Fish forebrain functions. Anisimova I.M., Lavrovsky V.V. Ichthyology. The structure and some physiological features of fish. Nervous system and sense organs

CHAPTER I
STRUCTURE AND SOME PHYSIOLOGICAL FEATURES OF FISH

NERVOUS SYSTEM AND SENSORS

The nervous system of fish is represented by the central nervous system and the peripheral and autonomic (sympathetic) nervous systems associated with it. The central nervous system consists of the brain and spinal cord. The peripheral nervous system includes nerves that extend from the brain and spinal cord to the organs. The autonomic nervous system basically has numerous ganglia and nerves innervating the muscles of the internal organs and blood vessels of the heart. The nervous system of fish, in comparison with the nervous system of higher vertebrates, is characterized by a number of primitive features.

The central nervous system looks like a neural tube stretching along the body; part of it, lying above the spine and protected by the upper arches of the vertebrae, forms the spinal cord, and the expanded anterior part, surrounded by a cartilaginous or bone skull, makes up the brain.

The tube has a cavity inside (neurocoel), represented in the brain by the ventricles of the brain. In the thickness of the brain, gray matter is distinguished, which is composed of bodies of nerve cells and short processes (dendrites), and white matter, formed by long processes of nerve cells - neurites or axons.

The total brain mass in fish is small: it averages 0.06 - 0.44% in modern cartilaginous fish, 0.02 - 0.94% in bone fish, including 1/700 of body weight in burbot, pike 1/3000, sharks - 1/37000, while in flying birds and mammals 0.2 - 8.0 and 6.3 - 3.0%.

Primitive features are preserved in the structure of the brain: the parts of the brain are arranged linearly. It distinguishes forebrain, intermediate, middle, cerebellum and oblong, passing into the spinal cord (Fig. 27).

The cavities of the anterior, intermediate and medulla oblongata are called ventricles: the midbrain cavity is the Sylvian aqueduct (it connects the cavities of the diencephalon and medulla oblongata, i.e., the third and fourth ventricles).

Rice. 27. Fish brain (perch):
1 - olfactory capsules, 2 - olfactory lobes, 3 - forebrain, 4 - midbrain, 5 - cerebellum, 6 - medulla oblongata, 7 - spinal cord, 8, 9, 10 - head nerves

The forebrain, due to the longitudinal groove, has the appearance of two hemispheres. They are adjacent to the olfactory bulbs (primary olfactory center) either directly (in most species) or through the olfactory tract (carp, catfish, cod).

There are no nerve cells in the roof of the forebrain. Gray matter in the form of striatal bodies is concentrated mainly in the base and olfactory lobes, lines the cavity of the ventricles and makes up the main mass of the forebrain. The fibers of the olfactory nerve connect the bulb with the cells of the olfactory capsule.

The forebrain is the center for processing information from the olfactory organs. Due to its connection with the diencephalon and midbrain, it is involved in the regulation of movement and behavior. In particular, the forebrain is involved in the formation of the ability to perform such acts as spawning, guarding eggs, flock formation, etc.

Visual tubercles are developed in the diencephalon. The optic nerves depart from them, forming a chiasma (crossover, i.e., part of the fibers of the right nerve passes into the left nerve and vice versa). On the bottom side diencephalon(hypothalamus) there is a funnel to which the pituitary gland, or pituitary gland, is adjacent; in the upper part of the diencephalon, the epiphysis, or pineal gland, develops. The pituitary and pineal glands are endocrine glands.

The diencephalon performs numerous functions. He perceives irritation from the retina of the eye, participates in the coordination of movements, in the processing of information from other sensory organs. The pituitary and pineal glands carry out hormonal regulation of metabolic processes.

The midbrain is the largest. It has the appearance of two hemispheres (visual lobes). The visual lobes are the primary visual centers that perceive excitation. The fibers of the optic nerve originate from these lobes. In the midbrain, signals from the organs of vision and balance are processed; here are located communication centers with the cerebellum, medulla oblongata and spinal cord.

The cerebellum is located in the back of the brain and can take the form of either a small tubercle adjacent to the back of the midbrain, or a large saccular-elongated formation adjacent to the top of the medulla oblongata. Especially great development reaches the cerebellum in catfish, and in mormirus its relative value is the largest among other vertebrates. In the cerebellum of fish, as well as higher vertebrates, there are Purkinje cells. The cerebellum is the center of all motor innervation during swimming, grasping food. It provides coordination of movements, maintaining balance, muscle activity, and is associated with lateral line organ receptors.

The fifth part of the brain, the medulla oblongata, passes into the spinal cord without a sharp border. The cavity of the medulla oblongata - the fourth ventricle - continues into the cavity of the spinal cord - the neurocoel. A significant mass of the medulla oblongata consists of white matter.

Most (six out of ten) of the cranial nerves depart from the medulla oblongata. It is the center of regulation of the activity of the spinal cord and the autonomic nervous system. It contains the most important vital centers that regulate the activity of the respiratory, musculoskeletal, circulatory, digestive, excretory systems, organs of hearing and balance, taste, lateral line, electrical organs in fish that have them, etc. Therefore, when the medulla oblongata is destroyed, for example, when cutting the body behind the head, a quick death of the fish occurs. Through the spinal fibers coming to the medulla oblongata, the connection between the medulla oblongata and the spinal cord is carried out.

10 pairs of cranial nerves leave the brain:

I - olfactory nerve (nervus olfactorius) - from the sensory epithelium of the olfactory capsule brings irritation to the olfactory bulbs of the forebrain;
II - optic nerve (n. opticus) - stretches to the retina from the visual tubercles of the diencephalon;
III - oculomotor nerve (n. oculomotorius) - innervates the muscles of the eye, moving away from the midbrain;
IV - trochlear nerve (n. trochlearis), oculomotor, stretching from the midbrain of the code from the muscles of the eye;
V - trigeminal nerve (n. trigeminus), extending from the lateral surface of the medulla oblongata and giving three main branches: ophthalmic, maxillary and mandibular;
VI - abducent nerve (n. abducens) - stretches from the bottom of the brain to the rectus muscle of the eye;
VII - facial nerve (n. facialis) - departs from the medulla oblongata and gives numerous branches to the muscles of the hyoid arch, oral mucosa, scalp (including the lateral line of the head);
VIII - auditory nerve (n. acusticus) - connects the medulla oblongata and the auditory apparatus;
IX- glossopharyngeal nerve(n. glossopharingeus) - goes from the medulla oblongata to the pharynx, innervates the mucous membrane of the pharynx and the muscles of the first gill arch;
X - vagus nerve (n. vagus) - the longest. Connects the medulla oblongata with the gill apparatus, intestinal tract, heart, swim bladder, lateral line.

The degree of development of different parts of the brain is different in different groups of fish and is associated with lifestyle.

The forebrain (and olfactory lobes) is relatively more developed in cartilaginous fish (sharks and rays) and weaker in teleosts. In sedentary, for example, bottom fish, the cerebellum is small, but the anterior and medulla oblongata are more developed in accordance with big role smell and touch in their lives (flounders). In well-swimming fish (pelagic, plankton-feeding, or predatory), on the contrary, the midbrain (visual lobes) and cerebellum (due to the need for rapid movement coordination) are much more developed. Fish that live in muddy waters have small visual lobes, a small cerebellum.

The visual lobes are poorly developed in deep-sea and blind fish.
The spinal cord is a continuation of the medulla oblongata. It has the shape of a rounded cord and lies in the canal formed by the upper arches of the vertebrae.

In the spinal cord, gray matter is on the inside and white matter is on the outside. From the spinal cord, metamerically, corresponding to each vertebra, the spinal nerves that innervate the surface of the body, the trunk muscles, and, due to the connection of the spinal nerves with the ganglia of the sympathetic nervous system, also the internal organs.

