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Cross-striped muscle tissue. Striated muscle tissue. Functions of the striated muscles

Muscle tissue: types, structural features, location in the body

Muscular tissue (textus musculares)- These are specialized tissues that provide movement (movement in space) of the body as a whole, as well as its parts and internal organs. The contraction of muscle cells or fibers is carried out with the help of myofilaments and special organelles - myofibrils and is the result of the interaction of contractile protein molecules.

According to the morphological classification, muscle tissues are divided into two groups:

I - striated (striated) muscle tissue - constantly contains complexes of actin and myosin myofilaments - myofibrils and has a transverse striation;

II - smooth (non-striated) muscle tissue - consists of cells that constantly contain only actin myofilaments and do not have transverse striation.

striated muscle tissue

The striated muscle tissue is subdivided into skeletal and cardiac. Both of these varieties develop from mesoderm.

Striated skeletal muscle tissue. This tissue forms skeletal muscles, muscles of the mouth, pharynx, part of the esophagus, muscles of the perineum, etc. In different departments, it has its own characteristics. Has a high rate of contraction and fatigue. This type of contraction is called tetanic. striated skeletal muscle tissue shrinks arbitrarily in response to impulses coming from the cerebral cortex. However, some muscles (intercostal, diaphragm, etc.) not only have an arbitrary nature of contraction, but also contract without the participation of consciousness under the influence of impulses from the respiratory center, and the muscles of the pharynx and esophagus contract involuntarily.

Structural unit is a striated muscle fiber- symplast, cylindrical in shape with rounded or pointed ends, with which the fibers are adjacent to each other or are woven into the connective tissue of the tendons and fascia.

Their contractile apparatus are striated myofibrils. that form a bundle of fibers. These are protein filaments located along the fiber. Their length coincides with the length of the muscle fiber. Myofibrils are made up of dark and light areas - disks. Since the dark and light discs of all myofibrils of one muscle fiber are located at the same level, a transverse striation is formed; therefore, the muscle fiber is called striated. Dark disks in polarized light have birefringence and are called anisotropic, or A-disks; light discs do not have birefringence and are called isotropic, or I-discs.

The different refractive power of the disks is due to their different structure. Light (I) discs homogeneous in composition: formed only by parallel thin filaments - actin myofilaments composed primarily of protein actin, as well as troponin And tropomyosin. Dark (A) discs heterogeneous: formed as thick myosin myofilaments made up of protein myosin, and partially penetrating between them thin actin myofilaments.

In the middle of each I-disk there is a dark line called Z-line, or telophragm. One end of the actin filaments is attached to it. The area of myofibril between two telophragms is called sarcomere. Sarcomere is a structural and functional unit of a myofibril. A light band can be distinguished in the center of the A-disk, or zone H containing only thick filaments. In the middle of it stands out a thin dark line M, or mesophragm. In this way, each sarcomere contains one A-disk and two halves of an I-disk.

Striated cardiac muscle tissue. Forms the myocardium of the heart. Contains, like skeletal, myofibrils, consisting of dark and light discs. Consists of cells cardiomyocytes interconnected by intercalary disks. In this case, chains of cardiomyocytes are formed - functional muscle fibers that anastomose with each other (pass one into another), forming a network. Such a system of connections provides contraction of the myocardium as a whole. Reduction heart muscle involuntary, regulated by the autonomic nervous system.

Among cardiomyocytes, there are:

· contractile (working) cardiomyocytes - contain fewer myofibrils than skeletal muscle fibers, but a lot of mitochondria, so they contract with less force, but do not get tired for a long time; with the help of intercalated disks, mechanical and electrical connection of cardiomyocytes is carried out;

· atypical (conductive) cardiomyocytes - form the conduction system of the heart for the formation and conduction of impulses to contractile cardiomyocytes;

secretory cardiomyocytes - located in the atria, capable of producing a hormone-like peptide - sodium uretic factor that lowers blood pressure.

smooth muscle tissue

It develops from the mesenchyme, is located in the wall of tubular organs (intestine, ureter, bladder, blood vessels), as well as the iris and ciliary (ciliary) body of the eye and muscles that lift hair in the skin.

Smooth muscle tissue has cellular structure (smooth myocyte) and has contractile apparatus in the form of smooth myofibrils. It contracts slowly and is able to be in a state of contraction for a long time, consuming a relatively small amount of energy and not tiring. This type of contraction is called tonic. Autonomic nerves approach smooth muscle tissue, and unlike skeletal muscle tissue, it is not subject to consciousness, although it is under the control of the cerebral cortex.

The smooth muscle cell has a spindle shape and pointed ends. It has a nucleus, cytoplasm (sarcoplasm), organelles and a membrane (sarcolemma). Contractile myofibrils are located along the cell periphery along its axis. These cells are closely adjacent to each other. The supporting apparatus in smooth muscle tissue are thin collagen and elastic fibers located around the cells and connecting them with each other.

Similar information.

Muscle tissues (Latin textus muscularis - “muscle tissue”) are tissues that are different in structure and origin, but similar in ability to pronounced contractions. They consist of elongated cells that receive irritation from the nervous system and respond to it with a contraction. They provide movement in the space of the body as a whole, its movement of organs inside the body (heart, tongue, intestines, etc.) and consist of muscle fibers. Cells of many tissues have the property of changing shape, but in muscle tissues this ability becomes the main function.

The main morphological features of muscle tissue elements are: an elongated shape, the presence of longitudinally arranged myofibrils and myofilaments - special organelles that provide contractility, the location of mitochondria next to the contractile elements, the presence of inclusions of glycogen, lipids and myoglobin.

Special contractile organelles - myofilaments or myofibrils - provide contraction that occurs when the two main fibrillar proteins interact in them - actin and myosin - with the obligatory participation of calcium ions. Mitochondria provide energy for these processes. The supply of energy sources is formed by glycogen and lipids. Myoglobin is a protein that binds oxygen and creates its reserve at the time of muscle contraction, when blood vessels are compressed (oxygen supply drops sharply).

By origin and structure, muscle tissues differ significantly from each other, but they are united by the ability to contract, which ensures the motor function of organs and the body as a whole. The muscle elements are elongated and connected either with other muscle elements or with supporting formations.

Types of muscle tissue

Distinguish smooth, striated muscle tissue and muscle tissue of the heart.

