Fish brain. Nervous system of fish Medulla oblongata in fish functions

The nervous system of fish, like all other spinal vertebrates, is divided into central and peripheral. The central nervous system includes the brain and spinal cord. The peripheral includes nerve cells and fibers.

Brain

The fish brain is divided into three large parts: the forebrain, the midbrain and the hindbrain. The forebrain consists of the telencephalon (the telencephalon) and the diencephalon (the diencephalon). At the rostral (anterior) end of the telencephalon are the olfactory bulbs, which receive signals from the olfactory receptors. The olfactory lobes contain neurons (components of the olfactory nerve, or pairs of cranial nerves) that attach to the olfactory regions of the telencephalon, also called the olfactory lobes. The olfactory bulbs are usually enlarged in fish that actively use their sense of smell, such as sharks.

The diencephalon includes the epithalamus, thalamus and hypothalamus; it mainly performs regulatory functions in controlling the state of the internal environment of the body. The pineal organ, which contains neurons and photoreceptors, is located at the distal end of the pineal gland and is part of the epithalamus. In many species, the pineal organ is sensitive to light, which penetrates the bones of the skull, and can perform many specific functions, including the regulation of circadian rhythms of activity. The optic nerve (II pair of cranial nerves), which goes to the brain from the retina, enters the diencephalon and extends fibers to the thalamus, hypothalamus and midbrain.

The midbrain consists of the optic lobes and the tegmentum, or tegmentum; both structures are involved in processing optical signals. The optic nerve has numerous fibers that extend to the optic lobes; Similar to the olfactory lobes, large optic lobes are observed in the brains of fish that rely heavily on vision. The main function of the tegmentum is to control the internal muscles of the eye, which ensure focusing on an object. The tegmentum also performs part of the active control functions: for example, the locomotor region of the midbrain, which generates rhythmic swimming movements, is localized here.

The hindbrain consists of the cerebellum, the pons, and the medulla. The cerebellum is an unpaired organ. The function of the cerebellum is to maintain balance and control the position of the body in the environment. The pons and medulla oblongata form the brain stem. A large number of cranial nerves carry sensory information to the medulla oblongata and carry signals generated in it to the muscles. In general, most cranial nerves enter the skull through the hindbrain. The III, IV, and VI pairs of cranial nerves control the six external muscles of the eye, which carry out the movements of this organ. The V pairs of cranial nerves (trigeminal) receive sensory information and transmit responsive signals to the mandible, and the VII pairs (facial) carry sensory information from the hyoid arch structures. The VIII pair of cranial nerves (auditory) contains sensory fibers that are involved in hearing and maintaining balance. The ninth pair of cranial nerves (glossopharyngeal nerve) nerves the pharyngeal arch, conducting both sensory and dexterous signals. The X pair of cranial nerves (vagus nerve) nerves more caudally (closer to the posterior end of the body) where the branchial arches and internal organs are located.

Spinal cord

The spinal cord runs within the neural arches of the vertebrae along the entire length of the fish's spine. Similar to the myomeres in the spine, segmentation is observed in the structure of the spinal cord. In each body segment, sensory neurons enter the spinal cord through the dorsal roots, and sensory neurons exit through the ventral roots. Interneurons, which are located within the central nervous system, conduct information signals between sensory and dexterous neurons, as well as between neurons in the brain.

In nature there are many classes of different animals. One of them is fish. Many people don't even realize that these representatives of the animal kingdom have a brain. Read about its structure and features in the article.

Historical reference

Long ago, almost 70 million years ago, the World Ocean was inhabited by invertebrates. But fish, being the first to acquire a brain, destroyed a significant number of them. Since then they have dominated the waters. The modern fish brain is very complex. Indeed, it is difficult to follow a behavior without a program. The brain solves this problem using different options. Pisces preferred imprinting, when the brain is ready for the behavior that it sets at a certain point in its development.

For example, salmon have an interesting feature: they swim to spawn in the river in which they were born. At the same time, they cover enormous distances, and they do not have any map. This is possible thanks to this type of behavior, when certain parts of the brain are like a camera with a timer. The principle of operation of the device is this: there comes a moment when the diaphragm is triggered. Once in front of the camera, the images remain on film. So it is with fish. They are guided in their behavior precisely by images. Imprinting determines the individuality of fish. If given the same conditions, their different breeds will behave differently. In mammals, the mechanism of this method of behavior, that is, imprinting, has been preserved, but the scope of its important forms has narrowed. In humans, for example, sexual skills have been preserved.

