NEET BIOLOGY

Detailed explanation-1: -The individual cardiac muscle cell (cardiomyocyte) is a tubular structure composed of chains of myofibrils, which are rod-like units within the cell. The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells.

Detailed explanation-2: -All types of striated muscle contain a branched network of membrane invaginations called T-tubules that enable synchronous calcium release throughout the entire cell volume. The T-tubules contact the sarcoplasmic reticulum (SR) between the A and I bands in skeletal muscle and at the Z-disc in cardiac muscle.

Detailed explanation-3: -Cardiac muscle cells are located in the walls of the heart, appear striped (striated), and are under involuntary control. Smooth muscle fibers are located in walls of hollow visceral organs (such as the liver, pancreas, and intestines), except the heart, appear spindle-shaped, and are also under involuntary control.

Detailed explanation-4: -Cardiac muscle is made up of specialised cells called cardiomyocytes. These cells are sometimes called contractile myofibrils because they are long and cylindrical (shaped like a fibril) and they contract at a regular rate to keep blood flowing through the heart.