How many parts of the fish's brain are there? Structure of the brain of bony fish
Much more primitive nervous system higher vertebrates and consists of a central and associated peripheral and autonomic (sympathetic) nervous systems.
fish central nervous system includes the brain 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 muscles 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 and pineal glands are glands internal secretion.
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, 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 role in their lives significant role. 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 special feature of the fish spinal cord is its ability to fast regeneration and restoration of activity in case of damage. 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 associated with 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. In addition, fish can develop conditioned reflexes to light, shape, smell, sound, taste, and water temperature.
Fish are quite amenable to training and developing behavioral reactions in them.
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 consider anterior section 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.
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. 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.
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 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 front choroid plexus(vascular tectum of the third ventricle) and 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 for lungfishes and lobe-finned fish) are distinguished by an everted (inverted) structure of the hemispheres telencephalon. 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.
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 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 fibers of the optic nerves do not linger 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 the fibers of the optic nerve come to the optic lobes, and the optic lobes remain extremely important parts of the brain (however, in birds, the cerebral cortex begins to compete with the optic lobes 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. The middle part of the 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 side wall hemisphere or 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. Some bird species have been found to have better-than-average development of a portion of the neocortex, such as crows, known for their learning abilities.
Olfactory bulbs (bulbis olfactorius) located on the ventral side of the forebrain. They have small sizes and approximately triangular in shape. They enter from the front olfactory nerve.
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 brain and spinal cord).
The peripheral nervous system is divided into:
1) somatic (innervates striated muscles, provides sensitivity to the body, 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 includes five sections:
1) forebrain (telencephalon);
2) diencephalon;
3) midbrain (mesencephalon);
4) cerebellum (cerebellum);
5) medulla oblongata (myelencephalon).
Inside the parts of the brain there are cavities. The cavities of the forebrain, 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).
Forebrain in fish it is represented by two hemispheres with an incomplete septum between them and one cavity. In the forebrain, the bottom and sides consist of nervous substance, the roof in most fish is epithelial, in sharks it consists of nervous substance. The forebrain is the center of smell and regulates the functions of schooling behavior of fish. Outgrowths of the forebrain form the olfactory lobes (in cartilaginous fish) and the olfactory bulbs (in bony fish).
In the diencephalon, the bottom and side walls consist of nerve substance, the roof is made of a thin layer connective tissue. It has three parts:
1) epithalamus (supratubercular part);
2) thalamus (middle or tuberous part);
3) hypothalamus (subtubercular part).
The epithalamus forms the roof of the diencephalon, and the epiphysis (endocrine gland) is located in its posterior part. In lampreys, pineal and parapineal organs are located here, performing a photosensitive function. In fish, the parapineal organ is reduced, and the pineal organ turns into the pineal gland.
The thalamus is represented by visual hillocks,
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 gland) and the vascular sac, where the fluid that fills the ventricles of the brain is formed.
The diencephalon serves as the primary visual center; the optic nerves depart from it, which form a chiasm (decussation of nerves) in front of the infundibulum. Also, this diencephalon is the center for switching excitations that come from all parts of the brain associated with it, and through hormonal activity (epiphysis, pituitary gland) it participates in the regulation of metabolism.
The midbrain is represented by a massive base and optic lobes. Its roof consists of a nervous substance and has a cavity - the aqueduct of Sylvius. 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 substance, is responsible for coordinating movements associated with swimming, and is highly developed in fast-swimming species (shark, tuna). In lampreys, the cerebellum is poorly developed and is not distinguished as an independent section. In cartilaginous fish, the cerebellum is a hollow outgrowth of the roof of the medulla oblongata, which overlies the optic lobes of the midbrain and the medulla oblongata. In stingrays, the surface of the cerebellum is divided into 4 parts by grooves.
In the medulla oblongata, the bottom and walls consist of nerve substance, the roof is formed by a thin epithelial film, and the ventricular cavity is located inside it. Most of the brain nerves (from V to X) depart from the medulla oblongata, innervating the organs of breathing, balance and hearing, touch, sensory organs of the lateral line system, heart, digestive system. The posterior part of the medulla oblongata passes into the spinal cord.
