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The Muscular System

The Muscular System. The Muscular System. Muscles are responsible for all types of body movement Three basic muscle types found in the body Skeletal muscle Cardiac muscle Smooth muscle. Skeletal Muscle. Location: Attaches to bones or skin (face muscles) Cell Shape and Appearance:

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The Muscular System

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  1. The Muscular System

  2. The Muscular System • Muscles are responsible for all types of body movement • Three basic muscle types found in the body • Skeletal muscle • Cardiac muscle • Smooth muscle

  3. Skeletal Muscle • Location: • Attaches to bones or skin (face muscles) • Cell Shape and Appearance: • Multinucleated (many nuclei per cell) • Striations (stripes) • Single long cylindrical cells • Regulation of Contraction: • Voluntary • Nervous System control • Contraction Speed: • Slow to fast • Rhythmic contraction: • No

  4. Cardiac Muscle • Location: • Walls of heart • Cell Shape and Appearance: • Branching chains of cells • Striated • Uninucleate (1 nucleus per cell) • Regulation of Contraction: • Involuntary; has pacemaker • Nervous System control • Hormonal control (ex: ANP) • Contraction Speed: • Slow • Rhythmic contraction: • Yes (“lub dub”)

  5. Smooth Muscle • Location: • Wall of visceral organs (not the heart) • Ex: stomach, intestines, esophagus, rectum • Cell Shape and Appearance: • Single cells • No Striations • Fusiform (wide in middle; tapered at ends) • Uninucleate (1 nucleus per cell) • Regulation of Contraction: • Involuntary • Nervous System control • Hormonal control • Contraction Speed: • Slow • Rhythmic contraction: • Yes (in some)

  6. Characteristics of Muscles • Muscle cells are elongated (muscle cell = muscle fiber) • Contraction of muscles is due to the movement (sliding) of microfilaments • Micro = small • All muscles share some terminology • Prefix my(o)-refers to muscle • ex. myosin • Prefix mys-refers to muscle • ex. epimysium • Prefix sarc(o)-refers to flesh • ex. sarcomere • sarcophagus • phag(o) = eat

  7. Connective Tissue Wrappings of Skeletal Muscle • Endomysium • around single muscle fiber • Perimysium around a fascicle (bundle) of fibers • Epimysium covers the entire skeletal muscle Figure 6.1

  8. Skeletal Muscle Attachments • Epimysium blends into a connective tissue attachment • Tendon – cord-like structure • Aponeuroses – sheet-like structure • Sites of muscle attachment • Bones • Cartilages • Connective tissue coverings

  9. Function of Muscles • Produce movement • Maintain posture • Stabilize joints • Generate heat

  10. Microscopic Anatomy of Skeletal Muscle • Cells are multinucleate • Nuclei are just beneath the sarcolemma Figure 6.3a

  11. Microscopic Anatomy of Skeletal Muscle • Sarcolemma • specialized plasma membrane • Sarcoplasmic reticulum • specialized smooth endoplasmic reticulum Figure 6.3a

  12. Microscopic Anatomy of Skeletal Muscle • Myofibril • Bundles of myofilaments • Myofibrils are aligned to give distinct bands • I band = light band • A band = dark band Figure 6.3b

  13. Microscopic Anatomy of Skeletal Muscle • Sarcomere • Contractile unit of a muscle fiber Figure 6.3b

  14. Microscopic Anatomy of Skeletal Muscle • Organization of the sarcomere • Thick filaments = myosin filaments • Composed of the protein myosin • Has ATPase enzymes Figure 6.3c

  15. Microscopic Anatomy of Skeletal Muscle • Organization of the sarcomere • Thin filaments = actin filaments • Composed of the protein actin Figure 6.3c

  16. Microscopic Anatomy of Skeletal Muscle • Myosin filaments have heads (extensions or cross bridges) • Myosin and Actinoverlap Figure 6.3d

  17. Microscopic Anatomy of Skeletal Muscle • At rest, there is a bare zone that lacks actinfilaments • Sarcoplasmic Reticulum (SR)stores calcium Figure 6.3d

  18. Properties of Skeletal Muscle Activity • Irritability • ability to receive and respond to a stimulus • Contractility • ability to shorten when an adequate stimulus is received

  19. Nerve Stimulus to Muscles • Skeletal muscles must be stimulated by a nerve to contract • Motor unit • One neuron • Muscle cells stimulated by that neuron Figure 6.4a

  20. Nerve Stimulus to Muscles • Neuromuscular junctions = association site of nerve and muscle Figure 6.5b

  21. Nerve Stimulus to Muscles • Synaptic cleft – gap between nerve and muscle • Nerve and muscle do not make contact • Area between nerve and muscle is filled with interstitial fluid Figure 6.5b

  22. Transmission of Nerve Impulse to Muscle • Neurotransmitter = Chemical released by nerve upon arrival of nerve impulse Skeletal muscle neurotransmitter = Acetylcholine

  23. Transmission of Nerve Impulse to Muscle • 1. Neurotransmitter attaches to receptors on the Sarcolemma • 2. Sarcolemma becomes permeable to sodium (Na+) • 3. Sodium rushing into the cell generates an Action Potential • 4. Once started, muscle contraction cannot be stopped

  24. The Sliding Filament Theory of Muscle Contraction • Activation by nerve causes myosin heads (cross-bridges) to attach to binding sites on the thin filament • Myosin heads then bind to the next site of the thin filament Figure 6.7

  25. The Sliding Filament Theory of Muscle Contraction • This continued action causes a sliding of the myosin along the actin • The result is that the muscle is shortened (contracted) Figure 6.7

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