SMOOTH MUSCLE

Smooth muscle cells are found in the wall of the hollow viscera, blood vessels, and ducts.

These muscle cells (fibers) lack the transverse striations seen in either skeletal or cardiac muscle cells. In longitudinal sections, they appear fusiform or spindle-shaped and contain centrally-located nuclei. There is one long, oval or rod-shaped nucleus per cell. The cells fit together to form bands and sheets so that the thick part of one cell is adjacent to the thin part of the neighboring cells. In a cross-section, the cells appear rounded and vary in diameter depending on what part of the cell was cut in the section. In general, the nuclei are found in the thicker part of cells and they are centrally located in the cytoplasm. These muscles cells are smaller than skeletal or cardiac muscle cells. They do not branch or unite with each other, a feature that helps in differentiating a cross-section of this type of muscle from a cross-section of the cardiac muscle.

Smooth muscle can be easily confused with ordinary connective tissue. To differentiate between these two types of tissue, the following morphological characteristics may be employed: (1) smooth muscle fibers commonly stain darker with acid dyes (e.g., eosin); (2) nuclei lie inside the smooth muscle fibers, but occur between connective tissue fibers; (3) in longitudinal section, smooth muscle nuclei are often wrinkled (corkscrew shaped); (4) no other types of cells occur between smooth muscle fibers within a bundle or sheet; and (5) some stains differentiate smooth muscle from connective tissue sharply (for instance, the Mallory stain colors collagenous fibers blue and smooth muscle fibers pink).

Smooth Muscle (LM, H&E) [#28]- Smooth muscle is distinguished by the lack of striations and the presence of spindle-shaped nuclei which are centrally located.

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	Slide Text SMOOTH MUSCLE Smooth muscle cells are found in the wall of the hollow viscera, blood vessels, and ducts. These muscle cells (fibers) lack the transverse striations seen in either skeletal or cardiac muscle cells. In longitudinal sections, they appear fusiform or spindle-shaped and contain centrally-located nuclei. There is one long, oval or rod-shaped nucleus per cell. The cells fit together to form bands and sheets so that the thick part of one cell is adjacent to the thin part of the neighboring cells. In a cross-section, the cells appear rounded and vary in diameter depending on what part of the cell was cut in the section. In general, the nuclei are found in the thicker part of cells and they are centrally located in the cytoplasm. These muscles cells are smaller than skeletal or cardiac muscle cells. They do not branch or unite with each other, a feature that helps in differentiating a cross-section of this type of muscle from a cross-section of the cardiac muscle. Smooth muscle can be easily confused with ordinary connective tissue. To differentiate between these two types of tissue, the following morphological characteristics may be employed: (1) smooth muscle fibers commonly stain darker with acid dyes (e.g., eosin); (2) nuclei lie inside the smooth muscle fibers, but occur between connective tissue fibers; (3) in longitudinal section, smooth muscle nuclei are often wrinkled (corkscrew shaped); (4) no other types of cells occur between smooth muscle fibers within a bundle or sheet; and (5) some stains differentiate smooth muscle from connective tissue sharply (for instance, the Mallory stain colors collagenous fibers blue and smooth muscle fibers pink). Smooth Muscle (LM, H&E) [#28]- Smooth muscle is distinguished by the lack of striations and the presence of spindle-shaped nuclei which are centrally located.