Depending on their lifestyle, fish have differences in the development of individual parts of the brain. Thus, 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 the most developed (mackerel, flying fish, salmon), etc.
In fish, 10 pairs of nerves arise from the brain:
I. The olfactory nerve (nervus olfactorius) arises from the forebrain. In cartilaginous and some teleosts, the olfactory bulbs are adjacent directly to the olfactory capsules and are connected to the forebrain via a neural tract. In most bony fish, the olfactory bulbs are adjacent to the forebrain, and from them a nerve goes to the olfactory capsules (pike, perch).
II. The optic nerve (n. opticus) departs from the bottom of the diencephalon and forms a chiasm (chiasm), innervating the retina.
III. The oculomotor nerve (n. oculomotorius) arises from the bottom of the midbrain and innervates one of the eye muscles.
IV. The trochlear nerve (n. trochlearis) starts from the roof of the midbrain and innervates one of the eye muscles.
All other nerves begin 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 membrane oral cavity.
VI. The abducens nerve (n. abducens) innervates one of the eye muscles.
VII. The facial nerve (n. facialis) has many branches and innervates individual parts of the head.
VIII. The auditory nerve (n. acusticus) innervates inner ear.
IX. Glossopharyngeal nerve(n. glossopharyngeus) innervates the mucous membrane of the pharynx, the muscles of the first branchial arch.
X. The vagus nerve (n. vagus) has many branches and innervates the muscles of the gills, internal organs, and lateral line.
The spinal cord is located in the spinal canal formed by the upper arches of the vertebrae. In the center of the spinal cord there is a canal (neurocoel), a continuation of the ventricle of the brain. The central part of the spinal cord consists of gray matter, the peripheral part of white matter. The spinal cord has a segmental structure; from each segment, the number of which corresponds to the number of vertebrae, nerves extend from both sides.
The spinal cord, through nerve fibers, is connected to various parts of the brain, transmits excitations of nerve impulses, and is also the center of unconditioned motor reflexes.
The brain of fish is very small, amounting to thousandths of a percent of the body weight in sharks, and hundredths of a percent in bony fish and sturgeons. U small fish brain mass reaches about 1%.
The fish brain consists of 5 sections: the forebrain, intermediate, middle, cerebellum and medulla oblongata. The development of individual parts of the brain depends on the lifestyle of fish and their ecology. Thus, good swimmers (mostly pelagic fish) have a well-developed cerebellum and optic lobes. In fish with a well-developed sense of smell, the forebrain is enlarged. The fish are doing well developed vision(carnivores) – midbrain. Sedentary fish have a well-developed medulla oblongata.
The medulla oblongata is a continuation of the spinal cord. It, together with the midbrain and diencephalon, forms the brainstem. In the medulla oblongata, compared to the spinal cord, there is no clear distribution of gray and white matter. The medulla oblongata performs following functions: conductive and reflex.
The conductor function is to conduct nerve impulses between the spinal cord and other parts of the brain. Ascending pathways pass through the medulla oblongata from the spinal cord to the brain and descending paths, connecting the brain with the spinal cord.
Reflex function of the medulla oblongata. The medulla oblongata contains centers for both relatively simple and complex reflexes. Due to the activity of the medulla oblongata, the following reflex reactions are carried out:
1) regulation of breathing;
2) regulation of cardiac activity and blood vessels;
3) regulation of digestion;
4) regulation of the functioning of the taste organs;
5) regulation of chromatophores;
6) regulation of the operation of electrical organs;
7) regulation of fin movement centers;
8) regulation of the spinal cord.
The medulla oblongata contains the nuclei of six pairs of cranial nerves (V‑X).
V pair - the trigeminal nerve is divided into 3 branches: the ophthalmic nerve innervates the anterior part of the head, the maxillary nerve innervates the skin of the anterior part of the head and palate, and the mandibular nerve innervates the oral mucosa and mandibular muscles.
VI pair - the auricular nerve innervates the muscles of the eyes.
VII pair – facial nerve is divided into 2 lines: the first innervates the lateral line of the head, the second - the mucous membrane of the palate, sublingual area, taste buds of the oral cavity and muscles of the operculum.
