Levers in technology, everyday life and nature. Presentation on the topic: “Levers in the human body set a bone in motion, a muscle acts on it like a lever. In mechanics, a lever is a rigid body that has a fulcrum, about.” download for free and without registration What h

Bird movements are varied: walking, jumping, running, climbing, swimming, diving, flying. They are provided both by changes in the musculoskeletal system and by transformations of other organ systems that coordinate movements and spatial orientation, creating the necessary energy reserves. A peculiar feature of the bird skeleton is the well-defined pneumaticity of the bones. Flat bones have a spongy structure, maintaining great strength with a small thickness. Tubular bones are also thin-walled, and the cavities inside them are filled partly with air, partly with bone marrow. These features provide increased strength to individual bones and make them noticeably lighter.

It is necessary, however, to pay attention to the fact that the total mass of the skeleton is 8-18% of the body weight of birds - approximately the same as in mammals, whose bones are thicker and there are no air cavities in them. This is explained by the fact that in birds, lightening the bones made it possible to sharply increase their length (the length of the leg skeleton, and especially the wing, is several times greater than the length of the body), without noticeably increasing the total mass of the skeleton.

Like other higher vertebrates, the skeleton of birds is divided into the axial skeleton and the associated rib cage, skull, skeleton of the limbs and their girdles.

The axial skeleton - the spinal column is divided into five sections: cervical, thoracic, lumbar, sacral and caudal. The number of cervical vertebrae is variable - from 11 to 23-25 ​​(swans). As in reptiles, the first vertebra - the atlas, or atlas - has the shape of a bony ring, and the second - the epistropheus - articulates with it by an odontoid process; this ensures mobility of the head relative to the neck. The remaining cervical vertebrae of birds are of the heterocoelous type; the long body of each vertebra in front and behind has a saddle-shaped surface (in the sagittal section the vertebrae are opisthocoelous, and in the frontal section they are marginal). The articulation of such vertebrae ensures their significant mobility relative to each other in the horizontal and vertical planes. The strength of the vertebral joints is enhanced by the presence of articular processes at the bases of the upper arches, forming sliding joints between themselves.

The cervical ribs of birds are vestigial and fuse with the cervical vertebrae, forming a canal through which the vertebral artery and cervical sympathetic nerve pass. Only the last one or two cervical ribs articulate with the cervical vertebrae movably, but they do not reach the sternum. The peculiarities of the cervical vertebrae, together with complexly differentiated neck muscles, allow birds to freely turn their heads 180°, and some (owls, parrots) even 270°. This makes possible complex and rapid movements of the head when grasping mobile prey, cleaning plumage, and building a nest; in flight, by bending or straightening the neck, it allows you to change the position of the center of gravity within certain limits, facilitates orientation, etc.

Birds have 3-10 thoracic vertebrae. They grow together to form the dorsal bone, and are connected with a very tight joint to the complex sacrum. Thanks to this, the torso section of the axial skeleton becomes motionless, which is important when flying (oscillations of the torso do not interfere with the coordination of flight movements). The ribs are movably attached to the thoracic vertebrae. Each rib consists of two sections - dorsal and abdominal, movably articulated with each other and forming an angle with its apex directed backwards. The upper end of the dorsal section of the rib is movably articulated to the transverse process and body of the thoracic vertebra, and the lower end of the abdominal section is articulated to the edge of the sternum. The movable articulation of the dorsal and abdominal sections of the ribs between each other and their movable connection with the spinal column and sternum, along with the developed costal muscles, ensure a change in the volume of the body cavity. This is one of the mechanisms for intensifying breathing. The strength of the chest is enhanced by the hook-shaped processes attached to the dorsal sections and overlapping the subsequent rib. The large sternum has the appearance of a thin, wide and long plate, on which in all birds (except ostrich-like ones) a high keel of the sternum is located. The large size of the sternum and its keel provide space for the attachment of powerful muscles that move the wing.

