Pisces are the most developed parts of the brain. The structure and functions of the brain
The nervous system connects the body with the external environment and regulates the activity of internal organs.
The nervous system is represented by:
1) central (brain and spinal cord);
2) peripheral (nerves extending from the head and spinal cord).
The peripheral nervous system is divided into:
1) somatic (innervates striated muscles, provides body sensitivity, consists of nerves extending from the spinal cord);
2) autonomic (innervates internal organs, is divided into sympathetic and parasympathetic, consists of nerves extending from the brain and spinal cord).
The fish brain consists of five sections:
1) forebrain (telencephalon);
2) diencephalon (diencephalon);
3) midbrain(mesencephalon);
4) cerebellum (cerebellum);
5) medulla oblongata (myelencephalon).
Inside the parts of the brain are cavities. The cavities of the anterior, diencephalon and medulla oblongata are called ventricles, the cavity of the midbrain is called the sylvian aqueduct (it connects the cavities of the diencephalon and medulla oblongata).
The forebrain in fish is represented by two hemispheres with an incomplete septum between them and one cavity. In the forebrain, the bottom and sides are composed of nerve matter, the roof in most fish is epithelial, in sharks it consists of nerve matter. The forebrain is the center of smell, regulates the functions of schooling behavior of fish. outgrowths forebrain form olfactory lobes (in cartilaginous fish) and olfactory bulbs (in bony fish).
In the diencephalon, the bottom and side walls are composed of nerve matter, the roof is made of a thin layer of connective tissue. It has three parts:
1) epithalamus (supra-tuberous part);
2) thalamus (middle or tuberous part);
3) hypothalamus (hypothalamic part).
The epithalamus forms the roof diencephalon, in the back of it is the epiphysis (gland internal secretion). In lampreys, the pineal and parapineal organs are located here, which perform a light-sensitive function. In fish, the parapineal organ is reduced, and the pineal turns into the epiphysis.
The thalamus is represented by visual tubercles,
measures of which are related to visual acuity. With poor vision, they are small or absent.
The hypothalamus forms the lower part of the diencephalon and includes the infundibulum (hollow outgrowth), the pituitary gland (endocrine glands) and the vascular sac, where fluid is formed that fills the ventricles of the brain.
The diencephalon serves as the primary visual center, the optic nerves depart from it, which in front of the funnel form a chiasma (crossing of nerves). Also, this diencephalon is the center for switching excitations that come from all parts of the brain associated with it, and through hormonal activity (pineal gland, pituitary gland) is involved in the regulation of metabolism.
The midbrain is represented by a massive base and visual lobes. Its roof consists of nervous substance, has a cavity - the Sylvian aqueduct. The midbrain is the visual center and also regulates muscle tone and body balance. The oculomotor nerves arise from the midbrain.
The cerebellum consists of nerve matter, is responsible for the coordination of movements associated with swimming, is highly developed in fast-swimming species (shark, tuna). In lampreys, the cerebellum is poorly developed and does not stand out as an independent department. In cartilaginous fish, the cerebellum is a hollow outgrowth of the roof of the medulla oblongata, which from above rests on the visual lobes of the midbrain and on the medulla oblongata. In rays, the surface of the cerebellum is divided into 4 parts by furrows.
In the medulla oblongata, the bottom and walls are composed of nervous substance, the roof is formed by a thin epithelial film, inside it is the ventricular cavity. Most of the head nerves (from V to X) depart from the medulla oblongata, innervating the organs of respiration, balance and hearing, touch, the sense organs of the lateral line system, the heart, and the digestive system. The posterior part of the medulla oblongata passes into the spinal cord.
Fish, depending on their lifestyle, have differences in the development of individual parts of the brain. So, in cyclostomes, the forebrain with olfactory lobes is well developed, the midbrain is poorly developed and the cerebellum is underdeveloped; in sharks, the forebrain, cerebellum and medulla oblongata are well developed; in bony pelagic mobile fish with good eyesight, the midbrain and cerebellum are most developed (mackerel, flying fish, salmon), etc.