Smooth muscle tissue.

This tissue is formed from mesenchyme. The structural unit of this tissue is a smooth muscle cell. It has an elongated fusiform shape and is covered with a cell membrane. These cells are tightly adjacent to each other, forming layers and groups, separated from each other by a loose, unformed connective tissue.

The cell nucleus has an elongated shape and is located in the center. Myofibrils are located in the cytoplasm, they go along the periphery of the cell along its axis. They consist of thin threads and are the contractile element of the muscle.

Cells are located in the walls of blood vessels and most of the internal hollow organs (stomach, intestines, uterus, bladder). Smooth muscle activity is regulated by the autonomic nervous system. Muscle contractions do not obey the will of a person and therefore smooth muscle tissue is called involuntary muscles.

Striated muscle tissue.

This tissue was formed from myotomes, derivatives of the mesoderm. The structural unit of this tissue is the striated muscle fiber. This cylindrical body is a symplast. It is covered with a membrane - sarcolemma, and the cytoplasm is called - sarcoplasm, in which there are numerous nuclei and myofibrils. Myofibrils form a bundle of continuous fibers running from one end of the fiber to the other parallel to its axis. Each myofibril consists of discs that have a different chemical composition and appear dark and light under a microscope. Homogeneous discs of all myofibrils coincide, and therefore the muscle fiber appears to be striated. Myofibrils are the contractile apparatus of the muscle fiber.

All skeletal muscles are built from striated muscle tissue. Musculature is arbitrary, because. its contraction may occur under the influence of neurons in the motor cortex of the cerebral hemispheres.

Muscular tissue of the heart.

The myocardium, the middle layer of the heart, is made up of striated muscle cells (cardiomyocytes). There are two types of cells: typical contractile cells and atypical cardiac myocytes, which make up the conduction system of the heart.

Typical muscle cells perform a contractile function; they are rectangular in shape, in the center there are 1-2 nuclei, myofibrils are located along the periphery. There are intercalated discs between adjacent myocytes. With their help, myocytes are collected into muscle fibers, separated from each other by fine-fibrous connective tissue. Connecting fibers pass between adjacent muscle fibers, which provide contraction of the myocardium as a whole.

The conduction system of the heart is formed by muscle fibers, consisting of atypical muscle cells. They are larger than contractile ones, richer in sarcoplasm, but poorer in myofibrils, which often intersect. The nuclei are larger and not always in the center. The fibers of the conducting system are surrounded by a dense plexus of nerve fibers.

6. Muscle tissues: functions, types

Muscle tissues. The motor processes in the human and animal body are due to the contraction of muscle tissue, which has contractile structures. The muscle tissue is unstriated (smooth) And striated (striated) muscle tissue, including skeletal And cardiac.

The contractile elements are muscle fibrils - myofibrils(muscle filaments). Muscle tissue cells myocytes. Muscle tissues are excitable and contractile.

Muscle(Sterki P., 1984).

a - longitudinal section of the skeletal muscle; b - cardiac striated muscle tissue; c - unstriated (smooth) muscle tissue; 1 - sarcolemma; 2 - transverse striation; 3 - cores; 4 - insert discs; 5 - smooth muscle cells

Three types of muscle tissue:

smooth muscle tissue- consists of spindle-shaped cells with longitudinal striation.

Features: long-term reduction; has been in a reduced state for a long time; shrinks involuntarily.

Forms the walls of blood vessels and intestines.

smooth muscle fibers.

1 - protoplasm; 2 - core

striated musculoskeletal tissue- Cylindrical cells with striated striation.

Features: are reduced quickly; are in a reduced state for a long time; not much energy is spent on contraction; is reduced not arbitrarily, but at our will.

Forms skeletal muscles, muscles of the tongue, pharynx and parts of the esophagus.

striated cardiac muscle tissue.

Features: similar to striated musculoskeletal, but with intercalated discs and anastomoses; is reduced arbitrarily, regardless of our consciousness; there are atypical cells that form a conducting system.

Forms the muscles of the heart.

striated muscle fibers. Nuclei and transverse striation are visible.

The left fiber is torn; the sarcolemma is visible in the gap

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Muscle tissue: types, structural features, location in the body

According to the morphological classification, muscle tissues are divided into two groups:

I - striated (striated) muscle tissue - constantly contains complexes of actin and myosin myofilaments - myofibrils and has a transverse striation;

II - smooth (non-striated) muscle tissue - consists of cells that constantly contain only actin myofilaments and do not have transverse striation.

striated muscle tissue

The striated muscle tissue is subdivided into skeletal and cardiac.

Both of these varieties develop from mesoderm.

Striated skeletal muscle tissue. This tissue forms skeletal muscles, muscles of the mouth, pharynx, part of the esophagus, perineal muscles, etc.

It has its own characteristics in different departments. Has a high rate of contraction and fatigue. This type of contraction is called tetanic. striated skeletal muscle tissue shrinks arbitrarily in response to impulses coming from the cerebral cortex. However, some muscles (intercostal, diaphragm, etc.) not only have an arbitrary nature of contraction, but also contract without the participation of consciousness under the influence of impulses from the respiratory center, and the muscles of the pharynx and esophagus contract involuntarily.

Their contractile apparatus are striated myofibrils. that form a bundle of fibers.

These are protein filaments located along the fiber. Their length coincides with the length of the muscle fiber. Myofibrils are made up of dark and light areas - disks. Since the dark and light discs of all myofibrils of one muscle fiber are located at the same level, a transverse striation is formed; therefore, the muscle fiber is called striated. Dark disks in polarized light have birefringence and are called anisotropic, or A-disks; light discs do not have birefringence and are called isotropic, or I-discs.

The different refractive power of the disks is due to their different structure.

Light (I) discs homogeneous in composition: formed only by parallel thin filaments - actin myofilaments composed primarily of protein actin, as well as troponin And tropomyosin. Dark (A) discs heterogeneous: formed as thick myosin myofilaments made up of protein myosin, and partially penetrating between them thin actin myofilaments.

In the middle of each I-disk there is a dark line called Z-line, or telophragm.

