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UWL BIO 312 - Muscular System

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Lecture #19 Lecture Outline:1. Muscle characteristicsa. Basic characteristicsb. Classification2. Anatomy and Histologya. Muscle fiber structure 3. Muscle contraction physiologyMuscle Characteristics: One of the 4 primary tissues, 3 types- Skeletal, smooth, cardiac- Specialized to generate force, produce movement, perform work- Converts chemical energy (ATP) into mechanical energy and heat- Comprises about 40-50% of body weight (most skeletal)- Characteristics:o Excitability: ability to change membrane potentialo Contractility: ability to contract and move boneso Extensibility: ability to stretch and withstand forceo Elasticity: ability to recoil back to original length when stretched- Striated muscle: has striped appearance under microscopeo Skeletal and cardiac muscle- Unstriated muscle: has smooth non-striped appearance under scopeo Smooth muscle- Voluntary: skeletal muscle- Involuntary: smooth and cardiac muscleAnatomy and Histology:- Each muscle consists of:o muscle cells (fibers)o Endomysium: connective tissue that covers each muscle fibero Fascicle: bundle of parallel muscle fibers covered by perimysium Length of cells = muscle lengtho Epimysium: connective tissue that covers several fascicles that make up the muscle as a wholeo Blood and lymphatic vesselso Efferent and afferent nerves- Skeletal Muscle Fiber structure: much larger cells than smooth or skeletalo Sarcolema: muscle cell membrane, contains many sodium gated and voltage gated ion channelso Sarcoplasm: cytoplasm of muscle cello Mitochondria: very high density of mitochondria for ATP productiono Contain several nuclei on periphery of cell under sarcolemao Myofibril: tube like structures that compose majority of volume of muscle cells Number of myofibril per cell vary based on diameter of cell Arranged parallel to the long axis of the muscleBio 312 Structures that shorten and do the work during contraction Each myofibril loosely surrounded by series of membranes and sacs called sarcoplasmic reticulumo Striations: repeating pattern of bands along each myofibril Sarcomeres: one repeating unit of striations that is the basic unit of contraction in striated muscle- Z-line to z-line A band: dark bands of striated muscle, composed primarily of thick filaments- Length does not change during contraction I band: lighter bands of striated muscle- Gets shorter during contraction- Z line divides I band in half, anchors thin filaments and titin filamentso Myofilaments: 3 different types of protein fibers that make up sarcomeres- Sliding filament mechanism: (Huxley 1954) contraction results from sets of tin and thick filaments sliding past each other. To shorten, thin slide past thick filaments towards center of sarcomereso Length of myofilaments does not changeo Thick filament: thicker filaments composed of myosin, make up A band H zone: central portion of A band where thick and thin filaments do not overlap- Essentially disappears during contraction M line: anchor point for center of A band Composed of several hundred myosin molecules (shaped like golf clubs)- Shafts of bundles of myosin called tails, make up bare zone- Ends of golf clubs called heads that make up cross bridges and attach to thin filaments, responsible for contraction by pulling thin filaments inward- Contain ATPase binding site and Actin binding siteo Titin filaments: anchor thick filaments in place Not directly involved in contraction Elastic, structural proteino Thin filaments: thinner filaments made from actin, anchored to Z-lines G-Actin molecules: contain binding site for attachment with myosin F-Actin molecules: G-actin composed, double stranded, helical strand of protein Tropomyosin: thin filamentous protein that coat the outer surface of actin backbone Troponin: three different proteins associated with tropomyosino Cross-Bridge Cycle: Binding: myosin cross bridge to actin molecule Power Stroke: cross bridge bends, pulling thin myofilament inward Detachment: cross bridge detaches at end of power stroke and returns to original shape Binding: cross bridge binds to more distal actin molecule; cycle repeated Cycles operate asynchronously to provide smooth coordinated movement- Chemical events of cross bridge cycleo Myosin cross bridge attaches to actin filamento ATP  ADP + P during power stroke, waste products sloughed offo ADP + P ATP allows for usable energy to relax cross bridge/entire muscle- Thick and thin filaments are called contractile protein because their interaction produces tension and shortening of sarcomere- High degree of three dimensional order allows maximum amount of myosin-myosin and actin-actin


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UWL BIO 312 - Muscular System

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