In fish, 10 pairs of nerves leave the brain:
I. The olfactory nerve (nervus olfactorius) departs from the forebrain. In cartilaginous and some bony olfactory bulbs adjoin directly to the olfactory capsules and are connected to the forebrain by the nerve tract. In most bony fish, the olfactory bulbs adjoin the forebrain, and from them a nerve (pike, perch) goes to the olfactory capsules.
II. The optic nerve (n. opticus) departs from the bottom of the diencephalon and forms a chiasma (cross), innervates the retina.
III. oculomotor nerve(n. oculomotorius) departs from the bottom of the midbrain, innervates one of the eye muscles.
IV. Block nerve (n. trochlearis) starts from the roof of the midbrain, innervates one of the eye muscles.
All other nerves originate from the medulla oblongata.
V. Trigeminal nerve (n. trigeminus) is divided into three branches, innervates the jaw muscles, skin of the upper part of the head, mucous oral cavity.
VI. Abducens nerve (n. abducens) innervates one of the eye muscles.
VII. The facial nerve (n. Facialis) has many branches and innervates separate parts of the head.
VIII. Auditory nerve (n. acusticus) innervates the inner ear.
IX. The glossopharyngeal nerve (n. glossopharyngeus) innervates the mucous membrane of the pharynx, the muscles of the first gill arch.
X. The vagus nerve (n. vagus) has many branches, innervates the muscles of the gills, internal organs, and the lateral line.
The spinal cord is located in the spinal canal formed by the superior arches of the vertebrae. In the center of the spinal cord runs a canal (neurocoel), a continuation of the ventricle of the brain. central part the spinal cord consists of gray matter, the peripheral - of white. The spinal cord has a segmental structure, from each segment, the number of which corresponds to the number of vertebrae, nerves depart from both sides.
The spinal cord, with the help of nerve fibers, is connected with various parts of the brain, carries out the transmission of excitations nerve impulses, is also the center of unconditioned motor reflexes.
Bony fish are the largest class of vertebrates, with about 20,000 species. The most ancient representatives of this class originated from cartilaginous fish at the end of the Silurian. At present, 99% of the class belong to the so-called bony fish, which first appeared in the middle of the Triassic, but their evolution was slow for a long time and only at the end of the Cretaceous accelerated sharply and reached an amazing flowering in the Tertiary period. They inhabit a wide variety of water bodies (rivers, seas and oceans down to the greatest depth, found in arctic waters). Thus, bony fish are vertebrates most adapted to living in the aquatic environment. In addition to bony fish, the class includes several dozen more species of ancient bony fish, which retained some features of cartilaginous fish.
Most of the species in this class are adapted for fast swimming, and their body shape is similar to that of sharks. Less fast swimming fish have more high body(for example, in many species of cyprinids). Species leading sedentary image life on the bottom (for example, flounders) have the same flattened body shape as rays.
Bony fish:
1 - herring (herring family); 2 - salmon (fam. Salmon); 3 - carp (family Cyprinidae); 4- catfish (fam. Catfish); 5 - pike (fam. Pike); 6- eel (fam. Acne);
7 - pike perch (fam. Perch); 8 - river goby (family Goby); 9 - flounder (flounder family)
Covers. The length of the body of fish is different - from a few centimeters to several meters. Unlike cartilaginous and ancient bony fish, among the bony fish there are many small species that have mastered small biotopes inaccessible to larger species. The skin of the vast majority of bony fish is covered with small bony, relatively thin scales overlapping each other in a tiled manner. They protect fish well. mechanical damage and provide sufficient flexibility of the body. There are cycloid scales with a rounded upper edge and ctenoid scales with small teeth on the upper edge. The number of scales in the longitudinal and transverse rows for each species is more or less constant and is taken into account when determining the species of fish. In cold weather, the growth of fish and scales slows down or stops, so annual rings form on the scales, counting which you can determine the age of the fish. In a number of species, the skin is bare, devoid of scales. There are many glands in the skin, the mucus they secrete reduces friction when swimming, protects against bacteria, etc. In the lower layers of the epidermis there are various pigment cells, due to which the fish are hardly noticeable against the background of their environment. In some species, body color may change in accordance with changes in the color of the substrate. Such changes are carried out under the influence of nerve impulses.
