striated muscle; human biiceps muscles
This topic is briefly summarized below
Muscle, contractile tissue in animals that produces motion.
Movement is the complex cooperation between muscle and nerve fibers that allows an organism to interact with its environment. An animal’s normal activities can be performed by innervating muscle cells or fibres. A living organism must be able to move in order to find food, or if it is sedentary must be able to provide food for itself. A living organism must be capable of moving nutrients and fluids throughout its body and must also be able react to external and internal stimuli. Muscle cells use chemical energy from the metabolism of food to fuel their actions.
Muscle is contractile tissue that has been grouped together into a coordinated system for greater efficiency. The gross appearance and the location of cells are what distinguishes muscle systems in humans. There are three types of muscle: smooth, skeletal, and non-striated. The bulk of muscle tissue in the body is made up of striated muscle, which is attached almost exclusively to the skeleton. Multinucleated fibers, which are controlled by the somatic nerve system, cause movement through forces that exert on the skeleton in a manner similar to pulleys and levers. The heart’s pacemaker, the sinoatrial nude, regulates the rhythmic contraction of cardiac muscles. The cardiac muscle, a specialized striated muscle made up of many centrally located nuclei and elongated cells, is not subject to voluntary control. Smooth muscle lines blood vessels, viscera, and dermis. Its movements, just like cardiac muscle, are controlled by the autonomic nervous systems and are therefore not subject to voluntary control. Each short tapering cell’s nucleus is located in the central part.
Simple animals, unicellular organisms, and motile cells in complex animals don’t have large muscle systems. These organisms move primarily through hairlike extensions to the cell membrane, called cilia or flagella, and cytoplasmic extensions called pseudopodia.
Fact or fiction? Are people able to choose whether they are left- or right-handed? This quiz will test your ambidextrousness by asking you to choose between right and wrong. See muscle system, human for a description of the human muscular system in relation to upright posture.
Muscle and movement characteristics
Muscle is responsible for maintaining posture and powering multicellular animals’ movements. Its appearance is similar to meat and fish flesh. Muscle is the most abundant tissue in many animals. It makes up between 50-60 percent and 40-50 percent of many fish’s body mass, respectively. Some muscles can be controlled by the organism and are known as voluntary muscles. Others, known as involuntary muscle, can’t be controlled by the organism. In vertebrates, for example, the muscles of the heart contract in rhythmic motion, pumping blood around; the muscles of the intestines move food by peristalsis; the muscles of small blood vessels, on the other hand, constrict or relax and control blood flow to various parts of the body. The effects of muscle changes on blood vessels can be seen in blushing or paling, depending on whether there is increased or decreased blood flow to the skin.
Subscribe to Britannica Premium and get exclusive content. Muscles aren’t the only way animals can move. Many unicellular organisms, such as protists, move using flagella or cilia (actively beating processes on the cell surface that propel them through water). Unicellular organisms can be capable of amoeboid motion. In this case, the cell contents are able to flow into extensions called pseudopodia from the cell body. Some ciliated protozoans can move using rods called myonemes that are capable of shortening quickly.
Multicellular animals also need nonmuscular movements. Many microscopic creatures swim using beating cilia. Some small mollusks, flatworms, and other animals crawl with cilia on their undersides. Cilia are used by some invertebrates to make water currents. White blood cells in higher animals use amoeboid movement, while cells lining their respiratory tracts remove foreign particles.
Muscles are made up of long, thin cells (fibres), which contain a number of finer fibrils. Each fibril contains thick filaments of protein myosin, thin ones of actin, and other proteins. The filaments slide past each other when a muscle fiber lengthens or shrinks as illustrated in Figure 2. Cross bridges are projections of thick filaments onto thin filaments and exert force on them, creating tension in active muscles. Cross bridges are able to detach from the filaments as the active muscle grows or shrinks. They then reattach in new positions. They work in the same way as pulling a rope hand-over-hand. While some muscle fibers can be several centimetres in length, most cells are less than a millimetre. These long fibers are too complex to be adequately served by one nucleus so many nuclei are spread along their length.
Chemical energy is required to perform the work of muscle. This chemical energy comes from the metabolism food. Some of the chemical energy that is converted from food metabolism to work is used for muscle contractions. The chemical energy used to produce heat is also converted to heat when muscles are stretched while under tension. Warm-blooded animals have the ability to generate heat. Shivering refers to muscle activity that produces heat and warms the body. Insects vibrate their wings for a time before flying, heating the muscles to the ideal temperature.
