sarcomere

Definition

Target type: cellularcomponent

The repeating unit of a myofibril in a muscle cell, composed of an array of overlapping thick and thin filaments between two adjacent Z discs. [ISBN:0815316194]

The sarcomere is the fundamental unit of striated muscle contraction, composed of highly organized protein filaments that are responsible for generating force. Its key structural components include:

**1. Thick Filaments (Myosin):**
* Composed of myosin protein molecules, each with a globular head and a tail.
* Myosin heads bind to actin filaments, forming cross-bridges that drive muscle contraction.
* Organized in a central region of the sarcomere, known as the A band.

**2. Thin Filaments (Actin):**
* Composed of two strands of the protein actin, twisted together like a helix.
* Actin filaments extend from the Z-disc to the A band, overlapping with the thick filaments.
* Contains regulatory proteins troponin and tropomyosin, which control myosin binding.

**3. Z-Disc:**
* A dense protein structure that anchors the thin filaments at the ends of each sarcomere.
* Provides structural support and helps to connect sarcomeres in series.

**4. I Band:**
* The region of the sarcomere that contains only thin filaments, located between the Z-disc and the A band.
* Light-staining under a microscope due to the absence of thick filaments.

**5. A Band:**
* The central region of the sarcomere, containing both thick and thin filaments.
* Dark-staining under a microscope due to the presence of thick filaments.

**6. H Zone:**
* A narrow, light-staining region within the A band, containing only thick filaments.
* Found in the center of the sarcomere, where the thin filaments do not overlap with the thick filaments.

**7. M Line:**
* A protein structure that runs down the center of the H zone, anchoring the thick filaments.
* Provides structural support and helps to maintain the proper alignment of thick filaments.

**8. Sarcoplasmic Reticulum (SR):**
* A network of internal membranes that surround the myofibrils, the contractile units of muscle fibers.
* Stores and releases calcium ions, which play a crucial role in muscle contraction.

**9. Transverse Tubules (T-Tubules):**
* Invaginations of the cell membrane that extend deep into the muscle fiber, allowing for rapid transmission of nerve impulses.
* Connect with the SR, enabling the release of calcium ions upon nerve stimulation.

These components work together in a highly coordinated manner to generate the force necessary for muscle contraction.'
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Proteins (8)

Compounds (336)