 Produce skeletal movement  By contraction of muscle fibers  True of all = cardiac, smooth, skeletal  Maintain posture/body position  Some muscles are always “on” – fight against gravity  Support Tissues/Stabilize joints  Shoulder joint is VERY unstable – needs muscle and tendons to keep it steady

 Maintain Body Temp/Generate heat  Large amount of energy is given off as heat during muscle contraction  Guard Entrances and Exits  Openings of tracts encircled by skeletal muscles  Store Nutrient Reserves  Muscle broken down when there is an inadequate amount proteins

 Epimysium  Surrounds entire skeletal muscles  separates muscles from tissues and organs  Perimysium  Surround muscle fascicle  Endomysium  Surround muscle fibers

 Sarcolemma  The cell membrane of a muscle fiber  Sarcoplasm  Cytoplasm of a muscle fiber  Transverse Tubules  Narrow tubes continuous with sarcolemma  Passageways that the action potential travels through

 Myofibrils  Bundles of myofilament  Separated by sarcoplasmic reticulum  Contractile orgalles of skeletal muscle  Extend entire length of muscle fiber

 Myofilaments  Bundles of myofilament  Separated by sarcoplasmic reticulum  Contractile orgalles of skeletal muscle  Extend entire length of muscle fiber

 Myofilaments  Contractile proteins of the muscle  Thick and thin filaments overlap each other in a pattern that creates striations I band – only thin filaments Figure 6.3b

Myofilaments continued  The protein fibers that actually compose the myofibrils  Thick filaments  Made of protein myosin  Cross bridges link to thin filaments  Thin filaments  Made of protein actin

 Sarcoplasmic reticulum (SR)  fluid-filled system of membranous sacs  surrounds each myofibril  stores Ca 2+  Release of calcium into Sarcoplasm signals the beginning of a muscle contraction Figure 6.3a

 Basic functional unit of a myofilament  A band (darker) – extends the entire length of thick filaments  I band (lighter) – thin filaments  I band (lighter) – thin filaments thin ments  Proteins that stabilize the filaments  Proteins that regulate the interaction between filaments

A band (dark band) M-line:  central part of the thick filament  stabilize position of thick filament H-zone:  Contains thick filaments only Zone of overlap:  Where the think and thick filaments overlap

I-band (light band) Z-lines:  Boundaries between sarcomere Titin:  Elastic protein  Keeps filaments in proper alignment  Helps muscle fiber resist extreme stretching

 During a muscle contraction thin filaments are sliding toward the center of each sarcomere  Sliding occur within every sarcomere in a muscle fiber

When a skeletal muscle fiber contracts  The H zones and I bands get smaller  The zones of overlap get larger  The Z lines move closer together  The width of the A band remains constant