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 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 the 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 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 are composed of nerve matter, the roof is made of a thin layer 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 of the diencephalon, in the back of it is the epiphysis (endocrine gland). 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. The 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. The central part of 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, transmits excitations of nerve impulses, and is also the center of unconditioned motor reflexes.



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 an atrium and a 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 of the circulatory system of a 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 scattered top layer cell bodies. 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. Perform laboratory work"The external structure of a 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. In the head section there are 2 openings of the inner ear, on the border between the head and the body there 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

Intelligence. How your brain works Konstantin Sheremetiev

fish brain

fish brain

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

Rice. 9. Salmon

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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 in general small size.

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

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

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

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

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 big hemispheres 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, in connection with which, in fish with a high motor activity it is large and can make 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 on 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 gray matter nuclei, 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: the respiratory center, the center for the regulation of cardiovascular activity, through the nuclei of the vagus nerve, the regulation of the digestive organs and other organs is carried out.

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

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.

The brain of fish.

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

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

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

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

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

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

Spinal cord.

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