What is terminal cisternae?

Terminal cisternae are enlarged regions of the sarcoplasmic reticulum in muscle cells that are located on either side of a transverse tubule (T-tubule) in skeletal muscle. They play a crucial role in muscle contraction by storing and releasing calcium ions (Ca2+).

When a muscle cell is stimulated to contract, an action potential travels along the T-tubule, causing voltage-sensitive proteins in the membrane of the T-tubule to change shape. This triggers the release of stored Ca2+ ions from the terminal cisternae into the cytoplasm of the muscle cell.

The release of calcium ions from the terminal cisternae initiates a series of events that ultimately lead to muscle contraction. The calcium ions bind to proteins called troponin in the muscle cell, which causes a conformational change in the protein complex surrounding the actin filaments. This change allows myosin heads to bind to actin and generate the force required for muscle contraction.

After muscle contraction is complete, the calcium ions are actively pumped back into the sarcoplasmic reticulum by calcium pumps, including those located in the terminal cisternae. This allows the muscle to relax and prepare for the next contraction.

In summary, terminal cisternae are specialized structures in muscle cells that play a key role in regulating calcium ion concentrations and controlling muscle contraction.