Smooth muscle tissue: not subject to the will of man

As you know, all muscle cells have common features. But even the average medical student will easily distinguish samples of cells of different types. Smooth muscle tissue has a characteristic difference. And if you have at least a minimum of knowledge, you will never mistake striated and smooth muscles. It's quite simple. In this article we will talk about what is smooth muscle tissue, but also about its properties and structure.

The main feature that distinguishes this type of tissue from the muscle tissue, which is activated by the human consciousness (arbitrary), is the absence of transverse striation. One cell has only one single nucleus, located near the middle of it (the same line has cardiac muscle tissue). This you will see under the glass of the microscope.

For the most part, smooth muscle tissue is located in the walls of hollow organs of different systems, as well as in the walls of blood vessels. If this tissue is in the wall of the organs, then, as a rule, it forms two layers. The inner is annular, and the outer one is longitudinal. However, in some parts of different systems this rule is violated, and the fibers are spiraling, for example, in large arteries. Only at the level of arterioles the human muscular tissue is organized into annular fibers.

The layers of smooth-type tissue are divided into bundles of fibers, each of which is surrounded by a connective tissue through which nerves and blood vessels approach the muscle cells. The bundles are closely intertwined with each other, and therefore a kind of integrated network of muscle fibers is formed, which perform their work together.

Smooth muscle tissue, like the heart muscle, is administered by the autonomic nervous system, and therefore its functioning is not subject to conscious control. This tissue can for a long time be in a state of partial contraction (maintain a tone). Therefore, tubular structures can for a long time have a certain lumen. This is very important for such an indicator as a relatively constant blood pressure.

If the tone increases, the lumen may narrow. Sometimes this is pathological. For example, when a person suffers from asthma, the tone of the smooth muscles of the smallest bronchi becomes excessive, and the air can not circulate normally. The same process, according to some reports, lies at the basis of the formation of hypertension in people.

Smooth muscle tissue is also able to regulate the amount of elastin in the blood vessels. In the walls of the gastrointestinal tract, ureters and oviducts, smooth muscles contract rhythmically, forming so-called peristaltic waves that run through tubes and push their contents in the right direction.

If we compare striated and smooth muscle cells, it can be noted that smooth ones contract much more slowly. The exception is the smooth muscle structures of the pupil, which instantly react to light.

As is known, muscle proteins contain actin and myosin proteins. It turned out that actin in smooth muscle cells is greater than in the striated muscle cells. Also, studies using highly magnifying microscopes have revealed the fact that the sarcoplasmic reticulum in smooth muscle cells is less developed than in the striated muscle cells.

As we saw above, there are two types of the considered kind of tissue. The cells of the first, which is found in the organs, are able to contract very slowly. This type is called visceral. But smooth muscle tissue in the sphincter structure of the pupil, capable of contracting rapidly, is called a muscle tissue with individual innervation of the fibers. As is clear from the name of the second, every fiber there has its own nerve. The first type costs the body "cheaper" - one nervous process is engaged in a lot of fibers.

More information about smooth muscle tissue can be found in the histology textbooks. But for non-specialists the information in this article should be enough.