cardiac myofibril

Definition

Target type: cellularcomponent

A cardiac myofibril is a myofibril specific to cardiac muscle cells. [GOC:cjm, GOC:devbiol]

The cardiac myofibril is the fundamental contractile unit of heart muscle cells (cardiomyocytes). It is composed of highly organized arrays of thick and thin filaments, arranged in repeating units called sarcomeres. These sarcomeres are responsible for the striated appearance of cardiac muscle under a microscope.

**Thick Filaments:**
* Primarily composed of the protein myosin, which possesses a head region that binds to actin on thin filaments and a tail region that interacts with other myosin molecules.
* Myosin molecules aggregate to form bipolar thick filaments, with the heads projecting outward from the filament's central region.

**Thin Filaments:**
* Composed primarily of the protein actin, which exists as a polymer of globular actin monomers.
* Other proteins associated with thin filaments include:
* **Troponin:** A complex of three proteins (troponin T, troponin I, and troponin C) that regulate the interaction between actin and myosin.
* **Tropomyosin:** A long, fibrous protein that wraps around the actin filament and blocks the myosin binding sites in the absence of calcium.

**Sarcomeres:**
* The basic structural and functional unit of the myofibril, defined by the boundaries of two adjacent Z-discs.
* **Z-discs:** Dense, proteinous structures that anchor the thin filaments and serve as attachment points for other proteins involved in sarcomere organization.
* **A-band:** The central region of the sarcomere that contains both thick and thin filaments.
* **I-band:** The region on either side of the A-band that contains only thin filaments.
* **H-zone:** A lighter area in the center of the A-band where only thick filaments are present.
* **M-line:** A dense structure in the center of the H-zone that serves as an attachment point for thick filaments.

**Other Cellular Components:**
* **Sarcoplasmic Reticulum (SR):** A specialized endoplasmic reticulum that surrounds the myofibrils and stores calcium ions.
* **T-tubules:** Invaginations of the plasma membrane that extend deep into the muscle cell and allow action potentials to rapidly spread throughout the cell, triggering calcium release from the SR.
* **Mitochondria:** Abundant in cardiomyocytes, providing energy for muscle contraction through oxidative phosphorylation.

The precise arrangement and interaction of these components within the myofibril enable the coordinated contraction and relaxation of cardiac muscle, essential for pumping blood throughout the body.'
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Proteins (1)

Compounds (2)