Where are muscles located in the body of vertebrates?
What are the functions of muscles in an animal body?
The muscles of vertebrates are differentiated and represented by many differently located muscles; mammals are characterized by the presence of a diaphragm, subcutaneous muscles and facial expressions are developed.
An important feature of animals is their ability to move. The movement of most animals is the result of muscle contractions. Muscles are made up of muscle tissue. There are smooth and striated muscle tissues. Their main properties are excitability and contractility.
2. Where can you find smooth muscles, and where are striated muscles?
Smooth muscles form the walls of blood vessels, respiratory tract, stomach, and intestines. Skeletal muscles include the striated muscles of the head, trunk and limbs, as well as the heart.
3. How common property do all muscles have and what are the conditions for their work?
The main property of muscle tissue is contractility. The work of muscles is based on this property. In an excited state, the muscle shortens and thickens - contracts, then relaxes and returns to its previous size. When contracting, muscles perform work to move the body, limbs or hold a load. For normal muscle function, nutrients and oxygen supplied with the blood are necessary, since energy muscle contraction associated with biological oxidation organic matter muscle fiber. The breakdown products formed during muscle work are carried away by the blood. This is why deterioration in blood supply disrupts muscle activity and often causes pain.
4. How do facial muscles differ from chewing muscles?
The masticatory muscles move the lower jaw, ensure chewing of food and are involved in the formation of speech sounds. Facial muscles change facial expression. With the help of these muscles, a person’s face can express feelings of joy and grief, kindness and anger, friendliness and dissatisfaction.
5. Why are many of the muscles that move the shoulder and hip located on the torso? Why are the muscles that compress and unclench the fingers of the hand located on the forearm?
Amplitude - the range of movements - depends on the length of the muscle fibers, and strength - on the area cross section muscle bundle. To bend the hand into a fist, the muscles must be of sufficient length. That is why the muscles that flex and extend the fingers are located on the forearm, the muscles that lower and raise the shoulder are on the torso.
6. What human muscles ensure the vertical position of the body? Name the muscles involved in breathing.
The muscles of the legs hold the body, ensure that it maintains an upright position, and among the muscles of the body, the muscles of the chest, back and abdomen are distinguished. They perform the function of breathing and support the body in an upright position.
Smooth muscles are part of the internal organs. Thanks to contraction, they provide the motor (motor) function of their organs (digestive canal, genitourinary system, blood vessels, etc.). Unlike skeletal muscles, smooth muscles are involuntary.
Morpho-functional structure of smooth (non-striated) muscles. Basic structural unit smooth muscle is a muscle cell that has a spindle-shaped shape and is covered on the outside with a plasma membrane. Under an electron microscope, numerous depressions can be seen in the membrane - caveolae, which significantly increase the total surface of the muscle cell. The sarcolemma of a muscle cell includes a plasma membrane along with the basement membrane, which covers it from the outside, and adjacent collagen fibers. Main intracellular elements:
nucleus, mitochondria, lysosomes, microtubules, sarcoplasmic reticulum and contractile proteins.
Muscle cells form muscle bundles and muscle layers. The intercellular space (100 nm or more) is filled with elastic and collagen fibers, capillaries, fibroblasts, etc. In some areas, the membranes of neighboring cells lie very tightly (the gap between cells is 2-3 nm). It is assumed that these areas (nexus) serve for intercellular communication and transmission of excitation. It has been proven that smooth muscles alone contain a large number of nexus (pupillary sphincter, circular muscles of the small intestine, etc.), while others have few or none (vas deferens, longitudinal muscles of the intestines). There is also an intermediate, or desmopodibny, connection between non-skinned muscle cells (through thickening of the membrane and with the help of cell processes). Obviously, these connections are important for the mechanical connection of cells and the transmission of mechanical force by cells.
Due to the chaotic distribution of myosin and actin protofibrils, smooth muscle cells are not striated, like skeletal and cardiac cells. Unlike skeletal muscles, smooth muscles do not have a T-system, and the sarcoplasmic reticulum makes up only 2-7% of the myoplasm volume and has no connections with the external environment of the cell.