The autonomic nervous system in cartilaginous fish is represented by disjointed ganglia lying along the spine. Ganglion cells with their processes are in contact with the spinal nerves and internal organs.

In bony fish, the ganglia of the autonomic nervous system are connected by two longitudinal nerve trunks. The connecting branches of the ganglia connect the autonomic nervous system with the central one. The interrelationships of the central and autonomic nervous systems create the possibility of some interchangeability of nerve centers.

The autonomic nervous system acts autonomously to a certain extent, independently of the central nervous system and determines the involuntary, automatic activity of the internal organs, even if its connection with the central nervous system is broken.

The reaction of the fish organism to external and internal stimuli is determined by the reflex. Fish can develop a conditioned reflex to light, shape, smell, taste, sound. Compared to higher vertebrates, conditioned reflexes in fish are formed more slowly and die out faster. However, both aquarium and pond fish soon after the start of regular feeding accumulate at certain times at the feeders. They also get used to sounds during feeding (tapping on the walls of the aquarium, ringing a bell, whistling, blows) and for some time swim up to these stimuli even in the absence of food.

The organs of perception of the environment (sense organs) of fish have a number of features that reflect their adaptability to living conditions.

The ability of fish to perceive information from the environment is diverse. Their receptors can detect various stimuli of both physical and chemical nature: pressure, sound, color, temperature, electrical and magnetic fields, smell, taste.

Some stimuli are perceived as a result of direct touch (touch, taste), others at a distance, remotely.

Organs that perceive chemical, tactile (touch), electromagnetic, temperature and other stimuli have a simple structure. Irritations are caught by the free nerve endings of the sensory nerves on the surface of the skin. In some groups of fish, they are represented special bodies or are part of the sideline.

In connection with the peculiarities of the living environment in fish, chemical sense systems are of great importance. Chemical stimuli are perceived with the help of smell (sensation of smell) or with the help of non-olfactory reception organs, which provide the perception of taste, changes in the activity of the environment, etc. The chemical sense is called chemoreception, and the sensory organs are called chemoreceptors.

Organs of smell. In fish, as in other vertebrates, they are located in the anterior part of the head and are represented by paired olfactory (nasal) sacs (capsules) that open outward through nostrils. The bottom of the nasal capsule is lined with folds of epithelium, consisting of supporting and sensory cells (receptors). The outer surface of the sensory cell is provided with cilia, and the base is connected with the endings of the olfactory nerve. The olfactory epithelium contains numerous mucus-secreting cells.

The nostrils are located in cartilaginous fish on the underside of the snout in front of the mouth, in bony fish - on the dorsal side between the mouth and eyes. Cyclostomes have one nostril, real fish have two. Each nostril is divided by a leathery septum into two openings. Water penetrates into the anterior of them, washes the cavity and exits through the rear opening, washing and irritating the hairs of the receptors. Under the influence of odorous substances in the olfactory epithelium, complex processes occur: the movement of lipids, protein-mucopolysaccharide complexes and acid phosphatase.

The size of the nostrils is related to the way of life of fish: in moving fish they are small, since during fast swimming the water in the olfactory cavity is updated quickly; in sedentary fish, on the contrary, the nostrils are large, they pass a larger volume of water through the nasal cavity, which is especially important for poor swimmers, in particular those living near the bottom.

Fish have a subtle sense of smell, i.e., their thresholds for olfactory sensitivity are very low. This is especially true for nocturnal twilight fish, as well as for those living in muddy waters ah, for whom sight helps little in finding food and communicating with relatives. The most surprising is the sensitivity of smell in migratory fish. Far Eastern salmon definitely find their way from feeding grounds in the sea to spawning grounds in the upper reaches of the rivers, where they hatched several years ago. At the same time, they overcome huge distances and obstacles - currents, rapids, rifts. However, fish pass the path correctly only if their nostrils are open; if the sense of smell is turned off (the nostrils are filled with cotton wool or petroleum jelly), then the fish move randomly. It is assumed that salmon at the beginning of migration are guided by the sun and approximately 800 km from their native river accurately determine the path due to chemoreception.

In experiments, when washing the nasal cavity of these fish with water from their native spawning ground, a strong electrical reaction arose in the olfactory bulb of the brain. The reaction to water from downstream tributaries was weak, and the receptors did not react at all to water from foreign spawning grounds.

Juvenile sockeye salmon Oncorhynchus nerka can distinguish water from different lakes, solutions of various amino acids in a dilution of 10-4, as well as the concentration of calcium in water using the cells of the olfactory bulb. No less striking is the similar ability of the European eel migrating from Europe to spawning grounds located in the Sargasso Sea. It is estimated that the eel is able to recognize the concentration created by diluting 1 g of phenylethyl alcohol in a ratio of 1: 3 10-18. High selective sensitivity to histamine was found in carp.

The olfactory receptor of fish, in addition to chemical ones, is able to perceive mechanical influences (flow jets) and temperature changes.

organs of taste. They are represented by taste buds, formed by clusters of sensory (and supporting) cells. The bases of the sensory cells are entwined with terminal branches of the facial, vagus, and glossopharyngeal nerves.

Perception chemical irritants It is also carried out by free nerve endings of the trigeminal, vagus and spinal nerves. The perception of taste by fish is not necessarily associated with the oral cavity, since taste buds are located both in the oral mucosa and on the lips, and in the pharynx, on the antennae, gill filaments, fin rays and all over the surface of the body, including the tail.

Catfish perceives taste mainly with the help of whiskers: it is in their epidermis that clusters of taste buds are concentrated. In the same individual, the number of taste buds increases as body size increases. Fish distinguish the taste characteristics of food: bitter, salty, sour, sweet. In particular, the perception of salinity is associated with a pit-shaped organ located in the oral cavity.

The sensitivity of the taste organs in some fish is very high: for example, cave fish Anoptichthys, being blind, feel a glucose solution at a concentration of 0.005%.

lateral line sense organs. specific body, characteristic only of fish and amphibians living in the water, is the organ of the lateral sense, or lateral line. These are seismosensory specialized skin organs. The lateral line organs are most simply arranged in cyclostomes and larvae of cyprinids. Sensory cells (mechanoreceptors) lie among clusters of ectodermal cells on the surface of the skin or in small pits.

At the base, they are braided with terminal branches of the vagus nerve, and in the area that rises above the surface, they have cilia that perceive water vibrations. In most adult teleosts, these organs are channels immersed in the skin, stretching along the sides of the body along the midline. The channel opens outward through holes (pores) in scales located above it (Fig. 28).

Rice. 28. Organ of the lateral line of bony fish (according to Kuznetsov, Chernov, 1972):
1 - opening of the lateral line in the scales, 2 - longitudinal canal of the lateral line,
3 – sensitive cells, 4 - nerves

Branchings of the lateral line are also present on the head. At the bottom of the channel (groups lie sensory cells with cilia. Each such group of receptor cells, together with the nerve fibers in contact with them, forms the actual organ - the neuromast. Water flows freely through the channel, and the cilia feel its pressure. In this case, nerve impulses of different frequencies arise. Organs The lateral lines are connected to the central nervous system by the vagus nerve.

The lateral line may be complete, i.e., stretch along the entire length of the body, or incomplete and even absent, but in the latter case, the head canals are strongly developed (in herring). The lateral line enables the fish to feel changes in the pressure of flowing water, vibrations (oscillations) of low frequency, infrasonic vibrations, and for many fish - electromagnetic fields. The lateral line captures the pressure of a flowing, moving stream; it does not perceive pressure changes with immersion to depth.

Capturing fluctuations in the water column, the lateral line organs enable the fish to detect surface waves, currents, underwater stationary objects (rocks, reefs) and moving objects (enemies, prey), swim day and night, in muddy water and even being blinded.

