Thirst for knowledge, striving for higher ideals, phenomenal mental abilities… We are talking, of course, about a person. It is these qualities that distinguish us from the animal world. The material carrier, in other words, the hard disk, on which the psychosomatic programs that we have named, are recorded, are the cerebral hemispheres. This article will be devoted to the study of their structure and functions.
Big Brain
Organogenesis - the formation of a system of axial organs and other parts of the body in the human embryo - includes the stage of neurula. The notochord, intestines and neural tube appear immediately after the formation of the third germ layer - the mesoderm. The neural folds closing on the dorsal side of the embryo form the neural tube. Subsequently, it is completely separated from the rest of the ectoderm zone. The anterior end of the neural tube swells and divides into five parts - the primary cerebral vesicles. Now the main sections of the central nervous system will be formed from them.
The cerebral hemispheres and the cortex, whichcovers, phylogenetically are the youngest structures of the brain, as they arose later than other departments.
Architectonics of the cerebral cortex
Both hemispheres - right and left - are interconnected by the corpus callosum. It is not only a physical carrier of nerve endings - axons, performing the function of a stranded conducting organ containing a huge number of nerve endings.
The structure also carries the centers of motor and behavioral acts, and its pathology is expressed, for example, in the appearance of symptoms of a severe mental disorder - epilepsy.
The large hemispheres on the outside consist of accumulations of bodies of neurons - highly specialized cells of the nervous tissue. Visually, the upper structure of the brain has a gray color, which is why it is called: the gray matter of the brain. Inside, numerous processes branch off from it - dendrites. Together with very long fibers of axons that penetrate into the tissues of the cortex, dendrites form white matter, located under the zones of the cerebral cortex. In it, like a mosaic, clusters of neuron bodies, called nuclei, are scattered. In anatomy, it is customary to define this part of the brain as the subcortex. It is considered an ancient formation that arose already among the first representatives of vertebrates.
The structure of the cerebral hemispheres
In order to increase the total area of the brain while maintaining a small volume of the cranium, almost two-thirds of the surface is hidden in the form of folds. They are called convolutions. In anatomical atlases, there are threemain:
- lateral furrow,
- occipital-parietal,
- central.
The four lobes of the cerebral cortex are easy to distinguish from them. These are the temporal, occipital, frontal, parietal lobes, they anatomically correspond to the parts of the skull.
The unique internal structure of the bark, similar to a six-story house. Each floor - a layer - consists of neurons that are completely different in appearance, density and shape. Let's list these layers:
- inner pyramidal,
- polymorphic,
- inner grainy,
- pyramidal,
- outer grainy,
- molecular.
The postembryonic period of cortical development seems interesting. It has been established that the greatest changes occur in the first, and then in the six-month and one-and-a-half-year intervals of a child's life.
Sensory and motor areas of the brain
The areas of the cerebral hemispheres are responsible for the many-sided and complex life of the human body. A huge number of newly emerging reflex arcs, acting as material carriers of conditioned reflexes, are constantly created in the cerebral cortex. The five main sensory complexes - the olfactory system, visual, tactile, gustatory and auditory - are the channels through which we receive the greatest amount of various information. In addition to them, we are able to differentiate sensations of thirst, pain, temperature, spatial arrangement of the body, hunger.
Science clearly defines the boundaries of each of the listed zones,their characteristics are studied when considering the structure of each type of analyzers. In them, the areas of the cerebral hemispheres in which discrimination of sensations occurs are called the central or cortical section of any analyzer. For example, the visual sensory system includes, in addition to the receptors of the retina and two optic nerves, also the visual cortex located in the occipital lobe.
How motor reactions are controlled
The main zone that controls muscle work is located in the precentral gyrus of the cerebral hemispheres. Axons of efferent neurons emerge from this site and go to the skeletal muscles, causing contractions of actin and myosin myofibrils. The innervation of the main motor zone occurs according to the collateral principle: the muscles of the body part opposite to the brain hemisphere are excited. The exception is the facial area, which is directly innervated.
Additionally, there is another motor area in the brain located below the precentral gyrus. Contractions of skeletal muscles can also occur in the case of excitation of sensory zones, especially visual and auditory. For example, a sharp, sudden sound may cause the hands or head to shake.
Associative Zones
The most important functions of integrating various sensations that arise under the influence of signals from the outside world are performed by several sections of the right and left lobes of the cerebral hemispheres. Anatomically, they are located in the prefrontalassociation area, as well as in areas of the parietal-occipital-temporal part of the cortex. Associative zones are receivers of pulses coming from several analyzers at once.
Further, nerve cells analyze the received information and send excitation to certain parts of the body through their centrifugal axons, causing its mixed visual-auditory and motor reactions. For example, the zone of speech understanding (Wernicke's area) is the leading one not only in the process of formation of speech functions, but also ensures the development of higher properties of the intellect. In the upper occipital and posterior parietal lobes there is an associative zone that analyzes the position of the body in space.
Zones for naming objects and primary reading processing
There is another area in the cerebral cortex called the primary reading processing area. This zone can perceive impulses coming from the visual and auditory sensory systems. The area for naming objects is located in the temporal lobe and in the lateral part of the anterior zone of the occipital lobe, receives information from the auditory analyzer. At the same time, part of the impulses from the visual zone, located in the occipital region of the cerebral cortex, is connected. Both zones are the basis for the development of higher mental processes: abstract thinking, analysis and synthesis of the received visual and auditory information, which underlie human intellectual activity.
Basic processes of the cortex
Excitation and inhibition are the most important phenomena inherent innervous tissue. The neurons of the cerebral hemispheres, which form certain zones, distribute (radiate) electrical impulses to other brain structures. For example, the deterioration of falling asleep in a person sitting in front of a computer monitor for a long time is explained by the irradiation of the excitation of the visual center of the brain to its neighboring areas. The very process of falling asleep will serve as an example of the irradiation of inhibition. The concentration of nervous processes leads to opposite results: the zone of excitation or inhibition, on the contrary, reduces its area. The concentration of excitation is observed, for example, by an air traffic controller during work related to ensuring the takeoff or landing of an aircraft.
Induction is the induction of the opposite nervous process in a certain area of the cerebral hemispheres.
Thus, positive induction stimulates the strengthening of excited areas of the brain near the center of inhibition. Negative induction is characterized by the opposite course of nervous processes. In a unit of time, the brain receives a huge number of signals from the receptors of all organs and systems. All the above processes occurring in the cerebral cortex are the root cause of behavioral reactions in both higher mammals and humans.
In our article, we examined the structure and functions of the cortex covering the cerebral hemispheres, and also identified the most important functions of brain areas.
