Chapter 10: Muscle Tissue10-1 Specify the functions of skeletal muscle tissue.1. Identify the three types of muscle tissue. The three types of muscle tissue are skeletal muscle, cardiac muscle, and smooth muscle.2. Identify the six major functions of skeletal muscle. Skeletal muscles produce skeletal movements, maintain posture and body position, support soft tissues, guard entrances and exits, maintain body temperature, and store nutrient reserves. 10-2 Describe the organization of muscle at the tissue level.The connective tissues of the endomysium and perimysium contain the blood vessels and nerves that supply the muscle fibers. Muscle contraction requires tremendous quantities of energy. Within the endomysium, arterioles supply blood to a capillary network that services the individual muscle fiber. Skeletal muscle contract only when the central nervous system stimulates them. Axons, nerve fibers extending from the cell, penetrate the epimysium to innervate individual muscle fibers. Skeletal muscles are often called voluntary muscles, because we have voluntary control over their contractions. 3. Describe the connective tissue layers associated with skeletal muscle tissue. The epimysium is a dense layer of collagen fibers that surrounds the entire muscle; the perimysium divides the skeletal muscle into a series of compartments each containing a bundle of muscle fibers called a fascicle; and the endomysium surrounds individual skeletal muscle cells (fibers). The collagen fibers of the epimysium, perimysium, and the endomysium come together to form either bundles known as tendons, or broad sheets called aponeuroses. Tendons and aponeuroses generally attach skeletal muscles to bones. 4. How would severing the tendon attached to a muscle affect the muscle’s ability to move a body part? Because tendons attach muscles to bones, severingthe tendon would disconnect the muscle from the bone, and so the muscle couldnot move a body part. 10-3 Explain the characteristics of skeletal muscle fibers, and identify the structural components of a sarcomere.Differences of muscle fiber cells to typical cells: (1) Skeletal muscle fibers are enormous. (2) muscle fibers are multinucleate: each contains hundreds of nuclei just internal to the plasma membrane. These features are related. Muscle fibers develop through the fusion of mesodermal cells called myoblasts, forming an individual multinucleate skeletal muscle fibers. Some myoblasts do not fuse withdeveloping muscle fibers and instead remain in adult skeletal muscle tissue as myosatellite cells which after an injury enlarge, divide and fuse with damaged muscle fibers, thereby assisting in the repair of the tissue.The sarcolemma or plasma membrane of a muscle fiber, surrounds the sarcoplasm,or cytoplasm of the muscle fiber (p. 283), which has a characteristic transmembrane potential due to the unequal distribution of positive and negative charges across themembrane. In a skeletal muscle fiber, a sudden change in the transmembrane potential is the first step that leads to a contraction. Skeletal muscle fiber is very large, and all regions of the cell must contract at the same time. The signal that must be distributed quickly and throughout the interior of the cell is conducted through the transverse tubules. Transverse tubules or T tubules, are narrow tubes filled with extracellular fluid and form passageways through the muscle fiber, that are continuous with the sarcolemma, (and share general properties), and extend deep into the sarcoplasm. The electrical impulses, called action potentials, conducted by the sarcolemma travel along the T tubules into the cell interior and trigger muscle fiber contraction. Myofibrils are cylindrical structures that actively shorten and responsible for skeletal muscle fiber contraction. They consist of bundles of two protein filaments called myofilaments: thin filaments composed primarily of actin, and thick filaments composed primarily of myosin. At each end of the skeletal muscle fiber, the myofibrils are anchored to the inner surface of the sarcolemma. In turn, the outer surface of the sarcolemma is attached to collagen fibers of the tendon or aponeurosis of the skeletal muscle. As a result, when myofibrils contract, the entire cell shortens and pulls on the tendon. In skeletal muscle fibers, a membrane complex called the sarcoplasmic reticulum (p. 284)(SR) forms a tubular network around each individual myofibril, fitting over it like lacy shirt-sleeves. The SR is similar to the smooth endoplasmic reticulum of other cells. Skeletal muscle fibers pump calcium ions out across their plasma membranes and into extracellular fluid, but also remove calcium ions from the sarcoplasm by actively transporting them into the terminal cisternae of the SR. Levels of calcium ions are low in sarcoplasm of a resting skeletal muscle fiber; and levels of free calcium ions are high inside the terminal cisternae. In addition, cisternae contain the protein calsequestrin, which reversibly binds calcium ions. Inside Cisternae (both free and bound calcium) can be 40,000 times that of the surrounding sarcoplasm. A muscle contraction begins when stored calcium ions are released into the sarcoplasm. These ions then diffuse into individual contractile units called sarcomeres. A single Thin filament contains four proteins: F-actin, nebulin, tropomyosin, and troponin. (p. 286). A thick filament contains about 300 myosin (protein) molecules, each made up of a pair of myosin subunits twisted around one another. The long tail is bound to other myosin molecules in the thick filament. The free head, which projects outward toward the nearest thin filament, has two globular protein subunits. What happens when a skeletal muscle fiber contracts?: (1) the H bands and I bands of the sarcomeres get smaller; (2) the zones of overlap get larger; (3) the Z linesmove closer together, and (4) the width of the A band remains constant. Sliding filament theory: thin filaments are sliding toward the center of each sarcomere, alongside the thick filaments. The contraction wakens with the disappearance of theI bands, at which point the Z lines are in contact with the ends of the thick filaments. During contraction, sliding occurs in every sarcomere along the myofibril.As a result, the myofibril gets shorter and so does the muscle fiber since they are attached to the sarcolemma at each Z line and at either end of the muscle fiber. When muscle cells contract