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The microscope shows these muscles to consist not of fibers, but of long spindle-shaped cells, united to form sheets or bands. They have no sarcolemma, stripes, or cross markings like those of the voluntary muscles. Hence their name of non-striated, or unstriped, and smooth muscles. The involuntary muscles respond to irritation much less rapidly than do the voluntary.
They are of a pale, whitish color, and they have no tendons. Since they are controlled by the part of the nervous system which acts independently of the will, they are said to be involuntary. They contract and relax slowly. B. Three non-striated cells highly magnified.
The inner coat consists of a delicate lining of flat cells resting upon a thin layer of connective tissue. The inner coat is continuous with the lining of the heart and provides a smooth surface over which the blood glides with little friction. The middle coat consists mainly of non-striated, or involuntary, muscular fibers.
The voluntary muscles, from peculiarities revealed by the microscope, are also known as striped or striated muscles. The involuntary from their smooth, regular appearance under the microscope are called the unstriped or non-striated muscles. The two kinds of muscles, then, are the red, voluntary, striated muscles, and the smooth, involuntary, non-striated muscles. Structure of Voluntary Muscles.
These are known as the striated, or striped, muscular tissue; the non-striated, or plain, muscular tissue; and the muscular tissue of the heart. These are made up of different kinds of muscle cells and act in different ways to cause motion. The striated muscular tissue far exceeds the others in amount and forms all those muscles that can be felt from the surface of the body.
They are also much smaller than the striated cells, being less than one one-hundredth of an inch in length and one three-thousandth of an inch in diameter. In the formation of the non-striated muscles, the cells are attached to one another by a kind of muscle cement to form thin sheets or slender bundles. These differ from the striated muscles in several particulars.
The non-striated muscle is found in the walls of the food canal, blood vessels, air passages, and other tubes of the body; while the muscular tissue of the heart is confined entirely to that organ. Because of their great length they are called fibers, or fiber cells. A thin sac-like covering, called the sarcolemma, surrounds the entire cell and just beneath this are a number of nuclei.
*Work of the Non-striated Muscles.*—The work of the non-striated muscles, both in purpose and in method, is radically different from that of the striated. They do not change the position of parts of the body, as do the striated muscles, but they alter the size and shape of the parts which they surround.
These are grouped into working parts, called muscles, which in turn are attached to the movable parts of the body. The striated muscles, as a rule, are attached to the mechanical devices found in the skeleton, and bring about the voluntary, movements. The non-striated muscles surround the parts on which they act, and produce involuntary movements.
*To show Non-striated Cells.*—Place a clean section of the small intestine of a cat in a mixture of one part of nitric acid and four parts of water and leave for four or five hours. Thoroughly wash out the acid with water and separate the muscular layer from the mucous membrane.
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