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H zone

Recommended video: Skeletal muscle tissue [12:25]
This type of tissue is found in skeletal muscles and is responsible for the voluntary movements of bones.

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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