Skeletal muscle exhibits an alternating light and dark striped appearance when viewed under a light microscope and is, consequently, often referred to as striated muscle. This type of muscle is typically under conscious control and comprises the majority of the body’s muscle mass. Linked to the skeletal system, skeletal muscle also provides the basic shape of the body. The dark regions of skeletal muscle consist of Type I fibers, which employ oxidative metabolism and are especially adapted for activities that require endurance. The light regions are composed of Type II fibers that tire much faster but are useful for activities necessitating spurts of power or speed. Type II fibers utilize anaerobic metabolism rather than oxidative metabolism.

Each fiber in a skeletal muscle is sheathed in a fine layer of connective tissue termed the endomysium. Similarly, numerous fibers are bound together inside another connective tissue sheath known as the perimysium, forming a muscle bundle. Muscle groups, often referred to simply as muscles, are composed of multiple muscle bundles connected together at their ends by tendons. A protective external stratum of connective tissue called the epimysium surrounds individual muscle groups.

In order to localize a red fluorescent tag to F-actin in the sample of rat skeletal muscle tissue presented in the digital image above, the specimen was labeled with Alexa Fluor 568 conjugated to a phallotoxin (phalloidin). Oregon Green 488 conjugated to the lectin wheat germ agglutinin, which selectively binds to N-acetylglucosamine and N-acetylneuraminic residues, was also applied to the tissue sample, as was the nuclear counterstain Hoechst 33342. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.

Rat Skeletal Muscle Tissue Labeled with Wheat Germ Agglutinin and Phalloidin - Skeletal muscle contraction is instigated by signals from the nervous system and requires energy from adenosine triphosphate (ATP), which can be obtained from a number of bodily processes, such as glycolysis and oxidative phosphorylation. Most of the body’s skeletal muscles are arranged in pairs. This organization, in which each member of the pair pulls in the direction opposing the other member of the pair, allows the skeleton to be controlled with great precision.