home Audience 12 The forebrain of fish is well developed. Structure of the brain in fish

The forebrain of fish is well developed. Structure of the brain in fish

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

fish central nervous system includes head and spinal cord.
Peripheral nervous system- these are the nerves that extend from the brain and spinal cord to the organs.
Autonomic nervous system- these are ganglia and nerves that innervate the muscles of the internal organs and blood vessels hearts.

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

In the forebrain processing of information coming from . The forebrain also regulates the movement and behavior of fish. For example, the forebrain stimulates and is directly involved in the regulation of processes important for fish, such as spawning, egg protection, school formation, and aggression.
Diencephalon responsible for: the optic nerves depart from it. Adjacent to the lower side of the diencephalon is the pituitary gland; In the upper part of the diencephalon there is an epiphysis, or pineal gland. The pituitary gland and pineal gland are endocrine glands.
In addition, the diencephalon is involved in the coordination of movement and the functioning 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 visual organs, regulation of color, taste and balance; Here there is also a connection with the cerebellum, medulla oblongata and spinal cord.
Cerebellum often has the shape of a small tubercle adjacent to the medulla oblongata on top. Very large cerebellum soms, and 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 and synchronizes the activity of other parts of the brain.
Medulla comprises 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.
There are 10 pairs of cranial nerves leaving the brain.

Like most other organs and systems, the nervous system is developed differently in various types fish This also applies to the central nervous system ( varying degrees 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-dwelling fish have a small cerebellum and well-developed forebrain and medulla oblongata, since the sense of smell plays a significant role in their lives. Fast-swimming fish have a highly developed midbrain (optic lobes) and cerebellum (motor coordination). Weak visual lobes of the brain in deep-sea fish.

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

Autonomic nervous system of fish- These are ganglia located along the spine. Ganglion cells are connected to spinal nerves and internal organs.

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

One of the well-known manifestations of the nervous system of a fish is the reflex. For example, if they are always in the same place in a pond or aquarium, then they will accumulate in this particular place. Besides, conditioned reflexes Fish can be affected by light, shape, smell, sound, taste, and water temperature.

Fish are quite amenable to training and developing behavioral reactions in them.

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

Fish brain.

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 the bulbs responsible for the sense of smell. They receive signals from olfactory receptors.

Diagram 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 an olfactory nerve or pair of nerves. Neurons join the olfactory areas of the telencephalon, which are also called the olfactory lobes. Olfactory bulbs are especially prominent in fish that use sensory organs, such as sharks, which rely on smell to survive.

The diencephalon consists of three parts: epithalamus, thalamus And hypothalamus and acts as 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. Thanks to this, the pineal organ can act as a regulator of activity cycles and their changes.

In the midbrain of fish there are optic lobes And tegmentum or tire - both are used for processing optical signals. The optic nerve of fish is very branched and has many fibers extending from the optic lobes. As with the olfactory lobes, enlarged optic lobes can be found in fish that depend on vision for their livelihoods.

The tegmentum in fish controls the internal muscles of the eye and thereby ensures its focusing on an object. The tegmentum can also act as a regulator of active control functions - this is where the locomotor region of the midbrain, responsible for rhythmic swimming movements, is located.

The hindbrain of fish consists 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 fish’s body in the environment. The medulla oblongata and the pons together make up brain stem to which one is drawn a large number of cranial nerves carrying sensory information. The majority of all nerves communicate with and enter the brain through the brainstem and hindbrain.

Spinal cord.

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

The brain of bony fishes consists of five sections typical for most vertebrates.

