What is function of terminal cisternae?

Terminal cisternae are specialized regions of the sarcoplasmic reticulum (SR) in skeletal muscle cells. They play an important role in the process of muscular contraction by regulating the release of calcium ions into the muscle fiber.

When an action potential is generated in a motor neuron, it travels down the axon and stimulates the release of the neurotransmitter acetylcholine into the neuromuscular junction. This triggers a depolarization of the muscle fiber membrane, also known as the sarcolemma.

This depolarization spreads along the sarcolemma and down into the T-tubules, which are invaginations of the sarcolemma that penetrate the muscle fiber. The T-tubules then come into contact with the terminal cisternae of the SR, triggering the release of stored calcium ions into the cytoplasm of the muscle fiber.

The calcium ions then bind to the protein complex troponin, which is located on the thin filaments of the muscle fiber. This interaction causes a conformational change in the troponin-tropomyosin complex that exposes the binding site for myosin on the actin filaments.

This allows the myosin heads to form cross-bridges with the actin, which leads to the sliding of the filaments past each other and the shortening of the muscle fiber.

Ultimately, the function of the terminal cisternae is critical for the regulation of muscle contraction and the generation of force. Any dysfunctions or abnormalities in the SR can lead to muscular disorders or diseases.