External geniculate body. Lateral geniculate body

This is the subcortical center, which ensures the transmission of information already in the visual cortex.

In humans, this structure has six layers of cells, as in the visual cortex. Fibers from the retina come crossed and uncrossed to the chiasma opticus. 1st, 4th, 6th layers receive crossed fibers. 2nd, 3rd, 5th layers are received uncrossed.

All information coming to the lateral geniculate body from the retina is ordered and the retinotopic projection is preserved. Since the fibers enter the lateral geniculate body in a comb-like manner, there are no neurons in the NKT that receive information from two retinas simultaneously. It follows from this that there is no binocular interaction in NKT neurons. Fibers from M-cells and P-cells enter the tubing. The M-path, which communicates information from large cells, transmits information about the movements of objects and ends in the 1st and 2nd layers. The P-path is associated with color information and the fibers terminate in the 3rd, 4th, 5th, 6th layers. In the 1st and 2nd layers of the tubing, the receptive fields are highly sensitive to motion and do not distinguish spectral characteristics (color). Such receptive fields are also present in small amounts in other layers of the tubing. In the 3rd and 4th layers, neurons with an OFF center predominate. It is blue-yellow or blue-red + green. In the 5th and 6th layers, neurons with ON centers are mainly red-green. The receptive fields of the cells of the lateral geniculate body have the same receptive fields as the ganglion cells.

The difference between these receptive fields and ganglion cells:

1. In the sizes of receptive fields. The cells of the lateral geniculate body are smaller.

2. Some neurons of the NKT have an additional inhibitory zone surrounding the periphery.

For cells with an ON center, such an additional zone will have a reaction sign coinciding with the center. These zones are formed only in some neurons due to increased lateral inhibition between the neurons of the NKT. These layers are the basis for the survival of a particular species. Humans have six layers, predators have four.

Detector theory appeared in the late 1950s. In the frog retina (in ganglion cells), reactions were found that were directly related to behavioral responses. Excitation of certain retinal ganglion cells led to behavioral responses. This fact made it possible to create a concept according to which the image presented on the retina is processed by ganglion cells specifically tuned to the image elements. Such ganglion cells have a specific dendritic branching that corresponds to a certain structure of the receptive field. Several types of such ganglion cells have been found. Subsequently, neurons with this property were called detector neurons. Thus, a detector is a neuron that reacts to a certain image or part of it. It turned out that other, more highly developed animals also have the ability to highlight a specific symbol.

1. Convex edge detectors - the cell was activated when a large object appeared in the field of view;

2. A moving small contrast detector - its excitation led to an attempt to capture this object; in contrast corresponds to the captured objects; these reactions are associated with food reactions;

3. Blackout detector - causes a defensive reaction (the appearance of large enemies).

These retinal ganglion cells are tuned to highlight certain elements of the environment.

A group of researchers working on this topic: Letvin, Maturano, Mokkalo, Pitz.

Neurons of other sensory systems also have detector properties. Most detectors in the visual system are associated with motion detection. Neurons have increased reactions with an increase in the speed of movement of objects. Detectors have been found in both birds and mammals. The detectors of other animals are directly connected to the surrounding space. The birds were found to have horizontal surface detectors, which is associated with the need to land on horizontal objects. Detectors of vertical surfaces have also been found, which provide the birds' own movements towards these objects. It turned out that the higher the animal in the evolutionary hierarchy, the higher the detectors are, i.e. these neurons can already be located not only in the retina, but also in the higher parts of the visual system. In higher mammals: in monkeys and humans, the detectors are located in the visual cortex. This is important because the specific way that provides responses to elements of the external environment is transferred to the higher levels of the brain, and at the same time, each animal species has its own specific types of detectors. Later it turned out that in ontogenesis the detector properties of sensory systems are formed under the influence of the environment. To demonstrate this property, experiments were done by researchers, Nobel laureates, Hubel and Wiesel. Experiments were carried out that proved that the formation of detector properties occurs in the earliest ontogeny. For example, three groups of kittens were used: one control and two experimental. The first experimental one was placed in conditions where mainly horizontally oriented lines were present. The second experimental was placed in conditions where there were mostly horizontal lines. The researchers tested which neurons formed in the cortex of each group of kittens. In the cortex of these animals, there were 50% of neurons that were activated both horizontally and 50% vertically. Animals brought up in a horizontal environment had a significant number of neurons in the cortex that were activated by horizontal objects, there were practically no neurons that were activated when perceiving vertical objects. In the second experimental group there was a similar situation with horizontal objects. The kittens of both horizontal groups had certain defects. Kittens in a horizontal environment could perfectly jump on steps and horizontal surfaces, but did not perform well relative to vertical objects (table leg). The kittens of the second experimental group had a corresponding situation for vertical objects. This experiment proved:

