The brain of fish is very small, and the larger the fish, the smaller the relative mass of the brain. In large sharks, the brain mass is only a few thousandths of a percent of body mass. In sturgeon and bony fish weighing several kilograms, its mass reaches hundredths of a percent of body weight. With a fish weighing several tens of grams, the brain is a fraction of a percent, and in fish weighing less than 1 g, the brain exceeds 1% of body weight. This shows that the growth of the brain lags behind the growth of the entire body. Obviously, the main development of the brain occurs during embryonic-larval development. Of course, interspecies differences in the relative mass of the brain are also observed.

The brain consists of five main regions: anterior, intermediate, middle, cerebellum and medulla oblongata ( SLIDE 6).

The structure of the brain various kinds of fish varies and to a greater extent depends not on the systematic position of the fish, but on their ecology. Depending on which receptor apparatus predominates in a given fish, brain regions develop accordingly. With a well-developed sense of smell, the forebrain increases, with well-developed vision - the midbrain, in good swimmers - the cerebellum. In pelagic fish, the visual lobes are well developed, the striatum is relatively poorly developed, and the cerebellum is well developed. In fish leading sedentary image life, the brain is characterized by a weak development of the striatum, a small cone-shaped cerebellum, sometimes a well-developed medulla oblongata.

Rice. 14. The structure of the brain of bony fish:

a - schematic representation of a longitudinal section of the brain; b - crucian brain, cut back view; c - yellowtail brain, side view; d - yellowtail brain, view from the back; forebrain; 2- the first cerebral ventricle; 3 - epiphysis; 4 - midbrain; 5- valve of the cerebellum; 6 - cerebellum; 7 - cerebral canal; 8 - fourth cerebral ventricle; 9 - medulla oblongata; 10 - vascular sac; 11 - pituitary gland; 12 - third cerebral ventricle; 13 - the nucleus of the optic nerve; 14 - diencephalon; 15 - olfactory tract; 16 - visual lobes; 11 - almond-shaped tubercles; 18 - vagal dilia 1U - spinal cord; 20 - roof of the cerebellum; 21 - olfactory lobes; 22 - olfactory bulb; 23 - olfactory tract; 24 - hypothalamus; 25 - projections of the cerebellum

Medulla. The medulla oblongata is a continuation of the spinal cord. In its anterior part, it passes into the posterior part of the midbrain. Its upper part - the rhomboid fossa - is covered by the ependyma, on which the posterior choroid plexus is located. The medulla oblongata performs a series important functions. Being a continuation of the spinal cord, it plays the role of a conductor of nerve impulses between the spinal cord and various parts of the brain. Nerve impulses are conducted as in descending, i.e. to the spinal cord, and in ascending directions - to the middle, intermediate and forebrain, as well as to the cerebellum.

The medulla oblongata contains the nuclei of six pairs of cranial nerves (V-X). From these nuclei, which are an accumulation of nerve cells, the corresponding cranial nerves originate, emerging in pairs from both sides of the brain. The cranial nerves innervate various muscles and receptor organs of the head. The fibers of the vagus nerve innervate various organs and the lateral line. The cranial nerves can be of three types: sensitive, if they contain branches that conduct afferent impulses from the sense organs: motor, not having only efferent impulses to organs and muscles; mixed containing sensory and motor fibers.

V pair - trigeminal nerve. It starts on the lateral surface of the medulla oblongata, is divided into three branches: the ophthalmic nerve, which innervates the anterior part of the head; maxillary nerve, passing under the eye along the upper jaw and innervating the skin of the anterior part of the head and palate; mandibular nerve that runs along the lower jaw, innervating the skin, mucous membrane oral cavity and mandibular muscles. This nerve contains motor and sensory fibers.

VI pair of abducens nerve. It originates from the bottom of the medulla oblongata, its middle line, and innervates the muscles of the eye,

VII - facial nerve. It is a mixed nerve, departs from the side wall of the medulla oblongata, directly behind the trigeminal nerve and is often associated with it, forms a complex ganglion, from which two branches depart: the nerve of the organs of the lateral line of the head and the branch that innervates the mucous membrane of the palate, the hyoid region, the taste buds of the cavity mouth and muscles of the operculum.

VIII - auditory, or sensitive, nerve. Innervates the inner ear

and labyrinth apparatus. Its nuclei are located between the nuclei of the vagus nerve and the base of the cerebellum.