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

Medulla oblongata (myelencephalon, medulla oblongata) the anterior section extends under the cerebellum, and at the rear, without visible boundaries, it passes into the spinal cord. To view the anterior part of the medulla oblongata, it is necessary to turn the body of the cerebellum forward (in some fish the cerebellum is small and the anterior part of the medulla oblongata is clearly visible). The roof of this part of the brain is represented by the choroid plexus. Underneath lies a large diamond-shaped fossa (fossa rhomboidea), widened at the anterior end and passing behind into a narrow medial fissure, 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 connecting various centers of the anterior parts of the brain with the spinal cord. However, the layer of white matter covering the medulla oblongata in fish is quite thin, since the body and tail are largely autonomous - they carry out most of the movements reflexively, without correlation 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 rhythmic bending of the body, which, apparently, is controlled mainly by local spinal reflexes. However, overall control over these movements is exercised by Mauthner cells. The respiratory center lies at the bottom of the medulla oblongata.

Looking at the brain from below, you can distinguish the origins of some nerves. Three round roots extend from the lateral side of the anterior part of the medulla oblongata. The first, lying most cranially, 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 extend together in several roots. The remaining nerves are thin and are usually cut off during dissection.

Cerebellum Quite well developed, round or elongated, it lies over the anterior part of the medulla oblongata directly behind the optic lobes. With its posterior edge it covers the medulla oblongata. The part that protrudes upward is body of the cerebellum (corpus cerebelli). The cerebellum is the center for the precise regulation of all motor innervations associated with swimming and grasping food.

Midbrain(mesencephalon) - part of the brain stem penetrated by the cerebral aqueduct. It consists of large, longitudinally elongated optic lobes (they are visible from above).

Optic lobes, or visual roof (lobis opticus s. tectum opticus) - paired formations separated from each other by a deep longitudinal groove. The optic lobes are the primary visual centers for sensing stimulation. They're running out of fiber optic nerve. In fish, this part of the brain is of primary importance; it is the center that has the main influence on the activity of the body. The gray matter covering the optic lobes has a complex layered structure, reminiscent of the structure of the cerebellar cortex or hemispheres

Thick optic nerves arise from the ventral surface of the optic lobes and cross beneath the surface of the diencephalon.

If you open the optic lobes of the midbrain, you can see that in their cavity a fold is separated from the cerebellum, called cerebellar valve (valvule cerebellis). On either side of it in the bottom of the midbrain cavity there are two bean-shaped elevations 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 telencephalon and diencephalon.

Parts diencephalon lie around a vertical slit third cerebral ventricle (ventriculus tertius). Lateral walls of the ventricle - visual cusps 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 choroid plexus (choroid cover of the third ventricle) and the superior medullary gland - pineal gland (epiphisis). 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 inferior medullary gland - pituitary gland (hypophisis). In many fish, this gland fits tightly into a special recess in the bottom of the skull and usually breaks off during preparation; then clearly visible funnel (infundibulum). In front, on the border between the bottom of the terminal and intermediate sections of the brain, there is optic chiasm (chiasma nervorum opticorum).

Telencephalon in bony fishes it is very small compared to other parts of the brain. Most fish (except lungfishes and lobe-finned fish) are distinguished by the everted (inverted) structure of the telencephalon hemispheres. They seem to be “turned” ventro-laterally. The roof of the forebrain does not contain nerve cells and consists of a thin epithelial membrane (pallium), which during dissection is usually removed along with the membrane of the brain. In this case, the preparation shows the bottom of the first ventricle, divided into two by a deep longitudinal groove striatum. Striatum (corpora striatum1) consist of two sections, which can be seen when viewing the brain from the side. In fact, these massive structures contain striatal and cortical material of a rather complex structure.

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

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 the 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 makes up a fraction of a percent, and in fish weighing less than 1 g, the brain exceeds 1% of the body weight. This shows that brain growth lags behind the growth of the rest of the body. Apparently, most brain development occurs during embryonic-larval development. Of course, there are also interspecies differences in relative brain mass.

The brain consists of five main sections: the forebrain, diencephalon, midbrain, cerebellum and medulla oblongata ( SLIDE 6).