Nervous system. The size of the brain in relation to the size of the body is somewhat larger than that of cartilaginous fish. The forebrain is relatively small in comparison with other sections, but its striatal bodies are large and, through their connections with other sections of the Central nervous system affect the implementation of some fairly complex behaviors. There are no nerve cells in the roof of the forebrain. The diencephalon and the epiphysis and pituitary gland separated from it are well developed. The midbrain is larger than other parts of the brain, in its upper part there are two well-developed visual lobes. The cerebellum in well-swimming fish is large. The size increased and the structure of the medulla oblongata and spinal cord became more complicated. The subordination of the latter to the brain, compared to what is observed in cartilaginous fish, has increased
Perch brain:
1 - olfactory capsule; 2 - olfactory lobes; 3 - forebrain; 4 - midbrain; 5 - cerebellum; 6 - medulla oblongata; 7 - spinal cord; 8 - ophthalmic branch of the trigeminal nerve; 9 - auditory nerve; 10 - vagus nerve
Skeleton. During the evolution of the class under consideration, the skeleton gradually ossified. The notochord was preserved only among the lower representatives of the class, the number of which is insignificant. When studying the skeleton, it must be borne in mind that some bones arise as a result of the replacement of cartilage with bone tissue, while others develop in the connective tissue layer of the skin. The first are called the main, the second - integumentary bones.
The medulla of the skull is a box that protects the brain and sense organs: smell, vision, balance and hearing.
Diagram of the arrangement of bones in the skull of a bony fish. The visceral skeleton is separated from cerebral skull. The gill cover is not drawn. The main bones and cartilage are covered with dots, the integumentary bones are white:
/ - angular; 2 - articular; 3 - main occipital; 4 - main wedge-shaped; 5 - copula; 6 - tooth; 7 - lateral olfactory; 8 - external pterygoid; 9 - internal pterygoid; 10 - lateral occipital; 11 - frontal; 12 - pendants; 13 - hyoid; 14 - ossified ligament; 15 - lateral wedge-shaped; 16 - middle olfactory; 17 - posterior pterygoid; 18 - maxillary; 19 - nasal; 20 - eye wedge-shaped; 21 - parietal; 22 - palatine; 23 - premaxillary; 24 - parasphenoid; 25 - square; 26 - upper occipital; 27 - additional; 28 - coulter; 29-33 - ear bones; I-V - gill arches
The roof of the skull is formed by paired nasal, frontal, parietal bones. The latter are adjacent to the superior occipital bone, which, together with the paired lateral occipital bones and the main occipital bone, forms the back of the skull. The underside of the skull consists (from front to back) of the vomer, parasphenoid (a wide long bone very characteristic of the skull of fish) and the basal bone. The front part of the skull is occupied by a capsule protecting the organs of smell; on the sides are the bones that surround the eyes, and a number of bones that protect the organs of hearing and balance.
The visceral part of the skull consists of a series of bony gill arches, which are the support and protection of the gill apparatus and the anterior part. digestive system. Each of the mentioned arcs includes several bones. The arcs to which the gills are attached, in most fish (on each side). At the bottom, the gill arches are interconnected, and the anterior one is connected to the hyoid arch, which consists of several bones. The upper of these bones - the hyoid-maxillary (hyomandibular) is attached to the brain region of the skull in the region of the auditory region and is connected through the square bone with the bones surrounding the oral cavity. Thus, the hyoid arch serves to connect the gill arches with the rest of the visceral region, and its upper bone- With brain department skulls.
The edges of the mouth and the entire oral cavity are reinforced with a series of bones. The maxillary row of bones is represented (on each side) by the premaxillary and maxillary bones. Next comes a series of bones: palatine, several pterygoid and square. The quadrate bone adjoins the suspension (hyomandibular) at the top, and the lower jaw at the bottom. The latter consists of several bones: the dentary (the largest), the angular and the articular, connected to the square bone. In ancient fish (which still had a cartilaginous skeleton), all the arches of the visceral part of the skull carried gills, but later the anterior of these arches turned into hyoid arches and jaw rows bones.
vertebral column comprises a large number biconcave (amphycoelous) vertebrae, between which remains of the chord are preserved. From each vertebra a long spinous process extends upward and somewhat backward. The bases of these processes are divided, and they form a canal through which the spinal cord passes. Two short transverse processes extend from the underside of the vertebral bodies, to which long curved ribs are attached in the trunk region. They freely terminate in the muscles and form the frame of the side walls of the body. In the caudal part of the body, only the lower spinous processes extend downward from the vertebrae.
