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Muscle Tissue

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Slide 1: Cross section (xs) of a group of striated muscle fibers. Note that fiber nuclei are at the extreme periphery of each cell and that there is heterogeneity in fiber diameter. Nuclei between fibers belong to C.T. cells or capillaries. Also present in the field is a venule lined by endothelium (simple squamous epithelium).  

Slide 2: Almost cross section of skeletal muscle fibers. Plastic-embedded tissue. Less shrinkage than slide l because of the better preservation, toluidine blue-acid fuschin stain. Because the cells are obliquely sectioned, cross-striations are apparent.  

Slide 3: Longitudinal section (l.s.) of portions of 4 skeletal muscle fibers. White spaces between myofibrils are shrinkage artifact. Muscle cell nuclei are large, cigar shaped, and more euchromatic than the nuclei of the C.T. cells which are between the fibers. Also present is a small blood vessel.  

Slide 4: High mag. of skeletal muscle fibers to demonstrate bands. The I and A bands are clear and the Z line is also prominent. H bands are not discernable.  

Slide 5: Higher mag. which shows A and I bands but Z lines are not evident. Bodian stain.  

Slide 6: Developing skeletal muscle obliquely sectioned. The light central areas of the cells at the myotube stage have been filled in by myofibrils. Embryonic pig head. What are the structures at the bottem of the field? (Ans. developing bone spicule and periosteum).  

Slide 7: Cross section of skeletal muscle fibers. PAS-H stained. The external lamina and glycogen granules are stained pink. Some glycogen localization is a diffusion artifact and some can be seen throughout the cytoplasm as discrete pink dots.  

Slide 8: Longitudinal section. Plastic-embedded. Smooth muscle cells are spindle shaped and have long, ovoid, fairly euchromatic nuclei. The cells are closely apposed and it is not always possible to see clearly the individual cell boundaries as they are here.  

Slide 9: Longitudinal section. Plastic embedded. Cells are relaxed (not contracted). C.T. (collagen bundles) is seen at the top & bottom of the field and here, (but not usually) stains more intensly than the muscle cells.  

Slide 10: Longitudinal section. Plastic-embedded tissue. The smooth muscle cells are contracted. Their borders are wavy and their nuclei have assumed the characteristic "corkscrew" configuration. The adjacent connective tissue has large bundles of collagen and a small blood vessel.  

Slide 11: Smooth muscle x.s. Plastic-embedded tissue. Since cells have tapered ends, cross sections are of different diameters. Many sections do not contain the nucleus. Perinuclear light areas contain cell organelles such as mitochondria, but contain fewer myofilaments than the peripheral cytoplasm. Cells are closely adherent.  

Slide 12: Cross section. Plastic-embedded tissue. Shrinkage artifact is responsible for the white spaces between cells but the cross sectional diameter range is clearly illustrated because of this artifact.  

Slide 13: Smooth muscle x.s. and l.s. (intestine)  

Slide 14: Smooth muscle, PAS-H stain, x.s. and l.s. The external lamina of each smooth muscle cell is PAS +. Mesothelium of the intestine is at the top of the field and connective tissue (of the intestinal submucosa) is at the bottom of the field.  

Slide 15: Smooth muscle cells are circumferentially oriented in the wall of an artery. The nuclei are the essential feature to identifying the muscle cells here.  

Slide 16: Bundles of smooth muscle on the right adjacent to irregular C.T. on the left.  

Slide 17: Smooth muscle cells intermixed with C.T. Difficult but examine the smooth muscle cell and fibroblast nuclei (myometrium).  

Slide 18: l.s. Plastic-embedded cardiac muscle. Cross-striations and intercalated discs are clear as is the central location of nuclei and the characteristic lighter staining perinuclear cytoplasm. Some shrinkage artifacts. Red blood cells in capillaries are stained very darkly.  

Slide 19: Cardiac muscle. Although banding is less prominent, the branching nature of the fibers is more evident. (Note: For cardiac muscle a fiber is more than one cell since individual cells are attached end to end by intercalated discs). Paraffin section.  

Slide 20: EM of intercalated disc region. SR = sarcoplasmic reticulum, GJ =gap junction, ML = M line, Z = Z line, L = lipid droplet, M =mitochondrian, BL = external lamina (called basal lamina in older texts although muscle cells do not have a "basal" aspect), FA =fascia adherens, Ca = caveoli.  

Slide 21: Cardiac muscle PAS-H. Glycogen has been pushed to the ends of the cells (diffusion artifact) and thus the intercalated discs are pink bands. Cells are somewhat obliquely sectioned (almost longitudinal at the top of the field and almost cross at the bottem of the field.) The abundant capillary network is demonstrated because the basal lamina of each is PAS+ and thus they appear "outlined" (Look for good cross or oblique sections of capillaries near the bottem of the field).  

Slide 22: Cardiac muscle x.s. and l.s. Plastic-embedded tissue. To both sides of the field the fibers are in x.s. Note the irregular shapes (due to branching) and central nuclei. The myofibrils are clearly delimited by lighter cytoplasm and shrinkage. In the center of the field the longitudinally sectioned fibers show clear cross-striations and intercalated discs. Capillaries (often containing pink erythrocytes) are abundant.  

Slide 23: Cardiac muscle x.s. Heidenhain's iron hematoxylin. The very irregular shape is evident as is the extensive shrinkage. What does the central light areas in some of the cells represent? (Ans. Perinuclear areas that have organelles like mitochondria but lack myofibrils).  

Slide 24: Purkinje cells l.s. are located just beneath the endocardium. Note their myofibrils and how much larger and lighter stained they are compared with regular cardiac muscle cells. Can you find the intercalated disc in one of the Purkinje fibers (difficult)?  

Slide 25: Purkinje fibers x.s.  

Slide 26: Dense C.T. tendon (lower part of the field) and striated muscle obliquely sectioned. This slide is difficult because there is only a faint indication of cross striation in the muscle cells and muscle often stains more intensly than adjacent connective tissue but not so in this image.  

Slide 27: Smooth and striated voluntary muscle, both in x.s. This is from the middle third of the esophagus where the external muscle layers change type. Why is the name "striated voluntary" the best name in this organ. (Ans. The muscle fibers are not attached to bone, i.e., not "skeletal").  

Slide 28: Both muscle types in cross and longitudinal section, from the esophagus. Here, but not always, the striated fibers stain more intensly than the smooth ones do. If you are reviewing this at the end of the course also find and identify the 5 clearly identifiable blood vessels.  

Slide 29: Smooth muscle bundles and C.T. Also note the three large blood vessels.  

Slide 30: Smooth muscle cells in a CT infiltrated with lymphocytes and polymorphs.  

Slide 31: A muscle spindle. It contains modified muscle cells that function as a receptor for stretch.  

Slide 32: Skeletal muscle tissue has with it named C.T. layers. Each muscle cells is surrounded by a small amount of C.T. containing capillaries - the endomysium. Skeletal muscle cells are usually found as bundles (fasicles) and each bundle is enveloped by a C.T.layer called the perimysium. Finally, an entire muscle is covered by the epimysium. This low power micrograph shows perimysium between bundles (cross sectioned) of skeletal muscle fibers and some endomysium within some of the fasicles. White spaces are shrinkage artifacts. Plastic embedded-tissue.


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