Introduction........................................................ ........................................................ ............3
1. There are many ways to see - it all depends on the goals.................................... ..4
2. Reptiles. General information........................................................ .............................8
3. Organs of infrared vision of snakes.................................................. .................12
4. “Heat-visioning” snakes.................................................. ........................................17
5. Snakes strike prey blindly.................................................... .......................20
Conclusion................................................. ........................................................ .......22
Bibliography................................................ ...........................................24
Introduction
Are you sure that the world looks exactly the way it appears to our eyes? But animals see it completely differently.
The cornea and lens in humans and higher animals have the same structure. The structure of the retina is similar. It contains light-sensitive cones and rods. Cones are responsible for color vision, rods for vision in the dark.
The eye is an amazing organ of the human body, a living optical device. Thanks to it, we see day and night, distinguish colors and the volume of the image. The eye is designed like a camera. Its cornea and lens, like a lens, refract and focus light. The retina lining the fundus of the eye acts as a sensitive photographic film. It consists of special light-receiving elements - cones and rods.
How do the eyes of our “smaller brothers” work? Animals that hunt at night have more rods in their retinas. Those representatives of the fauna that prefer to sleep at night have only cones in their retinas. The most vigilant in nature are diurnal animals and birds. This is understandable: without acute vision, they simply will not survive. But nocturnal animals also have their advantages: even with minimal lighting, they notice the slightest, almost imperceptible movements.
In general, humans see more clearly and better than most animals. The fact is that in the human eye there is a so-called yellow spot. It is located in the center of the retina on the optical axis of the eye and contains only cones. They receive rays of light that are least distorted when passing through the cornea and lens.
The “yellow spot” is a specific feature of the human visual apparatus; all other species lack it. It is precisely because of the lack of this important device that dogs and cats see worse than us.
1. There are many ways to see - it all depends on your goals
Each species has evolved its own visual abilities as a result of evolution. as much as is required for its habitat and way of life. If we understand this, we can say that all living organisms have “ideal” vision in their own way.
A person sees poorly under water, but a fish’s eyes are designed in such a way that, without changing its position, it distinguishes objects that for us remain “outside” our vision. Bottom-dwelling fish such as flounder and catfish have eyes located at the top of their heads to see enemies and prey that usually appear from above. By the way, the eyes of a fish can turn in different directions independently of each other. They see more clearly under water than others predatory fish, as well as inhabitants of the depths, feeding on the smallest creatures - plankton and bottom organisms.
The vision of animals is adapted to their familiar environment. Moles, for example, are short-sighted - they only see up close. But other vision is not needed in the complete darkness of their underground burrows. Flies and other insects have difficulty distinguishing the outlines of objects, but in one second they are able to fix big number separate "pictures". About 200 compared to 18 in humans! Therefore, a fleeting movement, which we perceive as barely perceptible, for a fly is “decomposed” into many individual images - like frames on a film. Thanks to this property, insects instantly find their way when they need to catch their prey in flight or escape from enemies (including people with a newspaper in their hand).
Insect eyes are one of nature's most amazing creations. They are well developed and occupy most of the surface of the insect's head. They consist of two types - simple and complex. There are usually three simple eyes, and they are located on the forehead in the form of a triangle. They distinguish between light and darkness, and when an insect flies, they follow the horizon line.
Compound eyes consist of many small eyes (facets) that look like convex hexagons. Each eye is equipped with a unique, simple lens. Compound eyes produce a mosaic image - each facet “fits” only a fragment of an object in the field of view.
Interestingly, in many insects, individual facets in compound eyes are enlarged. And their location depends on the insect’s lifestyle. If it is more “interested” in what is happening above it, the largest facets are in the upper part of the compound eye, and if below it, in the lower part. Scientists have repeatedly tried to understand what exactly insects see. Does the world around them really appear before their eyes in the form of a magical mosaic? There is no clear answer to this question yet.
Especially many experiments were carried out with bees. During the experiments, it turned out that these insects need vision for orientation in space, recognition of enemies and communication with other bees. Bees cannot see (or fly) in the dark. But they distinguish some colors very well: yellow, blue, bluish-green, purple and a specific “bee” color. The latter is the result of “mixing” ultraviolet, blue and yellow. In general, bees can easily compete with humans in their visual acuity.
Well, how do creatures who have very poor vision or those who are completely deprived of it? How do they navigate in space? Some people also “see” - just not with their eyes. The simplest invertebrates and jellyfish, consisting of 99 percent water, have light-sensitive cells that perfectly replace their usual visual organs.
The vision of the fauna that inhabit our planet still holds many amazing secrets, and they are waiting for their researchers. But one thing is clear: all the diversity of eyes in living nature is the result of the long evolution of each species and is closely related to its lifestyle and habitat.
People
We clearly see objects close up and distinguish the finest shades of colors. In the center of the retina are the cones of the “macula,” which are responsible for visual acuity and color perception. View - 115-200 degrees.
On the retina of our eye, the image is recorded upside down. But our brain corrects the picture and transforms it into the “correct” one.
Cats
Wide-set cat eyes provide a 240-degree field of view. The retina of the eye is mainly equipped with rods, the cones are collected in the center of the retina (the area of acute vision). Night vision is better than day vision. In the dark, a cat sees 10 times better than us. Her pupils dilate, and the reflective layer under the retina sharpens her vision. And the cat distinguishes colors poorly - only a few shades.
