Final answer:
The nuclei of skeletal muscle cells are moved to the sides by organelles called myofibrils, which fill the cytoplasm and are crucial for muscle contraction. These myofibrils are made up of sarcomeres that contain the contractile proteins actin and myosin, contributing to the striated appearance of the muscles.
Step-by-step explanation:
The nuclei of skeletal muscle cells are pushed aside by long ribbonlike organelles called myofibrils, which nearly fill the cytoplasm. Myofibrils are the predominant organelles in muscle fibers and are responsible for muscle contraction. They contain the protein filaments actin and myosin, which interact to cause movement. These myofibrils are arranged in a highly organized manner, which is also responsible for the striated appearance of the skeletal muscle fibers.
A skeletal muscle fiber is surrounded by a plasma membrane known as the sarcolemma, and the cytoplasm inside is termed the sarcoplasm. Contained within the sarcoplasm are the myofibrils, which are in turn made up of sarcomeres – the functional units of muscle contraction. This organization allows for the muscle fibers to contract effectively when they receive signals from the nervous system.