One end of the actin filaments is attached to it. The area of myofibril between two telophragms is calledsarcomere. Sarcomere is a structural and functional unit of a myofibril. A light band can be distinguished in the center of the A-disk, or zone H containing only thick filaments. In the middle of it stands out a thin dark line M, or mesophragm. In this way, each sarcomere contains one A-disk and two halves of an I-disk.

Striated cardiac muscle tissue. Forms the myocardium of the heart.

Contains, like skeletal, myofibrils, consisting of dark and light discs. Consists of cells cardiomyocytes interconnected by intercalary disks.

In this case, chains of cardiomyocytes are formed - functional muscle fibers that anastomose with each other (pass one into another), forming a network. Such a system of connections provides contraction of the myocardium as a whole. Reduction heart muscle involuntary, regulated by the autonomic nervous system.

Among cardiomyocytes, there are:

contractile (working) cardiomyocytes - contain fewer myofibrils than skeletal muscle fibers, but a lot of mitochondria, so they contract with less force, but do not get tired for a long time; with the help of intercalated disks, mechanical and electrical connection of cardiomyocytes is carried out;
atypical (conductive) cardiomyocytes - form the conduction system of the heart for the formation and conduction of impulses to contractile cardiomyocytes;
secretory cardiomyocytes - located in the atria, capable of producing a hormone-like peptide - sodium uretic factor that lowers blood pressure.

smooth muscle tissue

Smooth muscle tissue has cellular structure (smooth myocyte) and has contractile apparatus in the form of smooth myofibrils.

It contracts slowly and is able to be in a state of contraction for a long time, consuming a relatively small amount of energy and not tiring. This type of contraction is called tonic. Autonomic nerves approach smooth muscle tissue, and unlike skeletal muscle tissue, it is not subject to consciousness, although it is under the control of the cerebral cortex.

The smooth muscle cell has a spindle shape and pointed ends.

It has a nucleus, cytoplasm (sarcoplasm), organelles and a membrane (sarcolemma). Contractile myofibrils are located along the cell periphery along its axis. These cells are closely adjacent to each other. The supporting apparatus in smooth muscle tissue are thin collagen and elastic fibers located around the cells and connecting them with each other.

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Functions of muscle tissues, types and structure

The body of all animals, including humans, consists of four types of tissues: epithelial, nervous, connective and muscular. The latter will be discussed in this article.

Types of muscle tissue

It is of three types:

striated;
smooth;
cardiac.

The functions of muscle tissues of different types are somewhat different.

And so is the building.

Where are muscle tissues located in the human body?

Muscle tissues of different types occupy different locations in the body of animals and humans.

So, from the heart muscles, as the name implies, the heart is built.

Skeletal muscles are formed from striated muscle tissue.

Smooth muscles line the inside of the cavities of organs that need to contract. These are, for example, the intestines, bladder, uterus, stomach, etc.

The structure of muscle tissue of different types is different. We'll talk about it in more detail later.

How is muscle tissue structured?

It is made up of large cells called myocytes.

They are also called fibres. Muscle tissue cells have several nuclei and a large number of mitochondria - organelles responsible for energy production.

In addition, the structure of human and animal muscle tissue provides for the presence of a small amount of intercellular substance containing collagen, which gives the muscles elasticity.

Let's look at the structure and function of muscle tissues of different types separately.

Structure and role of smooth muscle tissue

This tissue is controlled by the autonomic nervous system.

Therefore, a person cannot consciously contract muscles built from smooth tissue.

It is formed from the mesenchyme. It is a type of embryonic connective tissue.

This tissue contracts much less actively and quickly than striated tissue.

Smooth tissue is built from spindle-shaped myocytes with pointed ends.

The length of these cells can be from 100 to 500 micrometers, and the thickness is about 10 micrometers. The cells of this tissue are mononuclear. The nucleus is located in the center of the myocyte. In addition, such organelles as agranular EPS and mitochondria are well developed. Also in the cells of smooth muscle tissue there is a large number of inclusions from glycogen, which are nutrient reserves.

The element that provides the contraction of this type of muscle tissue are myofilaments.

They can be built from two contractile proteins: actin and myosin. The diameter of myofilaments, which are composed of myosin, is 17 nanometers, and those that are built from actin are 7 nanometers. There are also intermediate myofilaments, the diameter of which is 10 nanometers. The orientation of myofibrils is longitudinal.

The composition of the muscle tissue of this type also includes an intercellular substance made of collagen, which provides a connection between individual myocytes.

Functions of this type of muscle tissue:

Sphincter.
It consists in the fact that circular muscles are arranged from smooth tissues that regulate the transfer of contents from one organ to another or from one part of an organ to another.
Evacuation. It lies in the fact that smooth muscles help the body to remove unnecessary substances, and also take part in the process of childbirth.
Creation of vascular lumen.
Formation of the ligament apparatus. Thanks to him, many organs, such as, for example, the kidneys, are held in place.

Now let's look at the next type of muscle tissue.

striated

It is regulated by the somatic nervous system.

Therefore, a person can consciously regulate the work of muscles of this type. Skeletal muscles are formed from striated tissue.

This fabric is made up of fibers. These are cells that have many nuclei located closer to the plasma membrane. In addition, they contain a large number of glycogen inclusions. Organelles such as mitochondria are well developed.

They are located near the contractile elements of the cell. All other organelles are localized near the nuclei and are poorly developed.

The structures that cause striated tissue to contract are myofibrils.

Their diameter is from one to two micrometers. Myofibrils occupy most of the cell and are located in its center. The orientation of myofibrils is longitudinal. They consist of light and dark discs that alternate, which creates a transverse "banding" of the tissue.

Functions of this type of muscle tissue:

Provide movement of the body in space.
Responsible for the movement of body parts relative to each other.
Capable of maintaining body posture.
Participate in the process of temperature regulation: the more actively the muscles contract, the higher the temperature.
When frozen, striated muscles may begin to contract involuntarily. This explains the trembling in the body.
They perform a protective function. This is especially true of the abdominal muscles, which protect many internal organs from mechanical damage.
They act as a depot of water and salts.

cardiac muscle tissue

This fabric is similar to both striated and smooth at the same time. Like smooth, it is regulated by the autonomic nervous system.

However, it is reduced as actively as the striated one.

It is made up of cells called cardiomyocytes.

Functions of this type of muscle tissue:

It is only one: ensuring the movement of blood throughout the body.