IX - glossopharyngeal nerve. Departs from the lateral wall of the oblong

brain and innervates the mucous membrane of the palate and the muscles of the first branchial arch.

X - vagus nerve. Departs from the lateral wall of the medulla oblongata with numerous branches that form two branches: the lateral nerve, which innervates the organs of the lateral line in the trunk; nerve of the gill cover, which innervates the gill apparatus and some internal organs. On the sides of the rhomboid fossa are thickenings - vagal lobes, where the nuclei of the vagus nerve are located.

Sharks have an XI nerve - the final one. Its nuclei are located on the anterior or underside of the olfactory lobes, the nerves pass along the dorso-lateral surface of the olfactory tracts to the olfactory sacs.

Vital centers are located in the medulla oblongata. This part of the brain regulates respiration, cardiac activity, the digestive apparatus, etc.

The respiratory center is represented by a group of neurons that regulate respiratory movements. The inspiratory and expiratory centers can be distinguished. If half of the medulla oblongata is destroyed, then the respiratory movements stop only on the corresponding side. In the region of the medulla oblongata there is also a center that regulates the work of the heart and blood vessels. The next important center of the medulla oblongata is the center that regulates the work of chromatophores. When this center is stimulated electric shock there is a lightening of the whole body of the fish. Here are the centers that regulate the work of the gastrointestinal tract.

In fish with electrical organs, the motor areas of the medulla oblongata grow, which leads to the formation of large electrical lobes, which are a kind of synchronization center for the discharges of individual electrical plates innervated by various motor neurons of the spinal cord.

In fish leading a sedentary lifestyle, the taste analyzer is of great importance, in connection with which they develop special taste lobes.

In the medulla oblongata are located in close proximity to the nuclei of the VIII and X pairs of nerves - the centers that control the movement of the fins. With electrical stimulation of the medulla oblongata behind the nucleus X of the pair, changes in the frequency and direction of movement of the fins occur.

Of particular importance in the composition of the medulla oblongata is a group of ganglion cells in the form of a kind of nervous network called the reticular formation. It begins in the spinal cord, then occurs in the medulla oblongata and midbrain.

In fish, the reticular formation is associated with afferent fibers of the vestibular nerve (VIII) and lateral line nerves (X), as well as with fibers extending from the midbrain and cerebellum. It contains giant mountner cells that innervate the swimming movements of fish. The reticular formation of the medulla oblongata, midbrain, and diencephalon is functionally a single formation that plays an important role in the regulation of functions.

The so-called olive of the medulla oblongata, the nucleus, is well expressed in cartilaginous fish and worse in bony fish, which has a regulatory effect on the spinal cord. It is associated with the spinal cord, cerebellum, diencephalon and is involved in the regulation of movements.

Some fish, which are highly active in swimming, develop an additional olive core, which is associated with the activity of the trunk and tail muscles. The regions of the nuclei of the VIII and X pairs of nerves are involved in the redistribution of muscle tone and in the implementation of complex coordinated movements.

Midbrain. The midbrain in fish is represented by two sections: the "visual roof" (tectum), located dorsally, and the tegmentum, located ventrally. The visual roof of the midbrain is swollen in the form of paired formations - visual lobes. The degree of development of the visual lobes is determined by the degree of development of the organs of vision. The blind and deep sea fish they are underdeveloped. On inside The tectum, facing the cavity of the third ventricle, has a paired thickening - a longitudinal torus. Some authors believe that the longitudinal torus is associated with vision, since the endings of visual fibers were found in it; this formation is poorly developed in blind fish. In the midbrain is the highest, visual center of the fish. In the tectum, the fibers of the second pair of nerves terminate - visual, coming from the retina of the eyes.

The important role of the fish midbrain in relation to the functions of the visual analyzer can be judged from the development of conditioned reflexes to light. These reflexes in fish can be developed by removing the forebrain, but with the preservation of the midbrain. When the midbrain is removed, the conditioned reflexes to light disappear, while the previously developed reflexes to sound do not disappear. After one-sided removal of the tectum in a minnow, the eye of the fish, lying on the opposite side of the body, becomes blind, and when the tectum is removed from both sides, complete blindness occurs. The center of the visual grasping reflex is also located here. This reflex consists in the fact that the movements of the eyes, head, and entire body, caused from the region of the midbrain, are pressed to maximize the fixation of the object in the region of greatest visual acuity - the central fovea of ​​the retina. With electrical stimulation of certain parts of the trout tectum, coordinated movements of both eyes, fins, and body muscles appear.