This is a very sensitive organ: migratory fish feel even very weak currents of fresh river water in the sea.

The ability to capture the waves reflected from living and inanimate objects is very important for deep-sea fish, since in the darkness of great depths the usual visual perception of surrounding objects and communication between individuals is impossible.

It is assumed that the waves created during the mating games of many fish, perceived by the lateral line of the female or male, serve as a signal for them.

The function of the skin sense is performed by the so-called skin buds - cells present in the integument of the head and antennae, to which the nerve endings fit, but they are of much lesser importance.

Organs of touch. The organs of touch are clusters of sensory cells (tactile bodies) scattered over the surface of the body. They perceive the touch of solid objects ( tactile sensations), water pressure, as well as temperature changes (hot-cold) and pain.

Especially many feeling skin buds found in the mouth and on the lips. In some fish, the function of the tactile organs is performed by elongated rays of the fins: in gourami, this is the first ray of the ventral fin, in trigly (sea cock) the sense of touch is associated with the rays of the pectoral fins that feel the bottom, etc. In inhabitants of muddy waters or bottom fish, the most active at night, the largest number of sensory buds are concentrated on the antennae and fins. However, in catfish, whiskers serve as receptors for taste, not touch.

Fish, apparently, feel less mechanical injuries and pain than other vertebrates: sharks that pounce on prey do not react to blows. sharp object to the head; during operations, the fish are often relatively calm, etc.

Thermoreceptors. They are the free endings of the sensory nerves located in the surface layers of the skin, with the help of which the fish perceive the temperature of the water. There are receptors that perceive heat (thermal) and cold (cold). Points of heat perception are found, for example, in pike on the head, cold perception points are found on the surface of the body. Bony fish catch temperature drops of 0.1–0.4 ° C.

Organs of electrical sense. The organs of perception of electric and magnetic fields are located in the skin on the entire surface of the body of fish, but mainly in different parts of the head and around it. They are similar to the organs of the lateral line - these are pits filled with a mucous mass that conducts current well; at the bottom of the pits are placed sensory cells (electroreceptors) that transmit nerve impulses to the brain. Sometimes they are part of the lateral line system. The ampullae of Lorenzini also serve as electrical receptors in cartilaginous fish. Analysis of the information received by electroreceptors is carried out by the lateral line analyzer (in the medulla and cerebellum). The sensitivity of fish to current is high - up to 1 μV/cm2. It is assumed that the perception of changes in the Earth's electromagnetic field allows fish to detect the approach of an earthquake 6–8 and even 22–24 hours before the start, within a radius of up to 2000 km.

organs of vision. The visual organs of fish are basically the same as those of other vertebrates. The mechanism of perception of visual sensations is similar to other vertebrates: light passes into the eye through the transparent cornea, then the pupil - a hole in the iris - passes it to the lens, and the lens transmits and focuses the light on inner wall the retina of the eye, where it is directly perceived (Fig. 29). The retina consists of light-sensitive (photoreceptor), nerve, as well as supporting cells.

Rice. 29. The structure of the eye of bony fish (according to Protasov, 1968):
1 - optic nerve, 2 - ganglion cells, 3 - layer of rods and cones, 4 - retina, 5 - lens, 6 - cornea, 7 - vitreous body

Light-sensitive cells are located on the side of the pigment membrane. In their processes, shaped like rods and cones, there is a photosensitive pigment. The number of these photoreceptor cells is very large - there are 50 thousand of them per 1 mm2 of the retina in carp (in squid - 162 thousand, spider - 16 thousand, human - 400 thousand, owl - 680 thousand). Through a complex system of contacts between the terminal branches of sensory cells and dendrites of nerve cells, light stimuli enter the optic nerve.

Cones in bright light perceive the details of objects and color. Rods perceive weak light, but they cannot create a detailed image.

The position and interaction of the cells of the pigment membrane, rods and cones change depending on the illumination. In the light, the pigment cells expand and cover the rods located near them; cones are drawn to the nuclei of cells and thus move towards the light. In the dark, sticks are drawn to the nuclei (and are closer to the surface); the cones approach the pigment layer, and the pigment cells reduced in the dark cover them (Fig. 30).

Rice. 30. Retinomotor reaction in the retina of the bony fish
A - installation on the light; B - setting to darkness (according to Naumov, Kartashev, 1979):
1 - pigment cell, 2 - rod, 3 - rod nucleus, 4 - cone, 5 - cone nucleus

The number of receptors of various kinds depends on the way of life of fish. In diurnal fish, cones prevail in the retina, in twilight and nocturnal fish, rods: burbot has 14 times more rods than pike. Deep-sea fish living in the darkness of the depths do not have cones, but the rods become larger and their number increases sharply - up to 25 million / mm2 of the retina; the probability of capturing even weak light increases. Most fish distinguish colors, which is confirmed by the possibility of developing conditioned reflexes in them to certain color- blue, green, red, yellow, blue.

Some departures from general scheme The structure of the eye of a fish is associated with the characteristics of life in the water. The eye of the fish is elliptical. Among others, it has a silvery shell (between the vascular and protein), rich in guanine crystals, which gives the eye a greenish-golden sheen.

The cornea is almost flat (rather than convex), the lens is spherical (rather than biconvex) - this expands the field of view. The hole in the iris - the pupil - can change the diameter only within small limits.

As a rule, fish do not have eyelids. Only sharks have a nictitating membrane that covers the eye like a curtain, and some herring and mullet have a fatty eyelid - a transparent film that covers part of the eye.

The location of the eyes on the sides of the head (in most species) is the reason why fish have mainly monocular vision, and the ability for binocular vision is very limited. The spherical shape of the lens and moving it forward to the cornea provides a wide field of view: light enters the eye from all sides. The vertical angle of view is 150°, horizontally 168–170°. But at the same time, the sphericity of the lens causes myopia in fish. The range of their vision is limited and fluctuates due to the turbidity of the water from a few centimeters to several tens of meters.

Vision on long distance becomes possible due to the fact that the lens can be pulled back by a special muscle, a sickle-shaped process extending from the choroid of the bottom of the eyecup.

With the help of vision, fish are also guided by objects on the ground. Improved vision in the dark is achieved by the presence of a reflective layer (tapetum) - guanine crystals, underlain by pigment. This layer does not transmit light to the tissues lying behind the retina, but reflects it and returns it back to the retina. This increases the ability of the receptors to use the light that has entered the eye.

Due to habitat conditions, the eyes of fish can change greatly. In cave or abyssal (deep water) forms, the eyes can be reduced and even disappear. Some deep-sea fish, on the contrary, have huge eyes that allow them to capture very faint traces of light, or telescopic eyes, the collecting lenses of which the fish can put in parallel and acquire binocular vision. The eyes of some eels and larvae of a number of tropical fish are carried forward on long outgrowths (stalked eyes).

An unusual modification of the eyes of a four-eyed bird from Central and South America. Her eyes are placed on the top of her head, each of them is divided by a partition into two independent parts: the upper fish sees in the air, the lower one in the water. In the air, the eyes of fish crawling ashore or trees can function.

The role of vision as a source of information from the outside world for most fish is very large: when orienting during movement, when searching for and capturing food, while maintaining a flock, during the spawning period (the perception of defensive and aggressive postures and movements by rival males, and between individuals of different sexes - wedding attire and spawning "ceremonial"), in the relationship of the victim-predator, etc.

The ability of fish to perceive light has long been used in fishing (fishing by the light of a torch, fire, etc.).

It is known that fish of different species react differently to light of different intensities and different wavelengths, i.e., different colors. Thus, bright artificial light attracts some fish (Caspian sprat, saury, horse mackerel, mackerel, etc.) and scares away others (mullet, lamprey, eel, etc.).

