The Histology of Muscle Tissue

MUSCLE TISSUE Objectives • Histologically identify and functionally characterize each of the 3 types of muscle tissues. • Describe the organization of the sarcomere as seen in light and electron microscopy. • Identify the endomysium, perimysium, and epimysium CT sleeves in muscle. • Relate the functional differences of the three muscle cell types. P. MUSCLE FUNCTION: • GENERATION OF CONTRACTILE FORCE DISTINGUISHING FEATURES: • HIGH CONCENTRATION OF CONTRACTILE PROTEINS ACTIN AND MYOSIN ARRANGED EITHER DIFFUSELY IN THE CYTOPLASM (SMOOTH MUSCLE) OR IN REGULAR REPEATING UNITS CALLED SARCOMERES (STRIATED MUSCLES, e.g., CARDIAC AND SKELETAL MUSCLES) MUSCLE • DISTRIBUTION: SKELETAL – STRIATED MUSCLES MOSTLY ASSOCIATED WITH THE SKELETON MUSCLE • DISTRIBUTION: SKELETAL – STRIATED MUSCLES MOSTLY ASSOCIATED WITH THE SKELETON CARDIAC – STRIATED MUSCLES ASSOCIATEWD WITH THE HEART MUSCLE • DISTRIBUTION: SKELETAL – STRIATED MUSCLES MOSTLY ASSOCIATED WITH THE SKELETON CARDIAC – STRIATED MUSCLES ASSOCIATEWD WITH THE HEART SMOOTH – FUSIFORM CELLS ASSOCIATED WITH THE VISCERA, RESPIRATORY TRACT, BLOOD VESSELS, UTERUS, ETC. MUSCLE HISTOLOGICAL INDENTIFICATION: SKELETAL MUSCLE – VERY LONG CYLINDRICAL STRIATED MUSCLE CELLS WITH MULTIPLE PERIPHERAL NUCLEI MUSCLE HISTOLOGICAL INDENTIFICATION: SKELETAL MUSCLE – VERY LONG CYLINDRICAL STRIATED MUSCLE CELLS WITH MULTIPLE PERIPHERAL NUCLEI CARDIAC MUSCLE – SHORT BRANCHING STRIATED MUSCLE CELLS WITH CENTRALLY LOCATED NUCLEI MUSCLE HISTOLOGICAL INDENTIFICATION: SKELETAL MUSCLE – VERY LONG CYLINDRICAL STRIATED MUSCLE CELLS WITH MULTIPLE PERIPHERAL NUCLEI CARDIAC MUSCLE – SHORT BRANCHING STRIATED MUSCLE CELLS WITH CENTRALLY LOCATED NUCLEI SMOOTH MUSCLE – CLOSELY PACKED SPINDLE-SHAPED CELLS WITH A SINGLE CENTRALLY PLACED NUCLEUS AND CYTOPLASM THAT APPEARS HOMOGENEOUS BY LIGHT MICROSCOPY MUSCLE HISTOLOGICAL INDENTIFICATION: SKELETAL MUSCLE – VERY LONG CYLINDRICAL STRIATED MUSCLE CELLS WITH MULTIPLE PERIPHERAL NUCLEI CARDIAC MUSCLE – SHORT BRANCHING STRIATED MUSCLE CELLS WITH CENTRALLY LOCATED NUCLEI SMOOTH MUSCLE – CLOSELY PACKED SPINDLE-SHAPED CELLS WITH A SINGLE CENTRALLY PLACED NUCLEUS AND CYTOPLASM THAT APPEARS HOMOGENEOUS BY LIGHT MICROSCOPY Myoepithelial cells Muscle Tissue • Muscle cells specialized for contraction with apparatus of actin and myosin proteins. • 3 types: Skeletal Muscle Smooth Muscle Cardiac Muscle Longitudinal sections - Peripheral nuclei - Striations - No branching Longitudinal sections - Central nuclei (often fusiform) - Meshwork appearance of cells - No striations Longitudinal sections - Central nuclei (often elongated) - Striations - Branching cells - Intercalated discs Cross section - Peripheral nuclei - Massive cytoplasm Cross section - Central nuclei - Low cytoplasm to nucleus ratio Cross section - Central nuclei - High cytoplasm to nucleus ratio Slide 11: Skeletal muscle (longitudinal and cross sections) Muscle fibers with peripheral nuclei Capillary Cross sections of muscle fibers with peripheral nuclei Slide 052: Skeletal muscle (longitudinal and cross sections) Muscle fibers with peripheral nuclei Capillary Cross striations (A and I bands) Slide 052: Skeletal muscle (longitudinal and cross sections) Muscle fibers with peripheral nuclei Capillary Cross striations (A and I bands) The increase in muscle mass during exercise results from stimulating formation of new myofibrils and enlargement in the diameter of individual muscle fibers (hypertrophy = increase in size). CONNECTIVE TISSUE LAYERS OF SKELETAL MUSCLE • EPIMYSIUM - COARSE CT EPIMYSIUM CONNECTIVE TISSUE LAYERS OF SKELETAL MUSCLE • • EPIMYSIUM - COARSE CT PERIMYSIUM - LESS COARSE CT PERIMYSIUM EPIMYSIUM CONNECTIVE TISSUE LAYERS OF SKELETAL MUSCLE • • • EPIMYSIUM - COARSE CT PERIMYSIUM - LESS COARSE CT ENDOMYSIUM - DELICATE CT PERIMYSIUM EPIMYSIUM ENDOMYSIUM CONNECTIVE TISSUE LAYERS OF SKELETAL MUSCLE EPIMYSIUM, PERIMYSIUM, and ENDOMYSIUM Slide 11: Skeletal muscle (longitudinal and cross sections) Epimysium Perimysium Endomysium Slide 052 Skeletal muscle (longitudinal and cross