Line UMK V.I. Sivoglazova. Biology (5-9)

Line UMK V.I. Sivoglazova. Biology (10-11)

Biology

Human muscles

But skeletal muscles are not all the muscles of the human body. Thanks to the work of the smooth muscles of the internal organs, a peristaltic wave travels through the intestines, contracting, ensuring life, the most important muscle of the human body - the heart.

Muscle Definition

Muscle(lat. muscle) - an organ of the human and animal body formed by muscle tissue. Muscle tissue has a complex structure: myocyte cells and the membrane covering them, the endomysium, form separate muscle bundles, which, when joined together, form the muscle itself, dressed for protection in a cloak of connective tissue or fascia.

Muscles of the human body can be divided into:

• skeletal,
• smooth,
• cardiac.

As the name suggests, the skeletal type of muscle is attached to the bones of the skeleton. Second name - striated ( due to transverse striations), which is visible under microscopy. This group includes the muscles of the head, limbs and torso. Their movements are voluntary, i.e. a person can control them. This human muscle group provides movement in space; it is these that can be developed or “pumped up” with the help of training.

Smooth muscle is part of the internal organs - the intestines, bladder, vascular walls, and heart. Thanks to its contraction, blood pressure increases during stress or the food bolus moves through the gastrointestinal tract.

Cardiac - characteristic only of the heart, ensures continuous blood circulation in the body.

It is interesting to know that the first muscle contraction occurs already in the fourth week of the embryo’s life - this is the first heartbeat. From this moment until the death of a person, the heart does not stop for a minute. The only cause of cardiac arrest during life is open heart surgery, but then the CPB (heart-lung machine) works for this important organ.

The navigator textbook is the main module of the innovative educational and methodological set “Navigator”. A simple and convenient navigation system connects the text of the textbook with the information field of the accompanying multimedia manual (disc): all terms and concepts found in the textbook are divided into main and additional material using a color indication. The methodological apparatus of the textbook consists of questions for self-testing, questions of an increased level of complexity (including those establishing interdisciplinary connections), as well as a system of tasks using other components of the teaching materials - both printed and electronic, which contributes to the effective assimilation of educational material.

The structure of human muscles

The unit of structure of muscle tissue is the muscle fiber. Even a single muscle fiber can contract, indicating that a muscle fiber is not only a single cell, but also a functioning physiological unit capable of performing a specific action.

An individual muscle cell is covered sarcolemma– a strong elastic membrane provided by proteins collagen And elastin. The elasticity of the sarcolemma allows the muscle fiber to stretch, and some people show miracles of flexibility - doing the splits and performing other tricks.

In the sarcolemma, like twigs in a broom, threads are tightly packed myofibrils, composed of individual sarcomeres. Thick filaments of myosin and thin filaments of actin form a multinucleated cell, and the diameter of the muscle fiber is not a strictly fixed value and can vary over a fairly wide range from 10 to 100 microns. Actin, which is part of the myocyte, is an integral part of the cytoskeletal structure and has the ability to contract. Actin consists of 375 amino acid residues, which makes up about 15% of the myocyte. The remaining 65% of muscle protein is myosin. Two polypeptide chains of 2000 amino acids form the myosin molecule. When actin and myosin interact, a protein complex is formed - actomyosin.

Description of human muscles difficult, and for a visual representation you can refer to the textbook, where

Name of human muscles

When anatomists in the Middle Ages began to dig up corpses on dark nights to study the structure of the human body, the question arose about the names of the muscles. After all, it was necessary to explain to the onlookers who had gathered in the anatomical theater what the scientist was currently cutting with a sharply sharpened knife.

Scientists have decided to name them either by the bones to which they are attached (for example, the sternocleidomastoid muscle), or by their appearance (for example, the latissimus dorsi or trapezius), or by the function they perform (extensor digitorum longus). Some muscles have historical names. For example, tailoring so named because it drove the sewing machine pedal. By the way, this muscle is the longest in the human body.

Muscle classification

There is no single classification, and muscles are classified according to various criteria.