Physiological properties of smooth muscles. Smooth muscle cells, like striated ones, contract due to the sliding of actin protofibrils between myosin protofibrils, but the speed of sliding and hydrolysis of ATP, and therefore the speed of contraction, is 100-1000 times less than in striated muscles. Thanks to this, smooth muscles are well adapted for long-term gliding with little energy expenditure and without fatigue.
Smooth muscles, taking into account the ability to generate AP in response to threshold or supra-horn stimulation, are conventionally divided into phasic and tonic. Phasic muscles generate a full-fledged potential action, while tonic muscles generate only a local one, although they also have a mechanism for generating full-fledged potentials. The inability of tonic muscles to perform AP is explained by the high potassium permeability of the membrane, which prevents the development of regenerative depolarization.
The magnitude of the membrane potential is smooth muscle cells in unstrained muscles varies from -50 to -60 mV. As in other muscles, including nerve cells, mainly +, Na +, Cl- take part in its formation. In the smooth muscle cells of the digestive canal, uterus, and some vessels, the membrane potential is unstable; spontaneous fluctuations are observed in the form of slow waves of depolarization, at the top of which AP discharges may appear. The duration of smooth muscle action potentials ranges from 20-25 ms to 1 s or more (for example, in muscles Bladder), i.e. she
longer than the duration of skeletal muscle AP. In the mechanism of action of smooth muscles, next to Na +, Ca2 + plays an important role.
Spontaneous myogenic activity. Unlike skeletal muscles, smooth muscles of the stomach, intestines, uterus, and ureters have spontaneous myogenic activity, i.e. develop spontaneous tetanohyodine contractions. They are stored under conditions of isolation of these muscles and with pharmacological switching off of the intrafusal nerve plexuses. So, AP occurs in the smooth muscles themselves, and is not caused by the transmission of nerve impulses to the muscles.
This spontaneous activity is of myogenic origin and occurs in muscle cells that function as a pacemaker. In these cells, the local potential reaches a critical level and passes into AP. But as the membrane repolarizes, a new local potential spontaneously arises, which causes another AP, etc. The AP, spreading through the nexus to neighboring muscle cells at a speed of 0.05-0.1 m/s, covers the entire muscle, causing its contraction. For example, peristaltic contractions of the stomach occur with a frequency of 3 times per 1 minute, segmental and pendulum-like movements of the colon occur 20 times per 1 minute in the upper sections and 5-10 per 1 minute in the lower sections. Thus, the smooth muscle fibers of these internal organs have automaticity, which is manifested by their ability to contract rhythmically in the absence of external stimuli.
What is the reason for the appearance of potential in pacemaker smooth muscle cells? Obviously, it occurs due to a decrease in potassium and an increase in sodium and (or) calcium permeability of the membrane. As for the regular occurrence of slow waves of depolarization, most pronounced in the muscles of the gastrointestinal tract, there is no reliable data on their ionic origin. Maybe, a certain role plays a decrease in the initial inactivating component of the potassium current during depolarization of muscle cells due to inactivation of the corresponding potassium ion channels. Thanks to this, the occurrence of repeated G1D becomes possible.
Elasticity and extensibility of smooth muscles. Unlike skeletal muscles, when stretched, smooth muscles behave like plastic, elastic structures. Thanks to plasticity, smooth muscle can be completely relaxed in both contracted and stretched states. For example, the plasticity of the smooth muscles of the wall of the stomach or bladder as these organs fill prevents an increase in intracavitary pressure. Excessive stretching often leads to stimulation of contraction, which is caused by the depolarization of pacemaker cells that occurs when the muscle is stretched, and is accompanied by an increase in the frequency of action potential, and as a result, an increase in contraction. Contraction, which activates the stretching process, plays a large role in the self-regulation of the basal tone of blood vessels.
