A sarcomere is the basic functional unit of a muscle fiber, responsible for muscle contraction. It is made up of long protein filaments called actin and myosin, which slide past each other to shorten the muscle. This sliding action is triggered by signals from the nervous system, allowing muscles to contract and produce movement. Each sarcomere is bordered by structures called Z-discs, which anchor the actin filaments. When a muscle contracts, many sarcomeres work together in a series, creating a powerful force. Understanding sarcomeres is essential for studying how muscles function and how they respond to exercise and injury.