Parts of the brain in fish

This organ in this class is small in size. Yes, in a shark, for example, its volume is equal to thousandths of a percent of the total body weight, in sturgeon and bony fish it is hundredths, and in small fish it is about one percent. The fish brain has a peculiarity: the larger the individuals, the smaller it is.

The stickleback fish family, which lives in Lake Mivan in Iceland, has a brain whose size depends on the sex of the individuals: females have a smaller brain, males have a larger one.

The fish brain has five sections. These include:

• Forebrain, consisting of two hemispheres. Each of them controls the sense of smell and schooling behavior of fish.
• midbrain, from which the nerves that respond to stimuli arise, causing the eyes to move. This is the center of vision for fish. It regulates body balance and muscle tone.
• Cerebellum- organ responsible for movement.
• Medulla is the most important department. Performs many functions and is responsible for different reflexes.

The parts of the fish brain do not develop equally. This is influenced by the lifestyle of aquatic inhabitants and the state of the environment. For example, pelagic species, having excellent movement skills in water, have a well-developed cerebellum, as well as vision. The structure of the fish brain is such that representatives of this class with a developed sense of smell are distinguished by an increased size of the forebrain, predators with good vision are of medium size, and sedentary representatives of the class are distinguished by an oblong brain.

Intermediate brain

It owes its formation to which are also called thalamus. Their location is the central part of the brain. The thalami have many formations in the form of nuclei, which transmit the received information to the fish’s brain. It contains various sensations associated with smell, vision, and hearing.

The main thing is the integration and regulation of the body's sensitivity. It is also involved in the reaction that allows fish to move. If the thalamus is damaged, the level of sensitivity decreases, coordination is impaired, and vision and hearing also decrease.

Forebrain

It consists of a mantle, as well as striped bodies. The mantle is sometimes called a cloak. The location is the top and sides of the brain. The cloak has the appearance of thin epithelial plates. are located underneath it. The forebrain of fish is designed to perform functions such as:

• Olfactory. If this organ is removed from fish, they lose the conditioned reflexes developed to stimuli. Motor activity decreases, attraction to the opposite sex disappears.
• Protective and defensive. It manifests itself in the fact that representatives of the Pisces class maintain a gregarious lifestyle and take care of their offspring.

The brain is average

It consists of two departments. One of them is the visual roof, which is called the tectum. It is located horizontally. It looks like swollen optic lobes arranged in pairs. In fish with high organization, they are better developed than in cave and deep-sea representatives with poor vision. The other section is located vertically, it is called the tegmentum. It contains the highest visual center. What functions does the midbrain perform?

• If you remove the visual roof from one eye, the other goes blind. The fish loses its vision when the roof, in which the visual grasping reflex is located, is completely removed. Its essence lies in the fact that the head, body, and eyes of the fish move in the direction of food objects, which are imprinted on the retina.
• The fish's midbrain records coloration. When the upper roof is removed, the body of the fish becomes lighter, and if the eyes are removed, it darkens.
• It has connections with the forebrain and cerebellum. Coordinates the work of a number of systems: somatosensory, visual and olfactory.
• The middle part of the organ includes centers that regulate movement and maintain muscle tone.
• The fish brain makes reflex activity diverse. First of all, this affects reflexes associated with visual and auditory stimuli.

Brain oblongata

It takes part in the formation of the organ trunk. The medulla oblongata of fish is designed in such a way that substances, gray and white, are distributed without a clear boundary.

Performs the following functions:

• Reflex. The centers of all reflexes are located in the brain, the activity of which ensures the regulation of breathing, the functioning of the heart and blood vessels, digestion, and the movement of fins. Thanks to this function, the activity of the taste organs is carried out.
• Conductor. It lies in the fact that the spinal cord and other parts of the brain conduct nerve impulses. The medulla oblongata is the site of the ascending tracts from the spinal cord to the brain, which go to the descending tracts connecting them.