It has a structure of myofibrils and protofibrils similar to skeletal muscle tissue and a mechanism of muscle contraction (myofibrils are few, they are thin, weak transverse striation)

Features of cardiac striated muscle tissue:

o Muscle fiber consists of chains of individual cells - cardiomyocytes(cells do not merge)

o All heart cells are connected by membrane contacts (intercalary discs) into a single muscle fiber, which ensures contraction of the myocardium as a whole (separately atrial myocardium and ventricular myocardium)

o Fibers have a small number of nuclei

Cardiac muscle tissue is divided into two types:

o working muscle tissue- makes up 99% of the mass of the myocardium of the heart (provides contraction of the heart)

o conductive muscle tissue- consists of modified, incapable of reduction, atypical cells

Forms nodes in the myocardium, where electrical impulses are generated and from where they propagate for heart contractions - conduction system of the heart

Functions of cardiac striated muscle tissue

1. Generation and propagation of electrical impulses for contraction of the myocardium of the heart

2. involuntary rhythmic contractions of the myocardium of the heart to push blood (automatic myocardium)

smooth muscle tissue

Localized only in internal organs (walls of the digestive tract, walls of the respiratory tract, blood and lymphatic vessels, bladder, uterus, oblique muscles of the hair of the skin, muscles surrounding the pupil)

Cells solitary, long, spindle-shaped, mononuclear, dividing throughout life

The internal structure of the cell is the same as that of the muscle fibers of striated tissue (myofibrils, consisting of protofibrils and proteins of actin and myosin)

Light areas of actin and dark areas of myosin of different myofibrils are disordered, which leads to the absence of transverse striation of smooth muscle cells

They form ribbons, layers, strands in the walls of internal organs (do not form separate muscles)

Innervated by autonomic nerves

The smooth muscles of the internal organs are weak, shrink involuntarily without the participation of consciousness, slowly, do not get tired, are able to be in a state of contraction for a very long time (hours, days) - tonic contractions (consume little power to operate)

Smooth muscle functions

1. Work (motor function) of internal organs (peristalsis, excretion of urine, childbirth, etc.)

2. The tone of the blood and lymphatic vessels (a change in the diameter of the vessels leads to a change in pressure and blood velocity)

nervous tissue

In the process of embryogenesis, it is formed by cell division of the ectoderm

properties of nervous tissue excitability And conductivity

Organs formed by nervous tissue: brain, spinal cord, ganglions (ganglia), nerves

· Consists of nerve cells (neurons)– 15% of all cells and neuroglia(intercellular substance)

Neuroglia has cells (gliocytes) - 85% of all cells

Functions of neuroglia

1. Trophic (supplying neurons with everything necessary for life)

2. Support (skeleton of nervous tissue)

3. Isolating, protective (protection from adverse conditions and electrical insulation of neurons)

4. Regeneration of nerve cell processes

· Nerve cells - neurons- mononuclear, with processes that do not divide after birth (the total number of neurons in the human nervous system, according to various estimates, ranges from 100 billion to 1 trillion)

· Have body(contains granules, lumps) and processes

In neurons many mitochondria, the Golgi complex and the system of support-transport microtubules are very well developed - neurofibrils for the transport of substances (neurotransmitters)

Distinguish two types of processes:

o axon- always one, long (up to 1.5 m), not branching (goes beyond the organ of the nervous system)

Axon functions- conducting a command (in the form of an electrical impulse) from a neuron to other neurons or to working tissues and organs

o Dendrites- numerous (up to 15), short, branched (have sensitive nerve endings at the ends - receptors)

Functions of dendrites- perception of irritation and conduction of an electrical impulse (information) from receptors to the body of a neuron (to the brain)

· Nerve fibers

Structure of a neuron:

The structure of a multipolar neuron:
1 - dendrites; 2 - neuron body; 3 - core; 4 - axon; 5 - myelin sheath; 6 - branching of the axon

· The gray matter of the brain is a collection of bodies of neurons- the substance of the cerebral cortex, the cerebellar cortex, the horns of the gray matter of the spinal cord and nerve nodes (ganglia)

· The white matter of the brain set of processes of neurons (axons and dendrites)

Types of neurons(according to the number of processes)

o Unipolar- have one process (axon)

o Bipolar- have two processes (one axon and one dendrite)

o Multipolar - have many processes (one axon and many dendrites) - neurons of the spinal cord and brain

Types of neurons(by function)

o Sensitive (centripetal, sensory, efferent) - perceive irritations from receptors, form feelings, sensations (bipolar)

o Insertion (associative)- analysis, the biological meaning of information received from receptors, the development of a response command, connection of sensory neurons with motor and other neurons (one neuron can connect to 20 thousand other neurons); 60% of all neurons, multipolar

o Motor (centrifugal, motor, effector)- transmission of the command of the intercalary neuron to the working organs (muscles, glands); multipolar, with a very long axon

o Brake

o Some neurons are capable of synthesizing hormones: oxytocin and prolactin ( neurosecretory cells hypothalamus diencephalon)

· Nerve fibers- processes of nerve cells covered with connective tissue membranes

There are two types of nerve fibers (depending on the structure of the sheath): pulpy and non-pulpy

Pulmonary (myelinated) nerve fibers	Unmyelinated (unmyelinated) nerve fibers
1. Sheathed with neuroglial cells (Schwann cells) to electrically insulate the fiber	1. Too
2. Membranes Schwann cell membranes contain a substance - myelin(significantly increases electrical insulation)	2. Do not contain myelin (less effective electrical insulation)
3. The fiber has areas without a sheath - intercepts of Ranvier (accelerate the conduction of a nerve impulse along the fiber)	3. No
4. Thick	4. Thin
5. The speed of nerve impulses up to 120 m / s	5. The speed of the nerve impulse is about 10 m / s
6. Form the nerves of the central nervous system	6. Form nerves of the autonomic nervous system

o Hundreds and thousands of pulpy and non-pulmonic nerve fibers that extend beyond the CNS, covered with connective tissue form nerves (nerve trunks)

Types of nerves

o Sensory nerves - formed exclusively by dendrites, serve to conduct sensitive information from the body's receptors to the brain (into sensitive neurons)

o motor nerves- formed from axons: they serve to conduct a brain command from a motor neuron to working tissues and organs (effectors)

o mixed nerves- consist of dendrites and axons; also serve to conduct sensitive information to the brain and brain commands to working organs (for example, 31 pairs of spinal nerves)

