Skeletal muscle tissue (fig. 5.28) forms muscles that usually attach to bones and that we control by conscious effort. For this reason, it is often called voluntary muscle tissue. Skeletal muscle cells are long—up to or more than 40 mm in length—and narrow—less than 0.1 mm in width. These threadlike cells of skeletal muscle have alternating light and dark cross-markings called striations. Each cell has many nuclei (multinucleate). A message from a nerve cell can stimulate a muscle fiber to contract by causing protein filaments within the muscle fiber to slide past one another. Then, the muscle fiber relaxes. Skeletal muscles move the head, trunk, and limbs and enable us to make facial expressions, write, talk, and sing, as well as chew, swallow, and breathe.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.