Bibliography
"Biological Resources of the World Ocean", Moiseev I. A., M., 1969;
"Life of the ocean", Bogorov V. G., M., 1969;
"Food resources of the seas and oceans", Zaytsev V.P., M., 1972;
"World Fisheries", Kuzmichev A. B., in 1972,
"Fishery", 1974, No. 7.
"Geographical picture of the world". V.P. Maksakovskiy, 2006,
"Fish farming", A.I. Isaev, M., 1991
"Security environment in fisheries", N.I. Osipova, M., 1986.
"Biological resources of the world ocean", P.A.Moiseev., M., 1989.
"Handbook of Fish Protection", Moscow., 1986
"Handbook of a fish farmer on the artificial breeding of commercial fish", N. I. Kozhin, M., 1971; maritime law fish farming
"Prudovoe fish farming", Martyshev F. G., M., 1973.
"Sea fishing vessels", K. S. Zaichik, G. V. Terentyev, L., 1965;
"Fleet of the fishing industry. Directory of typical ships", 2nd ed., L., 1972.
"Sea Law", Volkov A. A., M., 1969;
"Global problems and the" third world ". Dreyer O. K., Los V. V., Los V L., M., 1991.
"Earth and humanity. Global problems. Series "Countries and peoples". M., 1985, v. 20.
"This contrasting world. Geographical aspects of some global problems", Lavrov S. V., Sdasyuk G. V. M., 1985.
"Latin America: natural resource potential", M., 1986.
"Liberated countries: the use of resources for development", Lukichev G. A. M., 1990.
127. Draw a diagram external structure fish. Sign its main parts.
128. List the features of the structure of fish associated with the aquatic lifestyle.
1) A streamlined torpedo-shaped body, flattened in the lateral or dorsal-ventral (in demersal fish) directions. The skull is fixedly connected to the spine, which has only two sections - the trunk and tail.
2) Bony fish have a special hydrostatic organ - the swim bladder. As a result of a change in its volume, the buoyancy of the fish changes.
In cartilaginous fish, buoyancy of the body is achieved by accumulation in the liver, less often in other organs, of fat reserves.
3) The skin is covered with placoid or bone scales, rich in glands that abundantly secrete mucus, which reduces the friction of the body against water and performs a protective function.
4) Respiratory organs - gills.
5) Two-chambered heart (with venous blood), consisting of the atrium and ventricle; one circle of blood circulation. Organs and tissues are supplied with arterial blood, rich in oxygen. The life of fish depends on the temperature of the water.
6) Trunk kidneys.
7) The sense organs of fish are adapted to functioning in the aquatic environment. A flat cornea and an almost spherical lens allow the fish to see only close objects. The sense of smell is well developed, allows you to stay in the flock and detect food. The organ of hearing and balance is represented only by the inner ear. The lateral line organ allows one to navigate in water currents, to perceive the approach or removal of a predator, prey or pack partner, and to avoid collision with underwater objects.
8) Most have external fertilization.
129. Fill in the table.
Fish organ systems.
130. Look at the picture. Write the names of the sections of the fish skeleton, indicated by numbers.
1) skull bones
2) spine
3) tail fin rays
4) ribs
5) rays of the pectoral fin
6) gill cover
131. In the drawing, color the organs of the fish digestive system with colored pencils and sign their names.
132. Sketch and label the parts circulatory system fish. What is the importance of the circulatory system?
The circulatory system of fish provides the movement of blood, which delivers oxygen to the organs and nutrients and removes metabolic products from them.
133. Study the table “Superclass Pisces. Perch structure. Consider the drawing. Write the names of the internal organs of the fish, indicated by numbers.
1) kidney
2) swim bladder
3) bladder
4) ovary
5) intestines
6) stomach
7) liver
8) heart
9) gills.