VIII pair - auditory or sensory nerve - innervates the inner ear and labyrinth.
Pair IX - glossopharyngeal nerve - innervates the mucous membrane of the palate and the muscles of the first branchial arch.
X pair – nervus vagus is divided into two branching branches: the lateral nerve innervates the lateral line organs in the body, the nerve of the operculum innervates the gill apparatus and other internal organs.
The midbrain of fish is represented by two sections: the visual roof (tectum) - located horizontally and the tegmentum - located vertically.
The tectum or optic roof of the midbrain is swollen in the form of paired optic lobes, which are well developed in fish with high degree development of the visual organs and is poor in blind deep-sea and cave fish. On inside The tectum contains the longitudinal torus. It is associated with vision. The higher visual center of fish is located in the tegmentum of the midbrain. The fibers of the second pair of optic nerves end in the tectum.
The midbrain performs the following functions:
1) Function visual analyzer as evidenced next experiments. After removing the textum from one side of the fish's eyes, the one lying on the opposite side becomes blind. When the entire tectum is removed, complete blindness occurs. The tectum also houses the center of the visual grasping reflex, which consists in the fact that the movements of the eyes, head and torso are directed in such a way as to maximize the fixation of the food object in the area of greatest visual acuity, i.e. in the center of the retina. The tectum contains the centers of the III and IV pairs of nerves that innervate the muscles of the eyes, as well as the muscles that change the width of the pupil, i.e. performing accommodation, which allows you to clearly see objects at different distances due to the movement of the lens.
2) Participates in the regulation of fish coloration. So, after removing the tectum, the body of the fish becomes lighter, while when the eyes are removed, the opposite phenomenon is observed - darkening of the body.
3) In addition, the tectum is closely connected with the cerebellum, hypothalamus, and through them with the forebrain. Therefore, the tectum coordinates the functions of the somatosensory (balance, posture), olfactory and visual systems.
4) The tectum is connected with the VIII pair of nerves, which perform acoustic and receptor functions, and with the V pair of nerves, i.e. trigeminal nerves.
5) Afferent fibers from the lateral line organs, from the auditory and trigeminal nerves approach the midbrain.
6) The tectum contains afferent fibers from the olfactory and taste receptors.
7) In the midbrain of fish there are centers for regulating movement and muscle tone.
8) The midbrain has an inhibitory effect on the centers of the medulla oblongata and spinal cord.
Thus, the midbrain regulates a number of vegetative functions body. Due to the midbrain, the reflex activity of the body becomes diverse (orienting reflexes to sound and visual stimuli appear).
Diencephalon. The main structure of the diencephalon is the visual thalamus. Under the visual thalamus is the subtubercular region - the epithalamus, and under the thalamus is the subtubercular region - the hypothalamus. The diencephalon in fish is partially covered by the roof of the midbrain.
The epithalamus consists of the pineal gland, a rudiment of the parietal eye, which functions as endocrine gland. The second element of the epithalamus is the frenulum (habenula), which is located between the forebrain and the roof of the midbrain. The frenulum is the connecting link between the pineal gland and the olfactory fibers of the forebrain, i.e. participates in the functions of light reception and smell. The epithalamus is connected to the midbrain through efferent nerves.
The thalamus (visual thalamus) in fish is located in the central part of the diencephalon. In the visual thalamus, especially in the dorsal part, many nuclear formations were found. The nuclei receive information from receptors, process it and transmit it to certain areas of the brain, where corresponding sensations arise (visual, auditory, olfactory, etc.). Thus, the thalamus is an organ of integration and regulation of the body’s sensitivity, and also takes part in the implementation of motor reactions of the body.
When the visual tuberosities are damaged, there is a decrease in sensitivity, hearing, and vision, which causes a loss of coordination.
The hypothalamus consists of an unpaired hollow protrusion - a funnel, which forms a vascular sac. The vascular sac responds to changes in pressure and is well developed in deep-sea pelagic fish. The vascular sac is involved in the regulation of buoyancy, and through its connection with the cerebellum, it participates in the regulation of balance and muscle tone.
