Terminal cisternae are a structural feature of the organelle known as the sarcoplasmic reticulum. This organelle is primarily found in muscle cells and is crucial for the storage and regulation of calcium ions, which play a vital role in muscle contraction.
The sarcoplasmic reticulum (SR) consists of a network of tubules and vesicles that surround myofibrils – the contractile fibers in muscle cells. The terminal cisternae are enlarged areas of the sarcoplasmic reticulum that are located adjacent to the T-tubules. They form a triad structure with two terminal cisternae on either side of a T-tubule.
When a muscle cell is stimulated, the action potential travels along the T-tubules, which leads to the release of calcium ions from the terminal cisternae into the cytoplasm. This increase in calcium concentration triggers the interaction between actin and myosin filaments, resulting in muscle contraction. Therefore, the terminal cisternae play an essential role in muscle physiology and are critical for the proper functioning of skeletal and cardiac muscle fibers.