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Multiple Choice
The region of the sarcomere that always contains thin filaments is the:
A
M line
B
A band
C
H zone
D
I band
Verified step by step guidance
1
Understand the structure of a sarcomere: A sarcomere is the functional unit of a muscle fiber, composed of overlapping thick (myosin) and thin (actin) filaments. It is divided into distinct regions based on the arrangement of these filaments.
Define the regions of the sarcomere: The key regions include the A band (contains the entire length of thick filaments and overlapping thin filaments), the I band (contains only thin filaments), the H zone (contains only thick filaments), and the M line (the center of the sarcomere where thick filaments are anchored).
Focus on the I band: The I band is the region of the sarcomere that contains only thin filaments (actin) and no thick filaments. It spans the area between the ends of thick filaments in adjacent sarcomeres.
Compare the options: The M line is the center of the sarcomere and contains proteins that stabilize thick filaments. The A band includes the entire length of thick filaments and overlapping thin filaments. The H zone is a part of the A band that contains only thick filaments. The I band, however, contains only thin filaments, making it the correct answer.
Conclude: Based on the definitions and characteristics of each region, the I band is the region of the sarcomere that always contains thin filaments.