Muscle tissues are specialized for contraction. They are involved in the interaction between filaments of myosin, actin, and the proteins found in cytoskeletons of many cells.
In muscle cells, the filaments are many and arranged so that their interaction produces a contraction of the entire cell.
Types of muscle tissue – (type – structure – location – function)
- Skeletal: large cylindrical cells with striations and several nuclei each – attached to bones – moves the skeleton and produces heat. Skeletal muscle tissue contains very large multinucleated fibers tied together by loose connective tissue. Collagen and elastic fibers surround each cell and groups of cells. They blend into those of a tendon that conduct the force of contraction (usually to the bone causing it to move), but they will not usually contract unless stimulated by nerves. Because the actin and myosin filaments are arranged in organized groups, skeletal muscle fibers appear to be marked by a series of bands called striations. Since the nervous system provides voluntary control over its activities, skeletal muscle is described as striated voluntary muscle.
- Cardiac: branched cells with faint striations and one nucleus each – walls of the heart chambers – pumps blood. Cardiac muscle tissue is found only in the heart and is much smaller than skeletal muscle fiber. Each cardiac muscle cell usually has only one nucleus. The cells are interconnected at intercalated discs, specialized attachment sites. The muscle cells branch, forming a network that conducts the force and stimulus for contraction from one area of the heart to another. Cardiac muscle does not rely on nerve activity to begin a contraction. Instead, specialized cells called pacemaker cells, establish a regular rate of contraction. Even though the nervous system can alter the rate, it does not provide voluntary control over individual cardiac muscle cells. The cardiac muscle can be considered striated involuntary muscle.
- Smooth: small tapered cells with no striations and one nucleus each – walls of arteries, stomach, intestines, and iris of the eye – maintains blood pressure, peristalsis, and regulates size of pupil. Smooth muscle tissue is found in the walls of blood vessels, around such hollow organs as the urinary bladder, and in layers around the respiratory, circulatory, digestive, and reproductive tracts. A smooth muscle cell has only one nucleus. It is small and slender, tapering to a point at each end. The actin and myosin filaments are scattered throughout the cytoplasm and have no striations. Smooth muscle cells are able to contract on their own or they may be triggered by neural activity. Since the nervous system does not provide voluntary control over smooth muscle contractions, the smooth muscle is therefore categorized as nonstriated involuntary muscle.
