What is a sarcomere?

A sarcomere is the basic functional unit of muscle tissue, responsible for muscle contraction. It is the repeating unit between two Z lines (or Z discs) in a myofibril. Here's a breakdown of its components and function:

• Boundaries: A sarcomere is defined by two https://www.wikiwhat.page/kavramlar/Z%20lines, which are protein structures that run perpendicular to the muscle fibers and anchor the thin filaments.

• Major Components: It consists primarily of two types of protein filaments:

  • Thin Filaments: These are mainly composed of https://www.wikiwhat.page/kavramlar/Actin, along with https://www.wikiwhat.page/kavramlar/Tropomyosin and https://www.wikiwhat.page/kavramlar/Troponin. Actin filaments are attached to the Z lines.
  • Thick Filaments: These are primarily made up of https://www.wikiwhat.page/kavramlar/Myosin. Myosin filaments are located in the center of the sarcomere.

• Bands and Zones: The arrangement of these filaments creates distinct bands and zones within the sarcomere:

  • A band: Contains the entire length of the thick filaments (myosin). It appears dark under a microscope.
  • H zone: The central region of the A band, containing only thick filaments (myosin) and no thin filaments (actin).
  • I band: Contains only thin filaments (actin). It appears light under a microscope and spans two sarcomeres, being bisected by the Z line.
  • M line: A line in the middle of the H zone that helps to anchor the thick filaments.

• Muscle Contraction: Muscle contraction occurs via the https://www.wikiwhat.page/kavramlar/Sliding%20Filament%20Theory. During contraction, the thin filaments (actin) slide past the thick filaments (myosin), causing the sarcomere to shorten. The A band's length remains constant, but the I band and H zone shorten. The Z lines move closer together. This process requires https://www.wikiwhat.page/kavramlar/ATP and calcium ions.