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Chapter 9 The Muscular System Skeletal Muscle Tissue and Muscle Organization Lecture Presentation by Steven Bassett Southeast Community College © 2015 Pearson Education, Inc. Introduction • Humans rely on muscles for: • Many of our physiological processes • Virtually all our dynamic interactions with the environment • Skeletal muscles consist of: • Elongated cells called fibers (muscle fibers) • These fibers contract along their longitudinal axis © 2015 Pearson Education, Inc. Introduction • There are three types of muscle tissue • Skeletal muscle • Pulls on skeletal bones • Voluntary contraction • Cardiac muscle • Pushes blood through arteries and veins • Rhythmic contractions • Smooth muscle • Pushes fluids and solids along the digestive tract, for example • Involuntary contraction © 2015 Pearson Education, Inc. Introduction • Muscle tissues share four basic properties • Excitability • The ability to respond to stimuli • Contractility • The ability to shorten and exert a pull or tension • Extensibility • The ability to continue to contract over a range of resting lengths • Elasticity • The ability to rebound toward its original length © 2015 Pearson Education, Inc. Functions of Skeletal Muscles • Skeletal muscles perform the following functions: • Produce skeletal movement • Pull on tendons to move the bones • Maintain posture and body position • Stabilize the joints to aid in posture • Support soft tissue • Support the weight of the visceral organs © 2015 Pearson Education, Inc. Functions of Skeletal Muscles • Skeletal muscles perform the following functions (continued): • Regulate entering and exiting of material • Voluntary control over swallowing, defecation, and urination • Maintain body temperature • Some of the energy used for contraction is converted to heat © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Gross anatomy is the study of: • Overall organization of muscles • Connective tissue associated with muscles • Nerves associated with muscles • Blood vessels associated with muscles • Microscopic anatomy is the study of: • Myofibrils • Myofilaments • Sarcomeres © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Gross Anatomy • Connective tissue of muscle • Epimysium: dense tissue that surrounds the entire muscle • Perimysium: dense tissue that divides the muscle into parallel compartments of fascicles • Endomysium: dense tissue that surrounds individual muscle fibers © 2015 Pearson Education, Inc. Figure 9.1 Structural Organization of Skeletal Muscle Epimysium Nerve Muscle fascicle Muscle fibers Endomysium Blood vessels Perimysium SKELETAL MUSCLE (organ) Perimysium Muscle fiber Endomysium Epimysium Blood vessels and nerves MUSCLE FASCICLE (bundle of cells) Capillary Mitochondria Endomysium Endomysium Sarcolemma Myosatellite Tendon Myofibril cell Perimysium Axon Sarcoplasm Nucleus MUSCLE FIBER (cell) © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Connective Tissue of Muscle • Tendons and aponeuroses • Epimysium, perimysium, and endomysium converge to form tendons • Tendons connect a muscle to a bone • Aponeuroses connect a muscle to a muscle © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Gross Anatomy • Nerves and blood vessels • Nerves innervate the muscle by penetrating the epimysium • There is a chemical communication between a nerve and a muscle • The chemical is released into the neuromuscular synapse (neuromuscular junction) © 2015 Pearson Education, Inc. Figure 9.2 Skeletal Muscle Innervation Neuromuscular synapse Skeletal muscle fiber Axon Nerve LM x 230 SEM x 400 a A neuromuscular synapse as seen b Colorized SEM of a neuromuscular on a muscle fiber of this fascicle synapse © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Gross Anatomy • Nerves and blood vessels (continued) • Blood vessels often parallel the nerves that innervate the muscle • They then branch to form coiled networks to accommodate flexion and extension of the muscle © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Microanatomy of Skeletal Muscle Fibers • Sarcolemma • Membrane that surrounds the muscle cell • Sarcoplasm • The cytosol of the muscle cell • Muscle fiber (same thing as a muscle cell) • Can be 30–40 cm in length • Multinucleate (each muscle cell has hundreds of nuclei) • Nuclei are located just deep to the sarcolemma © 2015 Pearson Education, Inc. Figure 9.3ab The Formation and Structure of a Skeletal Muscle Fiber Muscle fibers develop through the fusion of mesodermal cells Myoblasts called myoblasts. a Development of a skeletal muscle fiber. Myosatellite cell Nuclei Immature muscle fiber b External appearance and histological view. © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Myofibrils and Myofilaments • The sarcoplasm contains