The hypothalamus is the main center where information from the forebrain arrives. The hypothalamus receives afferent fibers from taste endings and from the acoustic system. Efferent nerves from the hypothalamus go to the forebrain, to the dorsal thalamus, tectum, cerebellum and neurohypophysis, i.e. regulates their activities and influences their work.
The cerebellum is an unpaired formation, it is located in the back of the brain and partially covers the medulla oblongata. The body of the cerebellum is distinguished ( middle part) and cerebellar ears (i.e. two lateral sections). The anterior end of the cerebellum forms the valve.
In fish leading a sedentary lifestyle (for example, in bottom fish such as scorpion fish, gobies, anglers), the cerebellum is underdeveloped in comparison with fish leading active image life (pelagic, such as mackerel, herring or predators - pike perch, tuna, pike).
Functions of the cerebellum. At complete removal the cerebellum in active fish shows a decline muscle tone(atony) and impaired coordination of movements. This was expressed in the circular swimming of the fish. In addition, the fish’s reaction to painful stimuli weakens, sensory disturbances occur, and tactile sensitivity disappears. After approximately three to four weeks, the lost functions are restored due to the regulatory processes of other parts of the brain.
After removal of the cerebellar body in bony fishes, movement disorders in the form of body swaying from side to side. After removal of the body and valve of the cerebellum, motor activity is completely disrupted, and trophic disorders develop. This indicates that the cerebellum also regulates metabolism in the brain.
It should be noted that the cerebellar ears reach large sizes in fish that have a well-developed lateral line. Thus, the cerebellum is the place of closure of conditioned reflexes coming from the lateral line organs.
Thus, the main functions of the cerebellum are coordination of movement, normal distribution muscle tone and regulation of autonomic functions. The cerebellum exerts its influence through the nuclear formations of the midbrain and medulla oblongata, as well as motor neurons of the spinal cord.
The forebrain of fish consists of two parts: the mantle or cloak and the striatum. The mantle, or the so-called cloak, lies dorsally, i.e. from above and from the sides in the form of a thin epithelial plate above the striatum. In the anterior wall of the forebrain there are olfactory lobes, which are often differentiated into the main part, stalk and olfactory bulb. The mantle receives secondary olfactory fibers from the olfactory bulb.
Functions of the forebrain. The forebrain of fish performs the olfactory function. This is evidenced, in particular, by the following experiments. When the forebrain is removed, fish experience a loss of developed conditioned reflexes to olfactory stimuli. In addition, removal of the forebrain of fish leads to a decrease in their motor activity and to a decrease in pack conditioned reflexes. The forebrain also plays an important role in the sexual behavior of fish (when it is removed, sexual desire disappears).
Thus, the forebrain is involved in the defensive reaction, the ability to swim in schools, the ability to care for offspring, etc. It has a general stimulating effect on other parts of the brain.
7. Principles of reflex theory I.P. Pavlova
Pavlov's theory is based on the basic principles of conditioned reflex activity of the brain of animals, including fish:
1. The principle of structure.
2. The principle of determinism.
3. Principle of analysis and synthesis.
The principle of structure is as follows: each morphological structure corresponds to a specific function. The principle of determinism is that reflex reactions have strict causality, i.e. they are deterministic. For the manifestation of any reflex, a reason, a push, an impact from outside world or the internal environment of the body. Analytical and synthetic activity of the central nervous system is carried out due to the complex relationships between the processes of excitation and inhibition.
According to Pavlov's theory, the activity of the central nervous system is based on a reflex. A reflex is a causally determined (deterministic) reaction of the body to changes in the external or internal environment, carried out with the obligatory participation of the central nervous system in response to irritation of receptors. This is how the emergence, change or cessation of any activity of the body occurs.
Pavlov divided all reflex reactions of the body into two main groups: unconditioned reflexes and conditioned reflexes. Unconditioned reflexes are innate, inherited reflex reactions. Unconditioned reflexes appear in the presence of a stimulus without special, special conditions(swallowing, breathing, salivation). Unconditioned reflexes have ready-made reflex arcs. Unconditioned reflexes are divided into different groups according to a number of characteristics. By biological trait They are divided into food (search, intake and processing of food), defensive (defensive reaction), sexual (animal behavior), orientation (orientation in space), postural (adopting a characteristic pose), locomotor (motor reactions).
