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Lesson: Chapter 1 — Living Tissues

1.2.3. Muscle tissue 2 of 6

Smooth muscle

The muscle you never think about, doing work you never notice, all day and all night.

Figure to be added

Figure 1.18 — smooth muscle tissue: long spindle-shaped cells lying loosely alongside one another, tapering to a point at each end, each with a single nucleus in the middle and no cross bands on the cell.

Where it is found

Smooth muscle tissue is situated in the walls of organs — the alimentary canal wall, the walls of blood vessels, and the walls of the urinary bladder and the uterus.

The characteristics

  • They are spindle-shaped cells, existing separately from one another and not branched.
  • They are uninucleate, with the nucleus situated in the middle of the cell, and they do not bear cross striations.
  • They do not tire quickly, and they act involuntarily.

Every organ on the list is a hollow tube or bag

Gut, blood vessel, bladder, uterus — each is a container that has to squeeze. A sheet of spindle-shaped cells wrapped round a tube can narrow it, and a slow steady squeeze travelling along the tube pushes the contents forward. That is how food moves through the gut, and it is why this tissue must not tire.