In the process of studying how the brain changed in the course of evolution, an idea was developed that there were three levels of it. The first of these (highest) is the anterior section. It includes the basal basal ganglia, the cerebral cortex, the diencephalic region, and the olfactory brain. The middle section belongs to the middle level. And the lower part belongs to the posterior region, which consists of the medulla oblongata, cerebellum and pons.
The midbrain, 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. Therefore, its most important formations are related to the innervation of the eye.
Also, hearing centers were formed in it, later, together with the centers of vision, they grew and formed 4 mounds of the roof of the midbrain. We will consider its structure in detail below. And the functions of the midbrain are described in the second half of this article.
Midbrain development
The visual and auditory centers located in it became subcortical, intermediate, hittinga subordinate position with the appearance in humans and higher animals of the cortical end of the visual and auditory analyzers in the forebrain cortex. The development of the forebrain in humans and higher mammals led to the fact that the pathways connecting the terminal cortex with the spinal cord began to pass through the midbrain, the functions of which changed somewhat. As a result of this, the latter contains:
- subcortical auditory centers;
- visual subcortical centers, as well as the nuclei of the nerves that innervate the muscles of the eye;
- all descending and ascending pathways that connect the cerebral cortex with the spinal cord and pass through the middle transit;
- bundles of white matter connecting the midbrain with various parts of the central nervous system.
Building
The midbrain, the functions and structure of which we are interested in, is the simplest and smallest department (in the photo above it is indicated in brown). It has the following 2 main parts:
- legs, where the conducting paths mainly pass;
- subcortical centers of vision and hearing.
Midbrain Roof
The roof of the midbrain, the dorsal part, is hidden under the corpus callosum (its posterior end). It is subdivided into 4 mounds located in pairs by means of two grooves (transverse and longitudinal) running crosswise. The two upper mounds are the subcortical centers of vision, and the two lower ones are hearing centers. Between the upper tubercles in a flat groove is the pineal gland. The handle of the mound is directed laterally, upward andanteriorly, to the diencephalon. Every mound passes into it. The handle of the superior colliculus runs under the pillow of the thalamus towards the lateral geniculate body. The handle of the lower one disappears under the geniculate medial body. The geniculate bodies named above no longer belong to the middle, but to the diencephalon.
Brain legs
We continue to describe the human midbrain, functions and structure. The next thing we will focus on is his legs. What is it? This is the ventral part, in which all the pathways leading to the forebrain are located. Note that the legs are two semi-cylindrical thick white strands, diverging at an angle from the edge of the bridge and plunging into the hemispheres.
What is the midbrain cavity?
Many terms can be found in a section such as the anatomy of the midbrain. Its structure, functions require it in the description of strict scientific accuracy. We have omitted complex Latin names, leaving only the basic terms. This is enough for the first acquaintance.
Let's say a few words about the midbrain cavity. 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 cerebral aqueduct connects the fourth ventricle with the third. The cover 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 features of the human midbrain can be better understood by examining it in a transverse section. In this case, the following 3 main parts are distinguished in it:
-cover plate;
- tire;
- ventral section, that is, the base of the leg.
Mesencephalon nuclei
Under the influence of the visual receptor, according to how the midbrain is developed, there are various nuclei in it. The functions of the nuclei of the midbrain relate to the innervation of the eye. The superior colliculus in lower vertebrates is the main site where the optic nerve ends, as well as the main visual center. In humans and mammals, with the transfer of visual centers to the forebrain, the connection remaining between the superior colliculus and the optic nerve is important only for reflexes. In the geniculate medial body, as well as in the nucleus of the inferior colliculus, the fibers of the auditory loop terminate. The roof of the midbrain is connected to the spinal cord by a two-way 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.
Plumbing the brain
It is surrounded by a central gray matter, which in its function belongs to the vegetative system. Under its ventral wall, in the tegmentum of the brain stem, are the nuclei of two cranial motor nerves.