In the same way, different species are selectively different colors and different light sources - surface and underwater. All this is the basis for the organization of industrial fishing for electric light (this is how sprat, saury and other fish are caught).

Organ of hearing and balance of fish. It is located at the back cranium and is represented by a labyrinth; there are no ear openings, auricle and cochlea, i.e., the hearing organ is represented by the inner ear. It reaches its greatest complexity in real fish: a large membranous labyrinth is placed in a cartilaginous or bone chamber under the cover of the ear bones. It distinguishes between the upper part - an oval pouch (ear, utriculus) and the lower - a round pouch (sacculus). Three semicircular canals extend from the upper part in mutually perpendicular directions, each of which is expanded into an ampulla at one end (Fig. 31). An oval sac with semicircular canals constitutes the organ of balance (vestibular apparatus). Lateral extension the lower part of the round sac (lagena), which is the rudiment of the snail, does not receive in fish further development. An internal lymphatic (endolymphatic) canal departs from the round sac, which in sharks and rays goes out through a special hole in the skull, and in other fish it ends blindly at the scalp.

Rice. 31. Fish hearing organ
1 - anterior canal, 2 - endolymphatic canal, 3 - horizontal canal,
4 - lagena, 5 - posterior canal, 6 - sacculus, 7 - utriculus

The epithelium lining the sections of the labyrinth has sensory cells with hairs extending into the internal cavity. Their bases are braided with branches auditory nerve. The cavity of the labyrinth is filled with endolymph, it contains "auditory" pebbles, consisting of carbonic lime (otoliths), three on each side of the head: in an oval and round sac and lagen. On otoliths, as on scales, concentric layers are formed; therefore, otoliths, and especially the largest one, are often used to determine the age of fish, and sometimes for systematic determinations, since their sizes and contours are not the same in different species.

In most fishes, the largest otolith is located in a round sac, but in cyprinids and some others - in the lagen,

A sense of balance is associated with the labyrinth: when the fish moves, the pressure of the endolymph in the semicircular canals, as well as from the side of the otolith, changes and the resulting irritation is captured by the nerve endings. With the experimental destruction of the upper part of the labyrinth with semicircular canals, the fish loses the ability to maintain balance and lies on its side, back or belly. The destruction of the lower part of the labyrinth does not lead to a loss of balance.

The perception of sounds is connected with the lower part of the labyrinth: when the lower part of the labyrinth with a round pouch and lagen is removed, the fish are not able to distinguish sound tones (when trying to develop a conditioned reflex). At the same time, fish without an oval pouch and semicircular canals, that is, without the upper part of the labyrinth, are amenable to training. Thus, it was shown that the round sac and lagena are sound receptors.

Fish perceive both mechanical and sound vibrations: with a frequency of 5 to 25 Hz - by the organs of the lateral line, from 16 to 13,000 Hz - by the labyrinth.

Some species of fish pick up vibrations that are on the border of infra sound waves both sideline and labyrinth.

Hearing acuity in fish is lower than in higher vertebrates, and is not the same in different species: ide perceives vibrations with a wavelength of 25–5524 Hz, silver carp - 25–3840, eel - 36–650 Hz, and low sounds are captured by them better .

Fish also pick up those sounds whose source is not in the water, but in the atmosphere, despite the fact that such sound is 99.9% reflected by the surface of the water and, therefore, only 0.1% of the resulting sound waves penetrate the water. In the perception of sound in cyprinids, catfish, an important role is played by the swim bladder, connected to the labyrinth and serving as a resonator.

Fish can make their own sounds. The sound-producing organs in fish are different: the swim bladder (croakers, wrasses, etc.), the rays of the pectoral fins in combination with the bones of the shoulder girdle (soma), the jaw and pharyngeal teeth (perch and cyprinids), etc. In this regard, the nature of the sounds is not the same : they can resemble blows, clatter, whistle, grunts, grunts, squeaks, croaks, growls, crackles, rumbles, ringing, wheezing, horns, bird calls and insect chirping. The strength and frequency of sounds made by fish of the same species depends on gender, age, food activity, health, pain caused, etc.

The sound and perception of sounds is of great importance in the life of fish: it helps individuals of different sexes find each other, save a flock, inform relatives about the presence of food, protect the territory, nest and offspring from enemies, and is a maturation stimulator during mating games, i.e. serves as an important means of communication. It is assumed that in deep-sea fish dispersed in the dark at the depths of the ocean, it is hearing, in combination with the organs of the lateral line and the sense of smell, that provides communication, especially since the sound conductivity, which is higher in water than in air, increases at depth. Hearing is especially important for nocturnal fish and inhabitants of muddy waters.

The reaction of different fish to extraneous sounds is different: with noise, some go to the side, others - silver carp, salmon, mullet - jump out of the water. This is used in the organization of fishing (fishing for mullet with matting, a bell that scares it away from the gate of a purse seine, etc.). During the spawning period of carp in fish farms, passage near spawning ponds is prohibited, and in the old days, during the spawning of bream, bell ringing was prohibited.

In nature, there are many classes of different animals. One of them is fish. Many people do not even suspect that these representatives of the animal world have a brain. Read about its structure and features in the article.

History reference

For a long time, almost 70 million years ago, the oceans were inhabited by invertebrates. But fish, the first to acquire a brain, exterminated a significant number of them. Since then, they have dominated the water space. The modern fish brain is very complex. Indeed, it is difficult to follow some kind of behavior without a program. The brain decides this problem using different options. Fish preferred imprinting, when the brain is ready for the behavior that it sets at a certain point in its development.

For example, salmon have an interesting feature: they swim to spawn in the river in which they themselves were born. At the same time, they overcome huge distances, and they have no map. This is possible thanks to this variant of behavior, when certain parts of the brain are like a camera with a timer. The principle of operation of the device is as follows: there comes a moment when the diaphragm works. The images in front of the camera remain on the film. So it is with fish. They are guided in their behavior by images. Imprinting determines the individuality of fish. If provide same conditions, their different breeds will behave differently. Mammals have a mechanism this method behavior, that is, imprinting, but the scope of its important forms has narrowed. In humans, for example, sexual skills have been preserved.

Parts of the brain in fish

This organ in this class is small. Yes, in a shark, for example, its volume is equal to thousandths of a percent of the total body weight, in sturgeon and bony fish - hundredths, in small fish it is about one percent. The brain of fish has a feature: the larger the individuals, the smaller it is.

The family of stickleback fish that live in Lake Mivan, Iceland, has a brain, the size of which depends on the sex of the individuals: the female is smaller, the male is larger.

The fish brain has five sections. These include:

• forebrain consisting of two hemispheres. Each of them is in charge of the sense of smell and schooling behavior of fish.
• midbrain, from which the nerves that respond to stimuli depart, due to which the eyes move. This is the eye of the fish. They regulate the balance of the body and muscle tone.
• Cerebellum- the body responsible for the movement.
• Medulla is the most important department. Performs many functions and is responsible for different reflexes.

The parts of the fish brain do not develop in the same way. This is influenced by the lifestyle of aquatic inhabitants and the state of the environment. So, for example, pelagic species, having excellent skills of movement in water, have a well-developed cerebellum, as well as vision. The structure of the fish brain is such that representatives of this class with a developed sense of smell are distinguished by an increased size of the forebrain, predators with good eyesight, - medium, sedentary representatives of the class - oblong.

Intermediate brain

He owes his education to which are also called the thalamus. Their location is central part brain. The thalamus has many formations in the form of nuclei, which transmit the received information to the brain of the fish. There are various sensations associated with smell, sight, and hearing.

The main one is the integration and regulation of the body's sensitivity. It is also involved in the reaction by which fish are able to move around. If the thalamus is damaged, the level of sensitivity decreases, coordination is disturbed, and vision and hearing also decrease.

