External geniculate body. The structure of the external geniculate body Foreign countries or metathalamus

Anatomically, the LCT belongs to the metathalamus, its dimensions are 8.5 x 5 mm. The cytoarchitecture of the LCT is determined by its six-layer structure, which is found only in higher mammals, primates and humans.
Each LCT contains two main nuclei: dorsal (upper) and ventral (lower). There are six layers of nerve cells in the LCT, four layers in the dorsal nucleus and two in the ventral nucleus. In the ventral part of the LCT, the nerve cells are larger and respond in a special way to visual stimuli. The nerve cells of the dorsal nucleus of the LCT are smaller and similar to each other histologically and in electrophysiological properties. In this regard, the ventral layers of the LCT are called large cell (magnocellular), and the dorsal layers are called small cell (parvocellular).
The parvocellular structures of the LCT are represented by layers 3, 4, 5, 6 (P-cells); magnocellular layers - 1 and 2 (M cells). The axon endings of magno- and parvocellular ganglion cells of the retina are morphologically different, and therefore in different layers of LCT nerve cells there are synapses that differ from each other. Magnaxon terminals are radially symmetrical, have thick dendrites and large ovoid endings. Parvoaxon terminals are elongated, have thin dendrites and medium-sized round terminal endings.
The LCT also contains axon terminals with a different morphology, belonging to other classes of retinal ganglion cells, in particular the blue-sensitive cone system. These axon terminals create synapses in a heterogeneous group of LCT layers collectively called “koniocellular” or K layers.
Due to the intersection of optic nerve fibers in the chiasm from the right and left eyes, nerve fibers from the retinas of both eyes enter the LCT on each side. The endings of the nerve fibers in each of the layers of the LCT are distributed in accordance with the principle of retinotopic projection and form a projection of the retina onto the layers of nerve cells of the LCT. This is facilitated by the fact that 1.5 million LCT neurons with their dendrites provide a very reliable connection of synaptic impulse transmission from 1 million axons of retinal ganglion cells.
In the geniculate body, the projection of the central fossa of the macula is most fully represented. The projection of the visual pathway into the LCT contributes to the recognition of objects, their color, movement and stereoscopic depth perception (primary center of vision).

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In functional terms, the receptive fields of LCT neurons have a concentric shape and are similar to similar fields of retinal ganglion cells, for example, the central zone is excitatory, and the peripheral, ring zone is inhibitory. LCT neurons are divided into two classes: with an on-center and with an off-center (darkening of the center activates the neuron). LCT neurons perform various functions.
Pathological processes localized in the area of ​​the chiasm, optic tract and LCT are characterized by symmetrical binocular loss of the visual field.

These are true hemianopsias, which, depending on the location of the lesion, can be:

• homonymous (same name) right- and left-sided,
• heteronymous (different names) - bitemporal or binasal,
• altitudinal - upper or lower.

Visual acuity in such neurological patients decreases depending on the degree of damage to the papillomacular bundle of the optic pathway. Even with unilateral damage to the visual pathway in the LCT area (right or left), the central vision of both eyes is affected. In this case, one feature is noted that has important differential diagnostic significance. Pathological foci located peripherally from the LCT give positive scotomas in the field of view and are felt by patients as a darkening of vision or a vision of a gray spot. In contrast to these lesions, lesions located above the LCT, including lesions in the occipital lobe of the brain, usually produce negative scotomas, i.e., are not perceived by patients as visual impairment.

The lateral geniculate bodies are switches for signals from the anterior colliculus.

Through the anterior nuclei of the thalamus to the limbic cortex cerebral hemispheres olfactory and visceral reception is transmitted. The areas of visceral reception are located in morphological proximity to the nuclei that perceive exteroceptor signals. Hence the appearance of so-called referred pain. It is known that diseases of the internal organs cause a painful increase in the sensitivity of certain areas of the skin. Thus, pain in the heart associated with an attack of angina pectoris “radiates” to the left shoulder, under the shoulder blade.

The ventrolateral nuclei serve as switches for signals from the brainstem and cerebellum to the anterior central gyrus of the cerebral cortex. The posterior ventral nucleus receives impulses from the lemniscal sensory pathway, which carries signals from the Gaul and Burdach nuclei of the medulla oblongata and the spinothalamic tract. From here they go to the posterior central gyrus of the cerebral cortex.

The associative nuclei of the thalamus are located mainly in its anterior part (pulmonary nucleus, dorsal and lateral nuclei). They transmit impulses from the switching nuclei to the association zones of the cortex. The thalamus also functions as a subcortical pain center. In its nuclei, information from receptors is processed and pain sensations are formed.

“Human Physiology”, N.A. Fomin

The subcortical nuclei include the caudate nucleus, globus pallidus and putamen. They are located in the thickness of the cerebral hemispheres, between frontal lobes and diencephalon. The embryonic origin of the caudate nucleus and putamen is the same, so they are sometimes spoken of as a single body - the striatum. The globus pallidus, phylogenetically the most ancient formation, is separated from the striatum and morphologically, ...