Dogs
For a long time it was believed that a dog sees the world in black and white. However, canids can still distinguish colors. This information is simply not very meaningful to them.
Canines' vision is 20-40% worse than that of humans. An object that we can distinguish at a distance of 20 meters “disappears” for a dog if it is more than 5 meters away. But night vision is excellent - three to four times better than ours. The dog is a night hunter: it sees far in the dark. In the dark, a guard dog can see a moving object at a distance of 800-900 meters. View - 250-270 degrees.
Birds
Birds hold the record for visual acuity. They distinguish colors well. Most birds of prey have visual acuity several times higher than that of humans. Hawks and eagles spot moving prey from a height of two kilometers. Not a single detail escapes the attention of a hawk soaring at an altitude of 200 meters. His eyes “magnify” the central part of the image by 2.5 times. The human eye does not have such a “magnifier”: the higher we are, the worse we see what is below.
Snakes
The snake has no eyelids. Her eye is covered with a transparent membrane, which is replaced by a new one when molting. The snake focuses its gaze by changing the shape of the lens.
Most snakes distinguish colors, but the outlines of the image are blurred. The snake mainly reacts to a moving object, and only if it is nearby. As soon as the victim moves, the reptile detects it. If you freeze, the snake will not see you. But it can attack. Receptors located near the snake's eyes capture the heat emanating from a living creature.
Fish
The fish's eye has a spherical lens that does not change shape. To focus their gaze, the fish moves the lens closer or further away from the retina using special muscles.
In clear water, the fish sees on average 10-12 meters, and clearly - at a distance of 1.5 meters. But the angle of view is unusually large. Pisces fix objects in a zone of 150 degrees vertically and 170 degrees horizontally. They distinguish colors and perceive infrared radiation.
Bees
“Bees of day vision”: what to look at at night in the hive?
The bee's eye detects ultraviolet radiation. She sees another bee in a purple color and as if through optics that have “compressed” the image.
The bee's eye consists of 3 simple and 2 complex compound ocelli. Complex ones distinguish between moving objects and the outlines of stationary objects during flight. Simple - determine the degree of light intensity. Bees don’t have night vision”: what to look at at night in the hive?
2. Reptiles. General information
Reptiles have a bad reputation and few friends among humans. There are many misunderstandings related to their body and lifestyle that have persisted to this day. Indeed, the very word “reptile” means “an animal that creeps” and seems to recall the popular idea of them, especially snakes, as disgusting creatures. Despite the prevailing stereotype, not all snakes are poisonous and many reptiles play a significant role in regulating the number of insects and rodents.
Most reptiles are predators with a well-developed sensory system that helps them find prey and avoid danger. They have excellent vision, and snakes, in addition, have a specific ability to focus their gaze by changing the shape of the lens. Nocturnal reptiles, such as geckos, see everything in black and white, but most others have good color vision.
Hearing is not particularly important for most reptiles, and the internal structures of the ear are usually poorly developed. The majority also lack the outer ear, excluding the eardrum, or “tympanum,” which senses vibrations transmitted through the air; From the eardrum they are transmitted through the bones of the inner ear to the brain. Snakes do not have an external ear and can only perceive vibrations that are transmitted along the ground.
Reptiles are characterized as cold-blooded animals, but this is not entirely accurate. Their body temperature is mainly determined environment, but in many cases they can regulate it and, if necessary, maintain it at a higher level. Some species are able to generate and retain heat within their own body tissues. Cold blood has some advantages over warm blood. Mammals need to maintain their body temperature at a constant level within very narrow limits. To do this, they constantly need food. Reptiles, on the contrary, tolerate a decrease in body temperature very well; their life span is much wider than that of birds and mammals. Therefore, they are able to inhabit places that are not suitable for mammals, for example, deserts.
Once fed, they can digest food while at rest. Some of the most large species Several months may pass between meals. Large mammals would not survive with this diet.
Apparently, among reptiles, only lizards have well-developed vision, since many of them hunt fast-moving prey. Aquatic reptiles rely heavily on senses such as smell and hearing to track prey, find a mate, or detect the approach of an enemy. Their vision plays an auxiliary role and operates only at close range, visual images are blurry, and they lack the ability to focus on stationary objects for a long time. Most snakes have fairly poor vision, usually only able to detect moving objects that are nearby. The reaction of numbness in frogs when someone approaches them, for example, is a good thing. defense mechanism, since the snake will not realize the presence of the frog until it makes a sudden movement. If this happens, then visual reflexes will allow the snake to quickly deal with it. Only tree snakes, which coil around branches and grab birds and insects in flight, have good binocular vision.
Snakes have a different sensory system than other hearing reptiles. Apparently, they cannot hear at all, so the sounds of the snake charmer’s pipe are inaccessible to them; they enter a state of trance from the movements of this pipe from side to side. They do not have an external ear or eardrum, but may be able to detect some very low-frequency vibrations using the lungs as sensory organs. Basically, snakes detect prey or an approaching predator by vibrations of the ground or other surface on which they are located. The snake's entire body in contact with the ground acts as one large vibration detector.
Some species of snakes, including rattlesnakes and pit vipers, detect prey by infrared radiation from its body. Under their eyes they have sensitive cells that detect the slightest changes in temperature down to fractions of a degree and, thus, orient the snakes to the location of the prey. Some boas also have sensory organs (on the lips along the mouth opening) that can detect changes in temperature, but these are less sensitive than those of rattlesnakes and pit snakes.
