The middle brain: functions and structure. Functions of the midbrain and cerebellum

In the process of studying how the brain changed in the course of evolution, a concept was developed about the presence of its three levels. The first of them (the highest one) is the front department. It includes the basal subcortical nodes, the cortex of the large hemispheres, the diencephalic department and the olfactory brain. The middle section refers to the average level. And the lower part belongs to the posterior part, which consists of the medulla oblongata, the cerebellum and the variolium bridge.

The middle brain, the functions and structure of which we will consider in detail, develops mainly under the influence of the visual receptor in the process of phylogenesis. Consequently, the most important of its formations are related to the innervation of the eye.

Also in it centers of hearing were formed, in the future, together with the centers of vision, the roofs of the midbrain that had grown and formed 4 hills. We will discuss it in detail below. And the functions of the middle brain are described in the second half of this article.

Development of the midbrain

The visual and auditory centers in it became subcortical, intermediate, subordinate to the appearance in humans and higher animals of the cortical end of the visual and auditory analyzers in the cortex of the forebrain. The development of the forebrain in man and higher mammals led to the fact that the conducting paths connecting the cortex of the final with the dorsal cortex began to pass through the middle brain, whose functions changed somewhat. As a result, in the latter there are:

- subcortical auditory centers;

- visual subcortical centers, as well as nuclei of nerves, which innervate the muscles of the eye;

- all descending and ascending conducting paths that connect the cerebral cortex with the spinal cord and pass through the middle transit;

- bundles of white matter that connect the middle brain with different parts of the central nervous system.

Structure

The middle brain, the functions and structure of which we are interested in, is the most simply arranged and the smallest department (in the photo above it is indicated in brown color). It distinguishes the following 2 main parts:

- legs, where mainly conductive paths pass;

- subcortical centers of vision and hearing.

The roof of the midbrain

The roof of the midbrain, the dorsal part, is hidden under the corpus callosum (its posterior end). It is subdivided into 4 hamlets arranged in pairs by means of two grooves (transverse and longitudinal), going cross-wise. The two upper hills are subcortical centers of vision, and the two lower ones are hearing. Between the upper tubercles in the flat groove is the pineal body. The handle of the knoll is directed laterally, upward and anteriorly, to the intermediate brain. Every mound goes into it. The handle of the upper mound goes beneath the thalamus pillow towards the lateral geniculate body. The lower handle disappears under the elbowed medial body. The bent bodies, named above, refer not to the middle, but to the intermediate brain.

Legs of the brain

We continue to describe the human brain, functions and structure. The next thing we'll stop on is his legs. What is it? This is the ventral part, in which are all the conducting paths leading to the anterior brain. Note that the legs represent two semi-cylindrical thick white strands that diverge at an angle from the edge of the bridge and are submerged in the hemisphere.

What is the midbrain cavity?

Many terms can be found in a section such as the anatomy of the midbrain. The structure, its functions require in describing strict scientific accuracy. We omitted the complex Latin names, leaving only the basic terms. For the first acquaintance, this is enough.

Say a few words about the cavity of the midbrain. It is a narrow channel and is called a water pipe. This channel is lined with ependyma, it is narrow, its length is 1.5-2 cm. The brain drain connects the fourth ventricle with the third. The lid of the legs limits it ventrally, and dorsally - the roof of the midbrain.

Parts of the midbrain in cross section

Let's continue our story. The characteristics of the human midbrain can be better understood by considering it also on a transverse section. In this case, the following 3 main parts are distinguished in it:

- cover plate;

- tire;

- the ventral part, that is, the base of the leg.

The nuclei of the midbrain

Under the influence of the visual receptor according to how the middle brain is developed, there are various nuclei in it. The functions of the nuclei of the midbrain refer to the innervation of the eye. The upper dichotomy in lower vertebrates is the main place in which the optic nerve terminates, and also the main visual center. In humans and mammals, with the transfer to the forefront of the visual centers, the connection that remains between the upper mound and the optic nerve is important only for the reflexes. In the geniculate medial body, as well as in the nucleus of the lower hillock, the fibers of the auditory loop terminate. The roof of the midbrain is connected with a dorsal bilateral connection. The plate of this roof can be considered a reflex center for movements that arise mainly under the influence of auditory and visual stimuli.

The brain drain

It is surrounded by a central gray matter, which in its function is related to the vegetative system. Under the ventral wall, in the cover of the brain stem, there are the nuclei of two cranial motor nerves.

