Jenna Strauss BSCI 201 ANATOMY AND PHYSIOLOGY EXAM 3 REVIEW SHEET Muscular System 1 A Skeletal muscle organ Each muscle fiber skeletal muscle cell is wrapped in a delicate CT B Skeletal muscle organ Fascicle consists of a group of endomysium covered muscle fibers wrapped in C Skeletal muscle organ Skeletal muscle consists of a group of fascicles wrapped in a tough CT a coarse CT membrane called PERIMYSIUM membrane called ENDOMYSIUM membrane called EPIMYSIUM D microscopic anatomy of the skeletal muscle fiber Myoglobin a red pigment that binds and stores oxygen E microscopic anatomy of the skeletal muscle fiber Sarcolemma plasma membrane of muscle fiber F microscopic anatomy of the skeletal muscle fiber Sarcoplasm cytoplasm of the muscle fiber G 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 CISTERNAE H 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 shorten J Excitation Contraction Coupling The motor neuron and all the skeletal muscle fibers it innervates via its axonal terminals is called a MOTOR UNIT K 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 large 3 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 actin Elastic 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 sarcomere 4 In the sequence of events in Excitation Contraction Coupling the myosin e are activated because Calcium ions 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 of engery 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 UNIT Sequence 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 the POWERSTROKE from a right angle to a bent position pulling the attached thin filament inward into the H zone toward the M line sliding of thin filaments which results on skeletal muscle contraction Cross bridge detachment NEW ATP molecules bind to the attach myosin heads to cause them to detach Lack of new ATP results in skeletal muscle contracture termed RIGOR MORTIS occurs when an individual dies and ATP
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