The senses of taste and smell are very important for snakes. The snake's quivering, forked tongue, which some people think of as a "snake's stinger," actually collects traces of various substances that quickly disappear in the air and carries them to sensitive depressions on the inside of the mouth. There is a special device in the palate (Jacobson's organ), which is connected to the brain by a branch of the olfactory nerve. Constantly releasing and retracting the tongue is effective method air sampling for important chemical components. When retracted, the tongue is close to the Jacobson's organ, and its nerve endings detect these substances. In other reptiles, the sense of smell plays an important role, and the part of the brain that is responsible for this function is very well developed. The taste organs are usually less developed. Like snakes, the Jacobson's organ is used to detect particles in the air (in some species using the tongue) that carry a sense of smell.
Many reptiles live in very dry places, so keeping water in their bodies is very important to them. Lizards and snakes retain water better than anyone else, but not because of their scaly skin. They lose almost as much moisture through their skin as birds and mammals.
While in mammals the high respiratory rate leads to high evaporation from the surface of the lungs, in reptiles the respiratory rate is much lower and, accordingly, the loss of water through the lung tissue is minimal. Many species of reptiles are equipped with glands that can cleanse salts from the blood and body tissues, releasing them in the form of crystals, thereby reducing the need to separate large volumes of urine. Other unwanted salts in the blood are converted to uric acid, which can be eliminated from the body with minimal amounts of water.
Reptile eggs contain everything necessary for a developing embryo. This is a supply of food in the form of a large yolk, water contained in the protein, and a multi-layered protective shell that does not allow dangerous bacteria to pass through, but allows air to breathe.
The inner membrane (amnion) immediately surrounding the embryo is similar to the same membrane in birds and mammals. The allantois is a thicker membrane that acts as a lung and excretory organ. It ensures the penetration of oxygen and the release of waste substances. The chorion is the membrane surrounding the entire contents of the egg. The outer shell of lizards and snakes is leathery, but in turtles and crocodiles it is harder and calcified, like eggshell in birds.
4. Infrared vision organs of snakes
Infrared vision of snakes requires non-local image processing
The organs that allow snakes to “see” thermal radiation provide an extremely blurry image. Nevertheless, the snake forms a clear thermal picture of the surrounding world in its brain. German researchers have figured out how this can be.
Some species of snakes have a unique ability to capture thermal radiation, allowing them to look at the world around them in absolute darkness. However, they “see” thermal radiation not with their eyes, but with special heat-sensitive organs.
The structure of such an organ is very simple. Next to each eye is a hole about a millimeter in diameter, which leads into a small cavity of approximately the same size. On the walls of the cavity there is a membrane containing a matrix of thermoreceptor cells measuring approximately 40 by 40 cells. Unlike the rods and cones of the retina, these cells do not respond to the “brightness of light” of heat rays, but to the local temperature of the membrane.
This organ works like a camera obscura, a prototype of cameras. A small warm-blooded animal against a cold background emits “heat rays” in all directions - far infrared radiation with a wavelength of approximately 10 microns. Passing through the hole, these rays locally heat the membrane and create a “thermal image”. Thanks to the highest sensitivity of receptor cells (temperature differences of thousandths of a degree Celsius are detected!) and good angular resolution, a snake can notice a mouse in absolute darkness from a fairly long distance.
From a physics point of view, it is precisely good angular resolution that poses a mystery. Nature has optimized this organ so as to better “see” even weak sources of heat, that is, it has simply increased the size of the inlet - the aperture. But the larger the aperture, the blurrier the image ( we're talking about, we emphasize, about the most ordinary hole, without any lenses). In a snake situation, where the camera aperture and depth are approximately equal, the image is so blurry that nothing more than “there is a warm-blooded animal somewhere nearby” can be extracted from it. However, experiments with snakes show that they can determine the direction of a point source of heat with an accuracy of about 5 degrees! How do snakes manage to achieve such high spatial resolution with such terrible quality of “infrared optics”?
A recent article by German physicists A. B. Sichert, P. Friedel, J. Leo van Hemmen, Physical Review Letters, 97, 068105 (9 August 2006) was devoted to the study of this particular issue.
Since the real “thermal image,” the authors say, is very blurry, and the “spatial picture” that arises in the animal’s brain is quite clear, it means that there is some kind of intermediate neural apparatus on the way from the receptors to the brain, which, as it were, adjusts the sharpness of the image. This apparatus should not be too complex, otherwise the snake would “think about” each image received for a very long time and would react to stimuli with a delay. Moreover, according to the authors, this device is unlikely to use multi-stage iterative mappings, but is, rather, some kind of fast one-step converter that works according to a permanently hardwired nervous system program.
In their work, the researchers proved that such a procedure is possible and quite realistic. They carried out mathematical modeling of how a “thermal image” occurs and developed an optimal algorithm for repeatedly improving its clarity, dubbing it a “virtual lens.”
Despite the big name, the approach they used, of course, is not something fundamentally new, but just a type of deconvolution - restoring an image spoiled by the imperfection of the detector. This is the reverse of image blurring and is widely used in computer image processing.
There was, however, an important nuance in the analysis: the deconvolution law did not need to be guessed; it could be calculated based on the geometry of the sensitive cavity. In other words, it was known in advance what specific image a point source of light in any direction would produce. Thanks to this, a completely blurred image could be restored with very good accuracy (ordinary graphic editors with a standard deconvolution law would not have been able to cope even close to this task). The authors also proposed a specific neurophysiological implementation of this transformation.
