Question

What is a triad system?

Answer 1

The collection of several triads forming a whole process is known as the triad system. Moreover, the triads are usually seen at the junction of the A band and the I band in the sarcomere of the skeletal muscles.

Complete answer: The triad is formed by the T-tubule along with the sarcoplasmic reticulum (SR). It is known as the terminal cisterna on either side. It is found in the skeletal muscles. Every skeletal muscle fiber has thousands of triads. These triads are visible in muscle fibers that are sectioned longitudinally. The triads are located at the junction of the A band and the I band of the sarcomere. The smallest unit of the muscle fiber is known as the sarcomere. Triads help in the excitation-contraction coupling. They cause the muscle to be excited by a stimulus and then contract by it. The muscle contractions are caused due to the bonding of the calcium with troponin. Due to this, the unmasked binding sites get covered by the troponin-tropomyosin complex on the actin myofilament. This allows the myosin cross-bridges to connect with the actin.

Note: The triad system is different from the diad system. The diad system is found in the cardiac muscles of the heart. It is a structure that is found in the cardiac myocyte which is located at the sarcomere Z-line. The diad system is composed of a single T-tubule. It is paired with a terminal cisterna of the sarcoplasmic reticulum. The diad system plays an important role in excitation-contraction coupling. This happens by the juxtaposing of an inlet for the action potential near a source of the calcium ions. This causes the wave of depolarization to be coupled with the calcium-mediated cardiac muscle. This finally results in the contraction via the sliding filament mechanism theory.