The mechanism of smooth muscle contraction. A prerequisite for the occurrence is a contraction of smooth muscles, as well as skeletal muscles, and an increase in the concentration of Ca2 + in the myoplasm (up to 10-5 M). It is believed that the contraction process is activated primarily by extracellular Ca2+, which enters muscle cells through voltage-gated Ca2+ channels.
The peculiarity of neuromuscular transmission in smooth muscles is that innervation is carried out by the autonomic nervous system and it can have both an excitatory and an inhibitory effect. By type, there are cholinergic (mediator acetylcholine) and adrenergic (mediator norepinephrine) mediators. The former are usually found in muscles digestive system, the second - in the muscles of blood vessels.
The same transmitter in some synapses can be excitatory, and in others - inhibitory (depending on the properties of the cytoreceptors). Adrenergic receptors are divided into a- and b-. Norepinephrine, acting on α-adrenergic receptors, constricts blood vessels and inhibits the motility of the digestive tract, and acting on B-adrenergic receptors, stimulates the activity of the heart and dilates the blood vessels of some organs, relaxes the muscles of the bronchi. Described neuromuscular-. transmission in smooth muscles for help and other mediators.
In response to the action of an excitatory transmitter, depolarization of smooth muscle cells occurs, which manifests itself in the form of an excitatory synaptic potential (ESP). When it reaches a critical level, PD occurs. This happens when several impulses approach the nerve ending one after another. The occurrence of PGI is a consequence of an increase in the permeability of the postsynaptic membrane for Na +, Ca2 + and SI."
The inhibitory transmitter causes hyperpolarization of the postsynaptic membrane, which is manifested in the inhibitory synaptic potential (ISP). Hyperpolarization is based on an increase in membrane permeability, mainly for K +. The role of inhibitory mediator in smooth muscles excited by acetylcholine (for example, muscles of the intestine, bronchi) is played by norepinephrine, and in smooth muscles for which norepinephrine is an excitatory mediator (for example, muscles of the bladder), acetylcholine plays the role.
Clinical and physiological aspect. In some diseases, when the innervation of skeletal muscles is disrupted, their passive stretching or displacement is accompanied by a reflex increase in their tone, i.e. resistance to stretching (spasticity or rigidity).
In case of circulatory disorders, as well as under the influence of certain metabolic products (lactic and phosphoric acids), toxic substances, alcohol, fatigue, decreased muscle temperature (for example, during prolonged swimming in cold water) after prolonged active muscle contraction, contracture may occur. The more the muscle function is impaired, the more pronounced the contracture aftereffect is (for example, contracture of the masticatory muscles in pathology of the maxillofacial region). What is the origin of contracture? It is believed that the contracture arose due to a decrease in the concentration of ATP in the muscle, which led to the formation of a permanent connection between the cross bridges and actin protofibrils. In this case, the muscle loses flexibility and becomes hard. The contracture goes away and the muscle relaxes when the ATP concentration reaches normal levels.
In diseases such as myotonia, muscle cell membranes are excited so easily that even a slight irritation (for example, the introduction of a needle electrode during electromyography) causes the discharge of muscle impulses. Spontaneous APs (fibrillation potentials) are also recorded at the first stage after denervation of the muscle (until inaction leads to its atrophy).
Tonic contractions of some smooth muscles, especially the muscles of the vascular walls (basal or myogenic tone) are activated predominantly by extracellular Ca 2 +. Physiologically active substances and mediators can cause a decrease in smooth muscle tone by closing chemosensitive Ca2 + channels (through activation of chemoreceptors) or hyperpolarization, which causes suppression of spontaneous APs and closing voltage-dependent Ca2 + channels.
Important property of smooth muscle is its great plasticity, i.e. the ability to maintain the length given by stretching without changing the stress. The difference between skeletal muscle, which has little plasticity, and smooth muscle, which has good plasticity, is easily detected if they are first slowly stretched and then the tensile load is removed. immediately shortens after removing the load. In contrast, smooth muscle, after removing the load, remains stretched until, under the influence of some irritation, its active contraction occurs.