Whether this work said any new word in the theory of image processing is a moot point. However, it certainly led to unexpected findings regarding the neurophysiology of “infrared vision” in snakes. Indeed, the local mechanism of “ordinary” vision (each visual neuron takes information from its own small area on the retina) seems so natural that it is difficult to imagine something very different. But if snakes really use the described deconvolution procedure, then each neuron that contributes to the whole picture of the surrounding world in the brain receives data not from a point at all, but from a whole ring of receptors running across the entire membrane. One can only wonder how nature managed to construct such “nonlocal vision”, which compensates for the defects of infrared optics with non-trivial mathematical transformations of the signal.
Infrared detectors, of course, are difficult to distinguish from the thermoreceptors discussed above. The Triatoma thermal bedbug detector could be discussed in this section. However, some thermoreceptors are so specialized in detecting distant heat sources and determining the direction towards them that they are worth considering separately. The most famous of these are the facial and labial pits of some snakes. The first indications are that the family of pseudopods Boidae (boa constrictors, pythons, etc.) and the subfamily of pit vipers Crotalinae (rattlesnakes, including the true rattlesnake Crotalus and the bushmaster (or surukuku) Lachesis) have infrared sensors, were obtained from an analysis of their behavior when searching for victims and determining the direction of attack. Infrared detection is also used for defense or escape, which is caused by the appearance of a heat-emitting predator. Subsequently, electrophysiological studies of the trigeminal nerve innervating the labial fossae of propopods and the facial fossae of pit snakes (between the eyes and nostrils) confirmed that these recesses indeed contain infrared receptors. Infrared radiation provides an adequate stimulus to these receptors, although a response can also be generated by washing the fossa with warm water.
Histological studies have shown that the pits do not contain specialized receptor cells, but unmyelinated endings of the trigeminal nerve, forming a wide, non-overlapping branching.
In the pits of both pseudopods and pit snakes, the surface of the bottom of the pit reacts to infrared radiation, and the reaction depends on the location of the radiation source relative to the edge of the pit.
Activation of receptors in both pseudopods and pit snakes requires a change in the flow of infrared radiation. This can be achieved either as a result of the movement of a heat-emitting object in the "field of view" relative to the colder surroundings, or by the scanning movement of the snake's head.
The sensitivity is sufficient to detect the radiation flux from a human hand moving in the “field of view” at a distance of 40 - 50 cm, which means that the threshold stimulus is less than 8 x 10-5 W/cm2. Based on this, the temperature increase detected by the receptors is on the order of 0.005 ° C (i.e., approximately an order of magnitude better than the human ability to detect temperature changes).
5. Heat-visioning snakes
Experiments carried out by scientists in the 30s of the 20th century with rattlesnakes and related pit snakes (crotalids) showed that snakes can actually see the heat emitted by a flame. Reptiles were able to detect at great distances the subtle heat emitted by heated objects, or, in other words, they were able to sense infrared radiation, the long waves of which are invisible to humans. The ability of pit snakes to sense heat is so great that they can sense the heat emitted by a rat from a considerable distance. Snakes have heat sensors in small pits on their snouts, hence their name - pitheads. Each small, forward-facing pit located between the eyes and nostrils has a tiny, pinprick-like hole. At the bottom of these holes there is a membrane, similar in structure to the retina of the eye, containing the smallest thermoreceptors in quantities of 500-1500 per square millimeter. Thermoreceptors have 7,000 nerve endings connected to a branch of the trigeminal nerve located on the head and muzzle. Because the sensory zones of both pits overlap, the pit snake can perceive heat stereoscopically. Stereoscopic perception of heat allows the snake, by detecting infrared waves, not only to find prey, but also to estimate the distance to it. Fantastic thermal sensitivity is combined in pit snakes with a quick response, allowing snakes to instantly respond to a thermal signal in less than 35 milliseconds. It is not surprising that snakes with this reaction are very dangerous.
The ability to detect infrared radiation gives pit vipers significant capabilities. They can hunt at night and stalk their main prey, rodents, in their underground burrows. Although these snakes have a highly developed sense of smell, which they also use to find prey, their deadly strike is guided by heat-sensitive pits and additional thermoreceptors located inside the mouth.
Although infrared sense in other groups of snakes is less well understood, boa constrictors and pythons are also known to have heat-sensitive organs. Instead of pits, these snakes have more than 13 pairs of thermoreceptors located around the lips.
There is darkness in the depths of the ocean. The light of the sun does not reach there, and only the light emitted by the deep-sea inhabitants of the sea flickers there. Like fireflies on land, these creatures are equipped with organs that generate light.
Possessing a huge mouth, the black malacoste (Malacosteus niger) lives in complete darkness at depths from 915 to 1830 m and is a predator. How can he hunt in complete darkness?
Malacost is able to see what is called far red light. Light waves in the red part of the so-called visible spectrum have the longest wavelength, around 0.73-0.8 micrometers. Although this light is invisible to the human eye, some fish, including the black malacoste, can see it.
On the sides of a malacost's eyes are a pair of bioluminescent organs that emit a blue-green light. Most other bioluminescent creatures in this realm of darkness also emit a bluish light and have eyes that are sensitive to the blue wavelengths of the visible spectrum.
