3 types of muscles A. Function of Skeletal Muscles • Produce movement – Muscle pulls tendons to move the skeleton • Maintain posture and body position – Continuous muscle contraction • Guard entrances and exits – Encircle openings to digestive and urinary tracts. Control swallowing, defecation and urination • Maintain body temperature – Energy from contraction is converted to heat B. Anatomy of Skeletal Muscles – GrossAnatomy All three layers attach muscle to bone Surrounds muscle Bundle of muscle fibers Surround seachmuscle fiber, and tie adjacent fibers together Divides muscle into compartments,each contain a bundle of muscle fibers called fascicle B.Anatomyofa SkeletalMuscle– BloodVessels andNerves • Musclecontractions requireenergy – Bloodvesselsdeliveroxygenandnutrientsto produce energy(ATP) • Musclecontractionsareunderstimulation from the CNS(central nervous system) Microanatomy– Sarcolemmaand T-Tubules • Verylargecells • 100’sof nuclei • Cellmembrane • poresopentoT-tubules • Networkof narrow tubules • filled with extracellular fluid • form passageway s through muscle fiber Myofibrils • Cylinderaslongasentire muscle fiber • Eachfibercontains100sto 1000s • Responsibleforcontraction • Whenmyofibrilscontract the whole cell contracts • Consistof proteins – Actin–thinfilaments – Myosin –thickfilaments SarcoplasmicReticulum • Specialized formofSER • Tubularnetworkaround each myofibril • In contact with T-Tubule Sarcomere • Smallestfunctionalunit of muscle fiber • Each myofibril contains 10,000sarcomeresend to end • Interaction between thickandthinfilaments cause contraction • Bandedappearance Thickand ThinFilaments • Thin – twistedactinmolecules – Eachhasanactivesitewhere they interact with myosin – Resting–activesitecoveredby tropomyosin which is held in place by troponin • Thick – Myosin – Headattachestoactinduring contraction – Can only happen if troponin changes position, moving tropomyosintoexposeactive site Sliding Filaments andCross Bridges • Sarcomerecontraction– Sliding Filament Theory – Thin filaments slide towardcenterof sarcomere – Thickfilamentsare stationary – Myosin head attaches to activesiteonactin(cross bridge) – Pullactintowardscenter, then detaches ControlofMuscleFiber Contraction Undercontrolof thenervoussystem • • • • Electricalsignaltravels tothemuscle. Electrical signal spreads over entire sarcolemma,downt-tubulestosarcoplasmic reticulum Sarcoplasmicreticulumreleasesmassive amounts of calcium Increaseincalcium –sarcomeres contract TheContractionCycle • Step1 –Ca+ binds to troponin, changing the tropomyosin position, in turnexposingactivesite on actin • Step2 – Myosinheadattachesto actin • Step3 – Pullingofactintowards center of sarcomere • Step4 – Detachmentofcross bridge
