Muscle Tissue Basics
Muscle tissue is the only tissue in the body built to quickly move in the form of contract (muscle tissue can only shorten or “pull”). The major job of all muscle tissue is to convert the chemical energy of ATP into the kinetic energy of motion. Muscle comes in three types: skeletal, smooth, and cardiac.
- Skeletal muscle is almost always attached to bones, contracts only with innervation from the nervous system, and its cell structure is that of very long striated tubes with multiple nuclie on the inner sides of those tubes.
- Smooth muscle is mostly wrapped around tubed organs, contracts with innervation or or auto rhythmically (has its own rhythmic contractions), and its cell structure is that of relatively short cells that taper at the ends (fusiform shape) and have single nuclei.
- Cardiac muscle is only found in the heart, contracts only auto rhythmically (though this rhythm can be altered by nervous or endocrine signals), and its cell structure is that of branched tubes that are connected by dark staining intercalated discs and have usually single nuclei.
All of the above sections are of skeletal muscle:
These are different preparations of skeletal muscle tissue. The first one is from human tongue, the second one is a section through a large muscle (possibly a biceps brachii for example), and the last one is skeletal muscle with the cells teased apart.
The two images above are both of smooth muscle sections. They look a bit different, but notice that where you can see the outline of a cell well it appears fusiform (tapered at both ends) and that each cell contains a single nucleus.
Both of the above images are from sections of cardiac muscle that were prepared differently. Though the color is different you can see in each image the major features of cardiac muscle tissue: branched tubed cells that are connected with dark staining structures called intercalated discs (labeled below).