What is the h zone?

The H zone is a region within a sarcomere, which is the basic functional unit of a muscle fiber. It is located in the center of the sarcomere and is characterized by the presence of thick filaments made of myosin. The H zone is surrounded by thin filaments made of actin, which overlap with the thick filaments during muscle contractions.

During muscle contraction, the H zone shortens as the thick and thin filaments slide past each other, resulting in the sarcomere as a whole shortening. The H zone is typically lighter in color under a microscope due to the lack of overlapping actin filaments, which gives it a distinct appearance within the sarcomere.

The length of the H zone can vary depending on the degree of muscle contraction. In a fully contracted muscle, the H zone may appear very small or even disappear completely as the thick and thin filaments overlap extensively. In a relaxed muscle, the H zone will be at its maximum length.

Overall, the H zone plays a crucial role in muscle contraction and contributes to the overall functioning of skeletal muscle tissue.