The black malacoste's second pair of bioluminescent organs are located below its eyes and produce a distant red light that is invisible to others living in the depths of the ocean. These organs give the black malacoste an advantage over its rivals, as the light it emits helps it see prey and allows it to communicate with other individuals of its species without giving away its presence.
But how does the black malacost see far red light? According to the saying, "You are what you eat," it actually gets this opportunity by eating tiny copepods, which in turn feed on bacteria that absorb far-red light. In 1998, a team of scientists in the UK, including Dr. Julian Partridge and Dr. Ron Douglas, discovered that the retina of the black malacoste's eyes contains a modified version of the bacterial chlorophyll, a photopigment that can detect rays of far-red light.
Thanks to far-red light, some fish can see in water that would appear black to us. The bloodthirsty piranha in the murky waters of the Amazon, for example, perceives the water as dark red, a color more translucent than black. The water appears red due to red-colored vegetation particles that absorb visible light. Only the far-red light beams pass through the murky water and can be seen by the piranha. Infrared rays allow it to see prey, even if it hunts in complete darkness. Just like piranha, crucian carp in their natural habitats fresh water often muddy and overcrowded with vegetation. And they adapt to this by being able to see far red light. Indeed, their visual range (level) exceeds that of the piranha, since they can see not only in far-red light, but also in true infrared light. So your favorite is homemade gold fish can see much more than you think, including the "invisible" infrared rays emitted by common household electronic devices such as television remote control and security alarm system beams.
5. Snakes strike prey blindly
It is known that many species of snakes, even when deprived of vision, are capable of striking their victims with uncanny accuracy.
The rudimentary nature of their thermal sensors makes it difficult to argue that the ability to perceive the heat radiation of prey alone can explain these amazing abilities. Research by scientists from Munich technical university shows that it's probably all down to snakes having a unique "technology" for processing visual information, Newscientist reports.
Many snakes have sensitive infrared detectors, which helps them navigate in space. In laboratory conditions, snakes' eyes were covered with adhesive tape, and it turned out that they were able to kill a rat with an instant blow of poisonous teeth to the victim's neck or behind the ears. Such accuracy cannot be explained solely by the snake's ability to see the heat spot. Obviously, the whole point is in the ability of snakes to somehow process the infrared image and “clean” it from interference.
Scientists have developed a model that takes into account and filters both thermal “noise” emanating from moving prey, as well as any errors associated with the functioning of the detector membrane itself. In the model, a signal from each of the 2 thousand thermal receptors causes the excitation of its neuron, but the intensity of this excitation depends on the input to each of the other nerve cells. By integrating signals from interacting receptors into the models, the scientists were able to obtain very clear thermal images even with high levels of extraneous noise. But even relatively small errors associated with the operation of membrane detectors can completely destroy the image. To minimize such errors, the thickness of the membrane should not exceed 15 micrometers. And it turned out that the membranes of pit snakes have exactly this thickness, cnews.ru reports.
Thus, scientists were able to prove the amazing ability of snakes to process even images that are very far from perfect. Now it's a matter of confirming the model with studies of real snakes.
Conclusion
It is known that many species of snakes (in particular from the group of pit snakes), even being deprived of vision, are capable of striking their victims with supernatural “accuracy”. The rudimentary nature of their thermal sensors makes it difficult to argue that the ability to perceive the heat radiation of prey alone can explain these amazing abilities. A study by scientists from the Technical University of Munich shows that perhaps it’s all down to the presence of a unique “technology” for processing visual information in snakes, Newscientist reports.
It is known that many snakes have sensitive infrared detectors, which help them navigate in space and detect prey. In laboratory conditions, snakes were temporarily deprived of vision by covering their eyes with a plaster, and it turned out that they were able to hit a rat with an instant blow of poisonous teeth aimed at the victim’s neck, behind the ears - where the rat was unable to fight back with its sharp incisors. Such accuracy cannot be explained solely by the snake's ability to see a vague heat spot.
On the sides of the front of the head, pit snakes have depressions (which give the group its name) in which heat-sensitive membranes are located. How does a thermal membrane “focus”? It was assumed that this organ works on the principle of a camera obscura. However, the diameter of the holes is too large to implement this principle, and as a result, only a very blurry image can be obtained, which is not capable of providing the unique accuracy of a snake throw. Obviously, the whole point is in the ability of snakes to somehow process the infrared image and “clean” it from interference.
Scientists have developed a model that takes into account and filters both thermal “noise” emanating from moving prey, as well as any errors associated with the functioning of the detector membrane itself. In the model, a signal from each of the 2 thousand thermal receptors causes the excitation of its neuron, but the intensity of this excitation depends on the input to each of the other nerve cells. By integrating signals from interacting receptors into the models, the scientists were able to obtain very clear thermal images even with high levels of extraneous noise. But even relatively small errors associated with the operation of membrane detectors can completely destroy the image. To minimize such errors, the thickness of the membrane should not exceed 15 micrometers. And it turned out that the membranes of pit snakes have exactly this thickness.
Thus, scientists were able to prove the amazing ability of snakes to process even images that are very far from perfect. All that remains is to confirm the model with studies of real, not “virtual” snakes.