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

Rice. 14. Structure of the brain of bony fish:

a - schematic representation of a longitudinal section of the brain; b - crucian carp brain, cut back view; c - yellowtail brain, side view; d - yellowtail brain, dorsal view; forebrain; 2- first cerebral ventricle; 3 - pineal gland; 4 - midbrain; 5- cerebellar valve; 6 - cerebellum; 7 - brain canal; 8 - fourth cerebral ventricle; 9 - medulla oblongata; 10 - vascular sac; 11 - pituitary gland; 12 - third cerebral ventricle; 13 - optic nerve nucleus; 14 - diencephalon; 15 - olfactory tract; 16 - optic 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 - cerebellar protrusions

Medulla. The medulla oblongata is a continuation of the spinal cord. In its front part it turns into posterior section midbrain. Its upper part - the rhomboid fossa - is covered by ependyma, on which the posterior choroid plexus is located. The medulla oblongata performs a series of 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 both in a descending manner, i.e. to the spinal cord, and in the ascending directions - to the midbrain, 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 a cluster 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. Cranial nerves can be of three types: sensory, if they contain branches that conduct afferent impulses from the sense organs: motor, carrying only efferent impulses to organs and muscles; mixed containing sensory and motor fibers.

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

VI pair abducens nerve. Originates from the bottom of the medulla oblongata, its midline, and innervates the muscles of the eye,

VII - facial nerve. It is a mixed nerve, extends from the lateral wall of the medulla oblongata, directly behind the trigeminal nerve and is often connected with it, forms a complex ganglion from which two branches arise: the nerve of the lateral line of the head and the branch innervating the mucous membrane of the palate, the sublingual region, and the taste buds of the cavity mouth and muscles of the gill cover.

VIII - auditory, or sensory, nerve. Innervates 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 – nervus vagus. It departs from the lateral wall of the medulla oblongata by numerous branches that form two branches: the lateral nerve, which innervates the lateral line organs in the trunk; the nerve of the gill cover, innervating the gill apparatus and some internal organs. On the sides of the rhomboid fossa there are thickenings - the vagal lobes, where the nuclei of the vagus nerve are located.

Sharks have an XI nerve - the terminal one. Its nuclei are located on the anterior or inferior side of the olfactory lobes, and the nerves pass along the dorsolateral surface of the olfactory tracts to the olfactory sacs.

Vital centers are located in the medulla oblongata region. This part of the brain regulates breathing, cardiac activity, the digestive system, etc.

The respiratory center is represented by a group of neurons that regulate breathing movements. You can distinguish the centers of inhalation and exhalation. If half of the medulla oblongata is destroyed, then respiratory movements stop only on the corresponding side. In the region of the medulla oblongata there is also a center that regulates the functioning of the heart and blood vessels. The next important center of the medulla oblongata is the center that regulates the functioning of chromatophores. When this center is irritated by electric current, the entire body of the fish becomes lighter. There are also centers that regulate the functioning of the gastrointestinal tract.

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

In fish leading a sedentary lifestyle, great importance has a taste analyzer, and therefore they develop special taste lobes.

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

Of particular importance in 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 and 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 arising from the midbrain and cerebellum. It contains giant Mountner cells, which innervate the swimming movements of fish. The reticular formation of the medulla oblongata, midbrain and diencephalon is a functionally unified formation that plays important role in the regulation of functions.

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

In some fish, characterized by high swimming activity, an accessory olive nucleus develops, which is associated with the activity of the trunk and tail muscles. The areas 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 - the optic lobes. The degree of development of the optic lobes is determined by the degree of development of the visual organs. In blind and deep-sea fish they are poorly developed. On inside of the tectum, facing the cavity of the third ventricle, there is a paired thickening - the longitudinal torus. Some authors believe that the longitudinal torus is associated with vision, since the endings of the optic fibers are found in it; this formation is poorly developed in blind fish. The higher, visual center of fish is located in the midbrain. The fibers of the second pair of nerves, the optic ones, coming from the retina of the eyes, end in the tectum.