Irritation of the globus pallidus causes slow tonic contractions of skeletal muscles. The globus pallidus acts as a collector connecting the striatum with the nuclei of the hypothalamus, brainstem and thalamus. The globus pallidus also plays an important role in the regulation of hemodynamics. Destruction of the striatum causes in animals a decrease in sensitivity to tactile and painful stimuli. Orienting reflexes are lost, and “emotional dullness” appears. Memory processes are disrupted:...

Corticoreticular connections: A - diagram of the pathways of ascending activating influences; B - diagram of descending influences of the cortex; Cn - specific afferent pathways to the cortex with collaterals to the reticular formation (according to Magun). The brain and spinal cord exert two forms of regulatory influences: specific and nonspecific. A specific regulatory system includes nerve pathways that conduct efferent impulses from all receptors, centers...

The reticular formation increases the excitability of spinal cord motor neurons that regulate the activity of muscle spindles. As a result, the muscle spindles send a constant stream of impulses to the spinal cord and excite α-motoneurons. In turn, the flow of impulses from α-motoneurons maintains constant skeletal muscle tone. Regulatory tonic influences come from the tectum of the brain along two pathways of the reticulospinal tract, which conduct nerve signals with different...

The cerebellum coordinates complex motor acts and voluntary movements. The efferent influences of the cerebellum through the superior peduncles are directed to the red nucleus of the midbrain, to the nuclei of the thalamus and hypothalamus, to the subcortical nodes and to the motor zone of the cerebral cortex. Through the red nuclear spinal tract, the cerebellum regulates the activity of spinal cord motor neurons. Afferent impulses enter the cerebellum through the inferior and middle peduncles. By…

It is a small oblong elevation at the posterior-inferior end of the optic thalamus, lateral to the pulvinar. The ganglion cells of the lateral geniculate body end with the fibers of the optic tract and the fibers of the Graziole bundle originate from them. Thus, the peripheral neuron ends here and the central neuron of the visual pathway begins.

It has been established that although most of the fibers of the optic tract end in the external geniculate body, a small part of them goes to the pulvinar and the anterior quadrigeminal. These anatomical data served as the basis for the opinion, widespread for a long time, according to which both the external geniculate body and the pulvinar and anterior quadrigemale were considered primary visual centers.

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

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

The situation is similar with anterior quadrigeminal. 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 everything stated 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, it is necessary to note the following. Monakov in general denied the presence of any retinal projection 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 external geniculate body. Genshen proved the fallacy of this view back in the 90s of the last century. In 2 patients with homonymous lower quadrant hemianopia, during postmortem examination, he found limited changes in the dorsal part of the lateral geniculate body.

Ronne, in atrophy of the optic nerves with central scotomas due to alcohol intoxication, found limited changes in ganglion cells in the external geniculate body, indicating that the macula area projects to the dorsal part of the geniculate body.

The above observations undoubtedly prove the presence of a certain projection of the retina in the lateral geniculate body. But the clinical and anatomical observations available in this regard are too few in number and do not yet provide accurate ideas about the nature of this projection. The experimental studies we mentioned by Brouwer and Zeman on monkeys made it possible to study to some extent the projection of the retina in the lateral geniculate body. They found that most of the external geniculate body is occupied by the projection of the retinal sections 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 superior quadrants of the retina project ventromedially to the lateral geniculate body; lower quadrants - ventro-lateral. The projection of the retina in the external geniculate body in a monkey is shown in Fig. 8.

In the external geniculate body (Fig. 9)

Rice. 9. The structure of the external geniculate body (according to Pfeiffer).

there is also a separate projection of crossed and uncrossed fibers. The research of M. Minkowski makes a significant contribution to clarifying this issue. He found that in a number of animals after enucleation of one eye, as well as in humans with prolonged one-sided blindness, there are observed in the external geniculate body atrophy of optic nerve fibers and ganglion cell atrophy. Minkowski discovered at the same time characteristic feature: in both geniculate bodies, atrophy spreads with a certain pattern to various layers of ganglion cells. In the external geniculate body of each side, layers with atrophied ganglion cells alternate with layers in which the cells remain normal. The atrophic layers on the enucleation side correspond to identical layers on the opposite side, which remain normal. At the same time, similar layers that remain normal on the enucleation side atrophy on the opposite side. Thus, the atrophy of the cell layers in the external geniculate body that occurs after 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 external geniculate body. The crossed and uncrossed fibers thus terminate at different layers of ganglion cells, as is well depicted in Le Gros Clark's diagram (Fig. 10).

Rice. 10. Diagram of the end of the fibers of the optic tract and the beginning of the fibers of the Graziole bundle in the external geniculate body (according to Le Gros Clark).
Solid lines are crossed fibers, broken lines are uncrossed fibers. 1 - visual tract; 2 - external geniculate body 3 - Graziole bundle; 4 - occipital lobe cortex.