134. Look at the picture. Sign the names of the parts of the fish brain and parts of the nervous system, indicated by numbers.
1) brain
2) spinal cord
3) nerve
4) forebrain
5) midbrain
6) cerebellum
7) medulla oblongata
135. Explain how the structure and location of the nervous system of fish differ from the nervous system of hydra and beetle.
In fish, the nervous system is much more developed than in the hydra and the beetle. There is a dorsal and head mogz, consisting of departments. The spinal cord is located in the spine. Hydra has a diffuse nervous system, that is, it consists of cells scattered in the upper layer of the body. The beetle has a ventral nerve cord, with an extended oglo-pharyngeal ring and supra-oesophageal ganglion at the head end of the body, but no brain as such.
136. Complete the laboratory work "The external structure of the fish."
1. Consider the features of the external structure of the fish. Describe the shape of her body, the color of her back and abdomen.
The fish has a streamlined oblong body shape. The color of the abdomen is silver, the back is darker.
2. Make a drawing of the body of the fish, sign its departments.
See question #127.
3. Consider the fins. How are they located? How many? Write the names of the fins on the picture.
The fins of the fish are paired: ventral, anal, pectoral and unpaired: caudal and dorsal.
4. Examine the head of the fish. What sense organs are located on it?
On the head of the fish are eyes, taste buds in the mouth and on the surface of the skin, nostrils. There are 2 holes in the head inner ear, on the border between the head and the body are gill covers.
5. Look at the fish scales under a magnifying glass. Calculate the lines of annual growth and determine the age of the fish.
Scales bony, translucent, covered with mucus. The number of lines on the scales corresponds to the age of the fish.
6. Write down the features of the external structure of the fish associated with the aquatic lifestyle.
see question #128
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 weight. 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 whole body. Obviously, the main development of the brain occurs during embryonic-larval development. Of course, there are interspecies differences in relative mass brain.
The brain consists of five main regions: anterior, intermediate, middle, cerebellum and medulla oblongata ( SLIDE 6).
The structure of the brain of different fish species is different 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 a good developed vision- midbrain, in good swimmers - 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 a sedentary lifestyle, the brain is characterized by a weak development of the striatum, a small cone-shaped cerebellum, and 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 front part, it passes into back department midbrain. Its upper part - the rhomboid fossa - is covered by the ependyma, on which the posterior choroid plexus. 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 that runs under the eye along upper jaw and innervating the skin of the anterior part of the head and palate; mandibular nerve, running along the lower jaw, innervating the skin, oral mucosa 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 eye muscles,
VII - facial nerve. It is a mixed nerve, departs from the lateral 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 bottom side 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 breathing, cardiac activity, digestive apparatus and 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, great importance It has taste analyzer, 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. In blind and deep-sea fishes, they are poorly developed. On the 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 conditioned reflexes disappear into the light, but 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, innervating 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 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 extensor 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 begin (movements in a circle). 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 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.
AT thalamus distinguish between dorsal and ventral regions. In the dorsal thalamus in sharks, a number of nuclei are distinguished: external geniculate body, 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 cubic epithelium, here are located nerve cells called depth receptors. 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 in fish, there is a preoptic nucleus, the cells of which have morphological features nerve cells, but produce neurosecret.
Cerebellum. It is located in the back of the brain, partially covers the top of the medulla oblongata. Distinguish 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 it is removed or cut Bottom part cerebellum, where the lateral nucleus is located. At complete removal 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 from fish active image life (perches, pikes, etc.), causes severe violations 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 as the highest organ of integration. nervous activity. After removal of the body of the cerebellum in transverse and teleost fish, movement disorders in the form of swinging the body 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 motor and cardiac conditioned reflexes to light, sound, and interoceptive stimuli of the swim bladder can be developed in carp with a removed cerebellum on the first day after surgery.
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, which form the mantle, are repeated in general form 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 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 crucians and carps, 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 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.
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.
Representatives of this class have variations in the structure of the brain, but, nevertheless, common characteristic features can be distinguished for them. Their brain has a relatively primitive structure and is generally not big sizes.