The nucleus of the oculomotor nerve

It consists of several departments of innervation of various muscles of the eyeball. Behind and medially from it there is a pair small additional vegetative nucleus, and also the median unpaired nucleus. The unpaired median and additional nucleus innervate the eye muscles, which are involuntary. We refer this part of the oculomotor nerve to the parasympathetic system. The rostralnee (above) nucleus of the nerve of the oculomotor locates the nucleus of the longitudinal medial fascicle in the brain stem cover.

Legs of the brain

They are divided into the base of the leg (ventral part) and the tire. Black matter serves as a boundary between them. Its color is due to melanin - the black pigment, which is contained in the nerve cells that make up it. The cover of the midbrain is part of it, located between the black matter and the roof. From it departs the central tire path. This is the descending projection neural pathway, which is located in the cover of the midbrain (its central part). In its composition - the fibers that go from the red nucleus, pale sphere, the reticular formation of the brain of the middle and thalamus to the olive and the reticular formation of the medulla oblong. This path is part of the extrapyramidal system.

Functions of the midbrain

He plays a very important role in the formation of rectification and adjustment reflexes, which make walking and standing possible. In addition, the middle brain function has the following: it regulates muscle tone, takes part in its distribution. And this is a necessary condition for the implementation of coordinated movements. Another function is the regulation of a number of vegetative processes (swallowing, chewing, breathing, blood pressure). Due to watchful auditory and visual reflexes, as well as an increase in the tone of flexor muscles, the middle brain (in the photo above it is highlighted in red) prepares the body to respond to a sudden irritation. Statokinetic and static reflexes are realized at its level. Tonic reflexes provide restoration of balance, posture, which was broken as a result of the change in position. They appear when the position of the head and body in space changes due to the excitation of proprioceptors, as well as the tactile receptors on the skin. All these functions of the midbrain indicate that it plays an important role in the body.

Cerebellum

We now turn to the consideration of the cerebellum. What is it? This is the structure of the rhomboid brain. It is formed in ontogenesis from the cerebral rhomboid bladder (its dorsal wall). It is associated with various departments of the nervous system that control our movements. Its development occurs along the path of improving connections with the spinal cord, as well as weakening them with the vestibular system.

Research Luigi Luciani

The functions of the midbrain and the cerebellum were studied by Luigi Luciani, an Italian physicist. In 1893 he put experiments on animals with a fully or partially removed cerebellum. He also conducted an analysis of his bioelectric activity, registering it with irritation and at rest.

It turned out that the tone of the extensor muscles increases when half of the cerebellum is removed. The extremities of the animal are stretched, the trunk is bent, and the head deviates into the operated side. Circumstances ("maneuvers") occur in the operated side. The described disturbances are gradually smoothed out, however, a certain discoordination of motions persists.

If you remove the entire cerebellum, you experience severe movement disorders. They are smoothed out gradually due to the activation of the cerebral cortex (its motor zone). However, the animal still remains in violation of coordination. There are inaccurate, awkward, sweeping movements, a shaky walk.

Contribution of Academician Orbeli

In 1938, Academician Orbeli discovered that the cerebellum also affects the receptor apparatus, vegetative processes. In addition, there is a connection with the state of the muscles of the internal organs. Changes in blood composition, blood circulation, respiration, digestion, which occur under the influence of the cerebellum, are aimed at providing (trophic) activity of skeletal muscles.

Academician Orbeli cerebellum viewed not only as an assistant cerebral cortex in regulating muscle movements and tone, but also as an adaptation-trophic center. In this role, it affects all parts of the brain through the nervous system (sympathetic department). So the metabolism is regulated, and the CNS adapts to the environmental conditions. It was found that the activity of the cerebellum is inextricably linked to the cortex of the cerebral hemispheres and occurs under its control.

Conclusion

So, we briefly reviewed the cerebellum and the human brain. Their functions were described by us. Now you know what an important role they play. Our body is generally arranged in such a way that all its organs perform their work, they are all necessary. The functions of the medulla and the midbrain, as well as other parts of the body, should be known.

And in conclusion a few more words. The brain is a complex aggregate consisting of billions of cells working together. It supports life in a flexible and unique, but unchanging way and is able to respond to changing incentives, behavioral guidelines and needs. As we change from childhood to childhood, and then to adolescence, maturity and old age, our body makes the same path with us. Accordingly, the brain changes. It follows, on the one hand, rigidly programmed evolutionary and ontogenetic schemes of development. But on the other hand, it is able to adapt to changing interactions between the external environment and the body.