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

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

Based on the above data, it can be considered established that both eyes have separate representation in the external geniculate body and, therefore, crossed and uncrossed fibers end in different layers of ganglion cells.

Lateral geniculate body

Lateral geniculate body(external geniculate body, LCT) - an easily recognizable brain structure that is located on the lower lateral side of the thalamic cushion in the form of a fairly large flat tubercle. In the LCT of primates and humans, six layers are morphologically defined: 1 and 2 - layers of large cells (magnocellular), 3-6 - layers of small cells (parvocellular). Layers 1, 4 and 6 receive afferents from the contralateral (located in the hemisphere opposite to the LCT) eye, and layers 2, 3 and 5 - from the ipsilateral (located in the same hemisphere as the LCT).

Schematic diagram of primate LCT. Layers 1 and 2 are located more ventrally, closer to the incoming fibers of the optic tract.

The number of LCT layers involved in processing the signal coming from retinal ganglion cells varies depending on the eccentricity of the retina:

• - when the eccentricity is less than 1º, two parvocellular layers are involved in the processing;
• - from 1º to 12º (blind spot eccentricity) - all six layers;
• - from 12º to 50º - four layers;
• - from 50º - two layers connected to the contralateral eye

There are no binocular neurons in the LCT of primates. They appear only in the primary visual cortex.

Literature

1. Hubel D. Eye, brain, vision / D. Hubel; Per. from English O. V. Levashova and G. A. Sharaeva. - M.: “Mir”, 1990. - 239 p.
2. Morphology nervous system: Textbook. manual / D.K. Obukhov, N.G. Andreeva, G.P. Demyanenko and others; Rep. ed. V. P. Babmindra. - L.: Science, 1985.- 161 p.
3. Erwin E. Relationship between laminar topology and retinotopy in the rhesus lateral geniculate nucleus: results from a functional atlas / E. Erwin, F.H. Baker, W. F. Busen et al. // Journal of Comparative Neurology.- 1999.- Vol.407, No. 1.- P.92-102.

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See what “Lateral geniculate body” is in other dictionaries:

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Lateral geniculate body (LCT)- The main sensory center of vision, located in the thalamus, a region of the brain that plays the role of the main switching device in relation to incoming sensory information. Axons emanating from the LCT enter the visual area of ​​the occipital lobe of the cortex... Psychology of sensations: glossary

geniculate body lateral- (p. g. laterale, PNA, BNA, JNA) K. t., lying on the lower surface of the thalamus lateral to the handle of the superior colliculus of the quadrigeminal: the location of the subcortical center of vision ... Large medical dictionary

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External geniculate body (corpus genicu-latum laterale) is the location of the so-called “second neuron” of the visual pathway. About 70% of the fibers of the optic tract pass through the external geniculate body. The external geniculate body is a hill corresponding to the location of one of the nuclei of the optic thalamus (Fig. 4.2.26-4.2.28). It contains about 1,800,000 neurons, on the dendrites of which the axons of the retinal ganglion cells end.

It was previously assumed that the lateral geniculate body is just a “relay station”, transmitting information from retinal neurons through the optic radiation to the cerebral cortex. It has now been shown that quite significant and diverse processing of visual information occurs at the level of the lateral geniculate body. The neurophysiological significance of this formation will be discussed below. Initially it is necessary

Rice. 4.2.26. Model of the left lateral geniculate body (after Wolff, 1951):

A- rear and inside views; b - rear and external view (/ - optic tract; 2 - saddle; 3 - visual radiance; 4 - head; 5 - body; 6 - isthmus)

Let us dwell on its anatomical features.

The nucleus of the external geniculate body is one of the nuclei of the thalamus opticus. It is located between the ventroposteriolateral nucleus of the optic thalamus and the cushion of the optic thalamus (Fig. 4.2.27).

The external geniculate nucleus consists of the dorsal and phylogenetically more ancient ventral nuclei. The ventral nucleus in humans is preserved as a rudiment and consists of a group of neurons located rostral to the dorsal nucleus. In lower mammals, this nucleus provides the most primitive photostatic reactions. The fibers of the optic tract do not approach this nucleus.

The dorsal nucleus makes up the main part of the nucleus of the lateral geniculate body. It is a multilayer structure in the form of a saddle or an asymmetrical cone with a rounded top (Fig. 4.2.25-4.2.28). A horizontal section shows that the external geniculate body is connected anteriorly with the optic tract, on the lateral side with the retrolenticular part of the internal capsule, medially with the middle geniculate body, posteriorly with the hippocampal gyrus, and posteriolaterally with the inferior horn of the lateral ventricle. Adjacent to the nucleus of the external geniculate body is the cushion of the visual thalamus, anterolaterally - temporopontine fibers and the posterior part of the internal capsule, laterally - Wernicke's area, and with inside- medial nucleus (Fig. 4.2.27). Wernicke's area is the innermost part of the internal capsule. This is where visual radiance begins. Optic radiation fibers are located on the dorsolateral side of the lateral geniculate nucleus, while auditory tract fibers are located on the dorsomedial side.

