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Jenna StraussBSCI 201 ANATOMY AND PHYSIOLOGYEXAM 3 REVIEW SHEETMuscular System 1/A- Skeletal muscle (organ)- •Each muscle fiber ( = skeletal muscle cell) is wrapped in a delicate CT membrane called ENDOMYSIUMB- Skeletal muscle (organ)- •Fascicle – consists of a group of endomysium-covered muscle fibers wrapped in a coarse CT membrane called PERIMYSIUMC- Skeletal muscle (organ)- •Skeletal muscle – consists of a group of fascicles wrapped in a tough CT membrane called EPIMYSIUMD- microscopic anatomy of the skeletal muscle fiber- Myoglobin – a red pigment that binds and stores oxygenE- microscopic anatomy of the skeletal muscle fiber- Sarcolemma – plasma membrane of muscle fiberF- microscopic anatomy of the skeletal muscle fiber-Sarcoplasm – cytoplasm of the muscle fiberG- microscopic anatomy of the skeletal muscle fiber- Sarcoplasmic reticulum(SR) – specialized smooth endoplasmic reticulum that stores/releases calcium into the sarcoplasm; the expanded ends of SR are called TERMINAL CISTERNAEH- TRIAD- Composed of a transverse tubule in between 2 terminal cisternae: Terminal cisterna-Ttubule-Terminal cisterna. Function: for the release of calcium ions into the sarcoplasm when the sarcolemma depolarizes. I- Sacromeres- •Structural units of skeletal muscle = each skeletal muscle is composed of repeated units arranged end to end called sarcomeres•The distance between 2 successive Z lines = a sarcomere• Components of a Sarcomere:• A band = thick filament• M line = line that bisects and anchors the A bands• Thin filaments alternating with “A” bands; the alternating pattern of the thick and thin filaments results in the characteristic striated appearance of skeletal muscle• Z lines (= Z discs) – anchor the thin filaments• H zone – middle region of the A band not overlapping with the thin filaments I bands – regions of the thin filaments not overlapping with the A band*The sliding filament mechanisms of muscle contraction- states that the sliding of the thin filaments past the A bands result in muscle contraction. •According to this mechanism when a muscle contracts there is more overlap between the thin filaments and the A bands: H zone decreases or disappears::::I bands decrease or disappear. Sarcomere length shortens = Skeletal muscle shortens ( contracts). However, the lengths of the A bands and the thin filaments remain the same – they do not shortenJ- Excitation-Contraction Coupling-The motor neuron and all the skeletal muscle fibers it innervates via its axonal terminals is called a MOTOR UNITK- TENDONS-2. Each axonal terminal innervates one muscle fiber in the skeletal muscle to form the NEUROMUSCULAR JUNCTION. •The junction between the axonal terminal of a motor neuron and a skeletal muscle fiber separated by a small space called the neuromuscular cleft (synaptic cleft) •Each muscle fiber has only one neuromuscular junction•The highly folded region of the sarcolemma of the muscle fiber at the neuromuscular junction is called the Motor End Plate – express acetylcholine receptors on the surface•A motor neuron and all the muscle fibers it innervates via its axonal terminals is called a motor unit; motor units come in different sizes – small, medium, large3. •Thin filaments – 8nm in diameter; anchored by the Z lines; Thin filaments contain 3 different proteins: Actin – contains the binding sites for the myosin heads Tropomyosin –a rod-shaped regulatory protein that spirals around the actin and blocks myosin binding sites on actin in a relaxed skeletal muscle Troponin – a three-polypeptide complex namely TnC – binds calcium ions TnT – binds to tropomyosin TnI - inhibitory subunit that binds to actinElastic filaments are composed of the protein tictin - they extend from Z lines through the A bands to attach to the M line thus, anchoring the A bands in place within the sarcomere4. In the sequence of events in Excitation- Contraction Coupling- the myosin e are activated because Calciumions bind to Troponin;Typonon changes shape which results in a conformational change and the removal of tropomyosin from blocking the myosin-binding sites on actin. And then Contraction; myosin heads alternately attach to actin and detach, pulling the actin filaments toward the center of the sacromere; release ofengery by ATP hydrolysis powers the cycling process. •With the tropomyosin blockade ended, activated myosin heads = cross bridges bind to the accessible myosin-binding sites on actin•Myosin heads are activated when the myosin heads are attached by ADP +Pi (resulting from ATPase hydrolysis of ATP into ADP + Pi) 5. skeletal muscle contraction: •What stimulates skeletal muscles to contract? When they are stimulated by activated MOTOR NEURONS•Motor neurons conduct impulses to skeletal muscles.• Motor neuron makes contact with skeletal muscle fibers via its AXONAL TERMINALS•Each axonal terminal innervates one muscle fiber in the skeletal muscle to form the NEUROMUSCULAR JUNCTION•The motor neuron and all the skeletal muscle fibers it innervates via its axonal terminals is called a MOTOR UNITSequence of events in Excitation-Contraction Coupling•Motor neuron is activated•Axon of motor neuron generates and transmits action potential to the axonal terminals•Results in the release of the neurotransmitter, ACETYLCHOLINE from vesicles in the axonal terminals into the neuromuscular cleft•Acetylcholine binds to acetylcholine receptors on the motor end plate to cause depolarization which leads to the generation of action potential at the motor end plate•The action potential spreads across the entire sarcolemma and into the T-tubules of the triads•Results in the release of calcium ions from the terminal cisternae of the triads into the sarcoplasm•Calcium ions bind to TnC which results in a conformational change and the removal of tropomyosin from blocking the myosin-binding sites on actin.•With the tropomyosin blockade ended, activated myosin heads = cross bridges bind to the accessible myosin-binding sites on actin•Myosin heads are activated when the myosin heads are attached by ADP +Pi (resulting from ATPase hydrolysis of ATP into ADP + Pi)•When the ADP and Pi dissociate from the cross bridges, the attached cross bridges change their orientation termed thePOWERSTROKE from a right angle to a bent position pulling the


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UMD BSCI 201 - EXAM 3

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