By location:

• heads; in turn are divided into:
• – facial expressions
• – chewable
• torso
• belly
• limbs

By fiber direction:

• straight
• transverse
• circular
• oblique
• unipinnate
• bipinnate
• multipinnate
• semitendinosus
• semimembranosus

Muscles are attached to bones, extending over joints to produce movement.
Depending on the number of joints through which the muscle is thrown:

• single-joint
• two-joint
• multi-joint

By type of movement performed:

• flexion-extension
• abduction, adduction
• supination, pronation ( supination– outward rotation, pronation– inward rotation)
• compression, relaxation
• raising, lowering
• straightening

To ensure body movement and movement from place to place, muscles work harmoniously and in groups. Moreover, according to their work they are divided into:

• agonists - take on the main load when performing a certain action (for example, biceps when bending the arm at the elbow)
• antagonists - work in different directions (the triceps muscle, involved in extending the limb at the elbow joint, will be an antagonist to the triceps); agonists and antagonists, depending on the action we want to perform, can change places
• synergists - assistants in performing actions, or stabilizers

Smooth muscle is part of the walls of various hollow organs - the bladder, the walls of blood vessels and the heart, which contracts under the influence of the autonomic nervous system, i.e. does not depend on the desire and will of a person. Although they say that some yogis can slow down the heart rate to almost zero with the power of thought. But these are yogis, and an ordinary person cannot control the work of smooth muscles either by willpower or by the power of thought. However, it can indirectly influence through hormones.

Surely, you have all noticed that during an intense and long run, your heart begins to beat faster. And some, even well-prepared students, get sick before a difficult exam and constantly run to the toilet. All this is due to hormonal surges that affect the functioning of the body.

The main functions of skeletal muscles include:

• motor
• supporting or static - maintaining body position in space

Sometimes these two functions are combined into one stato-kinetic function.

The muscular system is also involved in respiration, digestion, urination and thermogenesis.
More details about the function of each group of skeletal muscles are written in the textbook edited by V.I. Sivoglazov.

The morpho-functional unit of smooth muscle tissue is the SMC. With their pointed ends, SMCs wedge between neighboring cells and form muscle bundles, which in turn form layers of smooth muscle (Fig. 7-26, 7-26A). In the fibrous connective tissue, nerves, blood and lymphatic vessels pass between the myocytes and muscle bundles. Single SMCs are also found, for example, in the subendothelial layer of blood vessels. The shape of the MMC is elongated, fusiform, often process-shaped (Fig. 7-27). The length of SMCs is from 20 µm to 1 mm (for example, SMCs of the uterus during pregnancy). The oval nucleus is localized centrally. In the sarcoplasm at the poles of the nucleus there is a well-defined Golgi complex, numerous mitochondria, free ribosomes, and the sarcoplasmic reticulum. Myofilaments are oriented along the longitudinal axis of the cell. The basement membrane surrounding SMCs contains proteoglycans, collagen types III and V. The components of the basement membrane and elastin of the intercellular substance of smooth muscles are synthesized both by the SMCs themselves and by connective tissue fibroblasts.

Rice. 7-26. Smooth muscle in longitudinal (A) and transverse (B) sections. In a cross section, myofilaments are visible as dots in the cytoplasm of smooth muscle cells.

Rice. 7-26A. Smooth muscle in longitudinal section. Smooth muscle cells (1) are spindle-shaped. In the central thickened part of the cells, rod-shaped nuclei are clearly visible (2). Hematoxylin and eosin staining.

Rice. 7-27. Smooth muscle cell. The central position in the MMC is occupied by a large core. At the poles of the nucleus are mitochondria, the endoplasmic reticulum and the Golgi complex. Actin myofilaments, oriented along the longitudinal axis of the cell, are attached to dense bodies. Myocytes form gap junctions among themselves.

The structure of smooth muscle differs from striated skeletal muscle and cardiac muscle. It consists of spindle-shaped cells with a length of 10 to 500 microns, a width of 5-10 microns, containing one nucleus. Smooth muscle cells lie in the form of parallel oriented bundles, the distance between them is filled with collagen and elastic fibers, fibroblasts, and feeding highways. The membranes of adjacent cells form nexuses, which provide electrical communication between cells and serve to transmit excitation from cell to cell. In addition, the plasma membrane of the smooth muscle cell has special invaginations - caveolae, due to which the area of ​​the membrane increases by 70%. The outside of the plasma membrane is covered by the basement membrane. The complex of the basal membrane and plasma membrane is called the sarcolemma. Smooth muscle lacks sarcomeres. The basis of the contractile apparatus is made up of myosin and actin protofibrils. There are much more actin protofibrils in SMCs than in striated muscle fibers. Actin/myosin ratio = 5:1.