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Rice. 4.2.27. External geniculate body and its relationship to brain structures:

A- horizontal section of the brain (/ - lateral geniculate body; 2 - internal capsule; 3 -pillow of the visual thalamus); b - sagittal section of the brain (histological section stained with hematoxylin and eosin) (NKT-external geniculate body)

The lateral geniculate body is connected to the superior quadrigeminal ligament by a ligament called the anterior humerus.

Even a macroscopic examination of the lateral geniculate body reveals that this formation has a layered structure. In monkeys and humans, six stripes of “gray matter” and the “white” layers located between them, consisting of axons and dendrites, are clearly distinguishable (Fig. 4.2.28). The first layer is the layer located on the ventral side. The two inner layers consist of large cells (magnocellular layers 1 and 2). They got this name

Rice. 4.2.28. External geniculate body:

/ - hippocampus; 2 - subarochnoid space; 3 - cerebral peduncle; 4 - layer 1; 5 - layer 2; 6 - inferior horn of the lateral ventricle; 7 - layer 3; 8 - layer 4; 9 - layer 5; 10 - layer 6. The external geniculate body is the nucleus of the visual thalamus. The presence of six dark layers of clusters of neurons, separated by light layers consisting of nerve fibers, is clearly visible. Layers 1 and 2 are composed of large neurons (magnocellular), and layers 3-6 are composed of small cells (parvocellular)

for the reason that they consist of large neurons with an eccentrically located nucleus and a large amount of Nissl substance in the cytoplasm. The axons of the neurons of the magnocellular layer form not only the optic radiance, but also are directed to the superior colliculus. The four outer layers are composed of small and medium-sized cells (parvocellular layers, 3-6). They contain neurons that receive information from the retina and transmit it only to the visual cortex of the brain (forming visual radiance). Neurons are also found that provide communication between the neurons of the lateral geniculate body. These are the so-called “interneurons” (interneurons). It is believed that two layers consisting of small neurons (parvocellular layers) appear in connection with the development of central vision.

It is important to note that fibers coming from different parts of the retina of both eyes are projected onto the listed layers of neurons. Thus, crossed fibers of the optic tract end in layers 1, 4 and 6, and uncrossed fibers end in layers 2, 3 and 5 (Fig. 4.2.29). This occurs in such a way that fibers from the corresponding parts of the two halves of the retina (for example, the right temporal and left nasal halves of the retina) terminate in adjacent layers. The given features of the projection onto the lateral geniculate body were established based on the use of various methods

Chapter 4. BRAIN AND EYE

Rice. 4.2.29. Representation of the retina in the external geniculate body:

Impulses from corresponding points (a, b) two retinas pass into the optic tract. Uncrossed fibers (a") end in layers 2, 3 and 5 of the lateral geniculate body. Crossed fibers (b") end in layers 1, 4 and 6. Impulses after passing tubing(c") are projected onto the cerebral cortex

research. Thus, in cases of destruction of the contralateral optic nerve or previous removal of the eyeball, degeneration of neurons of the 1st, 4th and 6th layers of the lateral geniculate body develops (Fig. 4.2.30). When the homolateral fibers of the optic nerve are destroyed, degeneration of neurons of layers 2, 3 and 5 occurs. This phenomenon is called transsynaptic degeneration. It has also been established that if the eyelids of one eye are sewn together at birth in a kitten, then after three months degeneration of 25-40% of the neurons of the lateral geniculate body will occur. This form of transsynaptic degeneration can explain some of the mechanisms of development of amblyopia that develops with congenital strabismus.

Experimental studies also indicate different projections of crossed and uncrossed fibers onto the lateral geniculate body. In these studies, a radioactive amino acid is injected into one of the eyeballs, spreading transaxonally towards the external geniculate body and accumulating in its neurons (Fig. 4.2.31).

Rice. 4.2.31. Distribution of a radioactive tracer in the external geniculate bodies after injection of a radioactive amino acid into the left eyeball of a monkey:

A- left lateral geniculate body; b - right external geniculate body. (The amino acid is taken up by retinal ganglion cells and transported along axons through the optic nerve, optic chiasm, and optic tract to the lateral geniculate body. The illustration indicates that layers 2, 3, and 5 receive information from the ipsilateral eye, and layers 1, 4 and 6 - from the contralateral eye)

Rice. 4.2.30. Changes in the microscopic structure of the external geniculate body on both sides when one eyeball is removed (after Alvord, Spence, 1997):

