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H zone
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The H zone, from the German word 'helle' meaning 'bright', is the central region of the A band within the sarcomere which does not contain thin (actin) filaments. This region appears paler in contrast to the rest of the A band, which contains the overlapping thin and thick (myosin) filaments and therefore appears darker. In the middle of the H zone is a vertical line known as the M line, which links the thick filaments to each other.
As sarcomeres shorten during a muscle contraction, the H zone, similar to the I band, narrows due to the increasing overlap of thick and thin filaments as the thin filaments are pulled closer to the M line. The H zone may no longer be visible when a muscle is fully contracted.
| Terminology |
English: H zone Latin: Stria H |
| Definition | Central region of the A band containing only thick filaments |
| Function | Shortens during a muscle contraction as thin filaments are pulled towards the M line |
Learn more about the structure of skeletal muscle with this study unit (and article):
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