Thick and thin myofilaments are scattered throughout the sarcoplasm of the smooth myocyte and do not have such a harmonious organization as in striated skeletal muscle. In this case, thin filaments are attached to dense bodies. Some of these bodies are located on the inner surface of the sarcolemma, but most of them are found in the sarcoplasm. Dense bodies are composed of alpha-actinin, a protein found in the structure of the Z-membrane of striated muscle fibers. Some of the dense bodies located on the inner surface of the membrane come into contact with the dense bodies of the adjacent cell. Thus, the force created by one cell can be transferred to the next. Thick smooth muscle myofilaments contain myosin, and thin ones contain actin and tropomyosin. At the same time, troponin was not found in thin myofilaments.

Smooth muscles are found in the walls of blood vessels, skin and internal organs.

Smooth muscle plays an important role in the regulation

lumen of the airways,

tone of blood vessels,

motor activity of the gastrointestinal tract,

uterus, etc.

Classification of smooth muscles:

Multiunitary, they are part of the ciliary muscle, the muscles of the iris, and the levator pili muscle.

Unitary (visceral), found in all internal organs, ducts of the digestive glands, blood and lymphatic vessels, and skin.

Multiunitary smooth muscle.

consists of individual smooth muscle cells, each of which is located independently of each other;

has a high innervation density;

like striated muscle fibers, they are covered on the outside with a substance resembling a basement membrane, which includes collagen and glycoprotein fibers that insulate cells from each other;

each muscle cell can contract separately and its activity is regulated by nerve impulses;

Unitary smooth muscle (visceral).

is a layer or bundle, and the sarcolemmas of individual myocytes have multiple points of contact. This allows excitation to spread from one cell to another

membranes of adjacent cells form multiple tight junctions(gap junctions), through which ions are able to move freely from one cell to another

action potentials generated at the smooth muscle cell membrane and ionic currents can propagate throughout the muscle fiber, allowing large numbers of individual cells to contract simultaneously. This type of interaction is known as functional syncytium

An important feature of smooth muscle cells is their ability to self-excitation (automation), that is, they are able to generate an action potential without the influence of an external stimulus.

There is no constant resting membrane potential in smooth muscles; it constantly drifts and averages -50 mV. The drift occurs spontaneously, without any influence, and when the resting membrane potential reaches a critical level, an action potential occurs, which causes muscle contraction. The duration of the action potential reaches several seconds, so the contraction can also last several seconds. The resulting excitation then spreads through the nexus to neighboring areas, causing them to contract.

Spontaneous (independent) activity is associated with stretching of smooth muscle cells and when they stretch, an action potential occurs. The frequency of action potentials depends on the degree of fiber stretch. For example, peristaltic contractions of the intestine are enhanced when its walls are stretched by chyme.

Unitary muscles mainly contract under the influence of nerve impulses, but spontaneous contractions are sometimes possible. A single nerve impulse is not capable of causing a response. For it to occur, it is necessary to sum up several impulses.

All smooth muscles, when generating excitation, are characterized by activation of calcium channels, therefore, in smooth muscles all processes proceed more slowly compared to skeletal muscles.

The speed of excitation along nerve fibers to smooth muscles is 3-5 cm per second.

One of the important stimuli that initiates contraction of smooth muscles is their stretching. Sufficient stretching of smooth muscle is usually accompanied by the appearance of action potentials. Thus, two factors contribute to the appearance of action potentials when smooth muscle is stretched:

slow wave oscillations of membrane potential;

depolarization caused by stretching of smooth muscle.

This property of smooth muscle allows it to automatically contract when stretched. For example, during overflow of the small intestine, a peristaltic wave occurs, which moves the contents.

Contraction of smooth muscle.

Smooth muscles, like striated muscles, contain cross-bridged myosin, which hydrolyzes ATP and interacts with actin to cause contraction. In contrast to striated muscle, smooth muscle thin filaments contain only actin and tropomyosin and no troponin; regulation of contractile activity in smooth muscles occurs due to the binding of Ca ++ to calmodulin, which activates myosin kinase, which phosphorylates the myosin regulatory chain. This leads to ATP hydrolysis and starts the cycle of cross-bridge formation. In smooth muscle, the movement of actomyosin bridges is a slower process. The breakdown of ATP molecules and the release of energy necessary to ensure the movement of actomyosin bridges does not occur as quickly as in striated muscle tissue.

