Question

Question: Which of the following statements about the striated muscles is incorrect?

(i) In the centre of each I-band, is an elastic fibre (Z-line) which bisects it.

(ii) Thin filaments are firmly attached to the Z-line.

(iii) M-line is a fibrous membrane in the middle of A-bands.

(iv) A sarcomere comprises one full A-bands and 2 half I-bands.

A) All of these
B) Only (iv)
C) (i) and (ii)
D) None of these

Answer 1

Hint:
Bipolar thick filaments walk toward the plus end of two sets of thin filaments of opposite orientations, driven by dozens of independent myosin heads that are positioned to interact with thin filaments. During muscle contraction the, I-bands shortens.

Complete step by step answer:
The light bands are called I bands (isotropic) and contain only thin filaments. The dark bands of the sarcomere are called A-bands (anisotropic). both thick and thin filaments constitute A-band. In the center of the A-band, there is an H-zone present that has thick filaments and no thin filaments. Proteins that hold the thick filament forms the M-line at the center of the H-zone so it is called midline as it is in the middle of the sarcomere. Actin is the component of thin filaments and myosin is the component of thick filaments.
 Z line is in between the I band and it is an elastic fiber that is correct. Z line is connected to the thin filament. A fibrous membrane is the M line between A bands and this is also correct

Option ‘D’ is correct

Note:
The Centre of a band has a dark zone called the H zone and in the middle of the H zone, there is an M line here it is called the middle scheme line. The Centre of I band has a dark line in the middle which is called Z-line, Called the Zwishenschebe line.