The property of plasticity is very great importance for the normal activity of the smooth muscles of the walls of hollow organs, for example the bladder: due to the plasticity of the smooth muscles of the walls of the bladder, the pressure inside it changes relatively little with different degrees of filling.
Excitability and arousal
Smooth muscle less excitable than skeletal ones: their irritation thresholds are higher and their chronaxy is longer. The action potentials of most smooth muscle fibers have a small amplitude (about 60 mV instead of 120 in skeletal muscle fibers) and a long duration - up to 1-3 seconds. On rice. 151 The action potential of a single fiber of the uterine muscle is shown.
The refractory period lasts for the entire period of the action potential, i.e. 1-3 seconds. The speed of excitation varies in different fibers from several millimeters to several centimeters per second.
Exists big number various types smooth muscles in the body of animals and humans. Most of the hollow organs of the body are lined with smooth muscles of a sensitial type of structure. The individual fibers of such muscles are very closely adjacent to each other and it seems that morphologically they form a single whole.
However, electron microscopic studies have shown that there is no membrane and protoplasmic continuity between individual fibers of the muscle syncytium: they are separated from each other by thin (200-500 Å) slits. The concept of “syncytial structure” is currently more physiological than morphological.
Syncytium- this is a functional formation that ensures that action potentials and slow waves of depolarization can propagate unhindered from one fiber to another. Nerve endings are located only on a small number of syncytium fibers. However, due to the unimpeded spread of excitation from one fiber to another, the involvement of the entire muscle in the reaction can occur if the nerve impulse arrives at a small number of muscle fibers.
Smooth muscle contraction
With a large force of single irritation, contraction of the smooth muscle may occur. The latent period of a single contraction of this muscle is much longer than that of skeletal muscle, reaching, for example, 0.25-1 second in the intestinal muscles of a rabbit. The duration of the contraction itself is also long ( rice. 152): in the stomach of a rabbit it reaches 5 seconds, and in the stomach of a frog - 1 minute or more. Relaxation occurs especially slowly after contraction. The wave of contraction propagates through the smooth muscles also very slowly, it travels only about 3 cm per second. But this slowness of contractile activity of smooth muscles is combined with their great strength. Thus, the muscles of the stomach of birds are capable of lifting 1 kg per 1 cm2 of its cross section.
Smooth muscle tone
Due to the slowness of contraction, smooth muscle, even with rare rhythmic stimulation (for a frog’s stomach, 10-12 stimulations per minute is enough), easily goes into a long-term state of persistent contraction, reminiscent of skeletal muscle tetanus. However, the energy expenditure for such a sustained contraction of smooth muscle is very small, which distinguishes this contraction from tetanus of striated muscle.
The reasons why smooth muscles contract and relax much more slowly than skeletal muscles have not yet been fully elucidated. It is known that smooth muscle myofibrils, like those of skeletal muscle, consist of myosin and actin. However, smooth muscles do not have cross-striations, do not have a Z membrane, and are much richer in sarcoplasm. Apparently, these structural features of smooth muscle waves determine the slow pace of the contractile process. This also corresponds to the relatively low level of smooth muscle metabolism.
Automaticity of smooth muscles
A characteristic feature of smooth muscles that distinguishes them from skeletal muscles is the ability for spontaneous automatic activity. Spontaneous contractions can be observed when examining the smooth muscles of the stomach, intestines, gallbladder, ureters and a number of other smooth muscle organs.
Automaticity of smooth muscles is of myogenic origin. It is inherent in the muscle fibers themselves and is regulated by nerve elements that are located in the walls of smooth muscle organs. The myogenic nature of automaticity has been proven by experiments on strips of muscle of the intestinal wall, freed by careful preparation from the nerve plexuses adjacent to it. Such strips, placed in a warm Ringer-Locke solution, which is saturated with oxygen, are capable of automatic contractions. Subsequent histological examination revealed the absence of nerve cells in these muscle strips.