Oculomotor nucleus
It consists of several departments of innervation of various muscles of the eyeball. Behind and medially from it there is a paired small additional vegetative nucleus, as well as a median unpaired one. The unpaired median and accessory nuclei innervate the muscles of the eye, which are involuntary. We refer this part of the oculomotor nerve to the parasympathetic system. Rostral (higher)the nucleus of the oculomotor nerve is located in the tegmentum of the brain stem, the nucleus of the longitudinal medial bundle.
Brain legs
They are divided into the base of the leg (ventral part) and the tire. The black substance serves as the boundary between them. It owes its color to melanin, a black pigment found in the nerve cells that make it up. The midbrain tegmentum is the part of it located between the black substance and the roof. The central tire path departs from it. This is a descending projection nerve path, which is located in the tegmentum of the midbrain (its central part). It contains fibers that go from the red nucleus, the pale ball, the reticular formation of the middle brain and the thalamus to the olive and the reticular formation of the medulla oblongata. This pathway is part of the extrapyramidal system.
Midbrain Functions
It plays a very important role in the formation of rectifying and positioning reflexes that make walking and standing possible. In addition, the midbrain has the following functions: it regulates muscle tone, takes part in its distribution. And this is a necessary condition for the implementation of coordinated movements. Another function is that thanks to it, a number of vegetative processes are regulated (swallowing, chewing, breathing, blood pressure). Due to sentinel auditory and visual reflexes, as well as an increase in the tone of the flexor muscles, the midbrain (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, a posture that has been disturbed as a result of a change in position. They appear when the position of the head and body in space changes due to the excitation of proprioreceptors, as well as tactile receptors located on the skin. All these functions of the midbrain indicate that it plays an important role in the body.
Cerebellum
Now let's move on to the consideration of the cerebellum. What is it? This is the structure of the rhomboid brain. It is formed in ontogeny from the cerebral rhomboid bladder (its dorsal wall). It is associated with various parts 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 by Luigi Luciani
The functions of the midbrain and cerebellum were studied by Luigi Luciani, an Italian physicist. In 1893, he experimented on animals with a completely or partially removed cerebellum. He also analyzed his bioelectrical activity, registering it during stimulation and at rest.
It turned out that the tone of the extensor muscles increases when half of the cerebellum is removed. The limbs of the animal are extended, the body is bent, and the head is deviated to the operated side. There are movements in a circle ("manege movements") in the operated direction. The described violations are gradually smoothed out, however, a certain discoordinationmovement is saved.
If the entire cerebellum is removed, pronounced movement disorders occur. They are smoothed out gradually due to the fact that the cerebral cortex (its motor zone) is activated. However, the animal still remains with impaired coordination. There are inaccurate, awkward, sweeping movements, a wobbly gait.
Contribution of Academician Orbeli
In 1938, academician Orbeli discovered that the cerebellum also affects the receptor apparatus, the vegetative processes. In addition, its connection with the state of the muscles of the internal organs is observed. Changes in the composition of blood, circulation, respiration, digestion, which occur under the influence of the cerebellum, are aimed at ensuring (trophic) activity of skeletal muscles.
Academician Orbeli considered the cerebellum not only as an assistant to the cerebral cortex in regulating muscle movements and tone, but also as an adaptive-trophic center. In this role, it affects all parts of the brain through the nervous system (sympathetic). This is how metabolism is regulated, and the central nervous system adapts to environmental conditions. It was found that the activity of the cerebellum is inextricably linked with the cortex of the cerebral hemispheres and occurs under its control.
Conclusion
So, we briefly reviewed the cerebellum and the human midbrain. Their functions have been 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 theirwork, they are all needed. The functions of the medulla oblongata and midbrain, as well as other parts of the body, should be known.
And finally, a few more words. The brain is a complex unit, consisting of billions of cells working together. It sustains life in a flexible and unique yet unchanging way and is able to respond to changing stimuli, behaviors and needs. As we move through life from infancy to childhood, and then to youth, adulthood, and old age, so does our body. Accordingly, the brain changes. On the one hand, it follows rigidly programmed evolutionary and ontogenetic patterns of development. But on the other hand, it is able to adapt to changing interactions between the external environment and the body.