1) formation of neurons in early ontogenesis;

2) the animal cannot adequately interact.

Changing animal behavior in a changing environment. Each generation has its own set of external stimuli that produce a new set of neurons.

Specific features of the visual cortex

From the cells of the external geniculate body (has a 6-layer structure), axons go to 4 layers of the visual cortex. The bulk of the axons of the lateral geniculate body (NKT) is distributed in the fourth layer and its sublayers. From the fourth layer, information flows to other layers of the cortex. The visual cortex retains the principle of retinotopic projection in the same way as the LNT. All information from the retina goes to the neurons of the visual cortex. The neurons of the visual cortex, like the neurons of the underlying levels, have receptive fields. The structure of the receptive fields of neurons in the visual cortex differs from the receptive fields of the NKT and retinal cells. Hubel and Wiesel also studied the visual cortex. Their work made it possible to create a classification of the receptive fields of neurons in the visual cortex (RPNZrK). H. and V. found that RPNZrK are not concentric, but rectangular in shape. They can be oriented at different angles, have 2 or 3 antagonistic zones.

Such a receptive field can highlight:

1. change in illumination, contrast - such fields were called simple receptive fields;

2. neurons with complex receptive fields- can allocate the same objects as simple neurons, but these objects can be located anywhere in the retina;

3. supercomplex fields- can select objects that have gaps, borders or changes in the shape of the object, i.e. highly complex receptive fields can highlight geometric shapes.

Gestalts are neurons that highlight subimages.

The cells of the visual cortex can only form certain elements of the image. Where does constancy come from, where does the visual image appear? The answer was found in association neurons, which are also associated with vision.

The visual system can distinguish various color characteristics. The combination of opponent colors allows you to highlight different shades. Lateral inhibition is required.

Receptive fields have antagonistic zones. The neurons of the visual cortex are able to fire peripherally to green, while the middle is fired to the action of a red source. The action of green will cause an inhibitory reaction, the action of red will cause an excitatory reaction.

The visual system perceives not only pure spectral colors, but also any combination of shades. Many areas of the cerebral cortex have not only a horizontal, but also a vertical structure. This was discovered in the mid 1970s. This has been shown for the somatosensory system. Vertical or columnar organization. It turned out that in addition to the layers, the visual cortex also has vertically oriented columns. Improvement in registration techniques led to more subtle experiments. The neurons of the visual cortex, in addition to the layers, also have a horizontal organization. A microelectrode was passed strictly perpendicular to the surface of the cortex. All major visual fields are in the medial occipital cortex. Since the receptive fields have a rectangular organization, dots, spots, any concentric object does not cause any reaction in the cortex.

Column - type of reaction, the adjacent column also highlights the slope of the line, but it differs from the previous one by 7-10 degrees. Further studies have shown that columns are located nearby, in which the angle changes with an equal step. About 20-22 adjacent columns will highlight all slopes from 0 to 180 degrees. The set of columns capable of highlighting all the gradations of this feature is called a macrocolumn. These were the first studies that showed that the visual cortex can highlight not only a single property, but also a complex - all possible changes in a trait. In further studies, it was shown that next to the macrocolumns that fix the angle, there are macrocolumns that can highlight other image properties: colors, direction of movement, speed of movement, as well as macrocolumns associated with the right or left retina (columns of eye dominance). Thus, all macrocolumns are compactly located on the surface of the cortex. It was proposed to call sets of macrocolumns hypercolumns. Hypercolumns can analyze a feature set of images located in a local area of the retina. Hypercolumns is a module that highlights a set of features in a local area of the retina (1 and 2 are identical concepts).

