A myofibril is a long, thread-like structure found within muscle cells, specifically in skeletal and cardiac muscles. These organelles are composed of repeating units called sarcomeres, which are the basic functional units of muscle contraction. Myofibrils contain two main types of protein filaments: actin (thin filaments) and myosin (thick filaments). The interaction between these filaments allows muscles to contract and generate force. Myofibrils are organized in parallel bundles, contributing to the striated appearance of skeletal and cardiac muscles. When a muscle cell receives a signal from the nervous system, the myofibrils shorten, leading to muscle contraction. This process is essential for various bodily movements, from walking to lifting objects.