Functions of skeletal muscles 4 Movement 4 Maintain posture and body position 4 Support soft tissues, ex abdominal wall supports ventral body organs 4 Guards entrances and exits- openings of digestive tract are encircled w/ muscle 4 Maintain body temperature

Anatomy of Skeletal Muscle 4 Epimysium- dense layer of collagen that surrounds the entire muscle 4 Perimysium- divide muscle into smaller compartments called fascicles, which contain blood vessels and nerves 4 Endomysium- surrounds individual muscle fibers 4 These 3 fibers join together at the end of muscles to form tendons

Microanatomy of muscle tissue 4 Skeletal muscle cells are also called fibers 4 Myoblasts fuse together to make muscle fibers

The Sarcolemma 4 Sarcolemma- cell membrane of muscle fiber 4 Sarcoplasm- cytoplasm of muscle fiber 4 Transverse Tubules “T tubules”- passageways through the muscle 4 Electrical impulses, also called action potentials, travel through T tubules to begin muscle contraction

Myofibrils 4 Unit of muscle fibers 4 Contains myofilaments, thin “actin, and thick “myosin” 4 Myofilaments are organized into repeating units called sarcomeres

Sliding Filament Theory Zones of overlap get larger (overlap of actin and myosin) 4 Z lines get closer

Neuromuscular Junction 4 A neuron controls each muscle fiber using acetylcholine, which makes the muscle fibers more permeable to sodium causing an action potential to begin 4 The action potential triggers muscle fibers to allow Ca to pass into cells (quick.03s) 4 Ca binding to the active site of the thin filaments starts the contraction cycle

Contraction cycle 4 Cross bridges from between thick and thin filaments 4 Myosin heads of thick filaments pivot, shortening muscle fiber

Relaxation 4 Acetylcholinesterase breaks down acetylcholine to stop action potential 4 Ca is pumped out of muscle fibers into the extracellular fluid 4 Ca is transported back into the sarcoplasmic reticulum 4 Active site is covered up again

Types of contractions 4 Isotonic- tension increases, and muscle shortens, walking and running 4 Isometric- tension produces, but muscle size stays the same, pushing on a door

Aerobic Metabolism 4 Energy produced in muscle tissue in the presence of oxygen 4 Muscle cells only keep small reserves of ATP 4 Cellular respiration allows muscle cells to produce more ATP using glycogen and glucose reserves

Anaerobic Metabolism 4 Demands on muscle exceed bodies ability to supply oxygen 4 Lactic acid is produced and builds up in the muscle tissue 4 Muscle Fatigue- muscles can’t contract despite neural stimulation –Short peak levels (spinting) –Prolonged excertion, Ca can’t be regulated (marathon)

Recovery Period 4 Conditions in muscle fibers return to normal 4 Oxygen converts lactic acid into pyruvate which can then become ATP or glycogen 4 Oxygen debt occures after exercise until your cells use new incoming oxygen to generate ATP 4 85% of heat needed to thermoregulate comes from skeletal muscles

Muscle Performance 4 Fast twitch fibers “white muscle”- anaerobic, high intensity and short duration, low myoglobin, fewer mitochondria 4 Slow twitch fibers “red muscle”- opposite of above 4 Intermediate fibers- characteristics between fast and slow 4 % of fast to slow muscle fibers is genetically determined

Cardiac Muscle Tissue 4 Found only in the heart 4 Contracts with out neural stimulation 4 Longer contractions 4 Intercalated discs ensure cells contract in unison

Smooth Muscle Tissue 4 Oval shaped cells with a central nucleus 4 Found in almost every organ 4 Doesn’t have myofibrils or sarcomeres, so no striations 4 Involuntary control