Brain anterior

It includes a mantle, as well as striatal bodies. The mantle is sometimes called a cloak. The location is the top and sides of the brain. The cloak looks like thin epithelial plates. are located below it. The forebrain of fish is designed to perform such functions as:

• Olfactory. If this organ is removed from fish, they lose the conditioned reflexes developed to stimuli. Physical activity decreases, attraction to the opposite sex disappears.
• Protective and defensive. It manifests itself in the fact that representatives of the Pisces class maintain a flock of life, take care of their offspring.

brain average

It has two departments. One of them is the visual roof, which is called the tectum. It is located horizontally. It looks like swollen visual lobes arranged in pairs. In fish with a high organization, they are better developed than in cave and deep-sea representatives with poor eyesight. Another department is located vertically, it is called the tegmentum. It contains the highest visual center. What are the functions of the midbrain?

• If you remove the visual roof from one eye, the other goes blind. Fish lose their sight complete removal roof, in which the visual grasping reflex is located. Its essence lies in the fact that the head, body, eyes of the fish move in the direction of food objects, which are imprinted on the retina.
• The midbrain of the fish fixes the color. When the upper roof is removed, the body of the fish brightens, and if the eyes are removed, it darkens.
• It has connections with the forebrain and cerebellum. Coordinates the work of a number of systems: somatosensory, visual and olfactory.
• The composition of the middle part of the body includes centers that regulate movement and maintain muscle tone.
• The fish brain makes reflex activity diverse. First of all, this affects the reflexes associated with visual and auditory stimuli.

brain oblongata

He takes part in the formation of the organ trunk. The medulla oblongata of fish is arranged in such a way that substances, gray and white, are distributed without a clear boundary.

Performs the following functions:

• reflex. The centers of all reflexes are located in the brain, the activity of which ensures the regulation of breathing, the work of the heart and blood vessels, digestion, and the movement of the fins. Thanks to this function, the activity of the organs of taste is carried out.
• Conductor. It lies in the fact that the spinal cord and other parts of the brain conduct nerve impulses. The medulla oblongata is the site of the ascending tracts from the dorsal to the cephalic, which lead to the descending tracts that connect them.

Cerebellum

This is an education that unpaired structure, located in the back part partially covers the medulla oblongata. It consists of the middle part (body) and two ears (lateral sections).

Performs a number of functions:

• Coordinates movements and maintains normal muscle tone. If the cerebellum is removed, these functions are impaired, the fish begin to swim in circles.
• Provides the implementation of motor activity. When the body of the cerebellum of the fish is removed, it begins to swing in different directions. If you also remove the damper, the movements are completely disturbed.
• The cerebellum regulates metabolism. This body affects other parts of the brain through the nucleoli located in the spinal cord and medulla oblongata.

Spinal cord

Its location is the nerve arcs (more precisely, their channels) of the fish spine, which consists of segments. The spinal cord in fish is a continuation of the medulla oblongata. From him to the right and left side nerves branch out between pairs of vertebrae. Through them, irritating signals enter the spinal cord. They innervate the surface of the body, the muscles of the trunk and internal organs. What is the brain of a fish? Head and dorsal. The gray matter of the latter is inside it, the white is outside.

The brain of bony fish consists of five sections typical of most vertebrates.

Rhomboid brain(rhombencephalon) includes the medulla oblongata and cerebellum.

medulla oblongata the anterior section goes under the cerebellum, and behind without visible borders passes into the spinal cord. To view the anterior medulla oblongata, it is necessary to turn the body of the cerebellum forward (in some fish, the cerebellum is small and the anterior medulla oblongata is clearly visible). The roof in this part of the brain is represented by the choroid plexus. Underneath is a large rhomboid fossa (fossa rhomboidea), expanded at the anterior end and passing behind into a narrow medial gap, it is a cavity fourth cerebral ventricle (ventriculus quartus). The medulla oblongata serves as the origin of most of the brain nerves, as well as a pathway that connects the various centers of the anterior sections of the brain with the spinal cord. However, the layer of white matter covering the medulla oblongata is rather thin in fish, since the body and tail are largely autonomous - they carry out most of the movements reflexively, without correlating with the brain. In the bottom of the medulla oblongata in fish and tailed amphibians lies a pair of giant mauthner cells, associated with acoustic-lateral centers. Their thick axons extend along the entire spinal cord. Locomotion in fish is carried out mainly due to the rhythmic bending of the body, which, apparently, is controlled mainly by local spinal reflexes. However, the overall control of these movements is carried out by Mauthner cells. In the floor of the medulla oblongata lies respiratory center.

Viewing the brain from below, one can distinguish the places where some nerves originate. Three round roots extend from the lateral side of the anterior part of the medulla oblongata. The first, lying most cranial, belongs to V and VII nerves, middle root - only VII nerve, and finally, the third root, lying caudally, is VIII nerve. Behind them, also from the lateral surface of the medulla oblongata, the IX and X pairs depart together in several roots. The rest of the nerves are thin and are usually cut off during preparation.

Cerebellum quite well developed, round or elongated, it lies above the anterior part of the medulla oblongata directly behind the visual lobes. With its posterior edge, it covers the medulla oblongata. The raised part is the body of the cerebellum (corpus cerebelli). The cerebellum is the center of fine regulation of all motor innervations associated with swimming and grasping food.

midbrain(mesencephalon) - the part of the brain stem that is permeated by the cerebral aqueduct. It consists of large, longitudinally elongated visual lobes (they are visible from above).

Visual lobes, or visual roof (lobis opticus s. Tectum opticus) - paired formations separated from each other by a deep longitudinal furrow. The visual lobes are the primary visual centers that perceive excitation. They terminate the fibers of the optic nerve. In fish, this part of the brain is of paramount importance, it is the center that has the main influence on the activity of the body. The gray matter covering the visual lobes has a complex layered structure, reminiscent of the structure of the cerebellar cortex or hemispheres.

From the ventral surface of the visual lobes depart thick optic nerves, crossing under the surface of the diencephalon.

If you open the visual lobes of the midbrain, you can see that in their cavity a fold is separated from the cerebellum, which is called cerebellar valve (valvule cerebellis). On the sides of it in the bottom of the cavity of the midbrain, two bean-shaped elevations are distinguished, called semilunar bodies (tori semicircularis) and being additional centers of the statoacoustic organ.

forebrain(prosencephalon) less developed than the middle one, it consists of the terminal and diencephalon.

Parts intermediate brain (diencephalon) lie around a vertical slot third cerebral ventricle (ventriculus tertius). Lateral walls of the ventricle visual tubercles or thalamus ( thalamus) in fish and amphibians are of secondary importance (as coordinating sensory and motor centers). The roof of the third cerebral ventricle - the epithalamus or epithalamus - does not contain neurons. It consists of the anterior vascular plexus (the vascular tegmentum of the third ventricle) and the superior brain gland - epiphysis. The bottom of the third cerebral ventricle - the hypothalamus or hypothalamus in fish forms paired swellings - lower lobes (lobus inferior). In front of them lies the lower brain gland - the pituitary gland. In many fish, this gland fits snugly into a special recess in the bottom of the skull and usually breaks off during preparation; then clearly visible funnel (infundibulum). Ahead, on the border between the bottom of the final and intermediate departments brain is located optic chiasm (chiasma nervorum opticorum).

telencephalon (telencephalon) in bony fish, compared with other parts of the brain, it is very small. Most fish (except lungfish and crossopterygians) are distinguished by an everted (inverted) structure of the hemispheres telencephalon. They seem to be "turned out" ventro-laterally. The roof of the forebrain does not contain nerve cells, it consists of a thin epithelial membrane (pallium), which during preparation is usually removed along with the meninges. In this case, the bottom of the first ventricle is visible on the preparation, divided by a deep longitudinal groove into two striped bodies. Striped bodies (corpora striatum1) consist of two sections, which can be seen when considering the brain from the side. In fact, these massive structures contain striatal and crustal material of a rather complex structure.