A- external geniculate body (ECF), located ipsilaterally relative to the enucleated eye; b- tubing located contralateral to the enucleated eye. (After the death of a patient whose eyeball was removed long before death, the external geniculate bodies were examined microscopically. After the normal projection of the retinal ganglion cells onto the NKT neurons is disrupted, atrophy of the latter occurs. At the same time, the intensity of staining of the layers decreases. The figure shows that 3- The 1st and 5th layers of the NKT, located ipsilateral to the removed eye, are much weaker stained with hematoxylin and eosin. At the same time, layers 3 and 5 of the NKT, located contralateral to the removed eye, are stained more intensely than layers 4 and 6. It can also be noted that layers 1 and 2 are least affected)

Functional anatomy of the visual system

Features of the projection of the retina onto the lateral geniculate body. Recently, features of the projection of the retina onto the lateral geniculate body have been identified. They boil down to the fact that each point of half the retina is accurately projected onto a certain point of the nucleus of the external geniculate body (“point to point”). Thus, spatial excitation in the retinal ganglion cell layer is “mapped” by the spatial distribution of neuronal excitation in different layers of the lateral geniculate body. A strict topographic order of connections is also observed between cells of different layers. The projections of each point of the visual field in all layers are located directly under one another, so that a column-shaped area can be identified that crosses all layers of the lateral geniculate body and corresponds to the projection of the local area of ​​the visual field.

The given pattern of projection was revealed on the basis of experimental studies. Thus, it has been shown that local point damage to the retina leads to the development of transneuronal degeneration of small but well-defined clusters of cells in the three layers of the lateral geniculate body on both sides. Focal damage to the visual cortex or injection of a radioactive tracer into it results in “labeling” of cells or fibers located on a line extending across all layers of the lateral geniculate body at the same level. These areas correspond to the “receptive fields” of the lateral geniculate body and are called the “projective column” (Fig. 4.2.32).

At this point in the presentation of the material, it is advisable to dwell on the features of the receptive fields of the lateral geniculate body. The receptive fields of the lateral geniculate body resemble those of the retinal ganglion cells. There are several main types of receptive fields. The first type is characterized by the presence of an ON response when the center is excited and an OFF response when the periphery is excited (ON/OFF type). The second type of receptive fields is characterized by the inverse relationship - OFF/ON type. It is also characteristic of the external geniculate body that a mixture of receptive fields of the first and second types is found in layers 1 and 2. At the same time, in layers 3-6 only one type of receptive fields is found (in two layers of the field of the first type, and in the other two - of the second type). Linear receptive fields with different ratios of ON and OFF centers are also detected (Fig. 4.2.33). The use of electrophysiological methods revealed that the receptive fields of the lateral geniculate body have a more pronounced opponent reaction than the receptive fields of ganglion cells of the reticularis.

Lateral

Rice. 4.2.32. Schematic representation of the parasagitum

Thalal section of the lateral geniculate body. Projection

visual signal with the formation of a receptive

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* * *Z* x

Rice. 4.2.33. Structure of the receptive fields of the lateral geniculate body (a, b) and primary visual cortex (v-g) (according to Hubel, Weisel, 1962):

A- ON-center receptive field of the lateral geniculate body; b- OFF-center receptive field of the lateral geniculate body; V-and- various options for the structure of simple receptive fields. (Cross marks the fields corresponding to the ON reaction, and triangles mark the OFF reaction. The axis of the receptive field is marked by a solid line passing through the center of the receptive field)

chatki. This is what predetermines great importance external geniculate body in enhancing contrast. The phenomena of spatiotemporal summation of incoming signals, analysis of the spectral characteristics of the signal, etc. have also been identified. Neurons of the lateral geniculate body involved in color coding are localized in the parvocellular layers, where color-opponents are concentrated

Chapter 4. BRAIN AND EYE

The cells are “red-green” and “blue-yellow”. Like retinal ganglion cells, they are characterized by a linear summation of cone signals over the retinal area. Magnocellular layers also consist of opponent neurons with inputs from cones spatially distributed in receptive fields different types. It should be noted that the anatomical segregation of neurons with different functional properties is already observed in the retina, where the processes of bipolar and ganglion cells of the ON and OFF types are localized in different sublayers of the inner plexiform layer. This “anatomical separation” of neural systems, forming different channels for transmitting information, is a general principle in the construction of analyzer structures and is most pronounced in the columnar structure of the cortex, which we will discuss below.

Retina

the outer part of the lateral geniculate body (Fig. 4.2.29). The macular region of the retina projects onto the wedge-shaped sector, located in the posterior two-thirds or three-quarters of the lateral geniculate body (Fig. 4.2.34, 4.2.35).

It is noted that the representation of visual hemifields in the optic tract seems to “turn” at the level of the external geniculate body in such a way that the vertical section becomes horizontal. In this case, the upper part of the retina is projected onto the medial part, and the lower part onto the lateral part of the lateral geniculate body. This rotation reverses the visual radiance such that when the fibers reach the visual cortex, the superior quadrant of the retina is located at the top of the tract and the inferior quadrant at the bottom.

