7 The Muscular System

Five Skeletal Muscle Functions (7-1) Produce movement of the skeleton By pulling on tendons that then move bones Maintain posture and body position Support soft tissues With the muscles of the abdominal wall and the pelvic floor Guard entrances and exits In the form of sphincters Maintain body temperature When contraction occurs, energy is used and converted to heat © 2013 Pearson Education, Inc.

Organization of Skeletal Muscle Tissue (7-2) Skeletal muscles Are organs that contain: Connective tissue Blood vessels Nerves Skeletal muscle tissue Single skeletal muscle cells Also called skeletal muscle fibers © 2013 Pearson Education, Inc.

Three Layers of Connective Tissue (7-2) Epimysium Covers the entire muscle Perimysium Divides the muscle into bundles called fascicles Blood vessels and nerves are contained in the perimysium Endomysium Covers each muscle fiber and ties fibers together Contains capillaries and nerve tissue © 2013 Pearson Education, Inc.

Tendons (7-2) Where the ends of all three layers of connective tissue come together And attach the muscle to a bone Aponeurosis A broad sheet of collagen fibers that connects muscles to each other Similar to tendons, but do not connect to a bone © 2013 Pearson Education, Inc.

Blood Vessels and Nerves (7-2) Extensive network of blood vessels in skeletal muscle Provides high amounts of nutrients and oxygen To skeletal muscles which have high metabolic needs © 2013 Pearson Education, Inc.

Control of Skeletal Muscle (7-2) Mostly under voluntary control Must be stimulated by the central nervous system Axons Push through the epimysium Branch through the perimysium And enter the endomysium To control individual muscle fibers © 2013 Pearson Education, Inc.

Figure 7-1 The Organization of Skeletal Muscles. Skeletal Muscle (organ) Epimysium Perimysium Endomysium Nerve Muscle fascicle Muscle fibers Blood vessels Muscle Fascicle (bundle of fibers) Perimysium Epimysium Muscle fiber Blood vessels and nerves Endomysium Tendon Muscle Fiber (cell) Endomysium Capillary Myofibril Endomysium Sarcoplasm Perimysium Mitochondrion Stem cell Sarcolemma Nucleus Axon of neuron © 2013 Pearson Education, Inc.

Features of Skeletal Muscle Fibers (7-3) Are specifically organized to produce contraction and have specific names for general cell structures Can be very long and are multinucleated Composed of highly organized structures, giving them a striped or striated appearance © 2013 Pearson Education, Inc.

The Sarcolemma and Transverse Tubules (7-3) Specific name of muscle fiber plasma membrane Has openings across the surface that lead into a network of transverse tubules, or T tubules T tubules allow for electrical stimuli to reach deep into each fiber The sarcoplasm Specific name for muscle fiber cytoplasm © 2013 Pearson Education, Inc.

Myofibrils in Muscle Fiber (7-3) Hundreds to thousands in each fiber Are encircled by T tubules and are as long as the entire muscle fiber Are bundles of thick and thin myofilaments Actin molecules are found in thin filaments Myosin molecules are found in thick filaments Are the contractile proteins that shorten and are responsible for contraction © 2013 Pearson Education, Inc.

The Sarcoplasmic Reticulum (7-3) Or SR Specialized smooth endoplasmic reticulum Expanded end that is next to the T tubule is the terminal cisternae Contain high concentrations of calcium ions Triad A combination of two terminal cisternae and one T tubule © 2013 Pearson Education, Inc.

Sarcomeres (7-3) Smallest functional unit of skeletal muscle fiber Formed by repeating myofilament arrangements Each myofibril has about 10,000 sarcomeres Thick and thin filament arrangements are what produce the striated appearance of the fiber Overlapping filaments define lines and bands © 2013 Pearson Education, Inc.

Sarcomere Lines (7-3) Z lines M line Thin filaments at both ends of the sarcomere Another protein connects the Z lines to the thick filament to maintain alignment M line Made of connections between the thick filaments © 2013 Pearson Education, Inc.

Sarcomere Bands (7-3) A band I band Contains the thick filaments Contains the thin filaments, including the Z line © 2013 Pearson Education, Inc.

Figure 7-2 The Organization of a Skeletal Muscle Fiber. Terminal cisterna Sarcoplasmic reticulum T tubules Triad Sarcolemma Mitochondria Thick filament Thin filament Myofilaments MYOFIBRIL The structure of a skeletal muscle fiber. SARCOMERE Z line Zone of overlap M line Myofibril I band H band Zone of overlap A band The organization of a sarcomere, part of a single myofibril. Z line M line Z line A stretched out sarcomere. Z line M line Z line and thin filaments Myosin head Thick filaments Active site Actin molecules Myosin tail ACTIN STRAND MYOSIN MOLECULE Hinge Troponin Tropomyosin The structure of a thick filament. Thin filament © 2013 Pearson Education, Inc. The structure of a thin filament.

Figure 7-2a The Organization of a Skeletal Muscle Fiber. Terminal cisterna Sarcoplasmic reticulum T tubules Triad Sarcolemma Mitochondria Thick filament Myofilaments Thin filament MYOFIBRIL The structure of a skeletal muscle fiber. © 2013 Pearson Education, Inc.

Figure 7-2b The Organization of a Skeletal Muscle Fiber. SARCOMERE Zone of overlap Z line M line Myofibril I band H band Zone of overlap A band The organization of a sarcomere, part of a single myofibril. © 2013 Pearson Education, Inc.

Figure 7-2c The Organization of a Skeletal Muscle Fiber. Z line M line Z line A stretched out sarcomere. M line Z line Z line and thin filaments Thick filaments © 2013 Pearson Education, Inc.

Figure 7-2d The Organization of a Skeletal Muscle Fiber. Active site Actin molecules ACTIN STRAND Troponin Tropomyosin Thin filament The structure of a thin filament. © 2013 Pearson Education, Inc.

Figure 7-2e The Organization of a Skeletal Muscle Fiber. Myosin head Myosin tail Hinge MYOSIN MOLECULE The structure of a thick filament. © 2013 Pearson Education, Inc.

Thin and Thick Filaments (7-3) Actin A thin twisted protein, with specific active sites for myosin to bind to At rest, active sites are covered by strands of tropomyosin, held in position by troponin Myosin A thick filament with tail and globular head that attaches to actin active sites during contraction © 2013 Pearson Education, Inc.