1. Where is the M line located in a sarcomere?
A.
At the edge of the Z disc
B.
At the center of the sarcomere
C.
Between two actin molecules
D.
Outside the muscle fibre
Correct Answer:
At the center of the sarcomere
Explanation:
The M line is located at the center of a sarcomere and helps organize the thick filaments.
2. What is the main role of the M line in a skeletal muscle sarcomere?
A.
Anchoring thin filaments to the cell membrane
B.
Holding thick filaments in alignment
C.
Producing calcium ions
D.
Breaking down actin molecules
Correct Answer:
Holding thick filaments in alignment
Explanation:
The M line supports and keeps the thick myosin filaments properly aligned at the center of the sarcomere.
3. The M line is found in which region of the sarcomere?
A.
H zone
B.
I band only
C.
Z disc only
D.
Terminal cisterna
Correct Answer:
H zone
Explanation:
The M line lies at the center of the H zone, which is the central region containing thick filaments.
4. Which filament is directly organized by the M line?
A.
Actin filament
B.
Myosin filament
C.
Intermediate filament
D.
Keratin filament
Correct Answer:
Myosin filament
Explanation:
The M line organizes and stabilizes the thick myosin filaments in the middle of the sarcomere.
5. In a sarcomere, the M line lies midway between which structures?
A.
Two Z discs
B.
Two H zones
C.
Two I bands
D.
Two actin filaments
Correct Answer:
Two Z discs
Explanation:
A sarcomere extends from one Z disc to the next, and the M line is positioned halfway between these two Z discs.
6. Which statement about the M line is correct?
A.
It marks the boundary between two sarcomeres.
B.
It is located at the center of the thick filament region.
C.
It is made only of actin molecules.
D.
It disappears before muscle contraction begins.
Correct Answer:
It is located at the center of the thick filament region.
Explanation:
The M line is positioned centrally in the thick filament region and helps maintain the arrangement of myosin filaments.
7. What happens to the position of the M line during normal sliding-filament contraction?
A.
It moves toward one Z disc.
B.
It moves outside the sarcomere.
C.
It remains at the center of the sarcomere.
D.
It becomes part of the I band.
Correct Answer:
It remains at the center of the sarcomere.
Explanation:
During contraction, the filaments slide, but the M line remains at the central position of the sarcomere.
8. The M line is associated mainly with which type of protein structure?
A.
Proteins that connect and support thick filaments
B.
Proteins that form the cell nucleus
C.
Proteins that digest glucose
D.
Proteins that form red blood cells
Correct Answer:
Proteins that connect and support thick filaments
Explanation:
M-line proteins connect and support the thick myosin filaments, helping maintain their orderly arrangement.
9. Which region contains the M line at its center?
A.
The H zone
B.
The I band
C.
The Z disc
D.
The neuromuscular junction
Correct Answer:
The H zone
Explanation:
The M line is located in the middle of the H zone within the sarcomere.
10. Why is the M line important for muscle contraction?
A.
It provides a central support for thick filaments.
B.
It releases neurotransmitters into the blood.
C.
It forms the outer covering of the muscle.
D.
It prevents actin from binding to myosin.
Correct Answer:
It provides a central support for thick filaments.
Explanation:
The M line provides central support and alignment for thick filaments, which is important during their interaction with thin filaments.
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