Olfactory bulbs (bulbus olfactorius) adjacent to the anterior margin of the telencephalon. From them go forward olfactory nerves. In some fish (for example, cod), the olfactory bulbs are carried far forward, in which case they are connected to the brain olfactory tracts.

Representatives of this class have variations in the structure of the brain, but, nevertheless, common characteristic features can be distinguished for them. Their brain has a relatively primitive structure and is generally small in size.

The forebrain, or terminal, in most fish consists of one hemisphere (some sharks that lead a benthic lifestyle have two) and one ventricle. The roof does not contain nerve elements and is formed by the epithelium and only in shark nerve cells rise from the base of the brain to the sides and partly to the roof. The bottom of the brain is represented by two clusters of neurons - these are striatal bodies (corpora striata).

Anterior to the brain are two olfactory lobes (bulbs) connected by olfactory nerves to the olfactory organ located in the nostrils.

In lower vertebrates, the forebrain is a part of the nervous system that serves only the olfactory analyzer. It is the highest olfactory center.

The diencephalon consists of the epithalamus, thalamus, and hypothalamus, which are common to all vertebrates, although their degree varies. The thalamus plays a special role in the evolution of the diencephalon, in which the ventral and dorsal parts are distinguished. Later, in vertebrates, in the course of evolution, the size of the ventral part of the thalamus decreases, while the dorsal part increases. The lower vertebrates are characterized by the predominance of the ventral thalamus. Here are the nuclei that act as an integrator between the midbrain and olfactory system the forebrain, in addition, in lower vertebrates, the thalamus is one of the main motor centers.

Below the ventral thalamus is the hypothalamus. From below, it forms a hollow stalk - a funnel, which passes into the neurohypophysis, connected to the adenohypophysis. The hypothalamus plays a major role in hormonal regulation organism.

The epithalamus is located in the dorsal part of the diencephalon. It does not contain neurons and is associated with the pineal gland. The epithalamus, together with the pineal gland, constitutes a system of neurohormonal regulation of the daily and seasonal activity of animals.

Rice. 6. The brain of a perch (view from the dorsal side).

1 - nasal capsule.
2 - olfactory nerves.
3 - olfactory lobes.
4 - forebrain.
5 - midbrain.
6 - cerebellum.
7 - medulla oblongata.
8 - spinal cord.
9 - diamond-shaped fossa.

The midbrain of fish is relatively large. It distinguishes the dorsal part - the roof (tekum), which looks like a colliculus, and the ventral part, which is called the tegment and is a continuation of the motor centers of the brain stem.

The midbrain developed as a primary visual and seismosensory center. It contains visual and auditory centers. In addition, it is the highest integrative and coordinating center of the brain, approaching in its value to the large hemispheres of the forebrain of higher vertebrates. This type of brain, where the midbrain is the highest integrative center, is called ichthyopsid.

The cerebellum is formed from the posterior cerebral bladder and is laid in the form of a fold. Its size and shape vary considerably. In most fish, it consists of the middle part - the body of the cerebellum and of the lateral ears - the auricles. For bony fish characteristically anterior growth - flap. The latter in some species takes on such a large size that it can hide part of the forebrain. In sharks and bony fish, the cerebellum has a folded surface, due to which its area can reach a considerable size.

Through ascending and descending nerve fibers, the cerebellum is connected to the middle, medulla oblongata and spinal cord. Its main function is the regulation of coordination of movements, and therefore, in fish with high motor activity, it is large and can be up to 15% of the total mass of the brain.

The medulla oblongata is a continuation of the spinal cord and generally repeats its structure. The border between the medulla oblongata and the spinal cord is considered to be the place where the central canal of the spinal cord in cross section takes the form of a circle. In this case, the cavity of the central canal expands, forming the ventricle. The side walls of the latter grow strongly to the sides, and the roof is formed by an epithelial plate, in which the choroid plexus is located with numerous folds facing the cavity of the ventricle. In the side walls are nerve fibers, providing innervation of the visceral apparatus, organs of the lateral line and hearing. In the dorsal parts of the side walls there are nuclei of gray matter, in which the switch occurs nerve impulses, coming along the ascending pathways from the spinal cord to the cerebellum, midbrain and to the neurons of the striatal bodies of the forebrain. In addition, there is also a switch of nerve impulses to descending pathways that connect the brain with the motor neurons of the spinal cord.

The reflex activity of the medulla oblongata is very diverse. It contains: the respiratory center, the center for the regulation of cardiovascular activity, through the nuclei of the vagus nerve, the regulation of the digestive organs and other organs is carried out.

From the brain stem (medium, medulla oblongata and pons) in fish, 10 pairs of cranial nerves depart.

The brain of fish is very small, making up thousandths of % of body weight in sharks, hundredths of % in teleosts and sturgeons. In small fish, the mass of the brain reaches about 1%.

The brain of fish consists of 5 sections: anterior, intermediate, middle, cerebellum and medulla oblongata. The development of individual parts of the brain depends on the way of life of fish and their ecology. So, in good swimmers (mainly pelagic fish), the cerebellum and visual lobes are well developed. In fish with a well-developed sense of smell, the forebrain is enlarged. In fish with good developed vision(predators) - midbrain. Sedentary fish have a well-developed medulla oblongata.

The medulla oblongata is a continuation of the spinal cord. Together with the midbrain and diencephalon, it forms the brainstem. In the medulla oblongata, compared with the spinal cord, there is no clear distribution of gray and white matter. The medulla oblongata performs the following functions: conduction and reflex.

The conduction function is to conduct nerve impulses between the spinal cord and other parts of the brain. Pass through the medulla oblongata ascending paths from the spinal cord to the brain and descending pathways connecting the brain with the spinal cord.

Reflex function of the medulla oblongata. In the medulla oblongata there are centers of both relatively simple and complex reflexes. Due to the activity of the medulla oblongata, the following reflex reactions are carried out:

1) regulation of breathing;

2) regulation of cardiac activity and blood vessels;

3) regulation of digestion;

4) regulation of the work of taste organs;

5) regulation of the work of chromatophores;

6) regulation of the work of electrical organs;

7) regulation of the centers of movement of the fins;

8) regulation of the spinal cord.

The medulla oblongata contains the nuclei of six pairs of cranial nerves (V-X).

V pair - the trigeminal nerve is divided into 3 branches: the ophthalmic nerve innervates the anterior part of the head, the maxillary nerve innervates the skin of the anterior part of the head and palate, and the mandibular nerve innervates the mucous membrane of the oral cavity and mandibular muscles.

VI pair - the opening nerve innervates the muscles of the eyes.

VII pair - the facial nerve is divided into 2 lines: the first innervates the lateral line of the head, the second - the mucous membrane of the palate, the hyoid region, the taste buds of the oral cavity and the muscles of the gill cover.

VIII pair - auditory or sensory nerve - innervates the inner ear and labyrinth.

IX pair - glossopharyngeal nerve - innervates the mucous membrane of the palate and the muscles of the first branchial arch.

X pair - the vagus nerve is divided into two branching branches: the lateral nerve innervates the organs of the lateral line in the trunk, the nerve of the operculum innervates the gill apparatus and other internal organs.

The midbrain of fish is represented by two sections: the visual roof (tectum) - located horizontally and the tegmentum - located vertically.

The tectum or visual roof of the midbrain is swollen in the form of paired visual lobes, which are well developed in fish with a high degree of development of the organs of vision and poorly developed in blind deep-sea and cave fish. On the inside The tectum has a longitudinal torus. It is associated with vision. In the tegmentum of the midbrain, the highest visual center of fish is located. The fibers of the second pair of optic nerves terminate in the tectum.

