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Triad (anatomy)
In the histology of skeletal muscle, a triad is the structure formed by a T tubule with a sarcoplasmic reticulum (SR) known as the terminal cisterna on either side. Each skeletal muscle fiber has many thousands of triads, visible in muscle fibers that have been sectioned longitudinally. (This property holds because T tubules run perpendicular to the longitudinal axis of the muscle fiber.) In mammals, triads are typically located at the A-I junction; that is, the junction between the A and I bands of the sarcomere, which is the smallest unit of a muscle fiber. Triads form the anatomical basis of excitation-contraction coupling, whereby a stimulus excites the muscle and causes it to contract. A stimulus, in the form of positively charged current, is transmitted from the neuromuscular junction down the length of the T tubules, activating dihydropyridine receptors (DHPRs). Their activation causes 1) a negligible influx of calcium and 2) a mechanical interaction with calcium-condu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Skeletal Muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle tissue, and are often known as muscle fibers. The muscle tissue of a skeletal muscle is striated – having a striped appearance due to the arrangement of the sarcomeres. Skeletal muscles are voluntary muscles under the control of the somatic nervous system. The other types of muscle are cardiac muscle which is also striated and smooth muscle which is non-striated; both of these types of muscle tissue are classified as involuntary, or, under the control of the autonomic nervous system. A skeletal muscle contains multiple fascicles – bundles of muscle fibers. Each individual fiber, and each muscle is surrounded by a type of connective tissue layer of fascia. Muscle fibers are formed from the fusion of developmental myobla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