Communication and interaction between nerve cells is carried out using synapses

Synapse - the place of contact of an axon with another process or body of another cell (nervous or somatic), in which the transmission of a nerve (electrical) impulse occurs

o The transmission of a nerve impulse in the synapse is carried out with the help of chemicals - neurotransmitters(adrenaline, norepinephrine, acetylcholine, serotonin, dopamine, etc.)

o Synapses are located on the branches of the end of the axon

o The number of synapses on one neuron can reach up to 10,000, so the total number of contacts in the nervous system approaches an astronomical figure

o It is possible that the number of contacts and multipolar neurons in the nervous system are one of the indicators of a person's mental development and labor specialization. With age, the number of contacts decreases significantly

animal tissue(human tissues)

Reflex. reflex arc

Reflex - response of the body to irritation (change) of the external and internal environment, carried out with the participation of the nervous system

o the main form of activity of the central nervous system

v The founder of the idea of reflexes as unconscious automatic acts associated with the lower parts of the nervous system is the French philosopher and naturalist R. Descartes (XVII century). In the XVIII century. Czech anatomist and physiologist G. Prohaska introduced the science of this term "reflex"

v I.P. Pavlov, Russian academician (XX century) divided the reflex into unconditional ( congenital, species, group) and conditional (purchased, individual)

Muscle tissues They are a group of tissues of different origin and structure, united on the basis of a common feature - a pronounced contractile ability, thanks to which they can perform their main function - to move the body or its parts in space.

The most important properties of muscle tissue. Structural elements of muscle tissues (cells, fibers) have an elongated shape and are capable of contraction due to the powerful development of the contractile apparatus. The latter is characterized by a highly ordered arrangement actin And myosin myofilaments, creating optimal conditions for their interaction. This is achieved by the connection of contractile structures with special elements of the cytoskeleton and the plasmolemma. (sarcolemma) performing a supporting function. In part of muscle tissue, myofilaments form organelles of special significance - myofibrils. Muscle contraction requires a significant amount of energy, therefore, in the structural elements of muscle tissues there are a large number of mitochondria and trophic inclusions (lipid drops, glycogen granules) containing substrates - energy sources. Since muscle contraction proceeds with the participation of calcium ions, the structures that carry out its accumulation and release are well developed in muscle cells and fibers - the agranular endoplasmic reticulum. (sarcoplasmic reticulum), caveolae.

Muscle tissue classification based on features of their (a) structure and function (morphofunctional classification) and (b) origin (histogenetic classification).

Morphofunctional classification of muscle tissues highlights striated (striated) muscle tissue And smooth muscle tissue. Striated muscle tissues are formed by structural elements (cells, fibers), which have a transverse striation due to a special ordered mutual arrangement of actin and myosin myofilaments in them. The striated muscle tissues are skeletal And cardiac muscle tissue. Smooth muscle tissue consists of cells that do not have transverse striations. The most common type of this tissue is smooth muscle tissue, which is part of the walls of various organs (bronchi, stomach, intestines, uterus, fallopian tube, ureter, bladder and blood vessels).

Histogenetic classification of muscle tissues identifies three main types of muscle tissue: somatic(skeletal muscle tissue) coelomic(heart muscle) and mesenchymal(smooth muscle tissue of internal organs), as well as two additional ones: myoepithelial cells(modified epithelial contractile cells in the terminal sections and small excretory ducts of some glands) and myoneural elements(contractile cells of neural origin in the iris).

Skeletal striated (striated) muscle tissue in its mass exceeds any other tissue of the body and is the most common muscle tissue of the human body. It ensures the movement of the body and its parts in space and the maintenance of a posture (part of the locomotor apparatus), forms the oculomotor muscles, the muscles of the wall of the oral cavity, tongue, pharynx, and larynx. A similar structure has non-skeletal visceral striated muscle tissue, which is found in the upper third of the esophagus, is part of the external anal and urethral sphincters.

Skeletal striated muscle tissue develops in the embryonic period from myotomes somites, giving rise to actively dividing myoblasts- cells that are arranged in chains and merge with each other at the ends to form muscle tubules (myotubules), turning into muscle fibres. Such structures, formed by a single giant cytoplasm and numerous nuclei, are traditionally referred to in Russian literature as symplasts(in this case - myosymplasts), however, this term does not exist in accepted international terminology. Some myoblasts do not fuse with others, being located on the surface of the fibers and giving rise to myosatellitocytes- small cells, which are the cambial elements of skeletal muscle tissue. Skeletal muscle tissue is made up of bundles striated muscle fibers(Fig. 87), which are its structural and functional units.

Muscle fibers skeletal muscle tissue are cylindrical formations of variable length (from millimeters to 10-30 cm). Their diameter also varies widely depending on belonging to a particular muscle and type, functional state, degree of functional load, nutritional status.

and other factors. In muscles, muscle fibers form bundles in which they lie parallel and, deforming each other, often acquire an irregular multifaceted shape, which is especially clearly seen in transverse sections (see Fig. 87). Between the muscle fibers are thin layers of loose fibrous connective tissue that carry blood vessels and nerves - endomysium. The transverse striation of skeletal muscle fibers is due to the alternation of dark anisotropic discs (bands A) and bright isotropic disks (bands I). Each isotropic disk is cut in two by a thin dark line Z - telophragm(Fig. 88). The nuclei of the muscle fiber are relatively light, with 1-2 nucleoli, diploid, oval, flattened - they lie on its periphery under the sarcolemma and are located along the fiber. Outside, the sarcolemma is covered with a thick basement membrane, into which reticular fibers are woven.

Myosatellitocytes (myosatellite cells) - small flattened cells located in shallow depressions of the sarcolemma of the muscle fiber and covered with a common basement membrane (see Fig. 88). The nucleus of the myosatellitocyte is dense, relatively large, the organelles are small and few. These cells are activated when muscle fibers are damaged and provide their reparative regeneration. Merging with the rest of the fiber under increased load, myosatellitocytes participate in its hypertrophy.

myofibrils form the contractile apparatus of the muscle fiber, are located in the sarcoplasm along its length, occupying the central part, and are clearly identified on the transverse sections of the fibers in the form of small dots (see Fig. 87 and 88).