Bibliography
1. Anfimova M.I. Snakes in nature. - M, 2005. - 355 p.
2. Vasiliev K.Yu. Reptile vision. - M, 2007. - 190 p.
3. Yatskov P.P. Snake breed. - St. Petersburg, 2006. - 166 p.
Reptile eyes
indicate their way of life. In different species we observe a unique structure of the visual organs. To protect their eyes, some “cry”, others have eyelids, and still others “wear glasses”.
Reptile vision
, like the diversity of species, is very different. From the way the eyes are located on the head of a reptile, in to the greatest extent depends on how much the animal sees. When the eyes are set on both sides of the head, the visual fields of the eyes do not overlap. Such animals see well everything that happens on both sides of them, but their spatial vision is very limited (they cannot see the same object with both eyes). When a reptile's eyes are set at the front of its head, the animal can see the same object with both eyes. This position of the eyes helps reptiles more accurately determine the location of prey and the distance to it. IN land turtles and many lizards have eyes set on both sides of their heads, so they can clearly see everything that surrounds them. The snapping turtle has excellent spatial vision because its eyes are set at the front of its head. Chameleons' eyes, like cannons in defensive towers, can rotate independently 180° horizontally and 90° vertically - they can see behind them.
How do snakes exhibit their heat source?.
The most important sensory organ of a snake is the tongue in combination with Jacobson's organ. However, reptiles also have other adaptations necessary for successful hunting. To identify prey, snakes need more than just their eyes. Some snakes can sense heat emitted by the animal's body.
Pit-headed snakes, which include the true pit snakes, got their name due to the fact that they have a paired sensory organ in the form of facial pits located between the nostrils and the eye. With the help of this organ, snakes can sense warm-blooded animals by the difference in temperature between its body and the external environment with an accuracy of 0.2 ° C. The size of this organ is only a few millimeters, but it can detect infrared rays emitted by potential prey and transmit the received information through nerve endings in the brain. The brain perceives this information and analyzes it, so the snake has a clear idea of what kind of prey it encountered on its way and where exactly it is located. Different kinds Reptiles see and perceive the world around them very differently. The field of vision, its expressiveness and the ability to distinguish colors depend on how the animal’s eyes are set, on the shape of the pupils, as well as on the number and type of light-sensitive cells. In reptiles, vision is also related to their lifestyle.
Color vision
Many of the lizards can perfectly distinguish colors, which is an important means of communication for them. Some of them recognize scarlet poisonous insects against a black background. In the retina of the eyes of diurnal lizards there are special elements of color vision - bulbs. Giant tortoises are color-sensitive, and some respond particularly well to red light. They are even thought to be able to see infrared light, which the human eye cannot distinguish. Crocodiles and snakes are color blind.
American night lizards react not only to shape, but also to color. However, their retina still contains more rods than cones.
Reptile vision
The class of reptiles, or reptiles, includes crocodiles, alligators, turtles, snakes, geckos and lizards such as the hatteria. The reptile needs to receive accurate information about the size and color of its potential prey. In addition, the reptile must detect and quickly react when other animals approach and determine who it is - a potential partner, a young animal of the same species, or an enemy that may attack it. Reptiles that live underground or in water have rather small eyes. Those of them that live on earth depend more on visual acuity. The eyes of these animals are structured in the same way as human eyes. Their very part is the eyeball with the optic nerve. In front of it is the cornea, which allows light to pass through. The cornea is the iris. At its center is the pupil, which contracts or dilates, allowing a certain amount of light to pass onto the retina. Under the pupil there is a lens through which rays hit the light-sensitive back wall of the eyeball - the retina. The retina is made up of layers of light- and color-sensitive cells connected by the optic nerves to the brain, where all signals are sent and where an image of an object is created.
Eye protection
Some species of reptiles use eyelids to protect their eyes, just like mammals. However, reptile eyelids differ from mammalian eyelids in that the lower eyelid is larger and more mobile than the upper.
The snake's gaze appears glassy because its eyes are covered with a transparent film formed by the fused upper and lower eyelids. This protective coating is a kind of “glasses”. During molting, this film comes off along with the skin. Lizards also wear “glasses,” but only some. Geckos do not have eyelids. To clean their eyes, they use their tongue, sticking it out of their mouth and licking the eye shell. Other reptiles have a "parietal eye". This is a light spot on the head of a reptile; like a regular eye, it can perceive certain light stimuli and transmit signals to the brain. Some reptiles protect their eyes from pollution using lacrimal glands. When sand or other debris gets into the eyes of such reptiles, the lacrimal glands secrete a large number of a liquid that cleanses the animal's eyes, making the reptile appear to "cry". Soup turtles use this method.
Pupil structure
The pupils of reptiles indicate their lifestyle. Some of them, for example, crocodiles, pythons, geckos, hatteria, snakes, lead a nocturnal or twilight lifestyle, and take sunbathing during the day. They have vertical pupils that dilate in the dark and constrict in light. In geckos, pinpoint holes are visible on the constricted pupils, each of which focuses an independent image onto the retina. Together they create the necessary sharpness, and the animal sees a clear image.
You can read interesting things about penguins on the website kvn201.com.ua.
Thermal locators of a different design have recently been studied in snakes. This discovery is worth telling in more detail.
In the east of the USSR, from the Caspian Volga region and the Central Asian steppes to Transbaikalia and the Ussuri taiga, there are small Poisonous snakes, nicknamed copperheads: their heads are covered on top not with small scales, but with large scutes.
People who have looked at copperheads up close claim that these snakes seem to have four nostrils. In any case, on the sides of the head (between the real nostril and the eye) two large (larger than the nostril) and deep pits are clearly visible in copperheads.