The important role of the midbrain of fish in relation to the functions of the visual analyzer can be judged by the development of conditioned reflexes to light. These reflexes in fish can be developed by removing the forebrain, but preserving the midbrain. When the midbrain is removed, conditioned reflexes to light disappear, but previously developed reflexes to sound do not disappear. After one-sided removal of the tectum from 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 located here. This reflex consists in the fact that the movements of the eyes, head, and entire body, caused from the midbrain region, are pressed to maximize the fixation of an object in the area of greatest visual acuity - the central fovea of the retina. When electrically stimulating certain areas of the trout tectum, coordinated movements of both eyes, fins, and body muscles appear.

The midbrain plays an important role in regulating the coloration of fish. When the eyes are removed from the fish, a sharp darkening of the body is observed, and after 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, which innervate the muscles of the eyes, as well as the autonomic nuclei, from which nerve fibers extend, 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 critical systems integration, it coordinates the functions of somatosensory, olfactory and visual systems. The tegmentum is connected 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 part of the central nervous system in fish in neuro-reflex activity, which has adaptive significance. 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. The endings of afferent fibers from the olfactory and taste receptors are found in the tectum. The midbrain of fish is the leading center for the regulation of movement. In the region of the tegmentum in fish there is a homologue of the red nucleus of mammals, the function of which is to regulate muscle tone.

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

Diencephalon. The diencephalon consists of three formations: the epithalamus - the uppermost supratubercular region; the thalamus - the middle part containing the visual hillocks and the hypothalamus - the subtubercular 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 habenular nuclei.

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

Efferent fibers go to the midbrain and to the lower centers. The visual tuberosities are located in the central part of the diencephalon; with their inner lateral walls they limit the third ventricle.

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

The nuclei of the visual thalamus are the site of differentiation of perceptions of various types of sensitivity. Afferent influences from various organs feelings, this is where the analysis and synthesis of afferent signaling takes place. 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 hypothalamus includes an unpaired hollow protrusion - the funnel, which forms a special organ entwined with blood 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 marine fish. Its walls are lined with ciliated cubic epithelium, and nerve cells called depth receptors are 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 forward movement of the fish. The vascular sac has neural connections with the cerebellum, thanks to this the vascular sac participates in the regulation of balance and muscle tone during active movements and body vibrations. In bottom fishes the vascular sac is rudimentary.

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

In the hypothalamus of fish there is a preoptic nucleus, the cells of which have the morphological characteristics of nerve cells, but produce neurosecretion.

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

In bottom-dwelling and sedentary fish (anglerfish, scorpionfish), the cerebellum is less developed than in fish with high mobility. The cerebellum in predators (tuna, mackerel, cod), pelagic or planktivorous (harengula). In mormyrids, the cerebellar valve is hypertrophied and sometimes extends over the callosal 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 teleost fish, in the posterior, 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 deleting in a shark with half of the auricular lobes, its body begins to bend sharply towards the operation (opisthotonus). When the body of the cerebellum is removed while preserving the auricular lobes, a disturbance in muscle tone and fish movement occurs only if the lower part of the cerebellum, where the lateral nucleus is located, is removed or cut. At complete removal cerebellum, a decrease in tone (atony) and impaired coordination of movements occur - the fish swim in a circle, first in one direction, then in the other. After about three weeks, the lost functions are restored due to regulatory processes in other parts of the brain.

Removal of the cerebellum from fish leading active image life (perch, pike, etc.), causes severe disturbances in coordination of movements, sensory disturbances, complete disappearance of tactile sensitivity, weak reaction 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 supreme body integration of nervous activity. After removal of the cerebellar body, transverse and bony fish exhibit movement disorders in the form of body swaying from side to side. If the body and the cerebellar valve are removed at the same time, 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.

