There are many classes of different animals in nature. One of them is fish. Many people do not even suspect that these representatives of the animal world have a brain. Read about its structure and features in the article.
Historical background
For a long time, almost 70 million years ago, the oceans were inhabited by invertebrates. But fish, the first to acquire a brain, exterminated a significant number of them. Since then, they have dominated the water space. The modern fish brain is very complex. Indeed, it is difficult to follow some kind of 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 themselves were born. At the same time, they overcome huge distances, and they have no map. This is possible thanks to this variant of behavior, when certain parts of the brain are like a camera with a timer. The principle of operation of the device is as follows: there comes a moment when the diaphragm works. Images that are in front of the camera remain onfilm. So it is with fish. They are guided in their behavior 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 mode of behavior, that is, imprinting, has been preserved, but the scope of its important forms has narrowed. A person, for example, has retained sexual skills.
Divisions of the brain in fish
This organ of this class is small. Do fish have a brain? 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 - hundredths, in small fish it is about one percent. The brain of fish has a peculiarity: the larger the individuals, the smaller it is.
The family of stickleback fish that live in Lake Mivan, Iceland, has a brain, the size of which depends on the sex of the individuals: the female has a smaller brain, the male has a larger one.
The brain of a fish has five sections. These include:
- Forebrain, consisting of two hemispheres. Each of them controls the sense of smell and schooling behavior of fish.
- The midbrain, from which the nerves that respond to stimuli depart, due to which the eyes move. This is the eye of the fish. It regulates body balance and muscle tone.
- The cerebellum is the organ responsible for movement.
- The medulla oblongata is the most important department. Performs many functions and is responsible for different reflexes.
Divisions of the fish brain do not develop in the same way. This is influenced by the imagelife of aquatic inhabitants and the state of the environment. So, for example, pelagic species, having excellent skills of movement in water, have a well-developed cerebellum, as well as vision. The structure of the brain of a fish 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 eyesight are of medium size, sedentary representatives of the class are oblong.
Intermediate brain
It owes its formation to the thalamus, which is also called the thalamus. Their location is the central part of the brain. The thalamus has many formations in the form of nuclei, which transmit the received information to the brain of the fish. It has various sensations associated with smell, sight, hearing.
The main function of the thalamus is to integrate and regulate the body's sensitivity. It is also involved in the reaction by which fish are able to move around. If the thalamus is damaged, the level of sensitivity decreases, coordination is disturbed, and vision and hearing also decrease.
Anterior Brain
It contains a mantle, as well as striatal bodies. The mantle is sometimes called a cloak. The location is the top and sides of the brain. The cloak looks like thin epithelial plates. Striped bodies are located under 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 onirritants. Physical activity decreases, attraction to the opposite sex disappears.
- Protective-defensive. It manifests itself in the fact that representatives of the Pisces class maintain a flock of life, take care of their offspring.
Medium brain
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 visual lobes arranged in pairs. In fish with a high organization, they are better developed than in cave and deep-sea representatives with poor eyesight. Another department is located vertically, it is called the tegmentum. It contains the highest visual center. What are the functions of the midbrain?
- If you remove the visual roof from one eye, the other goes blind. The fish loses its sight when the roof is completely removed, in which the visual grasping reflex is located. Its essence lies in the fact that the head, body, eyes of the fish move in the direction of food objects, which are imprinted on the retina.
- The midbrain of a fish fixes coloration. When the upper roof is removed, the body of the fish becomes lighter, and when the eyes are removed, it darkens.
- Has a connection with the forebrain and cerebellum. Coordinates the work of a number of systems: somatosensory, visual and olfactory.
- The composition of the middle part of the body includes centers that regulate movement and maintain muscle tone.
- The brain of a fish makes reflex activity diverse. First of all, it affects the reflexes associated with stimuli.visual and sound character.
Elongated brain
He takes part in the formation of the organ trunk. The medulla oblongata of fish is arranged 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 work of the heart and blood vessels, digestion, and the movement of the fins. Thanks to this function, the activity of the organs of taste 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 dorsal to the cephalic, which lead to the descending tracts that link them.
Cerebellum
This unpaired formation is located in the back of the brain. The cerebellum partially covers the medulla oblongata. Consists of a middle part (body) and two ears (side sections).
Performs a number of functions:
- Coordinates movements and maintains normal muscle tone. If the cerebellum is removed, these functions are impaired, the fish begin to swim in circles.
- Provides the implementation of motor activity. When the body of the cerebellum of the fish is removed, it begins to swing in different directions. If you also remove the damper, the movement is completely disrupted.
- The cerebellum regulates metabolism. This body influences othersections of the brain through the nucleoli located in the spinal cord and medulla oblongata.
Spinal cord
Its location is the nerve 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 sides between pairs of vertebrae. Through them, irritating signals enter the spinal cord. They innervate the surface of the body, the muscles of the trunk and internal organs. What is the brain of a fish? Head and dorsal. The gray matter of the latter is inside it, the white is outside.