Cottonmouths are close relatives of America's rattlesnakes, which locals sometimes call quartonarians, that is, four-nosed snakes. This means that rattlesnakes also have strange pits on their faces.
Zoologists combine all snakes with four “nostrils” into one family, the so-called crotalids, or pitheads. Pit snakes are found in America (North and South) and Asia. In their structure they are similar to vipers, but differ from them in the mentioned pits on the head.
For more than two hundred years, scientists have been solving nature's puzzle, trying to establish what role these pits play in the life of snakes. What assumptions were made!
They thought that these were organs of smell, touch, hearing amplifiers, glands that secrete lubricant for the cornea of the eyes, detectors of subtle air vibrations (like the lateral line of fish) and, finally, even air blowers that deliver oxygen to the oral cavity, supposedly necessary for the formation of poison.
Thorough research by anatomists thirty years ago showed that the facial pits of rattlesnakes are not connected to the ears, eyes, or
any other known organs. They are depressions in the upper jaw. Each pit at a certain depth from the inlet is divided by a transverse partition (membrane) into two chambers - internal and external.
The external chamber lies in front and opens outward with a wide funnel-shaped opening, between the eye and nostril (in the area of the auditory scales). The rear (inner) camera is completely closed. Only later was it possible to notice that it communicates with the external environment through a narrow and long channel, which opens on the surface of the head near the anterior corner of the eye with an almost microscopic pore. However, the size of the pore, when necessary, can apparently increase significantly: the opening is equipped with an annular closing muscle.
The partition (membrane) separating both chambers is very thin (about 0.025 millimeters thick). Dense interweaving of nerve endings penetrates it in all directions.
Undoubtedly, the facial pits represent organs of some senses. But which ones?
In 1937, two American scientists, D. Noble and A. Schmidt, published a large work in which they reported the results of their many years of experiments. They managed to prove, the authors argued, that the facial pits are thermolocators! They capture heat rays and determine by their direction the location of the heated body emitting these rays.
D. Noble and A. Schmidt experimented with rattlesnakes artificially deprived of all known to science sense organs. Electric light bulbs wrapped in black paper were brought to the snakes. While the lamps were cold, the snakes did not pay any attention to them. But when the light bulb got hot, the snake immediately felt it. She raised her head and became wary. The light bulb was brought even closer. The snake made a lightning-fast throw and bit the warm “victim.” I didn’t see her, but she bit her accurately, without missing a beat.
Experimenters have found that snakes detect heated objects whose temperature is at least 0.2 degrees Celsius higher than the surrounding air (if they are brought closer to the muzzle itself). Warmer objects are recognized at a distance of up to 35 centimeters.
In a cold room, thermolocators work more accurately. They are apparently adapted for night hunting. With their help, the snake searches for small warm-blooded animals and birds. It is not the smell, but the warmth of the body that gives away the victim! Snakes have poor eyesight and sense of smell and very poor hearing. A new, very special feeling came to their aid - thermal location.
In the experiments of D. Noble and A. Schmidt, the indicator that the snake had found a warm light bulb was its throwing. But the snake, of course, even before it rushed to attack, already felt the approach of a warm object. This means that we need to find some other, more accurate signs by which one could judge the subtlety of the snake’s thermolocation sense.
American physiologists T. Bullock and R. Cowles conducted more thorough studies in 1952. As a signal notifying that an object was detected by the snake's thermolocator, they chose not the reaction of the snake's head, but a change in biocurrents in the nerve serving the facial fossa.
It is known that all processes of excitation in the body of animals (and humans) are accompanied by those occurring in the muscles and nerves. electric currents. Their voltage is low - usually hundredths of a volt. These are the so-called “biocurrents of excitation”. Biocurrents are easy to detect using electrical measuring instruments.
T. Bullock and R. Cowles anesthetized snakes by injecting a certain dose of curare poison. We cleared one of the nerves branching in the membrane of the facial fossa from muscles and other tissues, brought it out and pressed it between the contacts of a device that measures biocurrents. Then the facial pits were subjected to various influences: they were illuminated with light (without infrared rays), strong-smelling substances were brought close to them, and they were irritated with strong sound, vibration, and pinches. The nerve did not react: biocurrents did not arise.
But as soon as a heated object, even just a human hand (at a distance of 30 centimeters), was brought closer to the snake’s head, excitement arose in the nerve - the device recorded biocurrents.
They illuminated the pits with infrared rays - the nerve became even more excited. The weakest reaction of the nerve was detected when it was irradiated with infrared rays with a wavelength of about 0.001 millimeters. As the wavelength increased, the nerve became more excited. The greatest reaction was caused by the longest wavelength infrared rays (0.01 - 0.015 millimeters), that is, those rays that carry the maximum thermal energy emitted by the body of warm-blooded animals.
It also turned out that the thermolocators of rattlesnakes detect not only objects that are warmer, but even colder than the surrounding air. It is only important that the temperature of this object is at least a few tenths of a degree higher or lower than the surrounding air.
The funnel-shaped openings of the facial fossae are directed obliquely forward. Therefore, the thermolocator's coverage area lies in front of the snake's head. Up from the horizontal it occupies a sector of 45 degrees, and downward - 35 degrees. To the right and left of the longitudinal axis of the snake’s body, the field of action of the thermolocator is limited to an angle of 10 degrees.