The midbrain plays an important role in the regulation of fish coloration. When the eyes of the fish are removed, a sharp darkening of the body is observed, and after the bilateral removal of the tectum, the body of the fish becomes lighter.

In the region of the tegmentum, there are nuclei of the III and IV pairs of nerves that innervate the muscles of the eyes, as well as autonomic nuclei, from which nerve fibers depart, innervating the muscles that change the width of the pupil.

The tectum is closely connected with the cerebellum, hypothalamus, and through them with the forebrain. The tectum in fish is one of the most important integration systems; it coordinates the functions of the somatosensory, olfactory, and visual systems. The tegmentum is associated with the VIII pair of nerves (acoustic) and with the receptor apparatus of the labyrinths, as well as with the V pair of nerves (trigeminal). Afferent fibers from the lateral line organs, from the auditory and trigeminal nerves. All these connections of the midbrain ensure the exclusive role of this section of the central nervous system in fish in neuroreflex activity, which has an adaptive value. The tectum in fish is apparently the main organ for closing temporary connections.

The role of the midbrain is not limited to its connection with the visual analyzer. Endings of afferent fibers from olfactory and taste receptors were found in the tectum. The midbrain of fish is the leading center for regulating movement. In the region of the tegmentum in fish, there is a homologue of the mammalian red nucleus, the function of which is to regulate muscle tone.

With damage to the visual lobes, the tone of the fins decreases. When the tectum is removed from one side, the tone of the extensors of the opposite side and the flexors on the side of the operation increases - the fish bends towards the side of the operation, arena movements (movements in a circle) begin. This indicates the importance of the midbrain in the redistribution of the tone of antagonistic muscles. With separation of the midbrain and medulla oblongata, increased spontaneous activity of the fins appears. From this it follows that the midbrain has an inhibitory effect on the centers of the medulla oblongata and spinal cord.

Intermediate brain. The diencephalon consists of three formations: epithalamus - the uppermost epithelium; thalamus - the middle part containing the visual tubercles and the hypothalamus - the hypothalamic region. This part of the brain in fish is partially covered by the roof of the midbrain.

Epithalamus consists of the epiphysis or pineal organ and the habenular nuclei.

epiphysis- a rudiment of the parietal eye, it functions mainly as an endocrine gland. The frenulum (gabenula), located between the forebrain and the roof of the midbrain, also belongs to the epithalamus. It is represented by two habenular nuclei connected by a special ligament, to which fibers from the epiphysis and olfactory fibers of the forebrain fit. Thus, these nuclei are related to light perception and smell.

Efferent fibers go to the midbrain and to the lower centers. Visual hillocks are located in the central part of the diencephalon, with their inner side walls they limit the third ventricle.

IN thalamus distinguish between dorsal and ventral regions. In the dorsal thalamus, a number of nuclei are distinguished in sharks: the external geniculate body, the anterior, internal and medial nuclei.

The nuclei of the visual hillocks are the site of differentiation of the perceptions of various types of sensitivity. Afferent influences from various sense organs come here, and analysis and synthesis of afferent signaling also take place here. Thus, the visual hillocks are an organ of integration and regulation of the body's sensitivity, and also take part in the implementation of motor reactions. With the destruction of the diencephalon in sharks, the disappearance of spontaneous movements, as well as impaired coordination of movements, were observed.

The composition of the hypothalamus includes an unpaired hollow protrusion - a funnel, which forms a special organ braided with vessels - the vascular sac.

On the sides of the vascular sac are its lower lobes. In blind fish they are very small. It is believed that these lobes are associated with vision, although there are suggestions that this part of the brain is associated with taste endings.

The vascular sac is well developed in deep sea fish. Its walls are lined with ciliated cuboidal epithelium, and nerve cells called depth receptors are also located here. It is believed that the vascular sac responds to changes in pressure, and its receptors are involved in the regulation of buoyancy; receptor cells of the vascular sac are related to the perception of the speed of the forward movement of the fish. The vascular sac has nerve connections with the cerebellum, due to which the vascular sac is involved in the regulation of balance and muscle tone during active movements and vibrations of the body. In bottom fish, the vascular sac is rudimentary.