Depending on the location of the irritated receptor, exteroceptive reflexes are distinguished, i.e. reflexes that occur when irritated outer surface body (skin, mucous membranes), interoreceptive reflexes, i.e. reflexes that occur when internal organs are irritated, proprioceptive reflexes that occur when receptors in skeletal muscles, joints, and ligaments are irritated.
Depending on the part of the brain that is involved in the reflex reaction, the following reflexes are distinguished: spinal (spinal cord) - the centers of the spinal cord are involved, bulbar - the centers of the medulla oblongata, mesencephalic - the centers of the midbrain, diencephalic - the centers of the diencephalon.
In addition, reactions are divided according to the organ that is involved in the response: motor or locomotor (muscle is involved), secretory (endocrine or exocrine gland is involved), vasomotor (vessel is involved), etc.
Unconditioned reflexes are specific reactions. They are characteristic of all representatives of this species. Unconditioned reflexes are relatively constant reflex reactions, stereotypical, unchangeable, inert. As a result, it is impossible to adapt to changing living conditions only through unconditioned reflexes.
Conditioned reflexes are a temporary nervous connection of the body with any stimulus from the external or internal environment of the body. Conditioned reflexes are acquired during the individual life of an organism. They are not the same among different representatives of a given species. Conditioned reflexes do not have ready-made reflex arcs; they are formed under certain conditions. Conditioned reflexes are changeable, easily arise and also easily disappear, depending on the conditions in which the given organism is located. Conditioned reflexes are formed on the basis of unconditioned reflexes under certain conditions.
For the formation of a conditioned reflex, it is necessary to combine two stimuli in time: indifferent (indifferent) for a given type of activity, which will later become a conditioned signal (knocking on glass) and an unconditioned stimulus that causes a certain unconditioned reflex (food). The conditioned signal always precedes the action of the unconditioned stimulus. Reinforcement of the conditioned signal with an unconditioned stimulus must be repeated. It is necessary that the conditioned and unconditioned stimuli meet the following requirements: the unconditioned stimulus must be biologically strong (food), the conditioned stimulus must have moderate optimal strength (knock).
8. Fish behavior
The behavior of fish becomes more complex during their development, i.e. ontogeny. The simplest reaction of the fish body in response to a stimulus is kinesis. Kinesis is an increase in motor activity in response to adverse influences. Kinesis is already observed at late stages embryonic development fish when there is a decrease in oxygen content in the environment. In this case, increasing the movement of larvae in the egg or in water helps improve gas exchange. Kinesis promotes the movement of larvae from poor habitats to better ones. Another example of kinesis is the random movement of schooling fish (top fish, uklya, etc.) when a predator appears. This confuses him and prevents him from focusing on one fish. This can be considered a defensive reaction of schooling fish.
A more complex form of fish behavior is taxis - this is the directed movement of fish in response to a stimulus. There are positive taxis (attraction) and negative taxis (avoidance). An example is phototaxis, i.e. fish reaction to the light factor. Thus, anchovy and big-eyed sprat have positive phototaxis, i.e. are well attracted to light, forming clusters, which makes it possible to use this property in fishing for these fish. In contrast to the Caspian sprat, the mullet exhibits negative phototaxis. Representatives of this species of fish strive to get out of the illuminated background. This property is also used by humans when fishing for this fish.
An example of negative phototaxis can be the behavior of salmon larvae. During the day they hide among stones and gravel, which allows them to avoid predators. And the larvae of carp fish exhibit positive phototaxis, which allows them to avoid stifling deep-sea areas and find more food.
Taxi directions may be subject to change age-related changes. Thus, salmon fry at the pied stage are typical bottom-dwelling sedentary fish, protecting their territory from their own kind. They avoid light, live among stones, and easily change color to match environment, when frightened, they are able to hide. As they grow before moving into the sea, they change color to a non-silver color, gather in flocks, and lose aggressiveness. When frightened, they quickly swim away, are not afraid of light, and, on the contrary, stay near the surface of the water. As you can see, the behavior of juveniles of this species changes to the opposite with age.
