Exam 2 Study Guide:The Muscular System3 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 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-nucleateSkeletal Muscle the organ- Composed of skeletal muscle fibers surrounded by the ENDONYSIUMo Bundle of endonysium covered skeletal muscle fibers form a FASICLEo Each fascicle is surrounded by the perimysiumo Bundle of perimysium covered fascicles form the skeletal muscle wrapped in epimysium- Attach to skeletal structures (bone and cartilage)- Types of Attachmento Direct Attachment epimysium of skeletal muscle directly fuses to the periosteum of bone Will not cause skeletal muscles to move No tendons involved Tend to be flat bones such as cranial boneso 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 Inserstiono Origin: bone that does not moveo Insertion: bone that moves when skeletal muscle contracts- Microscopic Anatomyo 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 Myosino Form a dark band called the A bando Consist of a tail and 2 globular headso Heads have binding sites for ATP- Thin Filament – anchored by z-lineso 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 appearanceo Myoglobin – unique red pigment that binds and stores oxygeno 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 ATPo Sarcoplasm – cytoplasm of muscle fibero Sarcoplasmic Recticulum – specialized smooth ER that stores/releases calcium into sarcoplasm to cause contraction Expanded ends of SR are called terminal cisternaeo 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 Filamneto Thin filament anchored by z discso 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 contractiono 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 SHORTENo Shortening of skeletal muscle occurs when the thin filaments in the sarcomeres slideinward 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- Excitation-Contraction Couplingo Muscle contracts when stimulated by activated motor neurons which conduct impulses to skeletal muscleso Neuron makes contact with muscle via axonal terminals Each axonal terminal innervates one muscle fiber to form the neuromuscular junction 1 to 1 ratioo 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 sarcolemmao Has an increased surface area, hence the end plate has the highest number of acetylcholine receptorso More acetylcholine that can bind = more contractiono 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 endplateo 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 Increase in the intracellular calcium levels in the skeletal muscle fiberso 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
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