Hypothalamus is the main center where information from the forebrain enters. Afferent influences come here from taste endings and from the acoustic-lateral system. Efferent fibers from the hypothalamus go to the forebrain, to the dorsal thalamus, tectum, cerebellum, neurohypophysis.

In the hypothalamus of fish, the preoptic nucleus is located, the cells of which have morphological features of nerve cells, but produce neurosecretion.

Cerebellum. It is located in the back of the brain, partially covers the top of the medulla oblongata. There is a middle part - the body of the cerebellum - and two lateral sections - the ears of the cerebellum. The anterior end of the cerebellum protrudes into the third ventricle, forming the cerebellar valve.

In bottom and sedentary fish (anglerfish, scorpionfish), the cerebellum is less developed than in fish with high mobility. In mormyrids, the cerebellar valve is hypertrophied and sometimes extends over the mosal surface of the forebrain. In cartilaginous fish, an increase in the surface of the cerebellum due to the formation of folds can be observed.

In bony fish, in the back, lower part of the cerebellum, there is a cluster of cells called the lateral cerebellar nucleus, which plays a large role in maintaining muscle tone.

When removed in a shark of half of the auricular lobes, its body begins to bend sharply towards the operation (opisthotonus). When the body of the cerebellum is removed with the preservation of the auricular lobes, a violation of muscle tone and movement of fish occurs only if the lower part of the cerebellum, where the lateral nucleus is located, is removed or cut. When completely removed cerebellum, a drop in tone (atony) and a violation of coordination of movements occur - the fish swim in a circle in one direction or the other. After about three weeks, the lost functions are restored due to the regulatory processes of other parts of the brain.

Removal of the cerebellum in fish leading an active lifestyle (perches, pikes, etc.) causes severe violations coordination of movements, sensory disturbances, complete disappearance tactile sensitivity, weak response to painful stimuli.

The cerebellum in fish, being connected through afferent and efferent pathways with the tectum, hypothalamus, thalamus, medulla oblongata and spinal cord, can serve as the highest organ for the integration of nervous activity. After removal of the body of the cerebellum in transverse and teleost fish, motor disturbances are observed in the form of body swaying from side to side. If the body and the valve of the cerebellum are removed at the same time, then motor activity is completely disrupted, trophic disorders develop, and after 3-4 weeks the animal dies. This indicates the motor and trophic functions of the cerebellum.

Fibers from the nuclei VIII and X pairs of nerves enter the ears of the cerebellum. The auricles of the cerebellum reach large sizes in fish with a well-developed buckline. The enlargement of the cerebellar valve is also associated with the development of the lateral line. In golden carp, the developed differentiation reflexes to the circle, triangle, and cross disappeared after coagulation of the cerebellar valve and subsequently were not restored. This indicates that the fish cerebellum is the site of closure of conditioned reflexes coming from the lateral line organs. On the other hand, numerous experiments show that in carp with a removed cerebellum on the first day after surgery, it is possible to develop motor and cardiac conditioned reflexes to light, sound, and interoceptive stimulation of the swim bladder.

Forebrain. It consists of two parts. Dorsal lies a thin epithelial plate - a mantle or cloak, delimiting the common ventricle from the cranial cavity; at the base of the forebrain lie the striatal bodies, which are connected on both sides by the anterior ligament. The sides and roof of the forebrain, forming the mantle, repeat in general the shape of the striatal bodies lying below them, from which the entire forebrain seems to be divided into two hemispheres, but a true division into two hemispheres is not observed in bony fish.

In the anterior wall of the forebrain, a paired formation develops - the olfactory lobes, which are sometimes located with their entire mass on the anterior wall of the brain, and sometimes they are significantly elongated and often differentiate into the main part (the olfactory lobe proper), the stalk and the olfactory bulb.

In lungfish, the anterior wall of the brain slides between the striatum in the form of a fold that separates the forebrain into two separate hemispheres.

Secondary olfactory fibers from the olfactory bulb enter the mantle. Since the forebrain in fish is the brain part of the olfactory apparatus, some researchers call it the olfactory brain. After removal of the forebrain, the developed conditioned reflexes to olfactory stimuli disappear. After dissociation of the symmetrical halves of the forebrain in crucian carp and carp, there are no disturbances in the spatial analysis of visual and sound stimuli, which indicates the primitiveness of the functions of this department.