Myofibrils have their own transverse striation, and in the muscle fiber they are arranged in such an orderly manner that the isotropic and anisotropic disks of different myofibrils coincide with each other, causing the transverse striation of the entire fiber. Each myofibril is formed by thousands of repeating successively interconnected structures - sarcomeres.

Sarcomere (myomer) is a structural and functional unit of a myofibril and is its section located between two telophragms (Z lines). It includes an anisotropic disk and two halves of isotropic disks - one half on each side (Fig. 89). The sarcomere is formed by an ordered system thick (myosin) And thin (actin) myofilaments. Thick myofilaments are associated with mesophragma (line M) and are concentrated in an anisotropic disk,

and thin myofilaments are attached to telophragms (Z lines), form isotropic disks and partially penetrate the anisotropic disk between thick filaments up to light H stripes at the center of the anisotropic disk.

The mechanism of muscle contraction described the theory of sliding threads, according to which the shortening of each sarcomere (and, consequently, myofibrils and the entire muscle fiber) during contraction occurs due to the fact that as a result of the interaction of actin and myosin in the presence of calcium and ATP, thin filaments are pushed into the gaps between thick ones without changing their length. In this case, the width of the anisotropic disks does not change, while the width of the isotropic disks and H bands decreases. The strict spatial ordering of the interaction of many thick and thin myofilaments in the sarcomere is determined by the presence of a complexly organized supporting apparatus, which, in particular, includes the telophragm and mesophragm. Calcium is released from sarcoplasmic reticulum, elements of which braid each myofibril, after receiving a signal from the sarcolemma through T-tubules(the set of these elements is described as sarcotubular system).

Skeletal muscle as an organ consists of bundles of muscle fibers connected together by a system of connective tissue components (Fig. 90). Covers the outside of the muscle epimysium- a thin, strong and smooth sheath made of dense fibrous connective tissue, extending deeper into the organ thinner connective tissue septa - perimysium, which surrounds the bundles of muscle fibers. From the perimysium into the bundles of muscle fibers depart the thinnest layers of loose fibrous connective tissue surrounding each muscle fiber - endomysium.

Types of muscle fibers in skeletal muscle - varieties of muscle fibers with certain structural, biochemical and functional differences. Typing of muscle fibers is carried out on preparations when setting up histochemical reactions for detecting enzymes - for example, ATPase, lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) (Fig. 91), etc. In a generalized form, three main types of muscle fibers can be conditionally distinguished, between which there are transitional options.

Type I (red)- slow, tonic, resistant to fatigue, with a small force of contraction, oxidative. Characterized by small diameter, relatively thin myofibrils,

high activity of oxidative enzymes (for example, SDH), low activity of glycolytic enzymes and myosin ATPase, predominance of aerobic processes, high content of myoglobin pigment (which determines their red color), large mitochondria and lipid inclusions, rich blood supply. Numerically predominate in muscles performing long-term tonic loads.

Type IIB (white)- fast, tetanic, easily tiring, with great force of contraction, glycolytic. They are characterized by large diameter, large and strong myofibrils, high activity of glycolytic enzymes (for example, LDH) and ATPase, low activity of oxidative enzymes, predominance of anaerobic processes, relatively low content of small mitochondria, lipids and myoglobin (which determines their light color), a significant amount of glycogen, relatively poor blood supply. They predominate in muscles that perform fast movements, for example, the muscles of the limbs.

Type IIA (intermediate)- fast, resistant to fatigue, with great strength, oxidative-glycolytic. On preparations, they resemble type I fibers. They are equally capable of using the energy obtained by oxidative and glycolytic reactions. According to their morphological and functional characteristics, they occupy a position intermediate between type I and IIB fibers.

Human skeletal muscles are mixed, that is, they contain fibers of various types, which are distributed in them in a mosaic pattern (see Fig. 91).

Cardiac striated (striated) muscle tissue occurs in the muscular membrane of the heart (myocardium) and the mouths of the large vessels associated with it. The main functional property of cardiac muscle tissue is the ability to spontaneous rhythmic contractions, the activity of which is influenced by hormones and the nervous system. This tissue provides the contractions of the heart that keep the blood circulating in the body. The source of development of cardiac muscle tissue is myoepicardial plate of the visceral leaf of the splanchnotome(coelomic lining in the neck of the embryo). The cells of this plate (myoblasts) actively multiply and gradually turn into cardiac muscle cells - cardiomyocytes (cardiac myocytes). Lined up in chains, cardiomyocytes form complex intercellular connections - insert discs, linking them to cardiac muscle fibers.

Mature cardiac muscle tissue is formed by cells - cardiomyocytes, connected to each other in the region of the intercalated discs and forming a three-dimensional network of branching and anastomosing cardiac muscle fibers(Fig. 92).

Cardiomyocytes (cardiac myocytes) - cylindrical or branching cells, larger in the ventricles. In the atria, they usually have an irregular shape and are smaller. These cells contain one or two nuclei and a sarcoplasm, covered with a sarcolemma, which is surrounded by a basement membrane on the outside. Their nuclei - light, with a predominance of euchromatin, well-marked nucleoli - occupy a central position in the cell. In an adult, a significant part of cardiomyocytes - polyploid, more than half - dual-core. The sarcoplasm of cardiomyocytes contains numerous organelles and inclusions, in particular, a powerful contractile apparatus, which is highly developed in contractile (working) cardiomyocytes (especially in ventricular ones). The contractile apparatus is presented cardiac striated myofibrils, skeletal muscle tissue fibers similar in structure to myofibrils (see Fig. 94); together they cause transverse striation of cardiomyocytes.

Between the myofibrils at the poles of the nucleus and under the sarcolemma are very numerous and large mitochondria (see Fig. 93 and 94). Myofibrils are surrounded by elements of the sarcoplasmic reticulum associated with T-tubules (see Fig. 94). The cytoplasm of cardiomyocytes contains the oxygen-binding pigment myoglobin and accumulations of energy substrates in the form of lipid drops and glycogen granules (see Fig. 94).

