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Physiology Review (ppt modified from http://www.recreation.ucsb.edu/ess/ess40/chap8.htm) The SARCOMERE is the functional unit of the muscle. A sarcomere is found between two Z lines. The Muscle Fiber Is Composed of Special Contractile Proteins • Myosin is the main, thick structural protein in the sarcomere. It has cross bridges for attaching to the Actin protein. • Actin is the main, thin structural protein in the sarcomere. Each actin molecule has a binding site that can attach with a Myosin cross bridge. • Actin and myosin are contractile proteins. Tropomyosin and Troponin Are Regulatory Proteins. These regulatory proteins control the muscle contraction process. • They either allow or block actin-myosin interaction depending on their configuration. TROPOMYOSIN • Tropomyosin covers the actin binding sites. • This prevents the union of actin with myosin cross bridges. TROPONIN • Troponin has three binding sites: – one binds to Tropomyosin, one to Actin, and one to Ca+ ions. – When calcium combines with troponin, tropomyosin slips away from its blocking position between actin and myosin. – With this change actin and myosin can interact and muscle contraction can occur. • fig.cox.miami.edu/.../150/neuro/tropomyosin.jpg Sliding Filament Mechanism • The myosin cross bridges can bind to the actin. • After binding the thin (actin) filaments are pulled toward the center of the sarcomere. • This is known as the Sliding Filament Mechanism. • http://people.eku.edu/ritchisong/crossbridge3.gif SLIDING FILAMENT MECHANISM • Neither the thick nor thin filaments change in length. They change their position with one another. • The actin slides closer together between the thick filaments. • http://3dotstudio.com/contract.gif • The myosin cross bridges pull the thin actin filaments inward. • A single power stroke pulls the actin inward only a small percentage of the total distance. • Complete shortening occurs by repeated cycles of the power stroke. • The link between myosin and actin is broken at the end of one cross bridge cycle. A cross bridge returns to its original position and can connect to the next actin molecule position, pulling the actin filament further. www.octc.kctcs.edu Muscle contraction • The process starts when the muscle cell is depolarized • A neuron sends action potentials to muscle fibers. • This neuron releases acetylcholine at the neuromuscular junction. • This produces an action potential over the entire muscle cell membrane. – Sodium/Potassium pumps are not working when Ach is on the receptors of muscle cells…chaos ensues! The Release of Calcium Ions from the sacroplasmic reticulum starts the Sliding Process. • Calcium from the SR binds with troponin. • By this event, tropomyosin is pulled off the binding sites of actin • This allows the myosin cross bridges to bind to actin and slide this protein. Test Information… • 60 points total –20 Anatomy ID—real people, pictures and microscope slides –Some anatomy on Physiology portion • Body movements • Draw a line drawing of sarcomere Name this muscle Muscle? Muscle? Notecardable items… • Fill in the blank (with words provided) of body movements (4) • Two short answers have choices…choose the question you can answer the MOST completely. – A diagnostic vs. muscle connections – Mitochondria’s role in contraction vs blood supply Short Answer Questions (notecardable…) • Explain the protein alignment within a sarcomere. Draw a diagram as well… Short Answer Questions (notecardable…) • Physiology of muscle cell— broken into 5 questions – Three phases of function of MC – Function of neuromuscular junction – Stimulation in detail – Contraction in detail – Mechanism for lengthening Short Answer Questions (notecardable…) • Antagonistic/Synergistic as it relates to function of muscles • Difference between strains, sprains and contusions • Three factors contributing to muscle aging • Steroid question—what have you learned about the pros/cons/debate?