Thus, the visual cortex consists of a set of modules that analyze the properties of images and create subimages. The visual cortex is not the final stage in the processing of visual information.

Properties of binocular vision (stereo vision)

These properties make it easier for both animals and humans to perceive the remoteness of objects and the depth of space. In order for this ability to manifest itself, eye movements (convergent-divergent) to the central fovea of the retina are required. When considering a distant object, there is a separation (divergence) of the optical axes and convergence for closely spaced ones (convergence). Such a system of binocular vision is presented in different animal species. This system is most perfect in those animals in which the eyes are located on the frontal surface of the head: in many predatory animals, birds, primates, most predatory monkeys.

In another part of the animals, the eyes are located laterally (ungulates, mammals, etc.). It is very important for them to have a large volume of perception of space.

This is due to the habitat and their place in the food chain (predator - prey).

With this method of perception, the perception thresholds are reduced by 10-15%, i.e. organisms with this property have an advantage in the accuracy of their own movements and their correlation with the movements of the target.

There are also monocular signs of the depth of space.

Properties of binocular perception:

1. Fusion - the fusion of completely identical images of two retinas. In this case, the object is perceived as two-dimensional, planar.

2. Fusion of two non-identical retinal images. In this case, the object is perceived three-dimensionally.

3. Rivalry of visual fields. Two different images come from the right and left retinas. The brain cannot combine two different images, and therefore they are perceived alternately.

The rest of the retinal points are disparate. The degree of disparity will determine whether the object is perceived three-dimensionally or whether it will be perceived with rivalry of fields of view. If the disparity is low, then the image is perceived three-dimensionally. If the disparity is very high, then the object is not perceived.

Such neurons were found not in the 17th, but in the 18th and 19th fields.

What is the difference between the receptive fields of such cells: for such neurons in the visual cortex, the receptive fields are either simple or complex. In these neurons, there is a difference in receptive fields from the right and left retinas. The disparity of the receptive fields of such neurons can be either vertical or horizontal (see next page):

This property allows for better adaptation.

(+) The visual cortex does not allow us to say that a visual image is formed in it, then constancy is absent in all areas of the visual cortex.

Similar information.

represents a small oblong elevation at the posterior-lower end of the visual mound on the side of the pulvinar. At the ganglion cells of the external geniculate body, the fibers of the optic tract end and the fibers of the Graziole bundle originate from them. Thus, the peripheral neuron ends here and the central neuron of the optic pathway originates.

It has been established that although most of the fibers of the optic tract end in the lateral geniculate body, still a small part of them goes to the pulvinar and anterior quadrigemina. These anatomical data formed the basis for a long-held opinion, according to which both the lateral geniculate body and the pulvinar and anterior quadrigemina were considered primary visual centers.

At present, a lot of data has accumulated that does not allow us to consider the pulvinar and the anterior quadrigemina as primary visual centers.

A comparison of clinical and pathoanatomical data, as well as embryological and comparative anatomy data, does not allow us to attribute the role of the primary visual center to pulvinar. So, according to Genshen's observations, in the presence of pathological changes in the pulvinar field of view remains normal. Brouwer notes that with an altered lateral geniculate body and an unchanged pulvinar, homonymous hemianopsia is observed; with changes in the pulvinar and unchanged lateral geniculate body, the visual field remains normal.

The same is true with anterior quadrigemina. The fibers of the optic tract form the visual layer in it and end in cell groups located near this layer. However, Pribytkov's experiments showed that enucleation of one eye in animals is not accompanied by degeneration of these fibers.

Based on all of the above, there is currently reason to believe that only the lateral geniculate body is the primary visual center.

Turning to the question of the projection of the retina in the lateral geniculate body, the following should be noted. Monakov in general denied the presence of any projection of the retina in the lateral geniculate body. He believed that all fibers coming from different parts of the retina, including papillomacular ones, are evenly distributed throughout the entire external geniculate body. Genshen back in the 90s of the last century proved the fallacy of this view. In 2 patients with homonymous lower quadrant hemianopsia, a post-mortem examination revealed limited changes in the dorsal part of the lateral geniculate body.

Ronne (Ronne) with atrophy of the optic nerves with central scotomas due to alcohol intoxication found limited changes in ganglion cells in the lateral geniculate body, indicating that the area of the macula is projected onto the dorsal part of the geniculate body.

