Final answer:
The sarcomere is the structural and functional unit of skeletal muscle that runs from one Z disc to the next and is crucial for muscle contraction.
Step-by-step explanation:
The Muscle's Structural and Functional Unit
The structural and functional unit of skeletal muscle that runs from Z disc to Z disc is called a sarcomere. This unit is the core of muscle contraction and is bordered by structures known as Z discs, or Z lines. Within each sarcomere, there is an entire A band and two halves of an I band flanking the A band. When muscles contract, the sarcomeres shorten, pulling the Z discs closer together, which in turn shortens the entire muscle.
Myofibrils, which are composed of many sarcomeres, run the length of the muscle fiber and attach to the sarcolemma at their ends. These myofibrils are the elements that contract, thus enabling the muscle cell as a whole to contract. Furthermore, the sarcomere consists of thin and thick filaments; thin filaments are made of actin and are attached to the Z discs, while thick filaments are primarily made up of myosin.