The midbrain performs the following functions:

1) The function of the visual analyzer, as evidenced by the following experiments. After removal of the textum on one side of the eye of the fish, lying with opposite side goes blind. When the entire tectum is removed, complete blindness occurs. The tectum also houses the center of the visual grasping reflex, which consists in the fact that the movements of the eyes, head, and torso are directed in such a way as to maximize the fixation of the food object in the region of greatest visual acuity, i.e. in the center of the retina. In the tectum there are centers of the III and IV pairs of nerves that innervate the muscles of the eyes, as well as muscles that change the width of the pupil, i.e. performing accommodation, allowing you to clearly see objects at different distances due to the movement of the lens.

2) Participates in the regulation of fish coloration. So, after the removal of the tectum, the body of the fish brightens, while when the eyes are removed, the opposite phenomenon is observed - darkening of the body.

3) In addition, the tectum is closely connected with the cerebellum, hypothalamus, and through them with the forebrain. Therefore, the tectum coordinates the functions of the somatosensory (balance, posture), olfactory, and visual systems.

4) The tectum is connected with the VIII pair of nerves, which perform acoustic and receptor functions, and with the V pair of nerves, i.e. trigeminal nerves.

5) Afferent fibers from the lateral line organs, from the auditory and trigeminal nerves approach the midbrain.

6) In the tectum there are afferent fibers from the olfactory and taste receptors.

7) In the midbrain of fish, there are centers for regulating movement and muscle tone.

8) The midbrain has an inhibitory effect on the centers of the medulla oblongata and spinal cord.

Thus, the midbrain regulates a number autonomic functions organism. Due to the midbrain, the reflex activity of the organism becomes diverse (orienting reflexes to sound and visual stimuli appear).

Intermediate brain. The main formation of the diencephalon is the visual tubercles - the thalamus. Under the visual tubercles is the hypothalamic region - the epithalamus, and under the thalamus is the hypothalamic region - the hypothalamus. The diencephalon in fish is partially covered by the roof of the midbrain.

The epithalamus consists of the pineal gland, a rudiment of the parietal eye that functions as endocrine gland. The second element of the epithalamus is the frenulum (gabenula), which is located between the forebrain and the roof of the midbrain. The frenulum is a link between the epiphysis and the olfactory fibers of the forebrain, i.e. participates in the performance of the function of light perception and smell. The epithalamus is connected to the midbrain through efferent nerves.

The thalamus (visual tubercles) in fish is located in the central part of the diencephalon. In the visual tubercles, especially in the dorsal part, many nuclear formations were found. The nuclei receive information from receptors, process it and transmit it to certain areas of the brain, where the corresponding sensations arise (visual, auditory, olfactory, etc.). Thus, the thalamus is an organ of integration and regulation of the body's sensitivity, and also takes part in the implementation of the body's motor reactions.

If the visual tubercles are damaged, there is a decrease in sensitivity, hearing, vision, which causes impaired coordination.

The hypothalamus consists of an unpaired hollow protrusion - a funnel that forms a vascular sac. The vascular sac responds to pressure changes and is well developed in deep sea pelagic fish. The vascular sac is involved in the regulation of buoyancy, and through its connection with the cerebellum, it is involved in the regulation of balance and muscle tone.

The hypothalamus is the main center for receiving information from the forebrain. The hypothalamus receives afferent fibers from taste endings and from the acoustic system. Efferent nerves from the hypothalamus go to the forebrain, to the dorsal thalamus, tectum, cerebellum and neurohypophysis, i.e. regulates their activities and influences their work.

The cerebellum is an unpaired formation, it is located in the back of the brain and partially covers the medulla oblongata. Distinguish between the body of the cerebellum (middle part) and the ears of the cerebellum (i.e., two lateral sections). The anterior end of the cerebellum forms a flap.

Leading fish sedentary image life (for example, in benthic, such as scorpions, gobies, anglerfish), the cerebellum is underdeveloped in comparison with fish that lead an active lifestyle (pelagic, such as mackerel, herring or predators - pike perch, tuna, pike).

Functions of the cerebellum. With the complete removal of the cerebellum in moving fish, a drop in muscle tone (atony) and impaired coordination of movements are observed. This was expressed in the circular swimming of fish. In addition, the reaction to pain stimuli weakens in fish, sensory disturbances occur, and tactile sensitivity disappears. Approximately, after three to four weeks, the lost functions are restored due to the regulatory processes of other parts of the brain.

After removal of the body of the cerebellum, bony fish show motor disturbances in the form of body swaying from side to side. After removal of the body and the valve of the cerebellum, motor activity is completely disrupted, and trophic disorders develop. This indicates that the cerebellum also regulates metabolism in the brain.

It should be noted that the auricles of the cerebellum reach large sizes in fish with a well-developed lateral line. Thus, the cerebellum is the site of closure of conditioned reflexes coming from the lateral line organs.

Thus, the main functions of the cerebellum are the coordination of movement, the normal distribution of muscle tone and the regulation of autonomic functions. The cerebellum realizes its influence through the nuclear formations of the middle and medulla oblongata, as well as the motor neurons of the spinal cord.

The forebrain of fish consists of two parts: the mantle or cloak and the striatum. The mantle, or the so-called cloak, lies dorsally, i.e. from above and from the sides in the form of a thin epithelial plate above the striatum. In the anterior wall of the forebrain are the olfactory lobes, which are often differentiated into the main part, stalk and olfactory bulb. Secondary olfactory fibers from the olfactory bulb enter the mantle.

Functions of the forebrain. The forebrain of fish performs an olfactory function. This, in particular, is evidenced by the following experiments. When the forebrain is removed, fish lose the developed conditioned reflexes to olfactory stimuli. In addition, the removal of the forebrain of fish leads to a decrease in their motor activity and to a decrease in schooling conditioned reflexes. The forebrain plays important role and in the sexual behavior of fish (when it is removed, sexual desire disappears).

Thus, the forebrain is involved in the protective-defensive reaction, the ability to swim in schools, the ability to take care of offspring, etc. It has a general stimulating effect on other parts of the brain.

7. Principles of the reflex theory I.P. Pavlova

Pavlov's theory is based on the basic principles of the conditioned reflex activity of the brain of animals, including fish:

1. The principle of structure.

2. The principle of determinism.

3. The principle of analysis and synthesis.

The principle of structurality is as follows: each morphological structure corresponds to a certain function. The principle of determinism is that reflex reactions have a strict causality, i.e. they are determined. For the manifestation of any reflex, a reason, a push, an impact from the outside world or internal environment organism. The analytical and synthetic activity of the central nervous system is carried out due to the complex relationship between the processes of excitation and inhibition.

According to Pavlov's theory, the activity of the central nervous system is based on a reflex. A reflex is a causally determined (deterministic) reaction of the body to changes in the external or internal environment, carried out with the obligatory participation of the central nervous system in response to irritation of the receptors. This is how the emergence, change or cessation of any activity of the body occurs.

Pavlov divided all the reflex reactions of the body into two main groups: unconditioned reflexes and conditioned reflexes. Unconditioned reflexes are congenital, inherited reflex reactions. Unconditioned reflexes appear in the presence of a stimulus without special, special conditions (swallowing, breathing, salivation). Unconditioned reflexes have ready-made reflex arcs. Unconditioned reflexes are divided into various groups according to a number of characteristics. By biological feature they distinguish food (search, intake and processing of food), defensive (defensive reaction), sexual (animal behavior), indicative (orientation in space), positional (taking a characteristic posture), locomotor (motor reactions).

Depending on the location of the irritated receptor, exteroceptive reflexes are isolated, i.e. reflexes that occur when stimulated outer surface body (skin, mucous membranes), interoreceptive reflexes, i.e. reflexes that occur when irritated by internal organs, proprioceptive reflexes that occur when receptors of skeletal muscles, joints, and ligaments are irritated.