Fish, unlike higher vertebrates, lack a cerebral cortex, which has leading value in the development of conditioned reflexes. However, fish are capable of producing them without it, for example, a conditioned reflex to sound (Frolov’s experiment). After the action of the sound stimulus, the current was turned on a few seconds later, to which the fish reacted with body movement. After a certain number of repetitions, the fish, without waiting for the action of the electric current, responded to the sound, i.e. reacted with body movement. In this case, the conditioned stimulus is sound, and the unconditioned stimulus is the induction current.
Unlike higher animals, fish have less developed reflexes and are unstable and difficult to develop. Fish are less capable of differentiation than higher animals, i.e. distinguish between conditioned stimuli or changes in the external environment. It should be noted that in bony fish conditioned reflexes are developed faster and they are more persistent than in others.
There are works in the literature that show fairly persistent conditioned reflexes, where the unconditioned stimuli are a triangle, a circle, a square, various letters, etc. If you place a feeder in a reservoir that gives a portion of food in response to pressing a lever, tugging a bead or other devices, then the fish master this device quickly enough and receive food.
Those who are involved in aquarium fish farming have observed that when approaching the aquarium, fish gather at the feeding area in anticipation of food. This is also a conditioned reflex, and in this case you are the conditioned stimulus; knocking on the glass of an aquarium can also serve as a conditioned stimulus.
In fish hatcheries, fish are usually fed at certain times of the day, so they often gather in certain areas at feeding time. Fish also quickly get used to the type of food, the method of distributing food, etc.
Big practical significance may have the development of conditioned reflexes to a predator in the conditions of fish hatcheries and NVH in juvenile commercial fish, which are then released into natural reservoirs. This is due to the fact that in the conditions of fish hatcheries and fisheries, juveniles have no experience of communicating with enemies and in the early stages become prey for predators until they receive an individual and spectacular experience.
Using conditioned reflexes, they study various aspects of the biology of various fish, such as the spectral sensitivity of the eye, the ability to distinguish silhouettes, the effect of various toxicants, the hearing of fish by the strength and frequency of sound, thresholds of taste sensitivity, the role of various departments nervous system.
In the natural environment, the behavior of fish depends on their lifestyle. Schooling fish have the ability to coordinate maneuvers when feeding, when they see a predator, etc. Thus, the appearance of a predator or food organisms at one edge of the flock causes the entire flock to react accordingly, including individuals who did not see the stimulus. The reaction can be very varied. So, at the sight of a predator, the flock instantly scatters. You can observe this in the spring in the coastal zone of our reservoirs; the fry of many fish are concentrated in schools. This is one of the types of imitation. Another example of imitation is following the leader, i.e. for an individual whose behavior lacks elements of oscillation. Leaders are most often individuals who have extensive individual experience. Sometimes even a fish of another species can serve as such a leader. Thus, carp quickly learn to take food on the fly if trout or carp individuals who know how to do this are placed next to them.
When fish live in groups, a “social” organization with dominant and subordinate fish may arise. Thus, in a flock of Mozambian tilapia, the main one is the most intensely colored male, the next ones in the hierarchy are lighter. Males, no different in color from females, are subordinate and do not participate in spawning at all.
The sexual behavior of fish is very diverse, including elements of courtship and competition, nest building, etc. Complex spawning and parental behavior is characteristic of fish with low individual fecundity. Some fish take care of eggs, larvae and even fry (guard the nest, aerate the water (pike perch, smelt, catfish)). The juveniles of some fish species feed near their parents (for example, discus even feed the juveniles with their mucus). The young of some fish species hide in their parents' mouth and gill cavities (tilapia). Thus, the plasticity of fish behavior is very diverse, as can be seen from the above materials.
Questions for self-control:
1. Features of the structure and function of nerves and synapses.
2. Parabiosis how special kind localized excitation.
3. Scheme of the structure of the nervous system of fish.
4. Structure and functions of the peripheral nervous system.
5. Features of the structure and function of parts of the brain.
6. Principles and essence of reflex theory.
7. Peculiarities of fish behavior.
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 olfactory nerve or pairs 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. Optic nerve 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 internal muscles eyes and thereby ensure its focusing on the subject. 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.