The cerebellar auricles receive fibers from the nuclei of the VIII and X pairs of nerves. The cerebellar auricles reach large sizes in fish with a well-developed tank line. Enlargement of the cerebellar valve is also associated with the development of the lateral line. In goldfish, the developed differentiation reflexes to the circle, triangle and cross disappeared after coagulation of the cerebellar valve and were not subsequently restored. This indicates that the cerebellum of fish is the place where conditioned reflexes coming from the lateral line organs are closed. On the other hand, numerous experiments show that in carp with the cerebellum removed, 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. Dorsally 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, are repeated in general shape underlying striatum, from which the entire forebrain appears to be divided into two hemispheres, but a true division into two hemispheres is not observed in bony fishes.

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 extend significantly in length and are often differentiated into the main part (the olfactory lobe itself), the stalk and the olfactory bulb.

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

The mantle receives secondary olfactory fibers from the olfactory bulb. 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 disappearance of developed conditioned reflexes to olfactory stimuli is observed. After the separation of the symmetrical halves of the forebrain, no disturbances are observed in crucian carps and carps spatial analysis 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 stimulation, 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 the olfactory functions, the forebrain of fish also performs some other functions. Removal of the forebrain leads to a decrease in motor activity in fish.

For the varied and complex behavior of fish in a school, the integrity of the forebrain is necessary. After its removal, the fish swim outside the school. The development of conditioned reflexes, observed in school conditions, is disrupted in fish lacking the forebrain. When the forebrain is removed, fish lose initiative. Thus, normal fish, swimming through a fine grid, select different ways, and fish lacking a forebrain are limited to one path and bypass the obstacle with great difficulty. Intact sea fish after 1-2 days in the aquarium they do not change their behavior in the sea. They return to the pack, occupy the previous hunting area, and if it is occupied, they enter into a fight and drive out the 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 for themselves, and if they remain in the previously occupied one, they do not protect it from competitors, although they do not lose the ability to defend themselves. If healthy fish when occurring dangerous situation in their area 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.

Removal of both lobes in hemichromis and the Siamese cockerel leads to a complete loss of sexual behavior, in tilapia the ability to mate is impaired, and in guppies there is a delay in mating. In stickleback, when various parts 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 removal of the forebrain, fish lose their defensive reaction, the ability to care for 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 unconditional reactions. These facts do not provide exhaustive evidence that the forebrain in fish acquires the significance of an organ of integration, but they suggest that it has a general stimulating (tonic) effect on other parts of the brain.

Structure of the brain of bony fish

The brain of bony fishes consists of five sections typical for most vertebrates.

Diamond brain(rhombencephalon)

the anterior section extends under the cerebellum, and at the rear, without visible boundaries, it passes into the spinal cord. To view the anterior part of the medulla oblongata, it is necessary to turn the body of the cerebellum forward (in some fish the cerebellum is small and the anterior part of the medulla oblongata is clearly visible). The roof of this part of the brain is represented by the choroid plexus. Underneath lies a large widened at the anterior end and passing behind into a narrow medial fissure, it is a cavity The medulla oblongata serves as the origin of most of the brain nerves, as well as a pathway connecting various centers of the anterior parts of the brain with the spinal cord. However, the layer of white matter covering the medulla oblongata in fish is quite thin, since the body and tail are largely autonomous - they carry out most of the movements reflexively, without correlation 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 rhythmic bending of the body, which, apparently, is controlled mainly by local spinal reflexes. However, overall control over these movements is exercised by Mauthner cells. The respiratory center lies at the bottom of the medulla oblongata.

Midbrain(mesencephalon) - part of the brain stem penetrated by the cerebral aqueduct. It consists of large, longitudinally elongated optic lobes (they are visible from above).

Optic lobes, or visual roof (lobis opticus s. tectum opticus) - paired formations separated from each other by a deep longitudinal groove. The optic lobes are the primary visual centers for sensing stimulation. The fibers of the optic nerve end in them. In fish, this part of the brain is of primary importance; it is the center that has the main influence on the activity of the body. The gray matter covering the optic lobes has a complex layered structure, reminiscent of the structure of the cerebellar cortex or hemispheres

Thick optic nerves arise from the ventral surface of the optic lobes and cross beneath the surface of the diencephalon.