myofibrils • Myofibrils are responsible for the contraction of muscles • Myofibrils are attached to the sarcolemma at each end of the muscle cell • Surrounding each myofibril is the sarcoplasmic reticulum © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Myofibrils and Myofilaments • Myofibrils are made of myofilaments • Actin • Thin protein filaments • Myosin • Thick protein filaments © 2015 Pearson Education, Inc. Figure 9.3b-d The Formation and Structure of a Skeletal Muscle Fiber b External appearance and histological view. Myofibril Sarcolemma Nuclei c The external organization Sarcoplasm MUSCLE FIBER of a muscle fiber. Mitochondria Terminal cisterna Sarcolemma Sarcolemma Sarcoplasm Myofibril Myofibrils Thin filament Thick filament Triad Sarcoplasmic T tubules d Internal organization of a muscle fiber. reticulum Note the relationships among myofibrils, sarcoplasmic reticulum, mitochondria, triads, and thick and thin filaments. © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Sarcomere Organization • Myosin (thick filament) • Actin (thin filament) • Both are arranged in repeating units called sarcomeres • All the myofilaments are arranged parallel to the long axis of the cell © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Sarcomere Organization • Sarcomere • Main functioning unit of muscle fibers • Approximately 10,000 per myofibril • Consists of overlapping actin and myosin • This overlapping creates the striations that give the skeletal muscle its identifiable characteristic © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Sarcomere Organization • Each sarcomere consists of: • Z line (Z disc) • I band • A band (overlapping A bands create striations) • H band • M line © 2015 Pearson Education, Inc. Figure 9.4b Sarcomere Structure I band A band H band Z line Titin Zone of overlap M line Thin Thick filament filament Sarcomere I band A band H band Z line TEM x 64,000 Z line Zone of overlap M line b A corresponding view of a sarcomere in a myofibril in Sarcomere the gastrocnemius muscle of the calf and a diagram showing the various components of this sarcomere © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Sarcomere Organization • Skeletal muscles consist of muscle fascicles • Muscle fascicles consist of muscle fibers • Muscle fibers consist of myofibrils • Myofibrils consist of sarcomeres • Sarcomeres consist of myofilaments • Myofilaments are made of actin and myosin © 2015 Pearson Education, Inc. Figure 9.5 Levels of Functional Organization in a Skeletal Muscle Fiber SKELETAL MUSCLE Surrounded by: Epimysium Contains: Muscle fascicles MUSCLE FASCICLE Surrounded by: Perimysium Contains: Muscle fibers MUSCLE FIBER Surrounded by: Endomysium Contains: Myofibrils MYOFIBRIL Surrounded by: Sarcoplasmic reticulum Consists of: Sarcomeres (Z line to Z line) SARCOMERE I band A band Contains: Thick filaments Thin filaments Z line M line Titin Z line H band © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Thin Filaments (Actin) • Consists of: • Twisted filaments of : • F actin strands • G actin globular molecules • G actin molecules consist of an active site (binding site) • Tropomyosin: A protein that covers the binding sites when the muscle is relaxed • Troponin: Holds tropomyosin in position © 2015 Pearson Education, Inc. Figure 9.6ab Thin and Thick Filaments Actinin Z line Titin a The attachment Sarcomere of thin filaments to the Z line H band Troponin Active site Nebulin Tropomyosin G actin molecules F actin strand Myofibril b The detailed structure of a thin filament showing the organization of G actin, troponin, and tropomyosin M line Z line © 2015 Pearson Education, Inc. Anatomy of Skeletal Muscles • Thick Filaments (Myosin) • Myosin filaments consist of an elongated tail and a globular head (cross-bridges) • Myosin is a stationary molecule. It is held in place by: • Protein forming the M line • A core of titin connecting to the Z lines • Myosin heads project toward the actin filaments © 2015 Pearson Education, Inc. Figure 9.6cd Thin and Thick Filaments Sarcomere H band Myofibril M line Z line Titin c The structure of thick filaments Myosin M line head Myosin tail Hinge d A single myosin molecule detailing the structure and movement of the myosin head after cross-bridge binding occurs © 2015 Pearson Education, Inc. Muscle Contraction • A contracting muscle shortens in length • Contraction is caused by interactions between thick and thin filaments within the sarcomere • Contraction is triggered by the presence of calcium ions • Muscle contraction requires the presence of ATP • When a muscle contracts, actin filaments slide toward each other • This sliding action is called the sliding filament theory © 2015 Pearson Education, Inc. Muscle
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