Which region is the lighter area in the midsection of the dark A band where filaments do not overlap?

Which region is the lighter area in the midsection of the dark A band where filaments do not overlap?

• A. I band
• B. H zone
• C. A band
• D. Z disc

Answer: (B)

In a sarcomere, the A band marks the length of the thick (myosin) filaments and includes areas where thin (actin) filaments overlap them. The lighter region in the middle of that dark A band is where there is no overlap between thick and thin filaments—the H zone. Since actin isn’t present to overlap with myosin there, this area looks lighter under a light microscope. The I band is the lighter region outside the A band that contains only actin, and the Z disc marks the boundaries between sarcomeres. So the described lighter midsection without filament overlap is the H zone.

In a sarcomere, the A band marks the length of the thick (myosin) filaments and includes areas where thin (actin) filaments overlap them. The lighter region in the middle of that dark A band is where there is no overlap between thick and thin filaments—the H zone. Since actin isn’t present to overlap with myosin there, this area looks lighter under a light microscope. The I band is the lighter region outside the A band that contains only actin, and the Z disc marks the boundaries between sarcomeres. So the described lighter midsection without filament overlap is the H zone.