OBJECTIVES: At the end of this laboratory you should be able to:
1. Recognize and describe the anatomical features of muscle types at the tissue, cellular, and subcellular levels.
2. Identify and distinguish between the muscle types in cross or longitudinal sections in the light microscope or in electron micrographs.
3. Identify the subcellular components of myofibers and understand how they contribute to contractility in each muscle type.
4. Identify and understand the functional significance of intercalated disks in cardiac muscle.
SLIDES FOR THIS LABORATORY: 33, 58, 55, 63, 77, 81, and Supplemental Slides 105, 106, and 107.
Before beginning this laboratory, be certain that you understand the use of the terms: filament, fibril, and fiber as they relate to muscle histological structure.
SKELETAL MUSCLE
Slide 77 Skeletal muscle, cross and longitudinally sectioned.
Study the striations of skeletal muscle. Locate a site where muscle fibers are clearly longitudinally sectioned . Compare your observations here with electron micrographs of skeletal muscle in your text and Hippocrates, particularly the structure of a longitudinally sectioned sarcomere. Note the location and content of A bands , I bands , and Z lines in this slide. H bands and M lines are better observed in the electron micrographs. In the cross-sectioned skeletal muscle of the slide, locate a group of cells (a fascicle) and look for nuclei near the edge (sarcolemmal region) of the muscle fibers (cells). Identify endomysium , perimysium , and epimysium .
Supplemental slide 107 Skeletal muscle, iron hematoxylin stain.
This slide has been stained to enhance the striations . Observe A bands , I bands , and even H bands in this specimen.
Slide 63 Tongue.
Reinforce your ability to recognize the special histological features of skeletal muscle. Note striations , nuclei , and fiber arrangement . Note the characteristic three planes of skeletal muscle in the tongue.
Slide 81 Spermatic cord.
Again examine skeletal muscle of this slide and observe the striations , nuclei , and fiber arrangement .
Supplemental Slide 105 Skeletal muscle, rat, frozen section.
Observe the special preservation of skeletal muscle in this slide. The freezing technique used in preparation of Slides 105 & 106 tends to preserve the cells more near to the living state. Therefore with the better preservation in these slides you can observe even mitochondria (variable density of dots and lines in the cells). Note also the absence of space between muscle cells.
Supplemental Slide 106 Skeletal muscle, human, frozen section.
Examine the skeletal muscle of this slide and its histological features. Again, try to resolve mitochondria .
SMOOTH MUSCLE
Slide 58 Gall bladder.
Smooth muscle is shown here in discrete bands beneath the epithelium. It is also present in the wall of several arteries present. Again observe the difference between the smooth muscle present and the collagen fibers which are also represented.
Slide 55 Appendix.
Find the smooth muscle in the outer perimeter of this section. It is represented here as two layers, an outer longitudinally oriented layer and an inner circularly arranged layer . You can readily observe the appearance of smooth muscle cells in cross and longitudinal profiles .
SKELETAL VS.
SMOOTH MUSCLE ON THE SAME SECTION
Slide 33 Prostate and prostatic urethra.
In this section smooth muscle and skeletal muscle are both present. Compare and contrast the two types of muscle. The smooth muscle is present as an integral part of the prostate surrounding the islands of epithelium and the skeletal muscle is present off to one side of the tissue section (apparently a small portion of one of the skeletal muscles in the lower abdominal wall). Most of the skeletal muscle cells (commonly referred to as skeletal muscle fibers) are cross sectioned . Note the position of the nuclei in the cross sectioned fibers as well as the few longitudinally sectioned fibers present in the slide. Note the delicate endomysium .
CARDIAC MUSCLE
Slide 78 Heart, muscular interventricular septum.
Note the acidophilic fibers that change direction frequently. Observes the striations present in cardiac muscle. Also observe fiber bundles which are cut in longitudinal , oblique and transverse section. Observe the centrally located nuclei of cardiac muscle. Locate a large area of longitudinally sectioned fibers and note:
1. The walls of individual fibers are parallel for short distances only.
2. The variation in width is produced by frequent branching and anastomosing of adjacent fibers.
3. The branches arising from individual fibers are variable in diameter.
Because of its fibrous appearance, cardiac muscle bears a superficial resemblance to skeletal muscle and dense connective tissue (regular and irregular). In longitudinal section, the regular branching and anastomosing pattern is the most distinctive and characteristic feature of cardiac muscle. Higher magnification will be required to confirm the presence or absence of myofibrils and cross striations .
Observe an appropriate branching area and examine the fibers carefully and note:
1. Careful examination of the fibers and branches reveals the presence of myofibrils and cross striations.
2. The presence of intercalated disks .
3. The nuclei frequently appear to be located in a mid-fiber position.
The presence of myofibrils and cross striations in branching fibers indicates the contractile nature of this tissue and confirms the diagnosis of cardiac muscle.