Anatomy Test 3 Third organ system muscular system Composed of muscles Blood vessels Nerves 3 types of muscles tissue 3 types of muscles as organs 3 Types of Muscle Tissue Skeletal muscle tissue Cardiac muscle tissue Smooth muscle tissue Structural Differences Cardiac Skeletal voluntary control involuntary control Smooth control Skeletal Muscle Tissue elongated cells called skeletal muscle fibers striated multinuclear striated highly branched cells that form intercalated discs uninuclear spindle shaped cells no obvious striation uninuclear involuntary Organized with connective tissue membrane s to form skeletal muscle the organ Structural organization each skeletal muscle fiber is covered by the endomysium A bundle of endomysium covered skeletal muscle fibers wrapped in the perimysium forms a fascicle The arrangement of the fascicle in the skeletal muscle may be o Parallel o Pennate o Convergent neurons muscle o Origin o Insertion contracts A bundle of perimysium covered fascicle wrapped in the epimysium forms the organ called skeletal muscle This skeletal muscle is infiltrated by blood vessels and axon terminals from motor Skeletal muscles attach to bones in the skeletal system hence the name skeletal Skeletal muscles have 2 attachment sites When the skeletal muscle contracts it pulls the insertion towards the origin The origin of a skeletal muscle is relatively stable when the skeletal muscle Attachment of skeletal muscle origin or insertion may be Direct attachment Indirect attachment Direct Attachment Epimysium of the skeletal muscles attaches directly to the surface of the bone An example is the skeletal muscle attached to the cranial bones Frontalis attaches directly to the frontal bone Indirect Attachment Skeletal muscle attaches indirectly to the bone by tendon which extends from the epimysium covering the skeletal muscle Most skeletal muscles in the human body use indirect attachment Advantages of indirect attachment o Attachment by tendons occupy smaller surface area on the bone allowing for other skeletal muscles to attach to the same bone for efficient attachment of skeletal muscles o Bones attached indirectly by skeletal muscles act as levers when the skeletal muscles contract to produce movements by the body o Tendons attaches skeletal muscle to the surface of bones protect skeletal muscle from direct contact when the bone surface rough surface that can cause tearing damage to skeletal muscle Each muscle fiber contains Myofibrils rod like structures that run the entire length of the muscle fiber 80 of the whole volume of the muscle fiber is occupied by the myofibrils Inclusions glycosoes contain glycogen Myoglobin a red pigment that binds and stores oxygen Mitochondria for aerobic respiration to produce energy Sarcoplasm cytoplasm of the muscle fiber Sarcoplasmic reticulum SR specialized smooth ER that stores releases calcium into the sarcoplasm the expanded ends of SR are called terminal cisternae Sarcolemma plasma membrane of muscle fiber Transverse tubules T tubules involutions of the sarcolemma into the sarcoplasm Physiology of Skeletal Muscle Contraction Explained at the cellular level structure function of skeletal muscle cells which we call skeletal muscle fibers Each skeletal muscle fiber o The plasma membrane is called a sarcolemma o In folding s invaginations of the sarcolemma are called transverse tubules o The cytoplasm of a skeletal muscle fiber is called sarcoplasm o The sarcoplasm contains several nuclei o Also present is all the cytoplasmic organelles such as mitochondria smooth ER called sarcoplasmic reticular a specialized smooth Er that stores releases ionic calcium o Also present is inclusions called glycosomes store glycogen polysaccharide storage form of glucose in animal cells o Red pigment called myoglobin is present in the sarcoplasm o Myoglobin binds releases oxygen to support aerobic respiration occurring in the mitochondria o Skeletal muscle fiber transverse tubules are located between the 2 terminal cisternae o Terminal cisternae are the extended ends of the sarcoplasmic reticular o Structure composed of terminal cisterm T tubule ksdjf TRIAD o Skeletal mucle fibers have rod like structures called myofibrils 80 of the volume of skeletal muscle fiber is occupied by myofibrils o Myofibris run the entire length of the skeletal muscle fibers o Skeletal muscle fibers run the entire length of a skeletal muscle o Each myofibril is composed of thinner rod like structures called myofilaments Thick filaments Thin filaments Skeletal Muscle fascicle skeletal muscle fibers myofibrils myofilaments Thick Filaments Composed of proteins called myosin Myosin has a rod like tail that ends in 2 myosin globular heads Each thick filament is composed of 300 molecules of myosin The tails form the core of the thick filaments with the globular heads exposed Myosin globular head has 2 binding sites o Binding site for actin o Binding site for ATP In addition the myosin globular heads contain the enzyme ATPase ATPase hydrolyzes ATP into ADP and an inorganic phosphate Thin Filaments Composed of three different proteins o Structural proteins called actin o Regulatory proteins troponin and tropomyosin Actin forms the structural framework of the thin filament Actin has a binding site for the myosin globular head Tropomyosin is a rod like flexible protein that spiral around the actin and block myosin binding sites on actin when the skeletal muscle is relaxed Troponin consists of 2 subuits o Troponin T TnT binds to tropomyosin o Inhibitor troponin TnI binds to actin o Troponin C TnC binds ionic calcium Anchored by disc like proteins called Z discs Z lines Myofibril In a myofibril the thick and thin filaments are arranged in an alternating pattern which explains the banded or striated appearance of skeletal muscle same striations appear in cardiac muscle The distance between 2 successive Z discs in a myofibril is called a sarcomere Sarcomeres are arranged end to end through the entire length of my myofibril The myofibril runs the entire length of the skeletal muscle fibers and the skeletal muscle fibers run the entire length of the skeletal muscle Sarcomeres The smallest contractile unit in a skeletal muscle hence sarcomeres are the structural and functional unit of skeletal muscle Skeletal muscle contraction can be explained as the level of the sarcomeres Structure of a sarcomere o Boundaries each sarcomere is located between two Z discs o Thick filaments called A bands
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