External geniculate body

Rice. 4.2.34. Projection of the retina onto the external geniculate body: / ​​- macula; 2 - monocular crescent

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Continuing the description of the features of the projection of the retina onto the lateral geniculate body, it should be noted that the peripheral temporal areas of the retina of the opposite eye are projected onto layers 2, 3 and 5 and are called the monocular crescent.

The most complete data on the retinotopic organization of optic nerve fibers, optic chiasm and nuclei of the lateral geniculate body in humans and monkeys were obtained by Brouewer, Zeeman, Polyak, Hoyt, Luis. We will initially describe the projection of non-macular fibers. Non-crossing fibers coming from the superior temporal quadrant of the retina are located dorsomedially in the optic chiasm and project onto the medial part of the nucleus of the lateral geniculate body. Non-crossing fibers coming from the inferotemporal quadrant of the retina are located inferiorly and laterally in the optic chiasm. They are projected onto

Rice. 4.2.35. Schematic representation of the coronary

section through the lateral geniculate body (posterior view)

(after Miller, 1985):

Noteworthy is the large representation in the external geniculate body of the macular region (1-6 numbers of NKT layers)

Functional anatomy of the visual system

Synaptic interactions of neurons in the lateral geniculate body. It was previously assumed that the axon of a ganglion cell contacts only one neuron of the lateral geniculate body. Thanks to electron microscopy, it has been established that afferent fibers form synapses with several neurons (Fig. 4.2.36). At the same time, each neuron of the lateral geniculate body receives information from several retinal ganglion cells. Based on ultrastructural studies, various synaptic contacts between them have also been identified. The axons of ganglion cells can end both on the body of neurons of the lateral geniculate body and on their primary or secondary dendrites. In this case, the so-called “glomerular” endings are formed (Fig. 4.2.37, see color on). In cats, the “glomeruli” are separated from the surrounding formations by a thin capsule consisting of processes of glial cells. Such isolation of “glomeruli” is absent in monkeys.

Synaptic “glomeruli” contain synapses of axons of retinal ganglion cells, synapses of neurons of the lateral geniculate body and interneurons (“interneurons”). These synaptic formations resemble the “triads” of the retina.

Each glomerulus consists of a zone of densely packed neurons and their terminals. In the center of this zone is the axon of the ganglion

Rice. 4.2.36. Schematic representation of the interaction of retinal ganglion cell axon terminals with lateral geniculate neurons in the monkey (after Glees, Le Gros, Clark, 1941):

optic nerve fiber bundle (A) enters the cell layer (b) of the external geniculate body (EC) on the right. Some fibers give off 5-6 branches, approach the body of NKT neurons and form a synapse. Axons of NKT cells (c) leave the NKT cell layer, pass through the fibrous layer and form optic radiance

retinal cells, which are presynaptic. It forms synapses with the neuron of the lateral geniculate body and interneurons. The dendrites of the neurons of the lateral geniculate body enter the “glomeruli” in the form of a spine, which directly forms a synapse with the retinal axon. The dendrite of interneurons (interneurons) forms a synapse with the adjacent “glomerulus”, forming successive synapses between them.

Lieberman distinguishes pre- and postsynaptic “inhibitory” and “excitatory” dendritic and “glomerular” synapses. They are a complex collection of synapses between axons and dendrites. It is these synapses that structurally provide the phenomenon of inhibition and excitation of the receptive fields of the lateral geniculate body.

Functions of the external geniculate bodies. It is assumed that the functions of the lateral geniculate body include: enhancing image contrast, organizing visual information (color, movement, shape), modulating the level of processing of visual information with their activation (through the reticular formation). It has an external geniculate body and binocular receptive fields. It is important to note that the functions of the lateral geniculate body are also influenced by higher located brain centers. Confirmation of the role of the lateral geniculate body in the processing of information coming from the higher parts of the brain is the discovery of a projection onto it efferent fibers, emanating from the cerebral cortex. They arise in layer VI of the visual cortex and are projected onto all layers of the lateral geniculate body. For this reason, minor damage to the visual cortex causes neuronal atrophy in all six layers of the lateral geniculate body. The terminals of these fibers are small and contain numerous synaptic vesicles. They end both on the dendrites of neurons of the lateral geniculate body and on interneurons (“interneurons”). It is believed that through these fibers the cerebral cortex modulates the activity of the external geniculate body. On the other hand, it has been shown that changes in the activity of neurons in the lateral geniculate body selectively activate or inhibit neurons in the visual cortex of the brain.

There are other connections of the lateral geniculate nucleus. This is a connection with the thalamus cushion, the ventral and lateral nuclei of the optic thalamus.