The efficiency of energy expenditure in smooth muscle is extremely important in the body’s overall energy consumption, since blood vessels, small intestines, bladder, gall bladder and other internal organs are constantly in good shape.

During contraction, smooth muscle can shorten up to 2/3 of its original length (skeletal muscle from 1/4 to 1/3 length). This allows hollow organs to perform their function by changing their lumen within significant limits.

This article describes the structure and function of smooth and striated muscle tissue.

There are several types of muscle tissue in any man or woman's body. Muscle tissues vary in structure and origin. In this article we will look at their properties, functions and characteristics.

What types of muscle tissue are found in the human body?

The following types of muscle tissue are found in our body:

• Smooth
• Skeletal
• Heart

Smooth muscle tissue found in the skin, the walls of our organs and the vessels through which blood flows. Its contractility is performed involuntarily and quite slowly. Unlike others, this type of muscle consumes a small amount of energy and does not get tired for quite a long time.

Striated skeletal muscle tissue present in the structure of the esophagus, in the pharyngeal structure and in the skeleton. Control is done by the human brain. These muscles have high contractile speed. This type of fabric requires a lot of energy and a long rest period.

Striated cardiac muscle tissue is an integral part of the heart, carries out a pumping function with the help of cellular contacts, which instantly transmit an impulse to each other, from which contraction occurs synchronously. Controlled involuntarily, capable of automaticity.

Features of the structure of human smooth muscle tissue: properties, what cells and fibers form?

All types of muscle tissue differ in pore structure and origin, but contract equally well. They contain myocytes - these are cells that receive impulses and respond by contracting. The structural features of human smooth muscle tissue include the presence of small spindle-shaped cells.

All muscles of the human body are represented by only 3 types:

• Smooth
• Cross-striped skeletal
• Cross-striped hearts

These are the cells and fibers that form smooth muscle:

• The structure of this type of muscle consists of a smooth myocyte.
• These cells contain a nucleus and the finest myofibrils.
• The smooth muscle cytolemma forms multiple invaginations in the form of small vesicles - caveolae.
• Smooth muscle cells are connected into bundles of 10-12 pieces.
• This feature is obtained due to the innervation of smooth muscles and this helps the impulse to travel better and faster throughout the entire group of cells.

The properties and functionality of smooth muscles are as follows:

• Excitability, contractility, elasticity. Contraction is regulated by the nervous system.
• Performing stable pressure in organs with a hollow structure.
• Regulation of blood pressure levels.
• Peristalsis of the digestive organs and unhindered movement of contents through them.
• Emptying the bladder.

Many organs in our body would not be able to function if they were not composed of smooth muscle tissue.

The structure of striated human skeletal muscle tissue: functions, signs

Skeletal muscle tissue is a tough, elastic tissue that contracts under the influence of nerve impulses. It consists of skeletal muscles in both humans and animals. Its work consists, for example, of contracting the vocal cords, breathing, and moving the body.

As mentioned above, people have several types of muscles:

• Striated cardiac muscle
• Striated skeletal muscles
• Smooth muscle

The structure of human striated skeletal muscles is special and consists of the following main aspects:

• Consists of myocytes, which are several centimeters in length.
• The diameter of these myocyte cells from 50 to 100 µm.
• Such cells have many nuclei - up to 100.
• If you look under a microscope, you can see dark and light stripes.
• The fibrous threads have a length up to 12 cm.

It is also worth noting the following:

• Skeletal muscles are an active tissue segment necessary to maintain the musculoskeletal system, consisting of bones, their joints, tendons, and ligaments.
• The motor apparatus also includes motor neurons, which send nerve “signals” to muscle fibers.
• The bodies of motor neurons are located in front, in special branches of the spinal cord, and the innervating muscles of the maxillofacial region are located in the nuclei of the brain stem. When a neuron enters a skeletal muscle cell, it bifurcates and creates a neuromuscular synapse on each fiber segment.

Functions of skeletal muscles:

• Holding the figure position
• Movement of a figure in space
• Movement of individual elements of the human figure relative to each other
• Performing breathing movements

Skeletal muscles, together with the skeleton, form the musculoskeletal system of the body, which helps a person maintain postures and move around. Skeletal muscles and the skeleton perform a protective function, protecting our heart, stomach, liver, and almost other organs from bruises.

