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Functions of skeletal muscles Movement Maintain posture and body position Support soft tissues, ex abdominal wall supports ventral body organs Guards entrances and exits- openings of digestive tract are encircled w/ muscle Maintain body temperature Anatomy of Skeletal Muscle Epimysium- dense layer of collagen that surrounds the entire muscle Perimysium- divide muscle into smaller compartments called fascicles, which contain blood vessels and nerves Endomysium- surrounds individual muscle fibers These 3 fibers join together at the end of muscles to form tendons Microanatomy of muscle tissue Skeletal muscle cells are also called fibers Myoblasts fuse together to make muscle fibers The Sarcolemma Sarcolemma- cell membrane of muscle fiber Sarcoplasm- cytoplasm of muscle fiber Transverse Tubules “T tubules”- passageways through the muscle Electrical impulses, also called action potentials, travel through T tubules to begin muscle contraction Myofibrils Unit of muscle fibers Contains myofilaments, thin “actin, and thick “myosin” Myofilaments are organized into repeating units called sarcomeres Sliding Filament Theory Zones of overlap get larger (overlap of actin and myosin) Z lines get closer Neuromuscular Junction A neuron controls each muscle fiber using acetylcholine, which makes the muscle fibers more permeable to sodium causing an action potential to begin The action potential triggers muscle fibers to allow Ca to pass into cells (quick .03s) Ca binding to the active site of the thin filaments starts the contraction cycle Contraction cycle Cross bridges from between thick and thin filaments Myosin heads of thick filaments pivot, shortening muscle fiber Relaxation Acetylcholinesterase breaks down acetylcholine to stop action potential Ca is pumped out of muscle fibers into the extracellular fluid Ca is transported back into the sarcoplasmic reticulum Active site is covered up again Types of contractions Isotonic- tension increases, and muscle shortens, walking and running Isometric- tension produces, but muscle size stays the same, pushing on a door Aerobic Metabolism Energy produced in muscle tissue in the presence of oxygen Muscle cells only keep small reserves of ATP Cellular respiration allows muscle cells to produce more ATP using glycogen and glucose reserves Anaerobic Metabolism Demands on muscle exceed bodies ability to supply oxygen Lactic acid is produced and builds up in the muscle tissue Muscle Fatigue- muscles can’t contract despite neural stimulation – Short peak levels (spinting) – Prolonged excertion, Ca can’t be regulated (marathon) Recovery Period Conditions in muscle fibers return to normal Oxygen converts lactic acid into pyruvate which can then become ATP or glycogen Oxygen debt occures after exercise until your cells use new incoming oxygen to generate ATP 85% of heat needed to thermoregulate comes from skeletal muscles Muscle Performance Fast twitch fibers “white muscle”- anaerobic, high intensity and short duration, low myoglobin, fewer mitochondria Slow twitch fibers “red muscle”- opposite of above Intermediate fibers- characteristics between fast and slow % of fast to slow muscle fibers is genetically determined Cardiac Muscle Tissue Found only in the heart Contracts with out neural stimulation Longer contractions Intercalated discs ensure cells contract in unison Smooth Muscle Tissue Oval shaped cells with a central nucleus Found in almost every organ Doesn’t have myofibrils or sarcomeres, so no striations Involuntary control