Blood supply of the external geniculate body carried out by the posterior cerebral and posterior villous arteries (Fig. 4.2.38). The main vessel supplying blood to the external geniculate body, especially its posterior-internal surface, is the posterior

Chapter 4. BRAIN AND EYE

90 80 70 60150 40 30 20-10

Rice. 4.2.38. Arterial blood supply to the surface of the lateral geniculate body:

/ - anterior villous (choroidal) artery; 2 - villous plexus; 3 - cerebral peduncle; 4 - gate of the external geniculate body; 5 - external geniculate body; 6 - medial geniculate body; 7 - oculomotor nerve; 8 - nucleus of the oculomotor nerve; 9 - posterior cerebral artery; 10 - posterior villous artery; // - substantia nigra

nya cerebral artery. In some cases, a branch arises from this artery - the posterior villous (choroidal) artery. If the blood circulation in this artery is impaired, disturbances in the field of the upper homonymous quadrant of the retina are detected.

The anterior villous (choroidal) artery almost completely supplies the anterior and lateral surface external geniculate body. For this reason, poor circulation in it leads to damage to the fibers emanating from the lower quadrant of the retina (Fig. 4.2.39). This artery arises from the internal carotid artery (sometimes from the middle cerebral artery) just distal to the origin of the posterior communicating artery. Upon reaching the anterior part of the lateral geniculate body, the anterior villous artery gives off a variable number of branches before entering the inferior horn of the lateral ventricle.

The part of the lateral geniculate body, to which fibers emanating from the macula are projected, is supplied by both the anterior and posterior villous arteries. In addition, numerous arterioles extend from a well-developed system of anastomoses located in the soft and arachnoid membranes of the brain, penetrating into the external geniculate body. There they form a dense network of capillaries in all its layers.

^--^--^ Horizontal meridian of the visual field - - - - - Lower oblique meridian of the visual field

I I Territory of the anterior villous artery VIV Territory of the external villous artery

Rice. 4.2.39. Diagram of the blood supply to the right lateral geniculate body and features of visual field loss (homonymous visual field defect) resulting from circulatory disorders in the villous (choroidal) artery basin (after Frisen et al., 1978):

A- retina; b- external geniculate body (/-anterior villous artery; 2 - medial surface; 3 - lateral surface; 4 - posterior villous artery; 5 - posterior cerebral artery)

Functional anatomy of the visual system

4.2.6. Visual radiance

Visual radiance (radiatio optica; Gra-siole, Gratiolet) is an analogue of other rays of the visual thalamus, such as auditory, occipital, parietal and frontal. All of the listed radiations pass through the internal capsule connecting the cerebral hemispheres and

brainstem, spinal cord. The internal capsule is located lateral to the thalamus optic and the lateral ventricles of the brain and medial to the lenticular nucleus (Fig. 4.2.40, 4.2.41). The most posterior part of the internal capsule contains auditory and optic radiation fibers and descending fibers running from the occipital cortex to the superior colliculus.

10

And

16

17

Rice. 4.2.41. Horizontal section of the brain at the level of the optic radiation:

/ - calcarine groove; 2 - visual radiance; 3 - internal capsule; 4 - outer capsule; 5 - fourth ventricle;

6 - plate of transparent septum;

7 - anterior horn of the lateral ventricle; 8 -
longitudinal fissure of the brain; 9 - moso knee
leaf body; 10 - cavity transparent
partitions; // - head of the caudate nucleus;
12 - fence; 13 - shell; 14 - pale
ball; 15 - visual thalamus; 16 - hippo-
camp; 17 - rear knee of the lateral jelly
daughter

Chapter 4. BRAIN AND EYE

The optic radiation connects the lateral geniculate body with the occipital cortex of the brain. In this case, the course of the fibers emanating from different parts of the lateral geniculate body differs quite significantly. Thus, fibers coming from the neurons of the lateral part of the lateral geniculate body bend around the lower horn of the lateral ventricle, located in the temporal lobe, and then, heading posteriorly, pass under the posterior horn of this ventricle, reaching the lower parts of the visual cortex, near the calcarine sulcus (Fig. 4.2 .40, 4.2.41). Fibers from the medial part of the lateral geniculate body take a somewhat more direct route to the primary visual cortex (Brodmann area 17), located in the medial part of the occipital lobe. The fibers of this path deviate laterally, passing immediately anteriorly from the entrance to the lateral ventricle, and then turn posteriorly, go in a caudal direction, bending around the posterior horn of this ventricle from above and ending in the cortex located along the upper edge of the calcarine groove.

The superior fibers leaving the lateral geniculate body go directly to the visual cortex. The lower fibers make a loop around the ventricles of the brain (Meer's loop) and are directed to the temporal lobe. The lower fibers are closely adjacent to the sensory and motor fibers of the internal capsule. Even a small stroke occurring in this area results in superior hemianoptic visual field defects and hemiparesis (contralateral).