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

Parts diencephalon lie around a vertical slit Lateral walls of the ventricle - visual cusps 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 choroid plexus (choroid cover of the third ventricle) and the superior medullary gland - pineal gland (epiphisis). 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 inferior medullary gland - pituitary gland (hypophisis). In many fish, this gland fits tightly into a special recess in the bottom of the skull and usually breaks off during preparation; then clearly visible funnel (infundibulum). optic chiasm (chiasma nervorum opticorum).

in bony fishes it is very small compared to other parts of the brain. Most fish (except lungfishes and lobe-finned fish) are distinguished by the everted (inverted) structure of the telencephalon hemispheres. They seem to be “turned” ventro-laterally. The roof of the forebrain does not contain nerve cells and consists of a thin epithelial membrane (pallium), which during dissection is usually removed along with the membrane of the brain. In this case, the preparation shows the bottom of the first ventricle, divided into two by a deep longitudinal groove striatum. Striatum (corpora striatum1) consist of two sections, which can be seen when viewing the brain from the side. In fact, these massive structures contain striatal and cortical material of a rather complex structure.

Cranial nerves of fish.

In total, 10 pairs of nerves extend from the fish’s brain. Basically (both in name and in function) they correspond to the nerves of mammals.

Structure of the frog brain

Brain frogs, like other amphibians, are characterized by the following features compared to fish:

a) progressive development of the brain, expressed in the separation of the paired hemispheres by a longitudinal fissure and the development of the gray matter of the ancient cortex (archipallium) in the roof of the brain;

b) weak development of the cerebellum;

c) weak expression of the bends of the brain, due to which the intermediate and middle sections are clearly visible from above.

Diamond brain(rhombencephalon)

Medulla oblongata (myelencephalon, medulla oblongata) , into which the spinal cord passes cranially, it differs from the latter in its greater width and the departure from its lateral surfaces of the large roots of the posterior cranial nerves. On the dorsal surface of the medulla oblongata there is diamond-shaped fossa (fossa rhomboidea), accommodating fourth cerebral ventricle (ventriculus quartus). On top it is covered with a thin vascular cap, which is removed along with the meninges. The ventral fissure, a continuation of the ventral fissure of the spinal cord, runs along the ventral surface of the medulla oblongata. The medulla oblongata contains two pairs of cords (bundles of fibers): the lower pair, separated by the ventral fissure, are motor, the upper pair are sensory. The medulla oblongata contains the centers of the jaw and sublingual apparatus, the organ of hearing, as well as the digestive and respiratory systems.

Cerebellum located in front of the rhomboid fossa in the form of a high transverse ridge as an outgrowth of its anterior wall. The small size of the cerebellum is determined by the small and uniform mobility of amphibians - in fact, it consists of two small parts, closely connected with the acoustic centers of the medulla oblongata (these parts are preserved in mammals as fragments of the cerebellum (flocculi)). The body of the cerebellum - the center of coordination with other parts of the brain - is very poorly developed.

Midbrain(mesencephalon) when viewed from the dorsal side, it is represented by two typical optic lobes(lobus opticus s. tectum opticus) , having the appearance of paired ovoid elevations forming the upper and lateral parts of the midbrain. The roof of the optic lobes is formed by gray matter - several layers of nerve cells. The tectum in amphibians is the most significant part of the brain. The optic lobes contain cavities that are lateral branches cerebral (Sylvii) aqueduct (aquaeductus cerebri (Sylvii), connecting the fourth cerebral ventricle with the third.

The bottom of the midbrain is formed by thick bundles of nerve fibers - cerebral peduncles (cruri cerebri), connecting the forebrain with the medulla oblongata and spinal cord.

Forebrain(prosencephalon) consists of the diencephalon and telencephalon, lying sequentially.

visible from above as a rhombus, with sharp angles directed to the sides.