After removal of the forebrain, fish retain conditioned reflexes to light, sound, magnetic field, swim bladder stimuli, lateral line stimulation, and taste stimuli. Thus, the arcs of conditioned reflexes to these stimuli are closed at other levels of the brain. In addition to olfactory, the forebrain of fish also performs some other functions. Removal of the forebrain leads to a decrease in motor activity in fish.

For diverse and complex forms of behavior of fish in a flock, the integrity of the forebrain is necessary. After its removal, the fish swim outside the flock. The development of conditioned reflexes, which is observed in a school, is disturbed in fish lacking a forebrain. When the forebrain is removed, the fish lose their initiative. Thus, normal fish, swimming through a dense lattice, choose different paths, while fish lacking a forebrain limit themselves to one path and bypass the obstacle with great difficulty. Intact marine fish after 1-2 days in the aquarium do not change their behavior in the sea. They return to the pack, occupy the former hunting area, and if it is occupied, they enter into a fight and expel a competitor. Operated individuals released into the sea do not join the flock, do not occupy their hunting area and do not secure a new one, and if they stay on the previously occupied one, they do not protect it from competitors, although they do not lose the ability to defend themselves. If healthy fish occur when dangerous situation on their site they skillfully use the features of the terrain, consistently move to the same shelters, then the operated fish seem to forget the system of shelters, using random shelters.

The forebrain also plays an important role in sexual behavior.

The removal of both lobes in the hemichromis and the Siamese cockerel leads to a complete loss of sexual behavior, the ability to mate is impaired in tilapia, and mating is delayed in guppies. In the stickleback, when various sections of the forebrain are removed, various functions change (increase or decrease) - aggressive, parental or sexual behavior. In male crucian carp, when the forebrain is destroyed, sexual desire disappears.

Thus, after the removal of the forebrain, fish lose their protective-defensive reaction, the ability to take care of their offspring, the ability to swim in schools, and some conditioned reflexes, i.e. there is a change in complex forms of conditioned reflex activity and general behavioral unconditioned reactions. These facts do not provide an exhaustive basis for the role of the forebrain in fish as an organ of integration, but suggest that it exerts a general stimulating (tonic) effect on other parts of the brain.

Nervous system fish divided by peripheral And central. central nervous system consists of the brain and spinal cord, and peripheral- from nerve fibers and nerve cells.

The brain of fish.

fish brain consists of three main parts: forebrain, midbrain and hindbrain. forebrain consists of the telencephalon ( telencephalon) and diencephalon - diencephalon. At the anterior end of the telencephalon are bulbs responsible for the sense of smell. They receive signals from olfactory receptors.

Schematic of the olfactory chain in fish can be described as follows: in the olfactory lobes of the brain there are neurons that are part of the olfactory nerve or a pair of nerves. Neurons join the olfactory tracts of the telencephalon, which are also called the olfactory lobes. Olfactory bulbs are particularly prominent in fish that use the senses, such as sharks, which survive on scent.

Diencephalon consists of three parts: epithalamus, thalamus And hypothalamus and performs the functions of a regulator of the internal environment of the fish body. The epithalamus contains the pineal organ, which in turn consists of neurons and photoreceptors. pineal organ located at the end of the epiphysis and in many fish species it can be sensitive to light due to the transparency of the skull bones. Due to this, the pineal organ can act as a regulator of activity cycles and their change.

The midbrain of fish contains visual lobes And tegmentum or a tire - both are used to process optical signals. The optic nerve of fish is very branched and has many fibers extending from the visual lobes. As with the olfactory lobes, enlarged visual lobes can be found in fish that rely on vision to survive.

The tegmentum in fish controls the internal muscles of the eye and thus ensures its focus on the object. Also, the tegmentum can act as a regulator of active control functions - it is here that the locomotor region of the midbrain is located, which is responsible for rhythmic swimming movements.

The hindbrain of fish is made up of cerebellum, elongated brain And bridge. The cerebellum is an unpaired organ that performs the function of maintaining balance and controlling the position of the body of the fish in the environment. The medulla oblongata and the pons together make up brain stem, to which a large number of cranial nerves that carry sensory information stretch. Most of all nerves communicate with and enter the brain through the brainstem and hindbrain.