All lumbar, sacral (there are two of them) and part of the caudal vertebrae motionlessly fuse with each other into a monolithic bone - a complex sacrum. In total, it includes 10-22 vertebrae, the boundaries between which are not visible. The bones of the pelvic girdle are immovably fused with the complex sacrum. This ensures the immobility of the trunk and creates a strong support for the hind limbs. The number of free caudal vertebrae does not exceed 5-9. The last 4-8 caudal vertebrae merge into the laterally flattened coccygeal bone, to which the bases of the tail feathers are attached like a fan. The shortening of the caudal region and the formation of a pygostyle provides strong support for the tail while maintaining its mobility. This is important, since the tail not only serves as an additional load-bearing plane, but also participates in flight control (as a brake and rudder).

The skull of birds is similar to that of reptiles and can be classified as diapsid type with a reduced upper arch. The skull is tropibasal (the eye sockets are located in front of the brain), formed by thin spongy bones, the boundaries between which are clearly visible only in young birds. This is apparently due to the fact that connection with sutures is impossible due to the small thickness of the bones. Therefore the skull is relatively light. Its shape is also unique compared to reptiles: the volume of the brain case is sharply increased, the eye sockets are large, the jaws are devoid of teeth (in modern birds) and form a beak. The displacement of the foramen magnum and occipital condyle to the bottom of the skull increases the mobility of the head relative to the neck and torso.

The foramen magnum is surrounded by four occipital bones: the main, two lateral and superior. The main and lateral occipital bones form a single (as in reptiles) occipital condyle, which articulates with the first cervical vertebra. The three auricular bones surrounding the otic capsule are fused with adjacent bones and with each other. In the cavity of the middle ear there is only one auditory bone - the stapes. The sides and roof of the braincase are formed by paired integumentary bones: squamosal, parietal, frontal and lateral sphenoid. The bottom of the skull is formed by the integumentary sphenoid bone, which is covered by the integumentary sphenoid bone, and the coracoid process of the parasphenoid. At its anterior end lies a vomer, along the edges of which the choanae are located.

The upper part of the beak - the beak - is formed by greatly overgrown and fused premaxillary bones. The crest of the beak, strengthened by the nasal bones, connects with the frontal bones and the anterior wall of the orbit, formed by the overgrown middle olfactory bone. The maxillary bones, which make up only the posterior part of the beak, merge with the palatine bones through their processes. A thin bone crossbar, consisting of two fused bones - the zygomatic and quadratozygomatic, grows to the posterior outer edge of the maxillary bone. This is a typical lower arch of a diapsid skull, bounding below the orbit and the temporal fossa. The quadratojugal bone articulates with the quadrate bone, the lower end of which forms an articular surface for articulation with the lower jaw, and the elongated upper end is attached to the squamosal and anterior auricular bones with a joint. The palatine bones at their ends overlap the coracoid process of the parasphenoid and are connected by a joint to the paired pterygoid bones, which in turn are connected by a joint to the quadrate bones of the corresponding side.

Leg of a bird (without skin) sitting on a branch

This structure of the bony palate is important for the kineticism (mobility) of the beak characteristic of most birds. With the contraction of the muscles connecting the forward-directed orbital process of the quadrate bone with the wall of the orbit, the lower end of the quadrate bone moves forward and shifts both the palatine and pterygoid bones (their connection with each other can slide along the coracoid process), and the quadratozygomatic and zygomatic. The pressure along these bone bridges is transmitted to the base of the beak and, thanks to the bending of the bones in the area of ​​the “bridge of the nose,” the top of the beak moves upward. In the bend zone of the beak, the bones are very thin, and in some species (geese, etc.) a joint is formed here. When the muscles connecting the skull to the lower jaw contract, the top of the beak moves downward. The mobility of the bony palate, in combination with complexly differentiated masticatory muscles, provides various, finely differentiated movements of the beak when grasping prey, cleaning plumage, and building nests. Probably, the mobility of the neck and the adaptation of the beak to various movements contributed to the transformation of the forelimbs into wings, since they replaced some of the secondary functions they performed (assisting in capturing food, cleaning the body, etc.).