Types of cardiomyocytes in cardiac muscle tissue differ in structural and functional features, biological role and topography. There are three main types of cardiomyocytes (see Fig. 93):

1)contractile (working) cardiomyocytes form the main part of the myocardium and are characterized by a powerfully developed contractile apparatus, which occupies most of their sarcoplasm;

2)conducting cardiomyocytes have the ability to generate and quickly conduct electrical impulses. They form knots, bundles and fibers conducting system of the heart and are divided into several subtypes. They are characterized by weak development of the contractile apparatus, light sarcoplasm and large nuclei. IN conductive heart fibers(Purkinje) these cells are large (see Fig. 93).

3)secretory (endocrine) cardiomyocytes located in the atria (especially right

vom) and are characterized by a process form and weak development of the contractile apparatus. In their sarcoplasm, near the poles of the nucleus, there are dense granules surrounded by a membrane containing atrial natriuretic peptide(a hormone that causes loss of sodium and water in the urine, vasodilation, lowering blood pressure).

Insert discs carry out communication of cardiomyocytes with each other. Under a light microscope, they look like transverse straight or zigzag stripes crossing the cardiac muscle fiber (see Fig. 92). Under an electron microscope, the complex organization of the intercalated disk is determined, which is a complex of intercellular connections of several types (see Fig. 94). In the area of transverse (oriented perpendicular to the location of myofibrils) sections of the intercalated disk, neighboring cardiomyocytes form numerous interdigitations connected by contacts of the type desmosome And adhesive fascias. Actin filaments are attached to the transverse sections of the sarcolemma of the intercalated disc at the level Z lines. On the sarcolemma of the longitudinal sections of the intercalary disc there are numerous gap junctions (nexuses), providing ionic bonding of cardiomyocytes and transmission of the contraction impulse.

smooth muscle tissue part of the wall of hollow (tubular) internal organs - bronchi, stomach, intestines, uterus, fallopian tubes, ureters, bladder (visceral smooth muscle) as well as vessels (vascular smooth muscle). Smooth muscle tissue is also found in the skin, where it forms the muscles that raise the hair, in the capsules and trabeculae of some organs (spleen, testis). Due to the contractile activity of this tissue, the activity of the organs of the digestive tract, the regulation of respiration, blood and lymph flow, the excretion of urine, the transport of germ cells, etc. are ensured. The source of development of smooth muscle tissue in the embryo is mesenchyme. The properties of smooth myocytes are also possessed by some cells of a different origin - myoepithelial cells(modified contractile epithelial cells in some glands) and myoneural cells irises of the eye (develop from the neural bud). The structural and functional unit of smooth muscle tissue is smooth myocyte (smooth muscle cell).

Smooth myocytes (smooth muscle cells) - elongated cells predominantly faith-

tenoid shape, not having transverse striation and forming numerous connections with each other (Fig. 95-97). Sarcolemma each smooth myocyte is surrounded basement membrane, into which thin reticular, collagen and elastic fibers are woven. Smooth myocytes contain one elongated diploid nucleus with a predominance of euchromatin and 1-2 nucleoli located in the central thickened part of the cell. In the sarcoplasm of smooth myocytes, moderately developed organelles of general importance are located together with inclusions in cone-shaped areas at the poles of the nucleus. Its peripheral part is occupied by the contractile apparatus - actin And myosin myofilaments, which in smooth myocytes do not form myofibrils. Actin myofilaments are attached in the sarcoplasm to oval or fusiform dense bodies(see Fig. 97) - structures homologous to Z lines in striated tissues; similar formations associated with the inner surface of the sarcolemma are called dense plates.

The contraction of smooth myocytes is provided by the interaction of myofilaments and develops in accordance with the model of sliding filaments. As in striated muscle tissues, the contraction of smooth myocytes is induced by the influx of Ca 2+ into the sarcoplasm, which is released in these cells. sarcoplasmic reticulum And caveoli- Numerous flask-shaped protrusions of the surface of the sarcolemma. Due to their pronounced synthetic activity, smooth myocytes produce and secrete (like fibroblasts) collagens, elastin, and components of an amorphous substance. They are also able to synthesize and secrete a number of growth factors and cytokines.

Smooth muscle tissue in organs usually represented by layers, bundles and layers of smooth myocytes (see Fig. 95), within which the cells are connected by interdigitations, adhesive and gap junctions. The arrangement of smooth myocytes in layers is such that the narrow part of one cell is adjacent to the wide part of the other. This contributes to the most compact packing of myocytes, ensuring the maximum area of their mutual contacts and high tissue strength. In connection with the described arrangement of smooth muscle cells in the layer, the cross sections adjoin sections of myocytes, cut in the wide part and in the region of the narrow edge (see Fig. 95).

MUSCLE TISSUE

Rice. 87. Skeletal striated muscle tissue

1 - muscle fiber: 1.1 - sarcolemma covered with a basement membrane, 1.2 - sarcoplasm, 1.2.1 - myofibrils, 1.2.2 - fields of myofibrils (Konheim); 1.3 - nuclei of the muscle fiber; 2 - endomysium; 3 - layers of loose fibrous connective tissue between bundles of muscle fibers: 3.1 - blood vessels, 3.2 - fat cells

Rice. 88. Skeletal muscle fiber (diagram):

1 - basement membrane; 2 - sarcolemma; 3 - myosatellitocyte; 4 - the core of the myosymplast; 5 - isotropic disk: 5.1 - telophragm; 6 - anisotropic disk; 7 - myofibrils

Rice. 89. Plot of myofibril fiber of skeletal muscle tissue (sarcomere)

Drawing with EMF

1 - isotropic disk: 1.1 - thin (actin) myofilaments, 1.2 - telophragm; 2 - anisotropic disk: 2.1 - thick (myosin) myofilaments, 2.2 - mesophragm, 2.3 - H band; 3 - sarcomere

Rice. 90. Skeletal muscle (cross section)

Stain: hematoxylin-eosin

1 - epimysium; 2 - perimysium: 2.1 - blood vessels; 3 - bundles of muscle fibers: 3.1 - muscle fibers, 3.2 - endomysium: 3.2.1 - blood vessels

Rice. 91. Types of muscle fibers (cross section of skeletal muscle)

Histochemical reaction for the detection of succinate dehydrogenase (SDH)

1 - fibers of type I (red fibers) - with high activity of SDH (slow, oxidative, resistant to fatigue); 2 - IIB type fibers (white fibers) - with low SDH activity (fast, glycolytic, fatigued); 3 - fibers of type IIA (intermediate fibers) - with moderate activity of SDH (fast, oxidative-glycolytic, resistant to fatigue)

Rice. 92. Cardiac striated muscle tissue

Stain: iron hematoxylin

A - longitudinal section; B - cross section:

1 - cardiomyocytes (form cardiac muscle fibers): 1.1 - sarcolemma, 1.2 - sarcoplasm, 1.2.1 - myofibrils, 1.3 - nucleus; 2 - insert disks; 3 - anastomoses between fibers; 4 - loose fibrous connective tissue: 4.1 - blood vessels

Rice. 93. Ultrastructural organization of cardiomyocytes of various types

Drawings with EMF

A - contractile (working) cardiomyocyte of the ventricle of the heart:

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria, 3.3 - lipid drops; 4 - core; 5 - insert disk.

