As you know, all muscle cells have common features. But even an average medical student can easily distinguish between different types of cell samples. Smooth muscle tissue has characteristic differences. And if you have at least minimal knowledge, you will never mix up striated and smooth muscles. It is quite simple. In this article, we will talk about what smooth muscle tissue is, and also about its properties and structure.
The main feature that distinguishes this type of tissue from muscle tissue, which is activated by the human consciousness (arbitrary), is the absence of transverse striation. One cell has only one single core located near its middle (cardiac muscle tissue has the same trait). This is what you will see under the glass of the microscope.
For the most part, smooth muscle tissue is located in the walls of the hollow organs of different systems, as well as in the walls of blood vessels. If this tissue is located in the wall of the organs, then it usually forms two layers. The inner is circular, and the outer is longitudinal. However, in some parts of various systems this rule is violated, and the fibers are arranged spirally, for example, in large arteries. Only at the level of arterioles is the human muscle tissue organized into circular fibers.
The layers of smooth tissue are divided into bundles of fibers, each of which is surrounded by 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 cardiac muscle, is managed by the autonomic nervous system, and therefore its functioning is not subject to conscious control. This tissue is able to be in a state of partial contraction for a long time (to maintain tone). Therefore, tubular structures can have a certain clearance for a long time. This is very important for such an indicator as a relatively constant blood pressure.
If the tone increases, the lumen may narrow. Sometimes it is pathological in nature. For example, when a person has asthma, the tone of the smooth muscles of the smallest bronchi becomes excessive, and air cannot circulate normally. According to some sources, the same process underlies 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 the so-called peristaltic waves that run through the tubes and push their contents in the right direction.
If we compare striated and smooth muscle cells, it can be noted that smooth contract much more slowly. An exception is the smooth muscle structures of the pupil, which instantly respond to light.
As you know, muscle tissue contains actin and myosin proteins. It turned out that actin in smooth muscle cells is greater than in striated muscle cells. Also, studies using strongly magnifying microscopes revealed the fact that the sarcoplasmic reticulum in smooth muscle cells is less developed than in striated ones.
As we saw above, there are two types of tissue in question. The cells of the first, which is part of the organs, are able to contract very slowly. This type is called visceral. But smooth muscle tissue in the structure of the sphincter of the pupil, which can contract quickly, is called muscle tissue with individual fiber innervation. As the name of the second one makes clear, each fiber there has its own nerve. The first type costs the body “cheaper” - one nerve process there is engaged in many fibers.
You can learn more about smooth muscle tissue from histology textbooks. But for non-specialists, the information in this article should be enough.