What does the muscle tissue of the human heart, tongue, and stomach consist of?

The structural unit of heart tissue is the cardiomyocyte. What does it consist of? Here is the answer:

• A cardiomyocyte is a rectangular-shaped cell.
• Myocytes are located one after another in columns and, together with intercalary discs, form the conduction system of the heart.
• In their structure, intercalary disks are parts of the plasmalemma of neighboring 2 cells.
• The fibers lying nearby are connected in the form of an anastomosis, which ensures synchronized contraction.
• Another feature is the large number of mitochondria, which allows the heart to work continuously and experience almost no fatigue.
• The contractility of this type of muscle does not depend on the will of our body. Their activity depends on the rhythm impulses of the conductive systematization of the heart.

Muscular tissue of the human tongue and stomach: what is it like? Here is the answer:

• The human tongue and stomach are represented by a striated skeletal type of muscle.
• This tissue consists of multinuclear cylindrical fibers, which, when arranged in parallel, form light and dark areas (the so-called discs and stripes).
• The diameter of the forming fibers is 100 microns, and the length is from 1000 to 40,000 microns.

The contraction of these muscles is voluntary. Their innervation occurs with the participation of the spinal and cranial nerves.

Which human organs are formed by smooth and striated muscle tissue?

The main function of any muscle tissue is the ability to change the shape and length of the fibers, that is, to contract when excited. Which organs are formed by smooth and striated muscle tissue? Here is the answer:

Most internal organs contain smooth muscle tissue:

• Bladder
• Stomach, intestines
• Vascular walls
• Uterus and other internal organs

The length of smooth muscles reaches 500 microns and contains one nucleus - spindle-shaped myocytes. It is involuntary and inactive, slowly contracting and relaxing.

Transversely striated muscle tissue is part of:

• Cardiovascular muscle
• Pharyngeal section
• Esophageal section
• Language
• Eye muscles

This is the basis of skeletal muscles, since such muscle tissue is a multinuclear structure. For example, cardiac muscle consists of 1-2 cores, skeletal contain up to 100 cores. It has increased speed when contracting and relaxing. The fibrous filaments of skeletal muscles are large in length - up to twelve centimeters.

In what form does striated and smooth muscle tissue exist in humans and what does it look like?

Transversely striated muscle tissue is located on the bones of the human skeleton and, due to the fact that it contracts, it moves the human body and joints. Its myofibrils form transverse striations.

In what form does striated human muscle tissue exist and what does it look like? Here is the answer:

• It includes numerous cells that are elongated in length.
• Thanks to it, a person can perform various motor exercises.
• Striated muscle tissue is divided into skeletal and cardiac.

Smooth muscle muscles:

• Its main function is contraction, due to which the motor process occurs in our body.
• There are no transverse stripes on this type of fabric.
• This tissue is found in the stenotic tissue of any internal organ. Consists of cellular myocytes, which have different appearances.
• The length of this cell is from 20 to 500 microns, and the nucleus is located inside it.

Myocytes can have the following form:

• Oval
• Rounded
• Process
• Fusiform

A clear expression of the excitability of body tissues is considered to be their contraction, that is, a change in length that is observed in muscle tissues.

Differences between smooth and striated muscle tissue: comparison

From the above, you can understand the difference between these two types of fabrics. Here is a comparison of smooth and striated muscle tissue in humans:

• Striated muscle tissue is the basis of skeletal muscles, cardiac muscle, and musculoskeletal system. When excitable, it has the property of rapid fluctuations. Innervated by the somatic nervous system.
• Smooth muscle tissue predominates in internal organs: gastrointestinal tract, uterus, urinary tract. Has the property of slowly changing the membrane potential. Innervated by the autonomic nervous system. It has sensitivity to bioactive substances, the ability to plastic tone, regeneration and restoration.

The following conclusions can be drawn:

• Differences. Smooth muscles are mononuclear, contract slowly, involuntarily and get little tired, striated muscles are multinucleated, contract quickly, voluntarily and get tired quickly.
• Similarity. The presence of nerves and blood vessels, a sheath of connective tissue and bundles of muscle fibers are present in both muscles.

Below you will find some more important information about these muscle groups that will be useful to you when preparing for exams. Read on.

