what does striated mean relative to muscle cells?
Learning Outcomes
- Classify the different types of muscle tissue and fibers
Muscle cells are specialized for contraction. Muscles allow for motions such every bit walking, and they as well facilitate bodily processes such equally respiration and digestion. The body contains three types of musculus tissue: skeletal muscle, cardiac muscle, and shine muscle (Figure 1).
Figure ane. The body contains three types of musculus tissue: skeletal musculus, smoothen muscle, and cardiac musculus, visualized here using light microscopy. Smooth muscle cells are curt, tapered at each stop, and have just one plump nucleus in each. Cardiac muscle cells are branched and striated, but curt. The cytoplasm may branch, and they have one nucleus in the center of the prison cell. (credit: modification of work by NCI, NIH; scale-bar information from Matt Russell)
Skeletal muscle tissue forms skeletal muscles, which attach to bones or skin and control locomotion and whatever move that can be consciously controlled. Considering information technology can be controlled by thought, skeletal muscle is as well called voluntary muscle. Skeletal muscles are long and cylindrical in appearance; when viewed under a microscope, skeletal muscle tissue has a striped or striated appearance. The striations are caused by the regular arrangement of contractile proteins (actin and myosin). Actin is a globular contractile protein that interacts with myosin for muscle contraction. Skeletal musculus also has multiple nuclei nowadays in a single prison cell.
Shine muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such every bit the respiratory tract and blood vessels. Smooth muscle has no striations, is not under voluntary control, has only one nucleus per prison cell, is tapered at both ends, and is called involuntary muscle.
Cardiac muscle tissue is only found in the heart, and cardiac contractions pump claret throughout the body and maintain claret force per unit area. Like skeletal muscle, cardiac muscle is striated, only unlike skeletal musculus, cardiac musculus cannot be consciously controlled and is called involuntary musculus. Information technology has one nucleus per cell, is branched, and is distinguished by the presence of intercalated disks.
Skeletal Muscle Fiber Structure
Each skeletal muscle fiber is a skeletal muscle cell. These cells are incredibly large, with diameters of up to 100 µm and lengths of up to thirty cm. The plasma membrane of a skeletal muscle fiber is called the sarcolemma. The sarcolemma is the site of activeness potential conduction, which triggers muscle contraction. Within each muscle fiber are myofibrils—long cylindrical structures that prevarication parallel to the muscle cobweb. Myofibrils run the entire length of the muscle fiber, and because they are merely approximately 1.2 µm in bore, hundreds to thousands can be constitute within one muscle fiber. They attach to the sarcolemma at their ends, and then that as myofibrils shorten, the unabridged muscle cell contracts (Effigy 2).
Effigy ii. A skeletal muscle prison cell is surrounded by a plasma membrane called the sarcolemma with a cytoplasm chosen the sarcoplasm. A muscle fiber is composed of many fibrils, packaged into orderly units.
The striated advent of skeletal musculus tissue is a result of repeating bands of the proteins actin and myosin that are present along the length of myofibrils. Dark A bands and light I bands echo along myofibrils, and the alignment of myofibrils in the cell causes the entire prison cell to appear striated or banded.
Figure 3. A sarcomere is the region from ane Z line to the side by side Z line. Many sarcomeres are present in a myofibril, resulting in the striation pattern characteristic of skeletal muscle.
Each I band has a dense line running vertically through the middle called a Z disc or Z line. The Z discs mark the border of units called sarcomeres, which are the functional units of skeletal muscle. One sarcomere is the space betwixt two consecutive Z discs and contains one unabridged A ring and 2 halves of an I band, ane on either side of the A band. A myofibril is equanimous of many sarcomeres running along its length, and as the sarcomeres individually contract, the myofibrils and muscle cells shorten (Figure 3).
Myofibrils are composed of smaller structures called myofilaments . There are two master types of filaments: thick filaments and thin filaments; each has different compositions and locations. Thick filamentsoccur only in the A band of a myofibril.Thin filaments attach to a protein in the Z disc called alpha-actinin and occur beyond the entire length of the I band and partway into the A band. The region at which thick and thin filaments overlap has a dense advent, as there is fiddling space betwixt the filaments. Sparse filaments practise not extend all the way into the A bands, leaving a cardinal region of the A band that just contains thick filaments. This central region of the A band looks slightly lighter than the rest of the A band and is called the H zone. The middle of the H zone has a vertical line chosen the M line, at which accessory proteins hold together thick filaments. Both the Z disc and the 1000 line concord myofilaments in place to maintain the structural organization and layering of the myofibril. Myofibrils are connected to each other by intermediate, or desmin, filaments that attach to the Z disc.
Thick and thin filaments are themselves equanimous of proteins. Thick filaments are equanimous of the poly peptide myosin. The tail of a myosin molecule connects with other myosin molecules to form the primal region of a thick filament near the M line, whereas the heads align on either side of the thick filament where the sparse filaments overlap. The main component of thin filaments is the actin protein. Two other components of the thin filament are tropomyosin and troponin. Actin has binding sites for myosin attachment. Strands of tropomyosin block the binding sites and prevent actin–myosin interactions when the muscles are at rest. Troponin consists of three globular subunits. One subunit binds to tropomyosin, one subunit binds to actin, and 1 subunit binds Caii+ ions.
Spotter this video showing the organization of muscle fibers.
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Source: https://courses.lumenlearning.com/wm-biology2/chapter/types-of-muscle-tissue-and-fibers/
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