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 to you. And they will help you better imagine the types of muscle tissue pictures that you will find in this article. First of all, we give a definition that is necessary when studying this topic.
Muscle 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 parts in space. This function corresponds to the structure of the basic 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, is a prefabricated tissue group, as its main elements develop from embryonic primordia.
Muscle contraction
Its cells, as well as nerve cells, can be excited under the influence of 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 nervous irritation, various types of muscle tissue contract. Contraction to the muscle is transmitted along the nerve process through the neurotransmitter, which is acetylcholine. Muscle cells in the body carry out energy-saving functions, since the energy expended during 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 what structure the contractile apparatus has: smooth and striated. They consist of histogenetic types differing in structure.
Muscle tissue striated
Myotome cells that form 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. 12 cm in length and 80 Ξm in diameter reach these formations. Symplasts (multinuclear formations) are contained in the center of muscle fibers. Outside, cells adjacent to them are called myosatellites. Sarcolemma is limited to fiber. It is formed by a plasmolemma symplast and a basement membrane. Myosatelliotocytes are located under the basal membrane of the fiber - so that the plasmolemma symplast touches their plasmolemma. These cells are a cambial reserve of skeletal muscle tissue, and it is due to it that fiber regeneration is carried out. Myosymplasts, in addition to plasmolemma, also include sarcoplasm (cytoplasm) and numerous nuclei located on the periphery.
The value of striated muscle tissue
Describing the types of muscle tissue, it should be noted that striated is the executive apparatus of the entire motor system. It forms skeletal muscle. 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 older people, as well as newborns, it share - 20-30%.
Features of striated muscle tissue
Reduction of this type of muscle tissue, as a rule, can be done with the participation of consciousness. It has a slightly higher speed 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 perceive 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. The signals that control muscle functions come from regulators in the form of nerve impulses along motor or autonomic efferent nerve fibers.
Smooth muscle tissue
Continuing to describe the types of muscle tissue of a person, we turn 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 one nucleus. In addition, they have no transverse striation.
The value 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. 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 eye, and also participates in many other functions of various body systems.
Muscle layers
The muscle layers form this type of tissue in the walls of the lymphatic and blood vessels, as well as all hollow organs. Usually these are two or three layers. Thick circular - the outer layer, the middle is not necessarily present, thin longitudinal - the inner. Blood vessels that feed muscle tissue, as well as nerves, run parallel to the axis of muscle cells between their bundles. Smooth muscle cells can be divided into 2 types: unitary (combined, grouped) and autonomous myocytes.
Autonomic 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 to 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). Bundles are formed as a result of this association. Their diameter is about 100 microns, and the length reaches several mm. They form a network, and collagen fibers are woven into its cells . The fibers of autonomic neurons are innervated by bundles, and they become functional units of smooth muscle tissue. Depolarization upon excitation of one beam cell spreads very quickly to neighboring cells, since there is little resistance to gap junctions. Unitary tissue cells are found in most organs. These include the ureters, the uterus, the digestive tract.
Myocyte contraction
Myocyte contraction is caused in smooth tissue, as in striated, by the interaction of myosin and actin filaments. In this, different types of muscle tissue in humans are similar. These threads are distributed within the myoplasm less orderly than in the striated muscle. Associated with this is the absence of transverse striation in smooth muscle tissue. Intracellular calcium is the final executive link that controls the interaction of myosin and actin filaments (i.e., myocyte contraction). The same applies to the striated muscle. However, the details of the control mechanism are significantly different from the latter.
The vegetative axons passing in the thickest muscle smooth muscle tissue do not form synapses, which is characteristic of striated tissue, but numerous thickenings that exist along the entire length, which play the role of synapses. Thickening secrete a mediator that diffuses to adjacent myocytes. Receptor molecules are located on the surface of these myocytes. The mediator interacts with them. It causes depolarization in the myocyte of the outer membrane.
Features of smooth muscle tissue
The nervous system, its autonomic department, is controlled without the participation of consciousness by the work of smooth muscles. Bladder muscles are the only exception. Control signals are either directly realized, or indirectly through hormonal (chemical, humoral) effects.
The energy and mechanical properties of this type of muscle tissue maintain the tone (controlled) of the walls of hollow organs and blood vessels. This is due to the fact that smooth tissue functions efficiently and does not require large expenditures of ATP. It has less speed than that of striated muscle tissue, however, it can contract for a longer time, in addition, it can develop significant tension and change its length over a wide range.
So, we examined the types of muscle tissue and the features of their structural organization. Of course, this is just basic information. It is possible to describe the types of muscle tissue for a long time. Drawings will help you visualize them.