Distinguish between smooth and striated muscle tissue: answers to questions on the Unified State Exam

At school, during biology lessons, the teacher told you that they distinguish between smooth and striated muscle tissue. All questions on this topic on the Unified State Exam will be related to the functions, structure and mechanism of muscle contraction. The answers should be:

Video: Lecture No. 7. Muscle tissue - 2. Lecture on histology

They perform a very important function in the organisms of living beings - they form and line all organs and their systems. Of particular importance among them is the muscular one, since its importance in the formation of the external and internal cavities of all structural parts of the body is a priority. In this article we will consider what smooth muscle tissue is, its structural features, and properties.

Varieties of these fabrics

There are several types of muscles in the animal body:

• transversely striped;
• smooth muscle tissue.

Both of them have their own characteristic structural features, functions performed and properties exhibited. In addition, they are easy to distinguish from each other. After all, both have their own unique pattern, formed due to the protein components included in the cells.

Striated is also divided into two main types:

• skeletal;
• cardiac.

The name itself reflects the main areas of location in the body. Its functions are extremely important, because it is this muscle that ensures the contraction of the heart, the movement of the limbs and all other moving parts of the body. However, smooth muscles are no less important. What are its features, we will consider further.

In general, it can be noted that only the coordinated work performed by smooth and striated muscle tissue allows the entire body to function successfully. Therefore, it is impossible to determine which of them is more or less significant.

Smooth structural features

The main unusual features of the structure in question lie in the structure and composition of its cells - myocytes. Like any other, this tissue is formed by a group of cells that are similar in structure, properties, composition and functions. The general features of the structure can be outlined in several points.

1. Each cell is surrounded by a dense plexus of connective tissue fibers that looks like a capsule.
2. Each structural unit fits tightly to the other, intercellular spaces are practically absent. This allows the entire fabric to be tightly packed, structured and durable.
3. Unlike its striated counterpart, this structure may include cells of different shapes.

This, of course, is not the whole characteristic that it has. Structural features, as already stated, lie precisely in the myocytes themselves, their functioning and composition. Therefore, this issue will be discussed in more detail below.

Smooth muscle myocytes

Myocytes have different shapes. Depending on the location in a particular organ, they can be:

• oval;
• fusiform elongated;
• rounded;
• process.

However, in any case, their general composition is similar. They contain organelles such as:

• well defined and functioning mitochondria;
• Golgi complex;
• core, often elongated in shape;
• endoplasmic reticulum;
• lysosomes.

Naturally, the cytoplasm with the usual inclusions is also present. An interesting fact is that smooth muscle myocytes are externally covered not only with plasmalemma, but also with a membrane (basal). This provides them with an additional opportunity to contact each other.

These contact points constitute the features of smooth muscle tissue. Contact sites are called nexuses. It is through them, as well as through the pores that exist in these places in the membrane, that impulses are transmitted between cells, information, water molecules and other compounds are exchanged.

There is another unusual feature that smooth muscle tissue has. The structural features of its myocytes are that not all of them have nerve endings. This is why nexuses are so important. So that not a single cell is left without innervation, and the impulse can be transmitted through the neighboring structure through the tissue.

There are two main types of myocytes.

1. Secretory. Their main function is the production and accumulation of glycogen granules, maintaining a variety of mitochondria, polysomes and ribosomal units. These structures got their name because of the proteins they contain. These are actin filaments and contractile fibrin filaments. These cells are most often localized along the periphery of the tissue.
2. Smooth They look like spindle-shaped elongated structures containing an oval nucleus, displaced towards the middle of the cell. Another name is leiomyocytes. They differ in that they are larger in size. Some particles of the uterine organ reach 500 microns! This is a fairly significant figure compared to all other cells in the body, except perhaps the egg.

The function of smooth myocytes is also that they synthesize the following compounds:

• glycoproteins;
• procollagen;
• elastane;
• intercellular substance;
• proteoglycans.

The joint interaction and coordinated work of the designated types of myocytes, as well as their organization, ensure the structure of smooth muscle tissue.

Origin of this muscle

There is more than one source of formation of this type of muscle in the body. There are three main variants of origin. This is what explains the differences in the structure of smooth muscle tissue.