The lower part of the beak - the mandible or lower jaw - is formed by the fusion of a number of bones, of which the largest are the tooth, articular and angular. The jaw joint is formed by the articular and quadrate bones. The movements of the mandible and mandible are very clearly coordinated thanks to a differentiated system of masticatory muscles. The hyoid apparatus consists of an elongated body that supports the base of the tongue and long horns. Some birds, such as woodpeckers, have very long horns that wrap around the entire skull. When the hyoid muscles contract, the horns slide along the connective tissue bed and the tongue moves out of the oral cavity almost to the length of the beak.

The skeleton of the forelimb, which turned into a wing in birds, has undergone significant changes. The powerful tubular bone - the shoulder - has a flattened head, which significantly limits rotational movements in the shoulder joint, ensuring wing stability in flight. The distal end of the shoulder articulates with two bones of the forearm: the straighter and thinner radius and the more powerful ulna, on the posterior-superior side of which tubercles are visible - the attachment points of the secondary flight feathers. Of the proximal elements of the wrist, only two small independent bones are preserved, which are connected by ligaments to the bones of the forearm. The bones of the distal row of the wrist and all the bones of the metacarpus merge into a common metacarpal bone, or buckle. The skeleton of the fingers is sharply reduced: only two phalanges of the second finger are well developed, continuing the axis of the buckle. Only one short phalanx is preserved from the first and third fingers. The primaries are attached to the buckle and to the phalanges of the second toe. Several wing feathers are attached to the phalanx of the first toe.

The transformation of the hand (formation of a buckle, reduction of the fingers, low mobility of the joint) provides strong support for the primary flight feathers, which experience the greatest loads in flight. The nature of the surfaces of all joints is such that it provides easy mobility only in the plane of the wing; the possibility of rotational movements is sharply limited. This prevents wing inversion and allows the bird to effortlessly change the wing area in flight and fold it at rest. The fold of skin connecting the wrist crease with the shoulder joint - the flying membrane - forms an elastic leading edge of the wing, smoothing the elbow crease and preventing the formation of air turbulences here. The wing shape characteristic of each species is determined by the length of the skeletal elements and the secondary and primary flight feathers.

Adaptations for flight are clearly expressed in the girdle of the forelimbs. Powerful coracoids with expanded lower ends are firmly connected by sedentary joints by the anterior end of the sternum. The narrow and long scapulae fuse with the free ends of the coracoids, forming a deep articular cavity for the head of the humerus. The strength of the bones of the shoulder girdle and their strong connection with the sternum provides support for the wings in flight. Lengthening the coracoids increases the area of ​​attachment of the wing muscles and brings them forward to the level of the cervical vertebrae and the shoulder joint; this allows the wing to be laid on the side of the body at rest and is aerodynamically beneficial, because in flight the bird’s center of gravity is on the line connecting the centers of the wing areas (stability is ensured). The clavicles fuse into a fork, located between the free ends of the coracoids and acting as a shock absorber, softening shocks during wing flapping.

The hind limbs and pelvic girdle undergo transformations due to the fact that when moving on land, the entire weight of the body is transferred to them. The skeleton of the hind limb is formed by powerful tubular bones. The total length of the leg, even in “short-legged” species, exceeds the length of the body. The proximal end of the femur ends with a rounded head that articulates with the pelvis, and at the distal end the relief surfaces form a knee joint with the bones of the lower leg. It is strengthened by the kneecap lying in the muscular tendon. The main element of the tibia is a bone complex, which can be called the tibia-tarsus, or tibiotarsus, since the upper row of tarsal bones grows to the well-developed tibia, forming its distal end. The tibia is greatly reduced and grows onto the upper part of the outer surface of the tibia. Its reduction is due to the fact that in most birds all elements of the limb move in the same plane, rotational movements in the distal part of the limb are limited.

