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thick myosin molecules protein form a myosin

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Unformatted text preview: allel responsible for contraction responsible • 3 kinds- thick, thin, & elastic filaments Myofilaments Myofilaments Myofilaments (cont.)~ • Thick= myosin molecules (protein) form a myosin filament myosin (golf club shaped) (golf • Each filament has a ‘head’ (cross-bridge) & polypeptide ‘tail’ • Bare zone= area btw bundle of heads • Thin= 2 iintertwined strands of fibrous (F) actin formed by ntertwined fibrous subunits of globular (G) actin (‘beaded necklace’) globular • Each G actin has an active site to bind w/ myosin heads • Tropomyosin protein blocks active sites when cell relaxed • Troponin protein are Ca2+-binding molecules on each -binding tropomyosin molecule tropomyosin Filaments (cont.) Filaments 3 kinds of filaments (cont.)~ • Elastic= huge, springy protein (connectin) that connects huge, thick filaments to Z disc (structure of anchorage) thick • Helps to keep thick & thin aligned, resist overstretching, & Helps recoil to resting length recoil Contractile proteins= myosin & actin (shorten fiber) Regulatory proteins= tropomyosin & troponin (‘switch’ determining when can/cannot contract) determining Striations Striations Striations= precise arrangement of myosin & actin • 2 proteins are not unique to SM, just in lrg quantities in both proteins skeletal & cardiac muslce skeletal • Dark band= A bands (anisotropic); region of thick filaments bands (+ partial overlapping thin filaments) • H band= w/in A band, region of no overlapping thin filaments • Light band= I bands (isotropic); region of elastic filaments + bands other ½ of thin filaments other • Bisected by Z disc (Z line) made of connectin which provides Bisected disc attachment (anchorage) for thin & elastic filaments attachment • Sarcomere= functional contractile unit; segment of myofibril functional form Z-line to Z-line form Striations (cont.) Striations Sarcomere (cont.)~ • Muscle shortens because each sarcomere shortens & pulls Muscle Z-lines closer together…Z-lines are connected to sarcolemma so entire fiber shortens sarcolemma Contraction preview~ • Nerve impulse…Ca2+ released by SR into sarcoplasm • Ca2+ binds to troponin…activates tropomyosin to shift & expose active sites on actin • Myosin heads bind to site to form cross-bridges…filaments Myosin ‘slide’ across each other ‘slide’ • Repeated binding & breaking of crossbridges leads to muscle contraction bridges Nerve-Muscle Relationship Nerve-Muscle Somatic motor neuron= innervates skeletal muscle • Cell bodies in brainstem/spinal cord & axons (somatic Cell motor fibers) lead to muscle motor • Axon branches ~200x to spread out & innervate individual Axon muscle fibers muscle Motor unit= 1 nerve fiber + all muscle fibers it stimulates nerve • Branching of nerve fiber (axon) results in muscle Branching contraction in unison contraction • Muscle fibers of a unit are dispersed throughout muscle to Muscle cause a weak, widespread contraction & NOT a lo...
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