The above observations unequivocally prove the presence of a certain projection of the retina in the external geniculate body. But the clinical and anatomical observations available in this regard are too few and do not yet give an accurate idea of the nature of this projection. The experimental studies of Brouwer and Zeman on monkeys, which we have mentioned, made it possible to study to some extent the projection of the retina in the lateral geniculate body. They found that most of the lateral geniculate body is occupied by the projection of the retinal regions involved in the binocular act of vision. The extreme periphery of the nasal half of the retina, corresponding to the monocularly perceived temporal crescent, is projected onto a narrow zone in the ventral part of the lateral geniculate body. The projection of the macula occupies a large area in the dorsal part. The upper quadrants of the retina project onto the lateral geniculate body ventro-medially; lower quadrants - ventro-laterally. The projection of the retina in the lateral geniculate body in a monkey is shown in Fig. eight.

In the outer geniculate body (Fig. 9)

Rice. nine. The structure of the external geniculate body (according to Pfeifer).

there is also a separate projection of crossed and non-crossed fibers. The studies of M. Minkowski make a significant contribution to the clarification of this issue. He established that in a number of animals after enucleation of one eye, as well as in humans with prolonged unilateral blindness, there are observed in the external geniculate body optic nerve fiber atrophy and ganglion cell atrophy. At the same time, Minkowski discovered a characteristic feature: in both geniculate bodies, atrophy with a certain regularity spreads to different layers of ganglion cells. In the lateral geniculate body of each side, layers with atrophied ganglion cells alternate with layers in which the cells remain normal. Atrophic layers on the side of enucleation correspond to identical layers on the opposite side, which remain normal. At the same time, similar layers, which remain normal on the side of enucleation, atrophy on the opposite side. Thus, the atrophy of the cell layers in the lateral geniculate body that occurs after the enucleation of one eye is definitely alternating in nature. Based on his observations, Minkowski came to the conclusion that each eye has a separate representation in the lateral geniculate body. Crossed and non-crossed fibers thus terminate at different ganglion cell layers, as is well illustrated in Le Gros Clark's diagram (Fig. 10).

Rice. ten. Scheme of the end of the fibers of the optic tract and the beginning of the fibers of the Graziola bundle in the lateral geniculate body (according to Le Gros Clark).
Solid lines are crossed fibers, dashed lines are non-crossed fibers. 1 - visual tract; 2 - external geniculate body 3 - Graziola bundle; 4 - cortex of the occipital lobe.

Minkowski's data were later confirmed by experimental and clinical and anatomical studies by other authors. L. Ya. Pines and I. E. Prigonnikov examined the lateral geniculate body 3.5 months after enucleation of one eye. At the same time, degenerative changes were noted in the ganglion cells of the central layers in the lateral geniculate body on the side of enucleation, while the peripheral layers remained normal. In the opposite side of the lateral geniculate body, inverse relationships were observed: the central layers remained normal, while degenerative changes were noted in the peripheral layers.

Interesting observations related to the case unilateral blindness long ago, was recently published by the Czechoslovak scientist F. Vrabeg. A 50-year-old patient had one eye removed at the age of ten. Postmortem examination of the lateral geniculate bodies confirmed the presence of alternating degeneration of ganglion cells.

Based on the data presented, it can be considered established that both eyes have a separate representation in the lateral geniculate body and, therefore, crossed and non-crossed fibers end in different layers of ganglion cells.

activity of one of the most important endocrine glands of the adrenal glands. The posterior commissure of the brain is part of the walls of the third ventricle.

The foreign region of the metathalamus, consisting of the external and internal geniculate bodies, is related to the conduction of visual (external geniculate bodies) and auditory (internal geniculate bodies) impulses.

The hypothalamus hypothalamus is functionally very important.

2.3 Hypodermic region (hypothalamus)

The hypothalamic region (hypothalamus) lies down from the visual hillock and is a cluster of highly differentiated nuclei, which number 32 pairs (Fig. 8).