The distal (lower) row of tarsal bones and all metatarsal bones merge into a single bone - the tarsus, or metatarsus; an additional lever appears, increasing the length of the step. Since the movable joint is located between two rows of tarsal elements (between the bones fused with the tibia and the elements included in the tarsus), it, like in reptiles, is called intertarsal. The phalanges of the fingers are attached to the distal end of the tarsus.

Like all terrestrial vertebrates, the pelvic girdle of birds is formed by three pairs of bones fused together. The wide and long ilium fuses with the complex sacrum. The ischium grows to its outer edge, with which the rod-shaped pubic bone fuses. All three bones participate in the formation of the acetabulum, into which the head of the femur enters to form the hip joint. The pubic and ischial bones in birds do not fuse with each other along the midline of the body; such a pelvis is called open. It makes it possible to lay large eggs and, perhaps, helps to intensify breathing without limiting the mobility of the abdominal wall in the pelvic area.

LEVERS IN THE HUMAN BODY Moving a bone, a muscle acts on it like a lever. In mechanics, a lever is a rigid body that has a fulcrum around which it can rotate under the influence of opposing forces. Based on the relationship between the point of application of muscle force and the point of resistance to the fulcrum, levers of the first and second kind are distinguished.

LEVERS OF THE FIRST AND SECOND TYPE The lever of the first type, double-armed, or balance lever, in the human body is the head (A). The movable support of the skull is located in the atlanto-occipital joint. Lever arms of unequal size are located in front and behind it. The front shoulder is affected by the weight of the front part of the head, and the back shoulder is affected by the force of the muscles attached to the occipital bone. When the head is in a vertical position, the forces of action and reaction directed at the arms of the lever are balanced. The pelvis, balancing on the heads of the femurs, is also a first-class lever.

LEVERS OF THE FIRST AND SECOND TYPE The lever of the second type is single-armed. Here, the points of resistance and application of force are located on one side of the support. In the human body it has two varieties. For example, let’s take a hand resting on the elbow joint. The lever arm is affected by the weight of the forearm and hand. In case of tension of the brachioradialis muscle, which is attached near the hand and, therefore, near the application of gravity, favorable conditions for work are created and its efficiency increases. This type of single-arm lever is called a force lever. In the case of tension in the biceps muscle, which is attached near the fulcrum, a smaller effect is obtained when overcoming gravity, but the work is done with greater speed. This type of lever of the second kind is called the speed lever (B). Most muscles in the body work according to the principle of a second-class lever.

LEVERS IN THE BODY OF BIRDS Rowing flight. The main aircraft is the wing, a single-arm lever that rotates at the shoulder joint. The attachment of the flight feathers and the peculiarity of their mobility are such that when striking downward, the wing almost does not allow air to pass through. When the wing rises, due to the bending of the axial part of the skeleton, the surface of the wing's action on the air becomes smaller. Thanks to the rotation of the flight feathers, the wing becomes permeable to air. In order for a pigeon to stay in the air, its movements are necessary, that is, the wind created by flapping its wings. At the beginning of the flight, the movements of the wings are more frequent, then, as the flight speed and resistance increase, the number of wing beats decreases, reaching a certain frequency.

LEVERS IN THE BODY OF BIRDS The bones of the lower limbs in birds are fused. The fusion of a number of bones of the tarsus and all the bones of the metatarsus leads to the appearance of the tarsus. This creates an additional lever - a strong support for the fingers, which simultaneously increases the length of the step. The vast majority of birds have four fingers. The first one is directed backwards, and the other three are directed forwards.

SWIM BEETLE The flattened, streamlined shape of the body (due to the tight connection of the head, thoracic and abdominal segments), the almost complete absence of setae on the body, highly developed hind coxae fused with the hind thorax, which form a lever for the flattened hind legs lined with swimming hairs, provide efficient movement of beetles in the water column.