sections) Perimysium Endomysium with its capillaries CONNECTIVE TISSUE connect LAYERS OF SKELETAL MUSCLE • ENDOMYSIUM CONNECTIVE TISSUE LAYERS OF SKELETAL MUSCLE PERIMYSIUM CONNECTIVE TISSUE LAYERS OF SKELETAL MUSCLE PERIMYSIUM 052 • ENDOMYSIUM Striations in skeletal muscle 052 Skeletal muscles have striations, peripheral nuclei, same thickness throughout their length and do not branch. Specialized for powerful and rapid contraction. Voluntary. Found attached to the skeleton. Slide 12: Skeletal muscle (phosphotungstic acid/hematoxylin) Sarcomere: Z line to Z line Z line is In the I band I band A band STRIATED MUSCLE CARDIAC SKELETAL “A” BAND = dark band ANISOTROPIC = DOES ALTER POLARIZED LIGHT (BIREFRINGENT) A STRIATED MUSCLE CARDIAC SKELETAL “A” BAND = dark band ANISOTROPIC = DOES ALTER POLARIZED LIGHT (BIREFRINGENT) “I” BAND = light band ISOTROPIC = DOES NOT ALTER POLARIZED LIGHT A I STRIATED MUSCLE (SKELETAL) A SARCOMERES ARE ORGANIZED FOR RAPID AND HIGHLY CONTROLLED CONTRACTION I SKELETAL MUSCLE cell structure SKELETAL MUSCLE SKELETAL MUSCLE INTERMEDIATE FILAMENTS – FUNCTION in muscle cells • MYOFIBRIL ORGANIZATION – MUSCLE cells INTERMEDIATE FILAMENTS – FUNCTION in muscle cells • MYOFIBRIL ORGANIZATION – MUSCLE cells Cell = CONTRACTION OF THE SARCOMERE THIN FILAMENT ACTIN (F-ACTIN) TROPOMYOSIN TROPONIN T - ATTACHES TO TROPOMYOSIN C - BINDS CALCIUM IONS I - INHIBITS ACTIN-MYOSIN INTERACTION The stoppage of the neural impulse and depletion of free calcium ends the actinmyosin crossbridge cycle in skeletal muscle. ATP is required in this process. CALCIUM REGULATION TRANVERSE (T) TUBULE (INVAGINATION OF SARCOLEMMA) TRANSMIT DEPOLARIZATION OF MEMBRANE DEEP INTO THE CELL SARCOPLASMIC RETICULUM (SER OF CELL) RELEASE CA++ FOR CONTRACTION - THEN RECOVER CA++ AFTER CONTRACTION TRIAD = (T TUBULE AND TWO ENDS OF SER) EM 29 : Skeletal muscle 052 EM 46 and 47 : Skeletal muscle STIMULATION OF MUSCLE CELLS Slide 13: Skeletal Muscle – muscle spindles (trichrome) Intrafusal muscle fibers Muscle spindle: (stretch receptors) Nerve fibers INNERVATION OF MUSCLE MUSCLE SPINDLE MUSCLE SPINDLE Intracapsular fibers SMOOTH MUSCLE SMOOTH MUSCLE Has a PAS + basement membrane Slide 35: Urinary bladder Muscularis externa (smooth muscle) Smooth muscle fibers with central nuclei Smooth muscles are fusiform with tapered ends, single, central nuclei, and no striations. Involuntary. Found in sphincters and sheets of internal visceral organs and glands. Slide 63: Appendix Submucosa Muscularis externa Smooth muscle layer arrangement in tubular organs The layering of smooth muscle in the gut is responsible for contractions which mix and propel luminal contents forward. EM 49: Smooth muscle Actin Myosin SMOOTH MUSCLE MUSCULAR ARTERY Skeletal Muscle Smooth muscle CARDIAC MUSCLE IS STRIATED MUSCLE •INTERCALATED DISC • FASCIA ADHERENS • MACULAE ADHERENS • GAP JUNCTIONS - LATERAL PORTION CARDIAC MUSCLE INTERCALATED DISC The intercalated discs enables coordinated function via gap junctions to facilitate energy and calcium conductance between neighboring myocytes. pulmonary artery in the lungs of a rat INTERCALATED DISC pulmonary artery in the lungs of a rat nucleus mitochondria INTERCALATED DISC Slide 14: Heart & EM 48: Heart Intercalated discs CARDIAC MUSCLE – Diad located at Z line Diad = (T tubule + one end of SER) REGENERATION OF MUSCLE Which type of muscle cells can be replaced in adults? •SMOOTH – LOTS •SKELETAL – SOME •CARDIAC – NONE Clinical Correlation Ischemic heart disease is one of the most significant health problems in the US. Coronary artery thrombosis usually precedes and precipitates a myocardial infarct, resulting in the death of cardiac myocytes. Eventually scar tissue is formed and there is some loss of contractility. Image taken from adultstemcellawareness.wordpress.com Lacking muscle mesenchymal satellite cells, adult mammalian cardiac muscle has little potential to regenerate after injury. Damage is replaced by proliferating fibroblasts and connective tissue growth, forming myocardial scars. Summary of MUSCLE shapes and excitations of types