Sarcoplasmic reticulum

The sarcoplasmic reticulum is a specialized membrane network in muscle cells that stores and releases calcium ions to regulate contraction and relaxation.

Calcium-induced calcium release: A process in which calcium entering a cell triggers further calcium release from intracellular stores. This mechanism amplifies calcium signals in cardiac muscle through the sarcoplasmic reticulum.
Sarcoplasm: The cytoplasm of a muscle fiber, including its organelles and dissolved materials. Calcium released from the reticulum enters this fluid before activating contraction.
Cardiac muscle: Involuntary striated muscle that contracts the heart and pumps blood. Cardiac muscle uses calcium entry across the cell membrane to trigger reticulum release.
Malignant hyperthermia: A life-threatening reaction to certain anesthetics, involving uncontrolled skeletal-muscle calcium release and heat production. Mutations in sarcoplasmic-reticulum calcium-release channels cause many inherited cases.
Ryanodine receptor: A calcium-release channel in the membrane of the sarcoplasmic reticulum. These channels open to release stored calcium into the muscle-cell cytoplasm.
Myofibril: A contractile structure in a muscle cell, composed of repeating sarcomeres. Myofibrils respond to calcium released by the surrounding reticulum.
Skeletal muscle: Striated muscle attached to the skeleton that produces voluntary movement. Its reticulum releases calcium chiefly in response to voltage-sensing T-tubule proteins.
Central core disease: An inherited muscle disorder characterized by muscle weakness and distinctive cores in muscle fibers. Variants in the ryanodine receptor can disrupt calcium release from the reticulum.
SERCA: A calcium pump that uses ATP to move calcium ions into the sarcoplasmic reticulum. SERCA clears cytoplasmic calcium after contraction and replenishes the store.
Sarcomere: The repeating contractile unit of a myofibril, bounded by Z discs. Calcium from the reticulum enables sarcomeres to generate force.

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