Exam 2 Study Guide The Muscular System 3 Types of Muscle Tissue that organize with connective tissue wrappings blood vessels lymphatic vessels and nerves to form the 3 types of organs Skeletal Muscle the organ Skeletal Muscle striations long cylindrical cells called muscle fibers multi nucleate cells Cardiac Muscle striations branching cells with intercalated discs uni nucleate Smooth Muscle no striations spindle shaped cells uni nucleate Composed of skeletal muscle fibers surrounded by the ENDONYSIUM o Bundle of endonysium covered skeletal muscle fibers form a FASICLE o Each fascicle is surrounded by the perimysium o Bundle of perimysium covered fascicles form the skeletal muscle wrapped in Attach to skeletal structures bone and cartilage Types of Attachment o Direct Attachment epimysium of skeletal muscle directly fuses to the periosteum epimysium of bone Will not cause skeletal muscles to move No tendons involved Tend to be flat bones such as cranial bones o Indirect Attachment allows for movement Epimysium blends into tendon and tendon attaches skeletal muscle to skeletal structures Advantages Space Saver attachment via tendons occupies less space on surface of skeletal structures Makes it possible for skeletal structure to move when skeletal muscle contracts Attachment Sites At least 2 Origin and Inserstion o Origin bone that does not move o Insertion bone that moves when skeletal muscle contracts Microscopic Anatomy o Myofibrils rod like structures that run entire length of the muscle fiber 80 of volume of muscle fiber Runs entire length of skeletal muscle organ Contains 2 types of Myofilaments Thick Filament composed of protein Myosin o Form a dark band called the A band o Consist of a tail and 2 globular heads o Heads have binding sites for ATP Thin Filament anchored by z lines o Composed of 3 different proteins Actin binding site for myosin heads Tropomysin rod shaped regulatory protein that spirals around the actin and blocks myosin binding sites on actin in a relaxed skeletal muscle Tropinin a 3 polypeptide complex TnC binds calcium ions TnT binds tropomysin TnI inhibator subunit that binds to actin Alternating arrangement gives striated appearance o Myoglobin unique red pigment that binds and stores oxygen o Inclusions glycosomes containing glycogen storage form of glucose in animals o Mitochondria for aerobic respiration to produce energy Aerobic respiration is used by skeletal muscle fibers to produce energy ATP to sustain skeletal muscle contraction Aerobic catabolism yields 38 ATP per glucose Anerobic 2 ATP o Sarcoplasm cytoplasm of muscle fiber o Sarcoplasmic Recticulum specialized smooth ER that stores releases calcium into sarcoplasm to cause contraction Expanded ends of SR are called terminal cisternae o Sarcolemma plasma membrane of muscle fiber Invaginations infoldings called transverse tubules t tubules o Triad terminal cisternae T tubule terminal cisternae Function release of calcium ions into sarcoplasm when sarcolemma depolarizs Alternating Arrangment of Thick and Thin Filamnet o Thin filament anchored by z discs o Distance between 2 successive Z discs sarcomere structural unit of skeletal muscle Sarcomeres run the entire length of the myofibril myofibrils run the entire length of the skeletal muscle fibers which run the entire length of the skeletal muscle Components A band thick filament M line line that bisects and anchors A bands Thin filament alternating with A bands results in appearance of striation Z lines anchors thin filaments H zone middle region of A band not overlapping with the thin filaments I bands region of thin filaments not overlapping with A band Sliding Filament Meachanism of Muscle Contraction sliding of thin filaments bast the A band results in muscle contraction Excitation Contraction Coupling o When muscle contracts there is more overlap between the thin filaments and the A bands H zone decreases disappears I bands decrease disappear Sarcomere length shortens skeletal muscle chortens length of the A bands and thin filaments remain the same DO NOT SHORTEN o Shortening of skeletal muscle occurs when the thin filaments in the sarcomeres slide inward into the h zone toward the m line pulling the z disc inward hence the sliding of thin filaments results in the shortening of the sarcomere distance between 2 successive Z discs Sarcomere shortened myofibril shortened skeletal muscle fibers shortened skeletal muscle shortened o Muscle contracts when stimulated by activated motor neurons which conduct impulses to skeletal muscles o Neuron makes contact with muscle via axonal terminals Each axonal terminal innervates one muscle fiber to form the neuromuscular junction 1 to 1 ratio o Motor Unit motor neuron all the skeletal muscle fibers it makes contact via its axon terminals Sizes Sml 10 fibers contracted Med 50 100 Lg 1000 o Sequence of Events in Excitation Contraction Coupling Explains how action potential developed transmitted by the axon of the motor neuron is coupled to the shortening of the sarcomeres sliding of thin filaments into H zone Neuromuscular Junction thin gap separating the motor endplate and the axon terminal Motor Endplate highly folded region of sarcolemma o Has an increased surface area hence the end plate has the highest number of acetylcholine receptors o More acetylcholine that can bind more contraction o Acetylcholine neurotransmitter released into the neuromuscular cleft gap between axon terminal and motor end plate Diffused from the cleft to bind to its receptors on the motor end plate depolarizing the endplate o Depolarization develops into action potential which spreads across the entire sarcolemma including the t tubules invaginations of the sarcolemma and form the triad o When action potential enters t tubules of the triad terminal cisternae depolarize and ionic calcium is released from the sarcoplasmic recticulum into the sarcoplasm Activated Myosin Globular Head Increase in the intracellular calcium levels in the skeletal muscle fibers o Calcium binds to TnC leading to conformational change in the troponin which affect TnT bound to tropomyosin tropomyosin is moved from blocking the myosin binding sites makes the sites on the actin accessible to the myosin globular heads o Atpase splits ATP into ADP and Pi which attach to the myosin globular heads activated form o Activated heads binds to accessible site on actin at a right angle o Cross Bridge attached myosin globular to its site on actin o ADP and Pi
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