In smooth muscle fibers, the following spontaneous oscillations of membrane potential are distinguished: 1) slow waves of depolarization with a cycle duration of the order of several minutes and an amplitude of about 20 mV; 2) small rapid potential fluctuations preceding the occurrence of action potentials; 3) action potentials.
Smooth muscle reacts to all external influences by changing the frequency of spontaneous rhythms, which results in muscle contractions and relaxations. The effect of irritation of the smooth muscles of the intestine depends on the relationship between the frequency of stimulation and the natural frequency of the spontaneous rhythm: with low tone - with rare spontaneous action potentials - the applied irritation increases the tone; with a high tone, relaxation occurs in response to irritation, since an excessive increase in impulses leads to that each subsequent impulse falls into a refractory phase from the previous one.
Smooth muscles are present in the walls of the digestive canal, bronchi, blood and lymph vessels, bladder, uterus, as well as in the iris, ciliary muscle, skin and glands. Unlike striated muscles, they are not separate muscles, but form only part of the organs. Smooth muscle cells have an elongated spindle- or ribbon-like shape with pointed ends. Their length in humans is usually about 20 microns. Longest length(up to 500 microns) reach smooth muscle cells in the wall of the pregnant human uterus. In the middle part of the cell there is a rod-shaped nucleus, and in the cytoplasm along the entire cell, thin, completely homogeneous myofibrils run parallel to each other. Therefore, it has no transverse striations. Thicker myofibrils are located in the outer layers of the cell. They are called boundary and have uniaxial birefringence. An electron microscope shows that myofibrils are bundles of protofibrils and have cross-striations that are not visible in a light microscope. Smooth muscle cells can regenerate by division (mitosis). They contain a type of actomyosin - tonoactomyosin. Between smooth muscle cells there are the same areas of membrane contact, or nexuses, as between cardiac ones, along which excitation and inhibition are supposed to spread from one smooth muscle cell to another.
In smooth muscles, excitation spreads slowly. For example, in the muscle of the human small intestine it is carried out at a speed of 1 m/s, in the smooth muscles of the nictitating membrane of a cat - 50-80 cm/s, in the ureter of a rabbit - 18 cm/s, in the uterus of a cat - 7 cm/s. In muscles that slowly conduct excitation, the spaces between muscle fibers are 4 times larger than in rapidly conductive ones. Contractions of smooth muscle are caused by stronger and longer-lasting stimulation than skeletal muscle. The latent period of its contraction lasts several seconds. Smooth muscles contract much slower than skeletal muscles. Thus, the period of contraction of smooth muscle in the stomach of a frog is 15-20 s. Smooth muscle contractions can last for many minutes or even hours. Unlike skeletal muscles, smooth muscle contractions are tonic. Smooth muscles are capable of being in a state of tonic tension for a long time with an extremely low expenditure of substances and energy. For example, the smooth muscles of the sphincters of the digestive canal, bladder, gall bladder, uterus and other organs are in good shape for tens of minutes and many hours. The smooth muscles of the walls of the blood vessels of higher vertebrates remain in good shape throughout life.
There is a direct relationship between the frequency of impulses arising in the muscle and the level of its tension. The higher the frequency, the greater the tone up to a certain limit due to the summation of stresses of non-simultaneously tense muscle fibers.
Smooth muscles have tasticity - the ability to maintain their length when stretched without changing tension, unlike skeletal muscles, which are tense when stretched.
Unlike skeletal muscles, many smooth muscles exhibit automaticity. They contract under the influence of local reflex mechanisms, such as the Meissner and Auerbach plexuses in the digestive canal, or chemicals entering the digestive tract, such as acetylcholine, norepinephrine and adrenaline. Automatic contractions of smooth muscles are enhanced or inhibited under the influence of nerve impulses coming from nervous system. Therefore, unlike skeletal muscles, there are special inhibitory nerves that stop contraction and cause smooth muscle relaxation. Some smooth muscles that have a large number of nerve endings do not have automaticity, for example, the sphincter of the pupil, the nictitating membrane of a cat.