B - cardiomyocyte of the conduction system of the heart (from the subendocardial network of Purkinje fibers):

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria; 3.3 - glycogen granules, 3.4 - intermediate filaments; 4 - cores; 5 - insert disk.

B - endocrine cardiomyocyte from the atrium:

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria, 3.3 - secretory granules; 4 - core; 5 - insert disc

Rice. 94. Ultrastructural organization of the region of the intercalated disc between neighboring cardiomyocytes

Drawing with EMF

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.1.1 - sarcomere, 3.1.2 - isotropic disk, 3.1.3 - anisotropic disk, 3.1.4 - bright H band, 3.1.5 - telophragm, 3.1.6 - mesophragm, 3.2 - mitochondria, 3.3 - T-tubules, 3.4 - elements of the sarcoplasmic reticulum, 3.5 - lipid drops, 3.6 - glycogen granules; 4 - intercalary disc: 4.1 - interdigitation, 4.2 - adhesive fascia, 4.3 - desmosome, 4.4 - gap junction (nexus)

Rice. 95. Smooth muscle tissue

Stain: hematoxylin-eosin

A - longitudinal section; B - cross section:

1 - smooth myocytes: 1.1 - sarcolemma, 1.2 - sarcoplasm, 1.3 - nucleus; 2 - layers of loose fibrous connective tissue between bundles of smooth myocytes: 2.1 - blood vessels

Rice. 96. Isolated smooth muscle cells

stain: hematoxylin

1 - core; 2 - sarcoplasm; 3 - sarcolemma

Rice. 97. Ultrastructural organization of a smooth myocyte (section of a cell)

Drawing with EMF

1 - sarcolemma; 2 - sarcoplasm: 2.1 - mitochondria, 2.2 - dense bodies; 3 - core; 4 - basement membrane

These tissues are referred to as excitable tissues, i.e. they are capable of responding to irritation with excitation and conducting it at a distance.

Muscle tissues

There are smooth, striated muscle tissue and muscle tissue of the heart (Fig. 5).

Smooth muscle tissue.

Striated muscle tissue.

This tissue was formed from myotomes, derivatives of the mesoderm. The structural unit of this tissue is the striated muscle fiber. This cylindrical body is a symplast. It is covered with a shell - sarcolemma, and the cytoplasm is called - sarcoplasm, in which there are numerous nuclei and myofibrils. Myofibrils form a bundle of continuous fibers running from one end of the fiber to the other parallel to its axis. Each myofibril consists of discs that have a different chemical composition and appear dark and light under a microscope. Homogeneous discs of all myofibrils coincide, and therefore the muscle fiber appears to be striated. Myofibrils are the contractile apparatus of the muscle fiber.

Muscular tissue of the heart.

Myocardium - the middle layer of the heart - is built from striated muscle cells (cardiomyocytes). There are two types of cells: typical contractile cells and atypical cardiac myocytes, which make up the conduction system of the heart.

nervous tissue.

Nervous tissue consists of nerve cells with a specific function, and neuroglia, which perform protective, trophic and support functions. It comes from the ectoderm.

A nerve cell, or neuron, is characterized by the ability to perceive stimuli, enter a state of excitation and transmit it to other cells of the body. Thanks to this, the interconnection of organs and tissues, the regulation of all body functions and its adaptation to the environment is carried out.

Nerve cells have a different shape and size and consist of a body and processes (Fig. 6).

The processes of the nerve cell are divided into two types:

· Neurites, or axons, along which excitation (impulse) is transmitted from the cell body to the periphery. The axon always departs alone from the cell and ends with the terminal apparatus in the working organ or on another neuron.
· Dendrites- processes along which an impulse is transmitted from the periphery to the cell body. There are many of them and they branch.

According to the number of processes, nerve cells are divided into three types (Fig. 7):

· Unipolar - cells with one branch. Not found in humans.
· Bipolar- have one neurite in the CNS and one dendrite going to the periphery. They are located in the spinal ganglions.
· Multipolar- have one neurite and many dendrites. A person has the most of them.

The nucleus of the nerve cell has a rounded shape and is located in the center.

In the cytoplasm of neurons there are neurofibrils, which are thin threads. In the body of the nerve cell, they form a dense network. In the processes, neurofibrils are arranged parallel to each other.

neuroglia represented by cells of various shapes with a large number of processes. There are more of these cells than nerve cells.

Nerve fibres. The processes of nerve cells with sheaths are called nerve fibers. Distinguish between myelinated (pulp) and non-myelinated (non-pulp). The processes are located in the center of the nerve fiber and are called the axial cylinder, which is covered with a sheath formed by neuroglial cells (lemmocytes).

unmyelinated fibers are an axial cylinder covered only by a sheath of lemmocytes.

myelinated- much thicker. They also consist of an axial cylinder, but they have two layers of the membrane: an inner, thicker one - myelin, and an outer, thin one, consisting of lemmocytes. Outside, the myelin fiber is covered with a thin connective tissue sheath - neurilemma.

Nerve endings. All nerve fibers end in nerve endings. There are three groups:

· Efferent. They can be of two types: motor and secretory. Motor endings are the end devices of the axons of the somatic and autonomic nervous system.
· sensitive(receptors) are the terminal devices of the dendrites of sensitive neurons. They are divided into free, consisting of a branching of the axial cylinder, and non-free, containing all the components of the nerve fiber, covered with a capsule.
· end branches, forming interneuronal synapses, carrying out the connection of neurons with each other.