Parts of the diencephalon lie around a vertically located wide fissure third cerebral ventricle (ventriculus tertius). Lateral thickening of the walls of the ventricle - visual cusps or thalamus. In fish and amphibians, the thalamus is of secondary importance (as coordinating sensory and motor centers). The membranous roof of the third cerebral ventricle - the epithalamus or epithalamus - does not contain neurons. It contains the superior medullary gland - pineal gland (epiphisis). In amphibians, the pineal gland already serves as a gland, but has not yet lost the features of the parietal organ of vision. In front of the epiphysis, the diencephalon is covered with a membranous roof, which orally turns inward and passes into the anterior choroid plexus (choroid tectum of the third ventricle), and then into the endplate of the diencephalon. Inferiorly the ventricle narrows, forming pituitary funnel (infundibulum), the inferior medullary gland is attached to it caudoventrally - pituitary gland (hypophisis). In front, on the border between the bottom of the terminal and intermediate sections of the brain, there is chiasma nervorum opticorum). In amphibians, most of the fibers of the optic nerves are not retained in the diencephalon, but go further to the roof of the midbrain.

Telencephalon along its length almost equal to length all other parts of the brain. It consists of two parts: the olfactory brain and two hemispheres, separated from each other sagittal (arrow-shaped) fissure (fissura sagittalis).

Hemispheres of the telencephalon (haemispherium cerebri) occupy the posterior two-thirds of the telencephalon and hang over the anterior part of the diencephalon, partially covering it. There are cavities inside the hemispheres - lateral cerebral ventricles (ventriculi lateralis), caudally communicating with the third ventricle. In the gray matter of the cerebral hemispheres of amphibians, three areas can be distinguished: dorsomedially there is the old cortex or hippocampus (archipallium, s. hippocampus), laterally - ancient bark(paleopallium) and ventrolaterally - the basal ganglia, corresponding striata (corpora striata) mammals. The striatum and, to a lesser extent, the hippocampus are correlative centers, the latter associated with olfactory function. The ancient cortex is an exclusively olfactory analyzer. On the ventral surface of the hemispheres, grooves are noticeable, separating the striatum from the ancient cortex.

Olfactory brain (rhinencephalon) occupies the anterior part of the telencephalon and forms olfactory lobes (bulbs) (lobus olfactorius), soldered in the middle with each other. They are separated from the hemispheres laterally by the marginal fossa. The olfactory lobes anteriorly contain the olfactory nerves.

10 pairs extend from the frog's brain cranial nerves. Their formation, branching and zone of innervation are not fundamentally different from those in mammals

Bird brain.

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

Medulla oblongata (myelencephalon, medulla oblongata) behind it directly passes into the spinal cord (medulla spinalis). Anteriorly, it wedges between the optic lobes of the midbrain. The medulla oblongata has a thick bottom, in which lie the nuclei of gray matter - the centers of many vital functions of the body (including equilibrium-auditory, somatic motor and autonomic). The gray matter in birds is covered with a thick layer of white, formed by nerve fibers connecting the brain to the spinal cord. In the dorsal part of the medulla oblongata there is diamond-shaped fossa (fossa rhomboidea), which is a cavity fourth cerebral ventricle (ventriculus quartus). The roof of the fourth cerebral ventricle is formed by a membranous vascular tegmentum; in birds it is completely covered by the posterior part of the cerebellum.

Cerebellum in birds it is large and is represented practically only worm (vermis), located above the medulla oblongata. The cortex (gray matter located superficially) has deep grooves that significantly increase its area. The cerebellar hemispheres are poorly developed. In birds, the sections of the cerebellum associated with muscle sense are well developed, while the sections responsible for the functional connection of the cerebellum with the cerebral cortex are practically absent (they develop only in mammals). The cavity is clearly visible in the longitudinal section cerebellar ventricle (ventriculus cerebelli), as well as alternation of white and gray matter, forming a characteristic pattern tree of life (arbor vitae).