The most anterior fibers are found approximately 5 posterior to the apex of the temporal lobe. It has been noted that lobectomy, in which brain tissue is excised, 4 cm from apex of the temporal lobe does not lead to a visual field defect. If a larger area is damaged (deeply located tumors, temporal decompression due to injury or infectious disease), homonymous upper quadrant hemianopsia develops. The most typical forms of visual field defect due to damage to optic radiance are shown in Fig. 4.2.19, 4.2.43.

As stated above, optic radiance contains 3 main groups of fibers. The upper part contains fibers serving the lower visual fields, the lower part - the upper fields. The central part contains macular fibers.

The retinotopic organization of the fibers of the lateral geniculate body also extends to the optic radiation, but with some changes in the position of the fibers (Fig. 4.2.42). The dorsal bundle of fibers, representing the upper peripheral quadrant of the retina, arises from the medial part of the lateral geniculate body and passes to the dorsal lip of the bird.

whose spurs. The ventral bundle of fibers represents the periphery of the lower quadrant of the retina. It passes in the lateral part of the external geniculate body and approaches the ventral lip of the bird's spur. It is assumed that these projections of the retinal periphery lie in the optic radiation medial to the projection of the macular fibers. The macular fibers extend forward, occupying most of the central part of the optic radiation in the form of a wedge. They then move posteriorly and converge in the area of ​​the upper and lower lips of the bird's spur.

As a result of the separation of peripheral and central projections, damage to optic radiation can lead to quadrant loss of the visual field with a clear horizontal border.

The most peripherally located nasal projections of the retina, representing a “monocular crescent”, gather near the upper and lower boundaries of the dorsal and ventral optic radiation bundles.

Violations in the field of visual radiation lead to a number of specific disturbances in the visual fields, some of which are shown in Fig. 4.2.43. The nature of visual field loss is largely determined by the level of damage. The cause of such violations may be various

External geniculate body

(3(3

oo

Rice. 4.2.43. Diagram of fiber distribution in the optic tract, lateral geniculate body and optic radiation. Visual field impairment due to damage to areas located after the optic chiasm:

/ - compression of the optic tract - homonymous hemianopsia with an indistinct edge; 2 - compression of the proximal part of the optic tract, the external geniculate body or the lower part of the optic radiation - homonymous hemianopsia without preservation of the macular field with a clear edge; 3 - compression of the anterior loop of optic radiation - superior quadrant anopsia with unclear edges; 4 - compression of the upper part of the optic radiation - lower quadrant anopia with unclear edges;

5 - compression of the middle part of the optic radiation - homonymous
hemianopsia with unclear edges and central prolapse
vision; 6 - compression of the posterior part of the optic radiation -
congruent homonymous hemianopsia with preservation of the central
vision; 7 - compression of the anterior part of the cortex in the area of ​​the spine
ry - temporal loss of the visual field from the opposite
sides; 8 - compression of the middle part of the cortex in the area of ​​the spur -
homonymous hemianopia with preservation of central vision
side of the lesion and preservation of the temporal field of vision with
the opposite side; 9 - compression of the posterior part of the cortex behind
dorsal region - congruent homonymous hemianopsic

scotoma

novel diseases of the brain. Most often this is a circulatory disorder (thrombosis, embolism in hypertension, stroke) and the development of a tumor (glioma).

Due to the fact that disturbances in the structure and function of visual radiation are often associated with circulatory disorders, it is important to know

06 features of the blood supply to this area.
Blood supply to optic radiation

carried out at 3 levels (Fig. 4.2.24):

1. Part of the visual radiance passing through
cabbage soup laterally and above the lower horn of the lateral
ventricle, supplied by the anterior branch
villous (choroidal) artery.

2. Part of the visual radiance located
behind and lateral to the horn of the stomach
ka, supplied by the deep ophthalmic branch
middle cerebral artery. The last penetration

flows into this area through the anterior perforated substance together with the lateral striate arteries.

3. When the optic radiation approaches the cerebral cortex, the blood supply is carried out by perforating arteries of the cortex, mainly by branches of the artery of the bird's spur. The avian spur artery arises from the posterior cerebral artery and sometimes from the middle cerebral artery.

All perforating arteries belong to the so-called terminal arteries.

Visual cortex

As stated above, the neuronal systems of the retina and lateral geniculate body analyze visual stimuli, assessing their color characteristics, spatial contrast and average illumination in different parts of the visual field. The next stage of analysis of afferent signals is performed by the system of neurons in the primary visual cortex (visul cortex).

The identification of areas of the cerebral cortex responsible for processing visual information has a rather long history. As early as 1782, medical student Francesco German described a white stripe running through the gray matter of the occipital lobe. It was he who first suggested that the cortex might contain anatomically distinct regions. Before Gennari's discovery, anatomists assumed that the cortex was a homogeneous sheet of tissue. Gennari had no idea that he had stumbled upon the primary visual cortex. More than a century passed before Henschen proved that the stripe of Gennari corresponded to the primary visual cortex.