Spinal cord.

Spinal cord is located inside the neural arches of the vertebrae of the fish spine. The spine has segmentation. In each segment, neurons connect to the spinal cord via dorsal roots, and agile neurons exit them via ventral roots. Within the central nervous system are also interneurons that provide communication between agile and sensory neurons.

Intelligence. How your brain works Konstantin Sheremetiev

fish brain

fish brain

Fish were the first to have brains. The fish themselves appeared about 70 million years ago. The habitat of fish is already comparable to the area of ​​\u200b\u200bthe Earth. Salmon (Figure 9) swim thousands of miles to spawn from the ocean into the river where they hatched. If this does not surprise you, then imagine that without a map you need to get to an unknown river, while walking at least a thousand kilometers. All this is made possible by the brain.

Rice. 9. Salmon

Together with the brain in fish for the first time appears special variant learning - imprinting (imprinting). A. Hasler established in 1960 that at a certain point in their development, Pacific salmon remember the smell of the stream in which they were born. Then they descend the stream into the river and swim into the Pacific Ocean. On the ocean expanses, they frolic for several years, and then return to their homeland. In the ocean, they navigate by the sun and find the mouth of the desired river, and find their native stream by smell.

Unlike invertebrates, fish can travel long distances in search of food. There is a known case when ringed salmon swam 2.5 thousand kilometers in 50 days.

Fish are short-sighted and clearly see at a distance of only 2-3 meters, but they have a well-developed hearing and sense of smell.

It is generally accepted that fish are silent, although in fact they communicate with the help of sounds. Fish make sounds by squeezing their swim bladder or grinding their teeth. Usually fish make a crackling, rattle or chirp, but some can howl, and the Amazon catfish pirarara has learned to scream so that it can be heard at a distance of up to a hundred meters.

The main difference between the nervous system of fish and the nervous system of invertebrates is that the brain has centers responsible for visual and auditory function. As a result, fish can distinguish between simple geometric shapes, and interestingly, fish are also affected by visual illusions.

The brain took over the function of general coordination of fish behavior. The fish swims, obeying the rhythmic commands of the brain, which are transmitted through the spinal cord to the fins and tail.

Fish easily develop conditioned reflexes. They can be taught to swim to a certain place on a light signal.

In the experiments of Rosin and Mayer, goldfish maintained a constant temperature of the water in the aquarium by actuating a special valve. They accurately kept the water temperature at 34 ° C.

Like invertebrates, fish reproduction is based on the principle of large offspring. Herring annually lays hundreds of thousands of small eggs and does not care about them.

But there are fish that take care of the young. Female Tilapia natalensis holds the eggs in its mouth until the fry hatch. For some time, the fry stay in a flock near the mother and, in case of danger, hide in her mouth.

Hatching fish fry can be quite difficult. For example, a male stickleback builds a nest, and when the female lays eggs in this nest, he drives water into this nest with his fins to ventilate the eggs.

A big problem for fry is the recognition of parents. Cichlid fish consider any slowly moving object as their parent. They line up behind and swim after him.

Some types of fish live in schools. There is no hierarchy in the pack and no clear leader. Usually a group of fish is knocked out of the school, and then the whole school follows them. If a single fish breaks out of the flock, then it immediately returns. The forebrain is responsible for schooling behavior in fish. Erich von Holst removed the forebrain from a river minnow. After that, the minnow swam and ate as usual, except that he had no fear of breaking out of the pack. Minnow swam where he wanted, not looking back at his relatives. As a result, he became the leader of the pack. The whole pack considered him very smart and relentlessly followed him.

In addition, the forebrain enables fish to form an imitation reflex. The experiments of E. Sh. Airapetyants and V. V. Gerasimov showed that if one of the fish in a school exhibits a defensive reaction, then other fish imitate it. Removal of the forebrain stops the formation of the imitation reflex. Non-schooling fish have no imitation reflex.

The fish are sleeping. Some fish even lie down on the bottom to take a nap.

In general, the brain of fish, although it demonstrates good innate abilities, is not very capable of learning. The behavior of two fish of the same species is almost the same.

The brain of amphibians and reptiles has undergone minor changes compared to fish. Basically, the differences are associated with the improvement of the senses. Significant changes in the brain occurred only in warm-blooded animals.