Cerebellum

This formation, which has an unpaired structure, is located in the back part and partially covers the medulla oblongata. Consists of a middle part (body) and two ears (lateral sections).

Performs a number of functions:

• Coordinates movements and maintains normal muscle tone. If the cerebellum is removed, these functions are disrupted and the fish begin to swim in circles.
• Ensures the implementation of motor activity. When the body of the cerebellum is removed, the fish begins to swing in different directions. If you also remove the damper, movements are completely disrupted.
• The cerebellum regulates metabolism. This organ influences other parts of the brain through nucleoli located in the spinal cord and medulla oblongata.

Spinal cord

Its location is the neural arches (more precisely, their canals) of the fish spine, consisting of segments. The spinal cord in fish is a continuation of the medulla oblongata. Nerves extend from it to the right and left between pairs of vertebrae. They carry irritating signals to the spinal cord. They innervate the surface of the body, trunk muscles and internal organs. What kind of brain do fish have? Head and back. The gray matter of the latter is located inside it, the white matter is outside.

127. Draw a diagram of the external structure of the fish. Label its main parts.

128. List the structural features of fish associated with an aquatic lifestyle.
1) Streamlined torpedo-shaped body, flattened in the lateral or dorsal-abdominal (in benthic fish) directions. The skull is motionlessly connected to the spine, which has only two sections - the trunk and the caudal.
2) Bony fish have a special hydrostatic organ - a swim bladder. As a result of changes in its volume, the buoyancy of the fish changes.
In cartilaginous fish, body buoyancy is achieved by the accumulation of fat reserves in the liver, and less often in other organs.
3) The skin is covered with placoid or bony scales, rich in glands that abundantly secrete mucus, which reduces friction of the body with water and performs a protective function.
4) Respiratory organs - gills.
5) Two-chamber 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 activity of fish depends on water temperature.
6) Body buds.
7) The sensory organs of fish are adapted to function in the aquatic environment. The flat cornea and almost spherical lens allow fish to see only close objects. The sense of smell is well developed, allowing it to stay in a 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 water currents, perceive the approach or distance of a predator, prey or school partner, and avoid collisions with underwater objects.
8) For the majority - external fertilization.

129. Fill out the table.

Fish organ systems.

130. Look at the drawing. Write the names of the sections of the fish skeleton indicated by numbers.

1) skull bones
2) spine
3) rays of the caudal fin
4) ribs
5) rays of the pectoral fin
6) gill cover

131. In the drawing, use colored pencils to color the organs of the fish’s digestive system and write their names.

132. Draw and label the parts of the circulatory system of a fish. What is the significance of the circulatory system?

The circulatory system of fish ensures the movement of blood, which delivers oxygen and nutrients to the organs and removes metabolic products from them.

133. Study the table “Superclass Pisces. The structure of the perch." Look at 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 drawing. Write the names of the parts of the fish's 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 differs from the nervous system of hydra and beetle.
Fish have a much more developed nervous system than hydra and beetles. There is a spinal and cephalic brain, consisting of sections. 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 expanded ologopharyngeal ring and a suprapharyngeal ganglion at the head end of the body, but there is no brain as such.

136. Complete laboratory work “External structure of fish.”
1. Consider the features of the external structure of the fish. Describe the shape of its body, the color of its back and abdomen.
The fish has a streamlined, oblong body shape. The color of the abdomen is silver, the back is darker.
2. Draw a drawing of the fish’s body and label its sections.
See question #127.
3. Examine the fins. How are they located? How many are there? Label the names of the fins in the picture.
The fish has paired fins: ventral, anal, pectoral and unpaired: caudal and dorsal.
4. Examine the fish's head. What sense organs are located on it?
On the head of the fish there are eyes, taste buds in the mouth and on the surface of the skin, and nostrils. In the head section there are 2 openings of the inner ear; at the border between the head and the body there are gill covers.
5. Examine the scales of the fish under a magnifying glass. Calculate the annual growth lines and determine the age of the fish.
The scales are 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 No. 128

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

fish central nervous system includes 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 the muscles of the internal organs and blood vessels of the heart.

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

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

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

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

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

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

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

One of the well-known manifestations of the nervous system of a fish is the reflex. For example, if they are always in the same place in a pond or aquarium, then they will accumulate in this particular place. 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.