Midbrain(mesencephalon) represented by two very large ones, shifted to the side visual lobes (lobus opticus s. tectum opticus). Everyone has vertebrate size and the development of the optic lobes is related to eye size. They are clearly visible from the side and from the ventral side, while from the dorsal side they are almost completely covered by the posterior sections of the hemispheres. In birds, almost all fibers of the optic nerve come to the optic lobes, and the optic lobes remain extremely important parts brain (however, in birds with the optic lobes, the cerebral cortex begins to compete in importance). The sagittal section shows that in the forward direction the cavity of the fourth ventricle, narrowing, passes into the cavity of the midbrain - cerebral or Sylvian aqueduct (aquaeductus cerebri). Orally, the aqueduct passes, expanding, into the cavity of the third cerebral ventricle of the diencephalon. The conventional anterior border of the midbrain is formed posterior commissure (comissura posterior), clearly visible on a sagittal section in the form of a white spot.

Included forebrain(prosencephalon) there are the diencephalon and the telencephalon.

Diencephalon in birds it is visible from the outside only from the ventral side. Middle part longitudinal section of the diencephalon is occupied by a narrow vertical fissure third ventricle (ventriculus tertius). In the upper part of the ventricular cavity there is a hole (paired) leading into the cavity of the lateral ventricle - Monroe (interventricular) foramen (foramen interventriculare).

The lateral walls of the third cerebral ventricle are formed by a fairly well developed thalamus, the degree of development of the thalamus is related to the degree of development of the hemispheres. Although it does not have the significance of a higher visual center in birds, it nevertheless performs important functions as a motor correlative center.

In the anterior wall of the third ventricle lies anterior commissure (comissura anterior), consisting of white fibers connecting the two hemispheres

The floor of the diencephalon is called hypothalamus (hypothalamus). When viewed from below, lateral thickenings of the bottom are visible - visual tracts (tractus opticus). Between them the anterior end of the diencephalon includes optic nerves (nervus opticus), forming optic chiasm (chiasma opticum). The posterior lower corner of the third cerebral ventricle corresponds to the cavity funnels (infunbulum). From below, the funnel is usually covered by the subcerebral gland, which is well developed in birds - pituitary gland (hypophysis).

From the roof of the diencephalon (epithalamus) extending upward having a cavity pedicle of the pineal organ. Above is himself pineal organ- pineal gland (epiphysis), it is visible from above, between the posterior edge of the cerebral hemispheres and the cerebellum. The anterior part of the roof of the diencephalon is formed by the choroid plexus extending into the cavity of the third ventricle.

Telencephalon in birds it consists of cerebral hemispheres (hemispherium cerebri), separated from each other by deep longitudinal fissure (fissura interhemispherica). The hemispheres in birds are the largest formations of the brain, but their structure is fundamentally different from that of mammals. Unlike the brain of many mammals, the greatly enlarged hemispheres of the bird's brain do not bear grooves and convolutions; their surface is smooth on both the ventral and dorsal sides. The cortex as a whole is poorly developed, primarily due to the reduction of the olfactory organ. The thin medial wall of the forebrain hemisphere in the upper part is represented by nerve substance old bark (archipallium). Material neocortex(poorly developed) (neopallium) along with a significant mass striatum (corpus striatum) forms a thick lateral wall of the hemisphere or a lateral outgrowth, protruding into the cavity of the lateral ventricle. Therefore the cavity lateral ventricle (ventriculus lateralis) hemisphere is a narrow gap located dorsomedially. In birds, unlike mammals, significant development in the hemispheres is achieved not by the cerebral cortex, but by the striatum. It has been revealed that the striatum is responsible for innate stereotypical behavioral reactions, while the neocortex provides the ability for individual learning. Birds of some species showed better than average site development neocortex- These are, for example, crows, known for their learning abilities.

Olfactory bulbs (bulbis olfactorius) located on the ventral side of the forebrain. They are small in size and approximately triangular in shape. They enter from the front olfactory nerve.