The forebrain, or terminal, in most fish consists of one hemisphere (some sharks that lead a benthic lifestyle have two) and one ventricle. The roof does not contain nerve elements and is formed by the epithelium and only in shark nerve cells rise from the base of the brain to the sides and partly to the roof. The bottom of the brain is represented by two clusters of neurons - these are striatal bodies (corpora striata).
Anterior to the brain are two olfactory lobes (bulbs) connected by olfactory nerves to the olfactory organ located in the nostrils.
In lower vertebrates, the forebrain is a part of the nervous system that serves only the olfactory analyzer. It is the highest olfactory center.
The diencephalon consists of the epithalamus, thalamus, and hypothalamus, which are common to all vertebrates, although their degree varies. The thalamus plays a special role in the evolution of the diencephalon, in which the ventral and dorsal parts are distinguished. Later, in vertebrates, in the course of evolution, the size of the ventral part of the thalamus decreases, while the dorsal part increases. The lower vertebrates are characterized by the predominance of the ventral thalamus. Here are the nuclei that act as an integrator between the midbrain and the olfactory system of the forebrain, in addition, in lower vertebrates, the thalamus is one of the main motor centers.
Below the ventral thalamus is the hypothalamus. From below, it forms a hollow stalk - a funnel, which passes into the neurohypophysis, connected to the adenohypophysis. The hypothalamus plays a major role in hormonal regulation organism.
The epithalamus is located in the dorsal part of the diencephalon. It does not contain neurons and is associated with the pineal gland. The epithalamus, together with the pineal gland, constitutes a system of neurohormonal regulation of the daily and seasonal activity of animals.
Rice. 6. The brain of a perch (view from the dorsal side).
1 - nasal capsule.
2 - olfactory nerves.
3 - olfactory lobes.
4 - forebrain.
5 - midbrain.
6 - cerebellum.
7 - medulla oblongata.
8 - spinal cord.
9 - diamond-shaped fossa.
The midbrain of fish is relatively large. It distinguishes the dorsal part - the roof (tekum), which looks like a colliculus, and the ventral part, which is called the tegment and is a continuation of the motor centers of the brain stem.
The midbrain developed as a primary visual and seismosensory center. It contains visual and auditory centers. In addition, it is the highest integrative and coordinating center of the brain, approaching in its value to the large hemispheres of the forebrain of higher vertebrates. This type of brain, where the midbrain is the highest integrative center, is called ichthyopsid.
The cerebellum is formed from the posterior cerebral bladder and is laid in the form of a fold. Its size and shape vary considerably. In most fish, it consists of the middle part - the body of the cerebellum and of the lateral ears - the auricles. Bony fish are characterized by anterior growth - a flap. The latter in some species takes on such a large size that it can hide part of the forebrain. In sharks and bony fish, the cerebellum has a folded surface, due to which its area can reach a considerable size.
Through ascending and descending nerve fibers, the cerebellum is connected to the middle, medulla oblongata and spinal cord. Its main function is the regulation of coordination of movements, and therefore, in fish with high motor activity, it is large and can be up to 15% of the total mass of the brain.
The medulla oblongata is a continuation of the spinal cord and generally repeats its structure. The border between the medulla oblongata and the spinal cord is considered to be the place where the central canal of the spinal cord in cross section takes the form of a circle. In this case, the cavity of the central canal expands, forming the ventricle. The side walls of the latter grow strongly to the sides, and the roof is formed by an epithelial plate, in which the choroid plexus is located with numerous folds facing the cavity of the ventricle. In the side walls there are nerve fibers that provide innervation to the visceral apparatus, the organs of the lateral line and hearing. In the dorsal parts of the lateral walls there are nuclei of gray matter, in which the switching of nerve impulses occurs, coming along the ascending pathways from the spinal cord to the cerebellum, midbrain and to the neurons of the striatal bodies of the forebrain. In addition, there is also a switch of nerve impulses to descending pathways that connect the brain with the motor neurons of the spinal cord.
The reflex activity of the medulla oblongata is very diverse. It contains: respiratory center, the center of regulation of cardiovascular activity, through the nuclei of the vagus nerve, the regulation of the digestive organs and other organs is carried out.
From the brain stem (medium, medulla oblongata and pons) in fish, 10 pairs of cranial nerves depart.
