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Muscle tissue Specialized for contractility
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Classification of muscle tissue
Functional classification based on neural control Voluntary Involuntary Structural classification based on the presence of striations Striated Non-striated Striated Non-striated
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Types of muscle Skeletal muscle Cardiac muscle Smooth muscle
Voluntary & Striated Hypertrophy only Cardiac muscle Involuntary & Striated Smooth muscle Involuntary & Non-striated Hypertrophy and hyperplasia
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Skeletal muscle fibers (cells)
Largest fiber type Cylindrical Unbranched Heavy cross striations Multiple, peripheral nuclei Skeletal muscle fibers (cells) Longitudinal sections Cross sections
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Skeletal muscle fibers
Fibers contain numerous longitudinally arrayed myofibrils composed of myofilaments (actin and myosin) Myofibrils Cross sections
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Skeletal muscle fibers
Longitudinal sections Cross sections SER
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Banding pattern Sarcomere Z-line to Z-line Contractile unit
Muscle fibers Banding pattern A band (dark) - Myosin and actin I band (light) - Actin only Z line - Alpha actinin H band – Myosin only Sarcomere Z-line to Z-line Contractile unit BV A I Z Myofibrils I Z A Myofilaments H Sarcomere
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Organization of myofilaments
Actin Myosin 70,000x
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Changes in bands during contraction
Sarcomeres shorten Z-line interval narrows
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Changes in bands during contraction
Sarcomeres shorten Z-line interval narrows H and I bands narrow
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Changes in bands during contraction
Sarcomeres shorten Z-line interval narrows H and I bands narrow A band is unchanged
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Regulation of skeletal muscle contraction
T-tubule Triads: T-tubule (sarcolemma) Terminal cisterns of SER (sarcoplasmic reticulum) Ca+
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Connective tissues of skeletal muscle
1. Segregate the muscle fibers into fascicles 2. Transmit the force of contraction to the point of muscle insertion Endomysium - reticular fibers plus the external (basal) lamina produced by the muscle fiber Perimysium - dense connective tissue surrounding a group of fibers and dividing the muscle into fascicles Epimysium - dense connective tissue surrounding the entire muscle, blends with the deep fascia and tendons
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Connective tissues of skeletal muscle
RF Endomysium Fiber Epimysium Perimysium
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Neuromuscular junction
(Motor end plate)
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Cardiac muscle Most restricted distribution (myocardium)
Cardiac muscle fibers Intermediate size Cylindrical fibers Fibers branch, forming interwoven bundles Single, centrally located nucleus Moderate striations Myofibrils and myofilaments similar to skeletal muscle Highly vascular Large numbers of mitochondria Glycogen Longitudinal section, 400x Cross section, 1000x
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Cardiac muscle fibers M Nucleus M Myofibrils M
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Cardiac muscle - Intercalated discs
Unique to cardiac muscle fibers Composed of: Adherent junctions Gap junctions (ionic coupling)
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Regulation of contraction
T tubules No triads, reduced sarcoplasmic reticulum Contraction regulated by calcium Contraction spreads to adjacent cells due to current flow through gap junctions
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Smooth muscle Organized into sheets forming much of the wall of
hollow organs and blood vessels Smooth muscle fibers Smallest fiber type Spindle shaped Single, centrally placed nucleus Non-striated, no myofibrils External lamina Gap junctions Hypertrophy & hyperplasia
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Smooth muscle Longitudinal layers Circular layer Longitudinal section
Cross section Circular layer Longitudinal layers
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Myofilament organization
Actin and myosin present No myofibrils Myofilaments arranged as reticulum Dense bodies in cytoplasm Relaxed Dense body Contracted “Inchworm nuclei”
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Coordination of contraction
Small fibers, T-tubules are absent (caveolae) Sarcoplasmic reticulum is rudimentary Ionic coupling via gap junctions Contraction initiated by calcium release Contraction occurs by sliding filament mechanism unique to smooth muscle Caveolae Desmo- some Gap junction Dense bodies Nucleus Smooth muscle fiber (EM)
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Skeletal Cardiac Smooth
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