Smooth muscles can shorten greatly, much more than skeletal muscles. A single stimulation can cause smooth muscle contraction by 45%, and the maximum contraction with a frequent rhythm of stimulation can reach 60-75%.
A special type of stone is river rock. They form along the shores of lakes and rivers. These are mainly rocks that have been subject to constant exposure to fresh water over a very long period of time. Natural conditions processed and polished the surface of the stones so that they eventually acquired a pleasant to the touch, smooth surface and a surprisingly wide variety of patterns and shades. River stones are very popular in construction and architecture. Almost all of their types are not only construction, but also decorative, and are widely used for arranging and decorating the interior and exterior design of buildings, as well as as a material for a variety of architectural and decorative elements. Since they have the most incredible shapes and textures formed by constant exposure to fresh water, almost each of the river stones is a work of art embodied in stone and created by nature itself.
A distinctive feature of river stones is their ability to emit indescribable energy and freshness, charging a person with positive energy and that is why they can be found in any corner of the house as a decorative element or decoration.
What kind of stone can you find in the river?
Before you use this natural wealth, you should find out what kind of stone is found in the river and how it can be used. Basically, river stones include: limestone, sandstone, pebbles, boulders and other natural rocks formed at the bottom and under prolonged exposure to water, which received a characteristic texture, shade and properties.
Coral limestone or river coral is a sedimentary rock formed primarily from calcite and calcium carbonate. It is widely used in construction because of its amazing qualities - it can be easily processed, compared to other rocks it is quite easy to mine, it is moisture resistant, very beautiful and environmentally friendly, and at the same time very durable. Coral can be of several colors: white, gray, brown with various shades and even black.
It is used to make wall blocks, window sills, tabletops, furniture and decorative elements, and even decorate stairs.
Pisolite river coral is a type of limestone, which is a carbonate sedimentary rock formed by the gradual cementation of ancient sediments consisting of corals, fossilized shells and other organisms. The appearance is very picturesque and resembles large peas glued together, has a completely different colors, but the main ones are brown, beige and gray-green. Also, coral is often found in pink, brown and black colors.
It is used in such areas as agriculture, industry, arts and crafts, but most often in construction as building stone, crushed stone and thermal insulation material and in landscape design as a decorative material.
Organogenic river coral is also a type of limestone, but its composition includes admixtures of gypsum, dolomite and various clay formations, and appearance It is a large-pored, foamy mineral of yellow, white or light gray color. Organogenic coral has very high frost resistance, due to which it is used as a material for the production of facing and floor tiles. It is also very widely used as a finishing and decorative material.
Collecting stones on the river bank
If you walk along the banks of rivers, you can find a lot of useful construction and finishing materials. All stones on the river bank have undergone natural processing and do not require further polishing. These are great decorative elements any landscape.
Boulders are fragments of various rocks, rounded shape. Depending on their size, boulders are divided into cobblestone, pellet and round timber. Having a variety of shapes and colors, boulders are widely used in construction, paving roads and sidewalks, and in landscape design.
River pebbles - to a smooth surface, polished small fragments of various rocks up to 20 cm in diameter. Mainly used as construction and finishing material, as well as in landscape design.
These and other river stones on the river bank will help arrange your life and make landscape design completed. But there is also a special breed of river stones. They are used in making jewelry.
River (freshwater) pearls are rightfully considered the most beautiful, unique and rare - a precious stone that is a very hard round formation formed inside the shell of some mollusks as a result of falling into foreign body. Usually the color of pearls is white, sometimes pink and cream, yellow, blue, green and black are also found.
Unfortunately, freshwater pearls are extremely rare these days, due to their incredible popularity in the Middle Ages, which led to the almost complete destruction of the colonies of river mollusks that produced this unique stone.