Terminal cisternae
Terminal Cisternae[edit]
The terminal cisternae are specialized structures within the sarcoplasmic reticulum of skeletal muscle cells. They play a crucial role in the storage and release of calcium ions (Ca__), which are essential for muscle contraction.
Structure[edit]
Terminal cisternae are enlarged areas of the sarcoplasmic reticulum that are located adjacent to the T-tubules (transverse tubules). Together, a T-tubule and two terminal cisternae form a structure known as a triad. This arrangement is critical for the rapid transmission of the action potential from the T-tubules to the sarcoplasmic reticulum, facilitating the release of calcium ions.
Function[edit]
The primary function of the terminal cisternae is to sequester and release calcium ions. When a muscle cell is stimulated by an action potential, the signal travels down the T-tubules and triggers the opening of calcium channels in the terminal cisternae. This results in a rapid influx of calcium ions into the cytosol, initiating the interaction between actin and myosin filaments, which leads to muscle contraction.
Role in Muscle Contraction[edit]
During muscle contraction, the release of calcium ions from the terminal cisternae is a key step. The calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the binding sites on actin filaments. This allows the myosin heads to attach to actin and perform the power stroke, resulting in muscle contraction.
After contraction, calcium ions are actively pumped back into the terminal cisternae by calcium ATPase pumps, allowing the muscle to relax.
