In the article we will consider the types of muscle tissue. This is a very important topic in biology, because everyone should know how our muscles function. They are a complex system, the study of which, we hope, will be interesting for you. And they will help you better imagine the types of muscle tissue in the pictures that you will find in this article. First of all, let's give a definition that is necessary when studying this topic.
Muscular tissue is a special group of human and animal tissues, the main function of which is its contraction, which determines the movement of the body or its constituent parts in space. This function corresponds to the structure of the main elements that make up various types of muscle tissue. These elements have a longitudinal and elongated orientation of myofibrils, which include contractile proteins - myosin and actin. Muscle tissue, like epithelial tissue, is a prefabricated tissue group, since its main elements develop from embryonic rudiments.
Reduction of muscle tissue
Its cells, as well as nerve cells, can be excited when exposed to electrical and chemical impulses. Their ability to contract (shorten) in response to the action of a particular stimulus is associated with the presence of myofibrils, special protein structures, each of which consists of microfilaments, short protein fibers. In turn, they are divided into myosin (thicker) and actin (thin) fibers. In response to nerve stimulation, various types of muscle tissue contract. The contraction to the muscle is transmitted along the nerve process through the neurotransmitter, which is acetylcholine. Muscle cells in the body perform energy-saving functions, since the energy expended during the contraction of various muscles is then released in the form of heat. That is why, when the body is subject to cooling, trembling occurs. This is nothing but frequent muscle contractions.
The following types of muscle tissue can be distinguished, depending on the structure of the contractile apparatus: smooth and striated. They consist of structurally different histogenetic types.
Muscle tissue striated
Myotome cells, which are formed from the dorsal mesoderm, are the source of its development. This tissue consists of elongated muscle fibers that look like cylinders, the ends of which are pointed. These formations reach 12 cm in length and 80 microns in diameter. Symplasts (multinuclear formations) are contained in the center of muscle fibers. Outside, cells called "myosatellites" adjoin them. Sarcolemma limited fibers. It is formed by the plasmolemma symplast and the basement membrane. Under the basement membranefibers are located myosatelliootocytes - so that the plasmolemma of the symplast touches their plasmolemma. These cells are the cambial reserve of muscle skeletal tissue, and it is due to it that the regeneration of fibers is carried out. Myosymplasts, in addition to the plasmolemma, also include sarcoplasm (cytoplasm) and numerous nuclei located on the periphery.
The importance of striated muscle tissue
Describing the types of muscle tissue, it should be noted that the striated is the executive apparatus of the entire motor system. It forms skeletal muscles. In addition, this type of tissue is included in the structure of internal organs, such as the pharynx, tongue, heart, upper esophagus, etc. Its total mass in an adult is up to 40% of body weight, and in the elderly, as well as newborns, its share - 20-30%.
Features of striated muscle tissue
The reduction of this type of muscle tissue, as a rule, can be done with the participation of consciousness. It has a slightly higher performance compared to smooth. As you can see, the types of muscle tissue are different (we will talk about smooth very soon and note some other differences between them). In striated muscles, nerve endings receive information about the current state of muscle tissue, and then transmit it through afferent fibers to the nerve centers responsible for the regulation of motor systems. Signals that control muscle functions come from regulators in the form of nerveimpulses along motor or autonomic efferent nerve fibers.
Smooth muscle tissue
Continuing to describe the types of human muscle tissue, we move on to smooth. It is formed by spindle-shaped cells, the length of which is from 15 to 500 microns, and the diameter is in the range from 2 to 10 microns. Unlike striated muscle fibers, these cells have a single nucleus. In addition, they do not have transverse striation.
Importance of smooth muscle tissue
The functioning of all body systems depends on the contractile function of this type of muscle tissue, since it is included in the structure of each of them. So, for example, smooth muscle tissue is involved in controlling the diameter of the respiratory tract, blood vessels, in the contraction of the uterus, bladder, in the implementation of the motor functions of our digestive tract. It controls the diameter of the pupil of the eyes, and is also involved in many other functions of various body systems.
Muscle Layers
Muscular layers forms this type of tissue in the walls of the lymphatic and blood vessels, as well as all hollow organs. Usually it is two or three layers. Thick circular - the outer layer, the middle is not necessarily present, thin longitudinal - the inner. The blood vessels that feed the muscle tissue, as well as the nerves, run parallel to the axis of the muscle cells between their bundles. smooth muscle cellscan be divided into 2 types: unitary (combined, grouped) and autonomous myocytes.
Autonomous myocytes
Autonomous function quite independently of each other, since each such cell is innervated by a nerve ending. They were found in the muscle layers of large blood vessels, as well as in the ciliary muscle of the eye. Also of this type are the cells that make up the muscles that raise the hair.
Unitary myocytes
Unitary muscle cells, on the contrary, are closely intertwined, so that their membranes can not only adjoin tightly to each other, forming desmosomes, but also merge, forming nexuses (gap junctions). Beams are formed as a result of this union. Their diameter is about 100 microns, and their length reaches several mm. They form a network, and collagen fibers are woven into its cells. The fibers of autonomic neurons innervate bundles, and they become functional units of smooth muscle tissue. Depolarization upon excitation of one cell of the beam spreads very quickly to neighboring ones, since the resistance of gap junctions is low. Tissues consisting of unitary cells are found in most organs. These include the ureters, uterus, digestive tract.
Myocyte contraction
The contraction of myocytes is caused in smooth tissue, as in striated tissue, by the interaction of myosin and actin filaments. This is similar to different types of muscle tissue in humans. These threads are distributed within the myoplasm less ordered than in the striated muscle. Related to this is the lacktransverse striation in smooth muscle tissue. Intracellular calcium is the final executive link that controls the interaction of myosin and actin filaments (that is, the contraction of myocytes). The same applies to the striated muscle. However, the details of the control mechanism differ significantly from the latter.
The vegetative axons passing through the very thickness of the muscular smooth tissue do not form synapses, which is typical for striated tissue, but numerous thickenings along the entire length, which play the role of synapses. The thickenings secrete a mediator that diffuses to nearby myocytes. Receptor molecules are found on the surface of these myocytes. The mediator interacts with them. It causes depolarization in the myocyte outer membrane.
Features of smooth muscle tissue
The nervous system, its vegetative department, is controlled without the participation of consciousness by the work of smooth muscles. The bladder muscles are the only exception. Control signals are either directly implemented or indirectly - through hormonal (chemical, humoral) effects.
Energy and mechanical properties of this type of muscle tissue ensure the maintenance of the (controlled) tone of the walls of hollow organs and blood vessels. This is due to the fact that the smooth tissue functions efficiently and does not require large expenditures of ATP. It has a slower response than that of the striated muscle tissue, however, it is able to contract for a longer time, in addition, it can develop significant tension and change its behavior over a wide range.length.
So, we examined the types of muscle tissues and the features of their structural organization. Of course, this is just basic information. You can describe the types of muscle tissue for a long time. Drawings will help you visualize them.