Fig.8. Hypodermic area (scheme):

1 corpus callosum; 2 pituitary gland: 3 visual tubercle; 4 pineal gland; 5 gray bump; 6, 7, 8 nuclei of the hypothalamus

All these nuclei are divided into three groups: anterior, middle, posterior. Each group of nuclei has its own functional significance. The middle section of the nuclei includes a gray tubercle, a funnel (infundibulum) and a lower cerebral appendage of the pituitary gland.

The hypothalamic region is a complex reflex apparatus, through which the internal environment of the body adapts to external activity in a constantly changing external environment, i.e. maintaining the constancy of the internal environment (homeostasis). The area of the hypothalamus is one of the integrative links involved in the regulation of the autonomic functions of the body (ie, in the regulation of the functions of internal organs, blood circulation, respiration, metabolic processes, etc.). Certain nuclei of the hypothalamus have neurosecretory properties, i.e. secrete hormones that regulate certain organ functions. These nuclei are closely related to the pituitary gland, the main endocrine gland of the body. In the neurons of the hypothalamus, substances are formed that, when they enter the pituitary gland, regulate the release of many hormones. The hypothalamus controls the activity of all endocrine glands, more than other sex glands, the thyroid gland and adrenal glands.

The nuclei of the hypothalamic region are involved in the regulation of all types of metabolism and thermoregulation (i.e., in the regulation of body heat transfer). The hypothalamus is one of the higher centers that regulate the activity of internal organs and systems. An important role belongs to the hypothalamus in the regulation of sleep. The defeat of the hypothalamus can be accompanied by sleep and wakefulness disorders.

The hypothalamus provides human activity in accordance with the needs of the body. For example, when the body needs salt, a violation of the colloid osmotic pressure of the blood occurs. This change in the composition of the blood acts as an irritant to specific cell groups of the hypothalamus, which, in the end, is reflected in the behavioral responses of the body in accordance with the satisfaction of salt needs. Similarly, the hypothalamic region is involved in the formation of sensations of thirst and hunger.

The hypothalamus takes part in the formation of emotions and emotionally adaptive behavior. Primitive types of behavioral motivations (hunger, thirst, sleep, sexual desire) are formed with the participation of the hypothalamus. The hypothalamus provides regulation of vegetative functions and carries out vegetative coloring of all emotions.

In the depth of the hypothalamus is third ventricle.

The third ventricle has a slit-like cavity and is located in the middle plane, communicating with the lateral ventricles through the interventricular openings and with the IV ventricle through the cerebral aqueduct. The lateral walls of the third ventricle are formed by the inner surfaces of the visual tubercles. Behind the third ventricle is the pineal gland. The bottom of the ventricle is the formation of the hypothalamus, the nucleus of the middle group of nuclei, the mamillary bodies, the gray tubercle, the funnel, and the pituitary gland.

Between the subcortical nuclei of the base (the thalamus and the caudate nucleus, on the one hand, and the nucleus on the other), there is a layer of white matter called internal capsule. It is divided into three sections: the anterior femur, located between the caudate and lenticular nuclei, the posterior femur, located between the thalamus and lenticular nucleus, and the knee of the internal capsule.

The internal capsule is a very important formation. Through it pass all the conductors heading to the cortex, and the conductors coming from the cortex to the underlying parts of the nervous system.

All sensory pathways pass through the internal capsule, as well as pathways from the cortex to the underlying parts of the nervous system. Sensory pathways approach the thalamus from which their new path to the cortex begins: fibers of the third neurons of all types of sensitivity, visual pathways of the external geniculate body, auditory pathways from the internal geniculate body. From the cerebral cortex begins the frontal path of the bridge (fibers from the frontal lobe to the bridge and then to the cerebellum), the occipital-temporal path of the bridge (from the occipital and temporal lobes of the cortex to the bridge and then to the cerebellum), the general motor (pyramidal) path (from the motor zone cortex to segments of the spinal cord and to the nuclei of the motor cranial nerves), paths from the cerebral cortex to the optic tubercle.

3. The structure of the subcortical region of the brain. Brain stem, cerebellum and medulla oblongata

3.1 The structure of the brain stem

The composition of the brain stem includes the legs of the brain with the quadrigemina, the bridge of the brain with the cerebellum, the medulla oblongata (see Fig. 9).

Brain peduncles and quadrigemina develop from the mesencephalon mesencephalon (see Fig. 10).