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It is much more primitive than the nervous system of higher vertebrates and consists of a central and associated peripheral and autonomic (sympathetic) nervous systems.

fish CNS includes the brain and spinal cord.
Peripheral nervous system- These are nerves extending from the brain and spinal cord to the organs.
autonomic nervous system are ganglia and nerves that innervate the muscles of the internal organs and blood vessels hearts.

central nervous system stretches along the entire body: part of it, located above the spine and protected by the upper arches of the vertebrae, forms the spinal cord, and the wide front part, surrounded by a cartilaginous or bone skull, forms the brain.
fish brain conditionally divided into anterior, intermediate, middle, oblong and cerebellum. The gray matter of the forebrain in the form of striatal bodies is located mainly in the base and olfactory lobes.

in the forebrain processing of information coming from . And also the forebrain regulates the movement and behavior of the fish. For example, the forebrain stimulates and is directly involved in the regulation of such important fish processes as spawning, spawn protection, flock formation, and aggression.
diencephalon responsible for: optic nerves depart from it. Adjacent to the underside of the diencephalon, or pituitary gland; in the upper part of the diencephalon is the epiphysis, or pineal gland. The pituitary and pineal glands are endocrine glands.
In addition, the diencephalon is involved in the coordination of movement, and the work of other sensory organs.
midbrain has the appearance of two hemispheres, as well as the largest volume. The lobes (hemispheres) of the midbrain are the primary visual centers that process excitation, signals from the organs of vision, regulation of color, taste and balance; here there is also a connection with the cerebellum, medulla oblongata and spinal cord.
Cerebellum often has the form of a small tubercle adjacent to the top of the medulla oblongata. Very large cerebellum soms, and at mormyrus it is the largest among all vertebrates.
The cerebellum is responsible for coordinating movements, maintaining balance, and muscle activity. It is associated with lateral line receptors, synchronizes the activity of other parts of the brain.
Medulla consists of white matter and smoothly passes into the spinal cord. The medulla oblongata regulates the activity of the spinal cord and the autonomic nervous system. It is very important for the respiratory, musculoskeletal, circulatory and other systems of fish. If you destroy this part of the brain, for example, by cutting the fish in the area behind the head, then it quickly dies. In addition, the medulla oblongata is responsible for communication with the spinal cord.
10 pairs of cranial nerves leave the brain.

Like most other organs and systems, the nervous system is developed differently in different fish species. This applies to the central nervous system (different degrees of development of the lobes of the brain) and to the peripheral nervous system.

cartilaginous fish (sharks and rays) have a more developed forebrain and olfactory lobes. Sedentary and bottom fish have a small cerebellum and a well-developed anterior and medulla oblongata, since the sense of smell plays a significant role in their lives. Fast-swimming fish have a highly developed midbrain (visual lobes) and cerebellum (coordination). Weak visual lobes of the brain in deep sea fish.

Spinal cord- continuation of the medulla oblongata.
A feature of the spinal cord of fish is its ability to quickly regenerate and restore activity in case of damage. The gray matter in the spinal cord of a fish is on the inside, while the white matter is on the outside.
The spinal cord is a conductor and catcher of reflex signals. Spinal nerves depart from the spinal cord, innervating the surface of the body, trunk muscles, and through the ganglia and internal organs. In the spinal cord of bony fish is the urohypophysis, whose cells produce a hormone involved in water metabolism.

The autonomic nervous system of fish are ganglia along the spine. Ganglion cells are associated with spinal nerves and internal organs.

The connecting branches of the ganglia unite the autonomic nervous system with the central one. The two systems are independent and interchangeable.

One of the well-known manifestations of the work of the nervous system of fish is a reflex. For example, if all the time in the same place in a pond or in an aquarium, then they will accumulate in this place. In addition, conditioned reflexes in fish can develop to light, shape, smell, sound, taste, and water temperature.

Fish are quite amenable to training and the development of their behavioral responses.

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. At the bottom of the medulla oblongata lies the 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 rather 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 contains 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 parts of the brain is optic chiasm (chiasma nervorum opticorum).

telencephalon (telencephalon) in bony fish, compared with other parts of the brain, it is very small. Most fish (except for lungfish and crossopterygians) are distinguished by an everted (inverted) structure of the hemispheres of the 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.