1. Mesenchymal origin. Most smooth fibers have this. It is from mesenchyme that almost all the tissues lining the inside of hollow organs are formed.
2. Epidermal origin. The name itself speaks about the places of localization - these are all the skin glands and their ducts. They are formed by smooth fibers that have this appearance. Sweat, salivary, mammary, lacrimal glands - all these glands secrete their secretions due to irritation of myoepithelial cells - structural particles of the organ in question.
3. Neural origin. Such fibers are localized in one specific place - this is the iris, one of the membranes of the eye. The contraction or dilation of the pupil is innervated and controlled by these smooth muscle cells.

Despite their different origins, the internal composition and performance properties of all in the fabric in question remain approximately the same.

Main properties of this fabric

The properties of smooth muscle tissue correspond to those of striated muscle tissue. In this they are united. This:

• conductivity;
• excitability;
• lability;
• contractility.

At the same time, there is one rather specific feature. If striated skeletal muscles are capable of contracting quickly (this is well illustrated by tremors in the human body), then smooth muscles can remain in a compressed state for a long time. In addition, its activities are not subject to the will and reason of man. Since it innervates

A very important property is the ability for long-term slow stretching (contraction) and the same relaxation. So, the work of the bladder is based on this. Under the influence of biological fluid (its filling), it is able to stretch and then contract. Its walls are lined with smooth muscles.

Cell proteins

The myocytes of the tissue in question contain many different compounds. However, the most important of them, providing the functions of contraction and relaxation, are protein molecules. Of these, here are:

• myosin filaments;
• actin;
• nebulin;
• connectin;
• tropomyosin.

These components are usually located in the cytoplasm of cells isolated from each other, without forming clusters. However, in some organs in animals, bundles or cords called myofibrils are formed.

The location of these bundles in the tissue is mainly longitudinal. Moreover, both myosin fibers and actin fibers. As a result, a whole network is formed in which the ends of some are intertwined with the edges of other protein molecules. This is important for fast and correct contraction of the entire tissue.

The contraction itself occurs like this: the internal environment of the cell contains pinocytosis vesicles, which necessarily contain calcium ions. When a nerve impulse arrives indicating the need for contraction, this bubble approaches the fibril. As a result, the calcium ion irritates actin and it moves deeper between the myosin filaments. This leads to the plasmalemma being affected and, as a result, the myocyte contracts.

Smooth muscle tissue: drawing

If we talk about striated fabric, it is easy to recognize by its striations. But as far as the structure we are considering is concerned, this does not happen. Why does smooth muscle tissue have a completely different pattern than its close neighbor? This is explained by the presence and location of protein components in myocytes. As part of smooth muscles, myofibril threads of different nature are localized chaotically, without a specific ordered state.

That is why the fabric pattern is simply missing. In the striated filament, actin is successively replaced by transverse myosin. The result is a pattern - striations, due to which the fabric got its name.

Under a microscope, smooth tissue looks very smooth and ordered, thanks to the elongated myocytes tightly adjacent to each other.

Areas of spatial location in the body

Smooth muscle tissue forms a fairly large number of important internal organs in the animal body. So, she was educated:

• intestines;
• genitals;
• blood vessels of all types;
• glands;
• organs of the excretory system;
• Airways;
• parts of the visual analyzer;
• organs of the digestive system.

It is obvious that the localization sites of the tissue in question are extremely diverse and important. In addition, it should be noted that such muscles form mainly those organs that are subject to automatic control.

Recovery methods

Smooth muscle tissue forms structures that are important enough to have the ability to regenerate. Therefore, it is characterized by two main ways of recovery from damage of various kinds.

1. Mitotic division of myocytes until the required amount of tissue is formed. The most common simple and fast method of regeneration. This is how the internal part of any organ formed by smooth muscles is restored.
2. Myofibroblasts are capable of transforming into smooth tissue myocytes when necessary. This is a more complex and rarely encountered way of regenerating this tissue.

Innervation of smooth muscles

Smooth does its work regardless of the desire or reluctance of a living creature. This occurs because it is innervated by the autonomic nervous system, as well as by the processes of the ganglion (spinal) nerves.

An example and proof of this is the reduction or increase in the size of the stomach, liver, spleen, stretching and contraction of the bladder.

Functions of smooth muscle tissue

What is the significance of this structure? Why do you need the following:

• prolonged contraction of organ walls;
• production of secrets;
• the ability to respond to irritation and influence with excitability.