At present, a lot of data has accumulated that does not allow us to consider the pulvinar and the anterior quadrigemina as primary visual centers.

Based on all of the above, there is currently reason to believe that only the lateral geniculate body is the primary visual center.

In the outer geniculate body (Fig. 9)

Rice. nine. The structure of the external geniculate body (according to Pfeifer).

Foreign countries or metathalamus

Metathalamus (lat. Metathalamus) is part of the thalamic region of the mammalian brain. Formed by paired medial and lateral geniculate bodies lying behind each thalamus.

The medial geniculate body is located behind the thalamus cushion; it, along with the lower hillocks of the midbrain roof plate (quadrigemina), is the subcortical center of the auditory analyzer. The lateral geniculate body is located downward from the pillow. Together with the upper mounds of the roof plate, it is the subcortical center of the visual analyzer. The nuclei of the geniculate bodies are connected by pathways with the cortical centers of the visual and auditory analyzers.

In the medial part of the thalamus, a mediodorsal nucleus and a group of midline nuclei are distinguished.

The mediodorsal nucleus has bilateral connections with the olfactory cortex of the frontal lobe and the cingulate gyrus of the cerebral hemispheres, the amygdala, and the anteromedial nucleus of the thalamus. Functionally, it is also closely connected with the limbic system and has bilateral connections with the cortex of the parietal, temporal and insular lobes of the brain.

The mediodorsal nucleus is involved in the implementation of higher mental processes. Its destruction leads to a decrease in anxiety, anxiety, tension, aggressiveness, elimination of obsessive thoughts.

The midline nuclei are numerous and occupy the most medial position in the thalamus. They receive afferent (i.e. ascending) fibers from the hypothalamus, from the raphe nuclei, the locus coeruleus of the brainstem reticular formation, and partly from the spinal-thalamic pathways as part of the medial loop. Efferent fibers from the midline nuclei are sent to the hippocampus, amygdala and cingulate gyrus of the cerebral hemispheres, which are part of the limbic system. Connections with the cerebral cortex are bilateral.

The midline nuclei play an important role in the processes of awakening and activation of the cerebral cortex, as well as in providing memory processes.

In the lateral (i.e., lateral) part of the thalamus, the dorsolateral, ventrolateral, ventral posteromedial, and posterior groups of nuclei are located.

The nuclei of the dorsolateral group have been relatively little studied. They are known to be involved in the pain perception system.

The nuclei of the ventrolateral group differ anatomically and functionally from each other. The posterior nuclei of the ventrolateral group are often considered as one ventrolateral nucleus of the thalamus. This group receives the fibers of the ascending tract of general sensitivity as part of the medial loop. Taste sensitivity fibers and fibers from the vestibular nuclei also come here. Efferent fibers, starting from the nuclei of the ventrolateral group, are sent to the cortex of the parietal lobe of the cerebral hemispheres, where they conduct somatosensory information from the whole body.

Afferent fibers from the superior colliculi of the quadrigemina and fibers in the optic tracts go to the nuclei of the posterior group (the nuclei of the thalamus cushion). Efferent fibers are widely distributed in the cortex of the frontal, parietal, occipital, temporal and limbic lobes of the cerebral hemispheres.

The nuclear centers of the thalamus cushion are involved in the complex analysis of various sensory stimuli. They play a significant role in the perceptual (associated with perception) and cognitive (cognitive, mental) activity of the brain, as well as in memory processes - the storage and reproduction of information.

The intralaminar group of the thalamic nuclei lies in the thickness of the vertical Y-shaped layer of white matter. The intralaminar nuclei are interconnected with the basal ganglia, the dentate nucleus of the cerebellum, and the cerebral cortex.

These nuclei play an important role in the activation system of the brain. Damage to the intralaminar nuclei in both thalamus leads to a sharp decrease in motor activity, as well as apathy and the destruction of the motivational structure of the personality.

The cerebral cortex, due to bilateral connections with the nuclei of the thalamus, is able to exert a regulatory effect on their functional activity.

Thus, the main functions of the thalamus are:

processing of sensory information from receptors and subcortical switching centers with its subsequent transfer to the cortex;

participation in the regulation of movements;

ensuring communication and integration of various parts of the brain

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