WINGS The movement of wings in insects is the result of a complex mechanism and is determined, on the one hand, by the peculiarity of the articulation of the wing with the body, and on the other, by the action of special wing muscles. In general terms, the main mechanism of wing movement is presented as follows (Fig. 319). The wing itself is a double-armed lever with arms of unequal length. The wing is connected to the tergite and lateral plate by thin and flexible membranes. Slightly moving away from the place of this connection, the wing rests on a small column-shaped outgrowth of the side plate, which is the fulcrum of the wing lever.

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1. Adaptation for flight in the external structure (streamlined body shape. Feather cover, wings, tail made of tail feathers).
2. The skeleton of birds is characterized by strength and lightness. These qualities are due to the fact that many bones have fused together and formed strong sections (skull, trunk spine, tarsus, hand bones, etc.), and tubular bones are hollow and contain air, which is why they are light.
3. Features of the muscles of birds associated with flight - strong development of the muscles that move the wings: the pectoralis major muscles lower the wing, the subclavian muscles raise it. Intercostal - are of great importance in the breathing of birds. The leg muscles are highly developed.
4. Adaptation to flight in the digestive system (beak without teeth, rapid digestion, frequent bowel movements, etc.).
5. Adaptation to flight in the respiratory system (air sacs help increase the volume of inhaled air, participate in the mechanism of double breathing, promote heat transfer, protecting the body from overheating, and lighten the bird’s body weight).
6. Features of the circulatory system (large size of the heart, the presence of 4 chambers, thanks to which the body tissues receive arterial blood rich in oxygen). Life processes proceed quickly (oxidation), providing intense metabolism and a high constant body temperature.
7. Due to flight and a varied lifestyle, the nervous system, in particular the brain, has a more complex structure. This is expressed in the larger size of its anterior section and cerebellum, in the presence of relatively large optic lobes, which is associated with a more complex structure of the visual organs.
8. The high development of the central nervous system is due to the more complex behavior of birds. It manifests itself in various forms of caring for offspring (nest building, laying and incubating eggs, warming chicks, feeding them), in seasonal movements, and in the development of sound signaling. Complex forms of caring for offspring in birds are progressive features that have developed in the process of their historical development.
9. Adaptation for flight in the reproductive organs (females have one left ovary and one left oviduct). They reproduce on land with the help of relatively large eggs, rich in yolk and covered with a number of shells; for the development of the embryo in the egg, nutrients, oxygen and heat are needed; similarities in the reproduction and development of birds and reptiles indicate the relatedness of vertebrates of these classes.

Birds are the only creatures that can imitate human speech. In addition to parrots, starlings, crows and other birds do this. The book tells about the lifestyle and behavior of “talking” birds, primarily parrots, their maintenance in captivity, and training. Particular attention is paid to the dictionary of the most prominent “talkers”. The structure and functions of the vocal apparatus and the auditory analyzer of birds are considered. A new teaching method is described, based on the formation of associations between a word and an object in parrots. Bird lovers who train budgies will find a lot of useful information.

“Talking” birds are a unique mystery of nature. Despite the fact that this phenomenon has been of interest to bird lovers for a long time, it has not yet been solved. Several decades ago, interest in teaching budgies to “talk” increased. It turned out that they not only copy human speech, but can connect a word and the object it denotes, a situation and a statement. Some of them answer the person’s questions and exchange remarks with him. What types of birds “speak”, where they live, how they behave in the wild, how their hearing and vocal apparatus work, how to teach a budgie to speak, how to choose a suitable bird, how to keep it, what to feed it, this book tells about all this .

For zoologists, bioacoustics, zoopsychologists and a wide range of readers.

On the 1st cover page: red macaw (photo by J. Holton).

Book:

The middle ear absorbs sound wave energy. The reflection coefficients of body and air are different. In order for sound to be absorbed and most of its energy to be used, a delicate eardrum with a complex supporting and regulating apparatus is necessary.

In mammals, the eardrum is very small compared to a bird's; in a house mouse, its area is only 2.7 mm 2, while in a warbler it is several times larger - 7.8 mm 2. And in mammals it is concave, and in birds it is convex, in the form of a high tent.

