The sarcolemma is the plasma membrane of the striated muscle fiber. It consists of three layers that surround and contain the sarcoplasm, which is the cytoplasm of the muscle fiber. The outer layer is a coat of polysaccharide (sugar) molecules, while the other two layers are lipid.
The sarcolemma wraps around every striated muscle fiber like an elastic sheath, holding and protecting the sarcoplasm inside. This protective covering of the muscle fiber contains numerous T-tubules which penetrate the mass of myofibrils that make up the myocyte (muscle fiber=cell). These tubules reach the sarcomeres contained in the myofibrils. Each sarcomere is served by two T-tubules which invaginate from the sarcolemma near the A band and I band junction.
The tubules contact the terminal cisternae in the myofibril. One T-tubule and two cisternae form a triad. In human skeletal muscle, triads are located near the junctions of A and I bands. The remainder of the I band is covered by mitochondria, which align somewhat perpendicular to the myofibril long axis.
0 Comments:
Post a Comment