Despite their unique shape, muscle fibers contain most of the same organelles that are present in other cells. That is, they contain mitochondria, lysosomes, and so on. However, unlike most other cells in the body, muscle cells are multinucleated (i.e., contain nu- merous nuclei. One of the most distinctive features of the microscopic appearance of skeletal muscles is their striated appearance (see Fig. 8.2). These stripes are produced by alternating light and dark bands that appear across the length of the fiber, the dark bands contain the primary muscle contractile proteins and will be discussed in detail later.