What Makes a Skeletal Muscle Slide Easy to Identify From Other Tissue Slides?

Slide 029-1 Small Intestine (simple columnar epithelium, simple squamous epithelium) H&E crossView Virtual Slide

Slide 169 jejunum H&E crossView Virtual Slide

Slide 155 gastro-esophageal junction H&E longitudinalView Virtual Slide

Slide 250-2 vagina MassonView Virtual Slide

Slide 250-1 vagina H&EView Virtual Slide

Smooth muscle may be studied using slide 029-1 smooth muscle View Image orslide 169 View Image, both in the intestine.  To find the muscle layer, look at the at slide at the lowest power (this is about the same as looking at the glass slide with the naked eye).  The purple layer is largely the epithelium and the lamina propria filled with plasma cell and lymphocytes.  Next to that you see a lighter region of connective tissue (the submucosa you looked at to see loose connective tissue and fibroblasts), then a darker pink region which is made up of the two layers of smooth muscle you want to look at.Slide 29 is across section of the intestine, so the inner, circular layer of muscle will have cells oriented longitudinally (or, in places, the cells may appear to be oriented more obliquely).  Move further out to see the outer sheet of smooth muscle, which runs longitudinally along the intestine, and will therefore be seen in cross section.

Look atslide 155, which is alongitudinal section of the GI tract at the gastro-esophageal junction, to see more smooth muscle in various planes of section.  The smooth muscle in the esophagus (the part lined with a stratified, non-keratinizing squamous epithelium) sample region from slide 155 View Image is organized in the "classic" inner circular and outer longitudinal arrangement (top half in longitudinal section and bottom half in cross section).  However, the stomach (the part lined by a columnar epithelium) has an inner oblique layer, a very prominent middle circular layer sample region from slide 155 View Image  (seen mostly in cross section here), and a sometimes less obvious outer longitudinal layer. Don't worry knowing about the specific layers or being able to tell esophagus from stomach. However, you should definitely be able to identify smooth muscle inany plane of section (tranverse, longitudinal, or even oblique).   In this particular slide, both the hematoxylin and eosin staining are quite intense, which should help you to see the cytoplasm more clearly, especially when the muscle is cut in cross section.

A. In longitudinally cut smooth muscle cells, observe the following points:

1. Cells are small and spindle-shaped (fusiform); this may be hard to appreciate because the cell membrane is indistinct.
2. Myofibirils and cross striation cannot be seen.
3. Nuclei are narrow, elongated and sometimes kinked or spiraling. They are centrally located.

B. In transversely cut smooth muscle cells, observe the following points:

1. The cell has a small diameter.
2. The nucleus is located centrally, but will not be seen in every cross section.
3. Myofibrils cannot be seen.
4. Cross-sectional diameters vary due to the spindle shape of the cells.

Now, look atslide 250 and see if you can distinguish between small fascicles of smooth muscle and collagen fibers in the lamina propria (this task will be easier if you look first at thetrichrome-stained section, which stains the muscle pink(ish) and the collagen blue) slide250-2 View Image.  It's more challenging to make this distinction in theH&E-stained sectionslide250-1 View Image.  You should note that smooth muscle is pink, wheras collagen is a bit more orange-red.  Also, smooth muscle tissue is mostlycellular (and therefore more nuclei are present), whereas the connective tissue is mostlyextracellular collagen fibers with fewer cells. The table below compares the differences in the morphology of the three types of muscle.

Major Histological Characteristics Of The Three Types Of Muscle As Seen With The Light Microscope

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Source: https://histology.medicine.umich.edu/resources/muscle

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