Title: Muscle Membrane, T Tubules, and Sarcoplasmic Reticulum | Neupsy Key
Headings: Muscle Membrane, T Tubules, and Sarcoplasmic Reticulum
Muscle Membrane, T Tubules, and Sarcoplasmic Reticulum
Only gold members can continue reading. Log In or Register to continue

Content: This provides not only more rapid dispersal of muscle membrane depolarization along the muscle fiber, but it allows for propagation along both the surface of the sarcolemma and into the muscle fiber, where it can interact with deep sarcoplasmic reticulum. T tubules interact directly with components of the sarcoplasmic reticulum, leading to Ca 2+ release into the sarcoplasm. They also harbor voltage-gated Ca 2+ channels, L-type Ca 2+ channels. These Ca 2+ channels do not contribute to depolarization or the muscle fiber action potential but, rather, act as voltage sensors of muscle membrane depolarization. The sarcoplasmic reticulum forms a network of tubules surrounding muscle fibrils inside the sarcolemma. Junctional sarcoplasmic reticulum (the terminal cisternae) stores Ca 2+ and is the site of Ca 2+ release in response to a muscle fiber action potential. Junctional sarcoplasmic reticulum contains high amounts of calsequestrin, which binds to Ca 2+ and accounts for the high Ca 2+ storage of the sarcoplasmic reticulum. The sarcoplasmic reticulum is so efficient in this role that the muscle fiber loses very little Ca 2+ even after repeated muscle contractions. Junctional sarcoplasmic reticulum is also the site of the Ca 2+ channel responsible for releasing large stores of calcium into the sarcoplasm, the ryanodine receptor, so named for its binding to the plant alkaloid ryanodine. Sarcoplasmic reticulum voltage-gated Ca2+ channels sense the depolarization of the T tubule, interact directly with the ryanodine receptor and induce it to release Ca 2+ from the sarcoplasmic reticulum.