Depending on the part of the brain that is involved in the reflex reaction, the following reflexes are distinguished: spinal (spinal) - centers of the spinal cord participate, bulbar - centers of the medulla oblongata, mesencephalic - centers of the midbrain, diencephalic - centers of the diencephalon.

In addition, reactions are divided according to the organ that is involved in the response: motor or motor (muscle participates), secretory (endocrine or external secretion gland participates), vasomotor (vessel participates), etc.

Unconditioned reflexes - specific reactions. They are common to all representatives of this species. Unconditioned reflexes are relatively constant reflex reactions, stereotyped, little changeable, inert. As a result of this, it is impossible to adapt to the changing conditions of existence only due to unconditioned reflexes.

Conditioned reflexes - a temporary nervous connection of the body with some stimulus of the external or internal environment of the body. Conditioned reflexes are acquired during the individual life of the organism. They are not the same in different representatives of this species. Conditioned reflexes do not have ready-made reflex arcs, they are formed when certain conditions. Conditioned reflexes are changeable, easily arise and also easily disappear, depending on the conditions in which the given organism is located. Conditioned reflexes are formed on the basis of unconditioned reflexes under certain conditions.

For the formation of a conditioned reflex, it is necessary to combine two stimuli in time: an indifferent (indifferent) for a given type of activity, which will later become a conditioned signal (knocking on glass) and an unconditioned stimulus that causes a certain unconditioned reflex(feed). The conditioned signal always precedes the action of the unconditioned stimulus. Reinforcement of the conditioned signal with an unconditioned stimulus must be repeated. It is necessary that the conditioned and unconditioned stimuli meet the following requirements: the unconditioned stimulus must be biologically strong (food), the conditioned stimulus must have a moderate optimal strength (knock).

8. Behavior of fish

The behavior of fish becomes more complicated in the course of their development, i.e. ontogeny. The simplest reaction of the body of a fish in response to an irritant is kinesis. Kinesis is an increase in motor activity in response to adverse effects. Kinesis has already been observed on final stages embryonic development of fish when there is a decrease in the oxygen content in the environment. An increase in the movement of larvae in eggs or in water in this case improves gas exchange. Kinesis promotes the movement of larvae from poor living conditions to better ones. Another example of kinesis is the erratic movement of schooling fish (verkhovka, uklya, etc.) when a predator appears. This confuses him and prevents him from focusing on one fish. This can be considered a defensive reaction of schooling fish.

A more complex form of fish behavior is taxis - this is a directed movement of fish in response to a stimulus. A distinction is made between positive taxis (attraction) and negative taxis (avoidance). An example is phototaxis, i.e. reaction of fish to the light factor. Thus, anchovy and big-eyed kilka have positive phototaxis, i.e. are well attracted to the light, forming clusters, which makes it possible to use this property in the fishery of these fish. In contrast to the Caspian sprat, the mullet exhibits negative phototaxis. Representatives of this species of fish tend to get out of the illuminated background. This property is also used by humans when fishing for this fish.

An example of negative phototaxis is the behavior of salmon larvae. During the day, they hide among stones, in gravel, which allows them to avoid meeting with predators. And in the larvae of cyprinids, positive phototaxis is observed, which allows them to avoid deadly deep-sea areas and find more food.

Taxis directions may undergo age-related changes. Thus, fry of salmon at the stage of the pestryanka are typical benthic sedentary fish that protect their territory from their own kind. They avoid light, live among stones, easily change color to the color of the environment, and when frightened, they are able to hide. As they grow in front of a slope in the sea, they change color to non-silver, gather in flocks, lose their aggressiveness. When frightened, they quickly swim away, are not afraid of light, and vice versa, stay near the surface of the water. As you can see, the behavior of juveniles of this species changes to the opposite with age.

In fish, unlike higher vertebrates, there is no cerebral cortex, which plays a leading role in the development of conditioned reflexes. However, fish are able to produce them without it, for example, a conditioned reflex to sound (Frolov's experiment). After the action of a sound stimulus, a current was switched on in a few seconds, to which the fish reacted by moving its body. After a certain number of repetitions, the fish, without waiting for the action electric current, reacted to the sound, i.e. reacted with body movements. In this case, the conditioned stimulus is the sound, and the unconditioned stimulus is the induction current.

In contrast to higher animals, fish develop reflexes worse, they are unstable and difficult to develop. Fish are less able than higher animals to differentiate, i.e. distinguish between conditioned stimuli or changes in the external environment. It should be noted that in bony fish conditioned reflexes are developed faster and they are more persistent than in others.

There are works in the literature that show rather persistent conditioned reflexes, where the unconditioned stimuli are a triangle, a circle, a square, various letters, etc. If a feeder is placed in a pond that gives a portion of food in response to pressing a lever, pulling a bead or other devices, then the fish master this device quickly enough and receive food.

Those who are engaged in aquarium fish farming, they have observed that when approaching the aquarium, the fish gather at the feeding place in anticipation of food. This is also a conditioned reflex, and in this case, you are the conditioned stimulus, and knocking on the glass of the aquarium can also serve as a conditioned stimulus.

In fish farms, fish are usually fed in certain time days, so they often gather in certain places at the time for feeding. The fish also quickly get used to the type of food, the way food is distributed, etc.

Of great practical importance may be the development of conditioned reflexes to a predator in the conditions of fish hatcheries and NVH in juveniles of commercial fish, which are then released into natural reservoirs. This is due to the fact that in the conditions of fish hatcheries and NVH, juveniles do not have the experience of communicating with enemies and at the first stages become the prey of predators until they get an individual and spectacular experience.

Using conditioned reflexes explore various parties biology of various fish, such as the spectral sensitivity of the eye, the ability to distinguish silhouettes, the effect of various toxicants, the hearing of fish by the strength and frequency of sound, taste sensitivity thresholds, the role various departments nervous system.

In the natural environment, the behavior of fish depends on the lifestyle. Schooling fish have the ability to coordinate maneuvers when feeding, at the sight of a predator, etc. Thus, the appearance of a predator or food organisms at one edge of the flock causes the entire flock to react accordingly, including individuals that did not see the stimulus. The reaction can be very diverse. So at the sight of a predator, the flock instantly scatters. You can see this in spring period time in the coastal zone of our reservoirs, fry of many fish are concentrated in flocks. This is one kind of imitation. Another example of imitation is following the leader, i.e. for an individual in whose behavior there are no elements of oscillation. The leader is most often individuals who have great individual experience. Sometimes even a fish of a different species can serve as such a leader. So, carps learn to take food on the fly faster if they are planted with trout or carp individuals that can do this.

When fish live in groups, a “social” organization can arise with dominant and subordinate fish. So, in a flock of Mozambian tilapia, the most intensely colored male is the main one, the next in the hierarchy are lighter. Males that do not differ in color from females are subordinate and do not participate in spawning at all.

The sexual behavior of fish is very diverse, this includes elements of courtship and rivalry, building nests, etc. Complex spawning and parental behavior is typical for fish with low individual fecundity. Some fish take care of eggs, larvae and even fry (protect the nest, aerate the water (zander, smelt, catfish)). Juveniles of some fish species feed near their parents (for example, discus even feed their juveniles with their mucus). Juveniles of some fish species hide with their parents in the oral and gill cavities (tilapia). Thus, the plasticity of fish behavior is very diverse, as can be seen from the above materials.

Questions for self-control:

1. Features of the structure and function of nerves and synapses.

2. Parabiosis as a special kind of localized excitation.

3. Scheme of the structure of the nervous system of fish.

4. Structure and functions of the peripheral nervous system.

5. Features of the structure and function of the brain.

6. Principles and essence of the reflex theory.

7. Features of the behavior of fish.