Final answer:
The statement in question is false; myofilaments do not shorten during muscle contraction. Instead, a sliding mechanism occurs where the myosin and actin filaments slide past each other, shortening the sarcomere but not the actual filaments or cross-bridges. Therefore given statement is false.
Step-by-step explanation:
The statement 'Myofilaments have two ends and a bridge; when the muscle contracts, the bridge part is shortened' is False. During muscle contraction, the thick and thin filaments that make up a muscle's myofibrils maintain their length. Instead, what occurs is a sliding mechanism where the thick (myosin) and thin (actin) filaments slide past each other. Myosin heads form cross-bridges with actin, and as they pull on the actin filaments, they slide inward, thereby shortening the sarcomere, not the cross-bridges themselves.
In other words, when the sarcomere shortens during muscle contraction, it is the result of a sliding action by the filaments, not a shortening of the individual myofilaments or the cross-bridges. This process is driven by the repeated detachment and attachment of myosin heads to actin, coupled with the hydrolysis of ATP, providing the energy for these movements. The coordination of many sarcomeres contracting simultaneously leads to the overall shortening of the muscle fiber and the muscle itself.