But the middle ear not only absorbs sound, it processes it and regulates its further transmission. In this sense, the logic - the more complex the middle ear, the more perfect the regulated transmission - seems to be justified. But only partly. Because the middle ear of birds is not simpler, but different.

A general view of the middle ear of birds is shown in Fig. 5. The eardrum, enlarged in size, rounded and convex outwards, in the form of a tent (in mammals it is relatively smaller and concave), is striking; the cartilaginous element attached to it from one edge is the extracolumella, which continues into the auditory ossicle, abutting the other end into the oval snail window. At the same time, birds have only one middle ear muscle, which regulates the tension of the eardrum.

Mammals have three auditory ossicles, connected in a zigzag pattern and controlled by two muscles. Due to this, the transmission of sound is accompanied by complex lever movements that make it possible to regulate this transmission. Weak sounds can be amplified, strong sounds can be weakened or even blocked, the shape of the signal and some of its other characteristics can change during the transmission process. The auditory ossicles that provide this can move like a piston, make circular movements, shift like a lever, and rotate along their axis. But in the ear of birds there is only one bone and plus a cartilaginous element connecting it to the eardrum - the extracolumella. And just one muscle. What lever movements are there!

For a long time, the lever mobility of the auditory column of the middle ear of birds was generally denied. Scientists believed that the single auditory bone moves like a piston, transmitting to the inner ear what comes to the eardrum with amplification determined by the ratio of the areas of the membrane and the round window. There is no regulation.

In order to prove lever mobility in birds, we had to resort to various tricks. Cut the cartilaginous extracolumella, through which the bone is connected to the eardrum. The extracolumella has the appearance of a tripod, one of the legs of which rests on the center of the membrane and stretches it (this is why the membrane in birds is convex and not concave, like in mammals), the other two are located in contact with the bony edge of the membrane. The bone grows to the point of the extracolumelli where all three of its legs meet.

Using the bioelectric activity of the receptor section as an indicator, caused by the action of a sound click (cochlear potentials), and cutting the supporting processes - the legs of the extracolumelli - at different levels, it is possible to obtain a purely piston or purely lever nature of the movements of the column and study their role in sound transmission separately. Experiments have shown that the importance of the lever mobility of the auditory column in the functioning of the auditory system of birds is great.

An employee of Moscow University V.D. Anisimov developed an interesting method for studying the sound transmission system of birds - the luminous point technique.

Rice. 5. Features of the structure and functioning of the middle ear of a bird capable of imitating speech (Anisimov, 1971) 1, 11 - location of the elements of the middle ear before muscle contraction; III, IV - displacements of elements during muscle contraction (on the right are the corresponding changes in the myogram - EMG and the microphone component - M cochlear potentials: before contraction - a, after contraction - b, c). 1 - eardrum; 2 - ligament; 3 - supracolumellar process; 4 - infracolumellar process; 5 - muscle tendon; 6 - extracolumellar process; 7 - Platner's ligament; 8 - auditory ossicle; 9 - sole of the bone; S - signal

By gluing pieces of shiny foil that reflected light onto various parts of the sound transmission system, he recorded the position of the auditory ossicle and cartilaginous extracolumelli in various dynamic states.

Another important technique developed by V.D. Anisimov was prototyping the sound transmission system and its functions on an enlarged kinematic model made of transparent plexiglass. By setting different modes of contraction of the middle ear muscle and the tension of the eardrum caused by it, it was possible to trace the nature of the mobility of the sound transmission system, the lever movements of the auditory column and extracolumelli.

Spraying crystalline silver onto various elements of the middle ear, tinting them and marking them made it possible to film the entire process of movements, including those of the lever sound transmission system. The same processes were repeated on an enlarged model of the middle ear of birds, proportionally enlarged in all parts.

Thus, it was proven that the middle ear of birds, which is structured differently than that of mammals, works according to the same laws and solves similar problems.