Physical principle, on which the thermolocators of snakes are based, is completely different from that of squids.
Most likely, in the thermoscopic eyes of squids, the perception of a heat-emitting object is achieved through photochemical reactions. Processes of the same type probably occur here as on the retina of an ordinary eye or on a photographic plate at the time of exposure. The energy absorbed by the organ leads to the recombination of light-sensitive (in squids, heat-sensitive) molecules, which act on the nerve, causing the brain to imagine the observed object.
Snake thermal locators They act differently - on the principle of a kind of thermoelement. The thinnest membrane separating the two chambers of the facial fossa is exposed from different sides to two different temperatures. The internal chamber communicates with the external environment through a narrow channel, the inlet of which opens in the opposite direction from the working field of the locator.
Therefore, the ambient air temperature is maintained in the inner chamber (neutral level indicator!) The outer chamber is directed towards the object under study with a wide opening - a heat trap. The heat rays it emits heat the front wall of the membrane. Based on the temperature difference on the inner and outer surfaces of the membrane, which are simultaneously perceived by the nerves in the brain, the sensation of radiating thermal energy subject.
In addition to pit snakes, thermolocation organs have been found in pythons and boas (in the form of small pits on the lips). The small pits located above the nostrils of the African, Persian and some other species of vipers apparently serve the same purpose.
Scientists have been observing the behavior of snakes for quite some time. The main organs for reading information are thermal sensitivity and smell.
The sense of smell is the main organ. The snake constantly works with its forked tongue, taking samples of air, soil, water and objects surrounding the snake.
Thermal sensitivity. A unique sensory organ that snakes have. allows you to “see” mammals while hunting even in complete darkness. In the viper, these are sensory receptors located in deep grooves on the muzzle. A snake like a rattlesnake has two large spots on its head. The rattlesnake not only sees warm-blooded prey, it knows the distance to it and the direction of movement.
The snake's eyes are covered with completely fused transparent eyelids. Vision varies among snake species, but serves primarily to track the movement of prey.
All this is interesting, but what about hearing?
It is absolutely known that snakes do not have hearing organs in the usual sense. The eardrum, auditory ossicles and cochlea, which transmit sound through nerve fibers to the brain, are completely absent.
However, snakes can hear, or rather feel, the presence of other animals. The sensation is transmitted through vibrations of the soil. This is how reptiles hunt and hide from danger. This ability to perceive danger is called vibration sensitivity. The vibration of the snake is felt by the whole body. Even very low sound frequencies are transmitted to the snake through vibration.
Quite recently, a sensational article appeared by zoologists from the Danish University of Aarhus (Aarhus University, Denmark) who studied the effect on the neurons of the python’s brain from a speaker turned on in the air. It turned out that the basics of hearing are present in the experimental python: there is an inner and outer ear, but there is no eardrum - the signal is transmitted directly to the skull. It was even possible to record the frequencies “heard” by the python bones: 80-160 Hz. This is an extremely narrow low-frequency range. Man is known to hear 16-20000 Hz. However, whether other snakes have similar abilities is not yet known.
Sense organs in snakes
In order to successfully detect, overtake and kill animals, snakes have at their disposal a rich arsenal of various devices that allow them to hunt depending on the prevailing circumstances.
One of the first places in importance among snakes is the sense of smell. Snakes have a surprisingly delicate sense of smell, capable of detecting the smell of the most insignificant traces of certain substances. The snake's sense of smell involves a forked, mobile tongue. The flickering tongue of a snake is as common a touch to a portrait as the absence of limbs. Through the trembling touches of the tongue, the snake “touches” - touches. If the animal is nervous or is in an unusual environment, the frequency of tongue flickering increases. With quick movements “outward - into the mouth,” she seems to take a sample of the air, receiving detailed chemical information about the environment. The forked tip of the tongue, curving, presses against two small pits on the palate - Jacobson's organ, consisting of chemically sensitive cells, or chemoreceptors. By vibrating its tongue, the snake captures microscopic particles of odorous substances and brings them to this unique organ of taste and smell for analysis.
Snakes lack auditory openings and eardrums, making them deaf in the usual sense. Snakes do not perceive sounds that are transmitted through the air, but they subtly detect vibrations passing through the soil. They perceive these vibrations with their ventral surface. So the snake is absolutely indifferent to screams, but it can be scared by stomping.
Snakes' vision is also quite weak and is of little importance to them. There is an opinion that snakes have some kind of special hypnotic snake look and can hypnotize their prey. In fact, there is nothing like that, it’s just that, unlike many other animals, snakes do not have eyelids, and their eyes are covered with transparent skin, so the snake does not blink, and its gaze seems intent. And the shields located above the eyes give the snake a gloomy, angry expression.
Three groups of snakes - boas, pythons and pit vipers - have a unique additional sensory organ that no other animal has.
This is a thermolocation organ, presented in the form of thermolocation pits on the snake’s face. Each hole is deep and covered with a sensitive membrane, which senses temperature fluctuations. With its help, snakes can detect the location of a warm-blooded animal, i.e. their main prey, even in complete darkness. Moreover, by comparing signals received from fossae on opposite sides of the head, i.e. Using the stereoscopic effect, they can accurately determine the distance to their prey and then strike. Boas and pythons have a whole series of such pits located in the labial scutes bordering the upper and lower jaws. Pit vipers have only one pit on each side of their head.
