Terminal cisternae

Terminal cisternae are specialized regions within muscle cells that play a crucial role in muscle contraction. These structures are found in close association with the T-tubules in skeletal muscle fibers and are essential for the regulation of calcium ions during muscle contraction.

Structure

Terminal cisternae are enlarged regions of the sarcoplasmic reticulum, a specialized type of endoplasmic reticulum found in muscle cells. They are located on either side of the T-tubules, forming a triad structure along with the T-tubule. The terminal cisternae store and release calcium ions, which are necessary for muscle contraction.

Function

During muscle contraction, an action potential travels along the T-tubules, causing the release of calcium ions from the terminal cisternae into the cytoplasm of the muscle cell. The calcium ions bind to the protein complex troponin, which initiates the contraction of the muscle fibers by allowing the myosin and actin filaments to interact.

Role in Muscle Contraction

The release of calcium ions from the terminal cisternae is a key step in the process of muscle contraction. The calcium ions bind to troponin, which leads to a conformational change in the protein complex tropomyosin, exposing the binding sites on the actin filaments. This allows the myosin heads to bind to the actin filaments and generate the force necessary for muscle contraction.

Clinical Significance

Disruption of the function of the terminal cisternae can lead to muscle disorders such as malignant hyperthermia, a rare but potentially life-threatening condition triggered by certain anesthetic agents. In malignant hyperthermia, there is uncontrolled release of calcium ions from the sarcoplasmic reticulum, leading to sustained muscle contractions and a dangerous increase in body temperature.