Final answer:
The functional unit of a skeletal muscle is the sarcomere. It is the smallest contractile portion of a muscle and is composed of myosin and actin filaments.
Step-by-step explanation:
The functional unit of a skeletal muscle is the sarcomere. A sarcomere is the smallest contractile portion of a muscle and is composed of thick and thin filaments made of proteins called myosin and actin, respectively. It is the interaction between these filaments that allows for muscle contraction.