Question

A narrow dark line seen in isotropic band of myofibril of a striated muscle fibre is called ______.

• A. M-line
• B. H-zone
• C. Z-line
• D. A-band

Hint:

Sarcomere extends from one Z-line to the next Z-line.

Answer 1

The Correct Option is C

Step 1: Understanding striated muscle structure.
A striated muscle fibre contains repeating functional units called sarcomeres. Each sarcomere shows alternating dark and light bands due to the arrangement of actin and myosin filaments.
Step 2: Isotropic (I) band features.
The I-band is the light band containing only thin actin filaments. In the middle of the I-band, a narrow dark line called the Z-line is present.
Step 3: Role of Z-line.
The Z-line marks the boundary of a sarcomere and serves as the anchoring point for actin filaments during muscle contraction.
Step 4: Analysis of options.
(A) M-line: Present in the center of the A-band.
(B) H-zone: A lighter region within the A-band.
(C) Z-line: Correct, narrow dark line in the I-band.
(D) A-band: Dark band containing thick filaments.
Step 5: Conclusion.
The narrow dark line in the isotropic band is the Z-line.