actin thin filaments slide inward over the myosin thick filaments during contraction.
8. Which statement about the H zone is correct?
A.
It contains only the overlapping region of actin and myosin
B.
It contains the central non-overlapping part of thick filaments
C.
It is formed by two adjacent Z lines
D.
It contains no contractile proteins
Correct Answer:
It contains the central non-overlapping part of thick filaments
Explanation:
The H zone is the central part of the A band where thick myosin filaments are not overlapped by thin actin filaments.
9. At maximum contraction, the H zone may:
A.
Become wider than the A band
B.
Disappear because of increased filament overlap
C.
Change into an I band
D.
Move outside the sarcomere
Correct Answer:
Disappear because of increased filament overlap
Explanation:
When contraction is strong, thin filaments slide inward enough to cover the H zone, so it may disappear.
10. Which feature distinguishes the H zone from the overlapping part of the A band?
A.
The H zone contains only thick filaments
B.
The H zone contains only thin filaments
C.
The H zone contains no myosin
D.
The H zone is found between two muscle fibres
Correct Answer:
The H zone contains only thick filaments
Explanation:
Unlike the overlapping part of the A band, the H zone has only thick myosin filaments and no overlapping thin actin filaments.
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