Skeletal System Composition - answer 206 Bones in adult body provides leverage, support, and protection Pulled on by muscles to allow the body to push or pull against external objects Axial Skeleton - answer Skull, Vertebral Column, Ribs and Sternum Appendicular Skeleton - answer Shoulder Girdle; bones of arms, wrists, hands, and pelvic girdle; bones of legs, ankles, and feet Joints - answer Junctions of bones Fibrous Joint - answer Allows virtually no movement (Sutures of skull) Cartilaginous Joint - answer Allows limited movement (intervetebral) Synovial Joint - answer Allows considerable movement (elbows/knees) Uniaxial - answer Hinge, rotate around one axis (elbow) Biaxial - answer Operate in two perpendicular planes (ankle/wrist) Multiaxial - answer Allow movement in all three axes (shoulder/hip) Vertebral Column - answer Cervical 7 (lordotic curve) Thoracic 12 (Kyphotic curve) Lumbar 5 (Lordotic) Sacral 5 ( Kyphotic) Coccygeal 3-5 Curves help to distribute forces Muscle Tissue - answer Epimysium (outer layer) Perimysium (surrounding group of fibers/fascicules) Endomysium (surrounding individual fibers) Fascia - answer Delicate "cobwebby" tissue Motor Unit - answer Motor Neuron and the muscle fibers it innervates Typically several hundred muscle fibers in a single motor unit Sarcolemma - answer The plasma membrane of a cell Transverse Tubules - answer Connect to plasma membrane to interior Action potentials travel through Ensures AP excites all parts of the muscle fiber at the same time Sarcoplasm (muscle cytoplasm) - answer Glycogen, myoglobin, mitochondrion Myofibrils - answer Contractile organelles Extend length of muscle fiber Sarcoplasmic Reticulum - answer Membranous sacs around each myofibril Stores Calcium ions (Ca2+) Release of Ca2+ triggers muscle contraction Filaments - answer Function in the contractile process Thick and thin filaments 2 thin for every 1 thick Sarcomere - answer Compartments of arranged filaments Basic functional unit of a myofibril Troponin & Tropomyosin - answer Regulating proteins that cover binding sites Skeletal Muscle Striated appearance - answer Arrangement of Actin (thin) and Myosin (thick) Sliding-Filament Theory of Muscular Contraction - answer Actin filament at each end of the sarcomere slide inward on the myosin filaments, pulling the Z-discs towards the M-line/center of the sarcomere (shortening the muscle fiber) Sliding-Filament phases - answer Resting Phase Excitation-contraction coupling phase Contraction phase Recharge phase Relaxation phase -70 resting, -55 threshold Maximal Contraction of Myofibril - answer Low force potential due to reduced crossbridge-actin alignment Muscle Action Potential - answer Release acetylcholine Activation of ACh receptors Production of muscle action potential Termination of ACh activity (rapidly broken down by AChE) Excitation-Contraction Coupling - answer Increase in Ca2+ concentration in the muscle starts contraction Decrease in Ca2+ stops it Action Potentials causes Ca2+ to be released from the SR into the muscle cell Muscle cell membrane pumps Ca2+ back into SR Myosin binding sites are covered and the muscle relaxes Contraction cycle - answer ATP hydrolysis Formation of cross-bridges = myosin attaches to myosin binding sites on actin Power Stroke = crossbridges rotate, sliding the filaments Detachment of myosin from Actin = as the next ATP binds to the myosin head the myosin head detaches from binding site Cycle will continue as long as ATP and Ca2+ Levels are high Force Production of a Muscle - answer Dictated by the number of crossbridges that are formed between actin and myosin Crossbridge Cycling - answer ATP and Calcium are necessary to cycle the actin and myosin filaments Activation of Muscle - answer Arrival of the action potential at the nerve terminal causes the release of acetylcholine, once a sufficient amount of acetylcholine is released an action potential is generated across the sarcolemma and the fiber contracts Muscles with precision - answer May have as few as one muscle fiber per motor nueron Muscles that require less precision - answer May have several hundred fibers served by one motor neuron All-or-None principle - answer All the muscle fibers in a motor unit contract and develop force at the same time Stimulated Motor Unit - answer Twitch