Sarcolemma: the plasma membrane of a muscle cell (fibre).
Sarcoplasm: the cytoplasm of a muscle fibre. The sarcoplasm includes a substantial amount of glycogen. Glycogen can be used for synthesis of ATP. The sarcoplasm contains a red-coloured protein called Myoglobin . Myoglobin: found only in muscle fibres, it binds oxygen molecules that diffuse into muscle fibres from interstitial fluid. Myoglobin releases oxygen when needed by the mitochondria to produce ATP. Mitochondria are in rows throughout the muscle fibre close to the proteins that use ATP to generate contraction. Transverse Tubules (T-tubules) : 1000s of tiny invaginations of the sarcolemma tunnel in from the surface toward the centre of each muscle fibre. Since T-tubules are open to the outside of the fibre they are filled with interstitial fluid. Muscle action potentials travel along the sarcolemma and into the muscle fibre through the T-tubules. This promotes even distribution of the action potential. Sarcoplasmic reticulum (SR): a fluid system of membranous sacs encircles each myofibril. This system is similar to smooth ER of non-muscular cells. Dilated end sacs of the sarcoplasmic reticulum called Terminal Cisterns (reservoirs) butt against the T-tubule from both sides. A T- tubule and two terminal cisterns on either side forms a Triad . In a relaxed muscle fibre, the SR stores Ca++ ions. Release of Ca++ from the terminal cisterns of the SR triggers muscle contraction. Myofibril – small structures that are the contractile organelles of skeletal muscle. There are about 2 micrometers in diameter and extend the entire length of a muscle fibre. Their striations give the entire skeletal muscle fibre its striated appearance.
93
Made with FlippingBook Publishing Software