Lateral geniculate body. articulated body

articulated body (corpus geniculatum)

Lateral geniculate body(c. g. laterale, BNA, JNA) - K. t., lying on the lower surface of the thalamus lateral to the handle of the upper mound of the quadrigemina; location of the subcortical center of vision.

geniculate body medial(c. g. mediale, PNA, BNA, JNA) - K. t., located anterior and lateral to the handle of the lower colliculus of the quadrigemina; location of the subcortical hearing center.

1. Small medical encyclopedia. - M.: Medical Encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic Dictionary medical terms. - M.: Soviet Encyclopedia. - 1982-1984.

See what "Cranked body" is in other dictionaries:

- (corpus geniculatlim) the general name of the roller-like formations of the diencephalon that make up the metathalamus ... Big Medical Dictionary

- (c. g. laterale, PNA, BNA, JNA) K. t., lying on the lower surface of the thalamus laterally from the handle of the superior colliculus of the quadrigemina: the location of the subcortical center of vision ... Big Medical Dictionary

- (s. g. mediale, PNA, BNA, JNA) K. t., located anteriorly and lateral to the handle of the lower colliculus of the quadrigemina; the location of the subcortical center of hearing ... Big Medical Dictionary

This article has a list of sources or external links, but the sources of individual statements remain unclear due to the lack of footnotes ... Wikipedia

Lateral geniculate body- two cell nuclei of the thalamus, located at the ends of each of the optical tracts. Paths from the left side of the left and right retinas approach the left body, to the right, respectively. right side retina. From here, the visual paths are directed to ... ... Encyclopedic Dictionary of Psychology and Pedagogy

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

BRAIN- BRAIN. Contents: Methods for studying the brain ..... . . 485 Phylogenetic and ontogenetic development of the brain ............... 489 Bee of the brain ............... 502 Anatomy of the brain Macroscopic and ... ... Big Medical Encyclopedia

The optic nerve fibers start from each eye and end on the cells of the right and left lateral geniculate body (LCT) (Fig. 1), which has a clearly distinguishable layered structure (“geniculate” - geniculate - means “curved like a knee”). In the LCT of a cat, three distinct, well-defined cell layers (A, A 1 , C) can be seen, one of which (A 1) has a complex structure and is further subdivided. In monkeys and other primates, including

Rice. 1. Lateral geniculate body (LCB). (A) Cat LCT has three cell layers: A, A, and C. (B) Monkey LCT has 6 major layers, including small cell (parvocellular), or C (3, 4, 5, 6), large cell (magnocellular ), or M (1, 2) separated by koniocellular layers (K). In both animals, each layer receives signals from only one eye and contains cells that have specialized physiological properties.

human, LKT has six layers of cells. Cells in deeper layers 1 and 2 are larger than in layers 3, 4, 5 and 6, which is why these layers are called large-celled (M, magnocellular) and small-celled (P, parvocellular), respectively. The classification also correlates with large (M) and small (P) retinal ganglion cells, which send their outgrowths to the LCT. Between each M and P layers lies a zone of very small cells: the intralaminar, or koniocellular (K, koniocellular) layer. Layer K cells differ from M and P cells in their functional and neurochemical properties, forming a third channel of information to the visual cortex.

In both the cat and the monkey, each layer of the LCT receives signals from either one eye or the other. In monkeys, layers 6, 4, and 1 receive information from the contralateral eye, and layers 5, 3, and 2 from the ipsilateral eye. The separation of the course of nerve endings from each eye into different layers has been shown using electrophysiological and a number of anatomical methods. Particularly surprising is the type of branching of an individual fiber of the optic nerve when horseradish peroxidase is injected into it (Fig. 2).

The formation of terminals is limited to the layers of the LCT for this eye, without going beyond the boundaries of these layers. Due to the systematic and specific division of the optic nerve fibers in the region of the chiasm, all the receptive fields of the LCT cells are located in the visual field of the opposite side.

Rice. 2. Endings of the optic nerve fibers in the LCT of a cat. Horseradish peroxidase was injected into one of the axons from the zone with the "on" center of the contralateral eye. Axon branches end on cells of layers A and C, but not A1.

Rice. 3. Receptive fields of ST cells. The concentric receptive fields of the LCT cells resemble the fields of ganglion cells in the retina, dividing into fields with "on" and "off" centers. The responses of the cell with the "on" center of the LCT of a cat are shown. The bar above the signal shows the duration of illumination. Central and peripheral the zones offset each other's effects, so diffuse illumination of the entire receptive field gives only weak responses (bottom notation), even less pronounced than in retinal ganglion cells.

Anatomically, the LCT refers to the metathalamus, its dimensions are 8.5 x 5 mm. The cytoarchitectonics of the LKT is determined by its six-layer structure, which is found only in higher mammals, primates, and humans.
Each LC 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 react differently to visual stimuli. Nerve cells of the dorsal nucleus of the LKT are smaller, similar to each other histologically and in electrophysiological properties. In this regard, the ventral layers of the LCT are called large-celled (magnocellular), and the dorsal layers are called small-celled (parvocellular).
Parvocellular structures of the LCT are represented by layers 3, 4, 5, 6 (P-cells); magnocellular layers - 1 and 2 (M-cells). The endings of the axons of the magno- and parvocellular ganglion cells of the retina are morphologically different, and therefore there are different synapses in different layers of the nerve cells of the LKT. The magno-axon terminals are radially symmetrical, have thick dendrites and large ovoid endings. The parvoaxon terminals are elongated, have thin dendrites, and medium-sized rounded terminals.
There are also axon endings in the LCT with a different morphology belonging to other classes of retinal ganglion cells, in particular the blue-sensitive cone system. These axon endings create synapses in a heterogeneous group of LCT layers collectively called "coniocellular" or K-layers.
In connection with the intersection in the chiasm of the fibers of the optic nerve from the right and left eyes, nerve fibers from the retinas of both eyes enter the LCT from each side. The endings of 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 neurons of the LCT with their dendrites provide a very reliable connection of synaptic transmission of an impulse from 1 million axons of retinal ganglion cells.
In the geniculate body, the projection of the central fossa of the macula is most expanded. The projection of the visual path in the LCT contributes to the recognition of objects, their colors, movements 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, annular zone is inhibitory. LCT neurons are divided into two classes: on-center and off-center (darkening of the center activates the neuron). LCT neurons perform different function.
For pathological processes localized in the chiasm, optic tract and LKT, symmetrical binocular loss of the visual field is characteristic.

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

• homonymous (of the same name) right- and left-sided,
• heteronymous (opposite) - 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 visual pathway. Even with a unilateral lesion of the visual pathway in the LKT (right or left), the central vision of both eyes suffers. At the same time, one feature is noted that has an important differential diagnostic value. Pathological foci located more 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 cortex of the occipital lobe of the brain, usually give negative scotomas, that is, they are not felt by patients as a visual impairment.

Outer geniculate body (corpus geniculatum 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 lateral geniculate body. The external geniculate body is a hill corresponding to the location of one of the nuclei of the thalamus opticus (Fig. 4.2.26-4.2.28). It contains about 1,800,000 neurons, on the dendrites of which the axons of the ganglion cells of the retina end.

Previously, it was assumed that the lateral geniculate body is only 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 takes place at the level of the lateral geniculate body. The neurophysiological significance of this formation will be discussed below. Initially, you need

Rice. 4.2.26. Model of the left external geniculate body (according to Wolff, 1951):

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

dimo to dwell on its anatomical features.

The nucleus of the lateral geniculate body is one of the nuclei of the optic tubercle. It is located between the ventroposterior lateral nucleus of the thalamus and the thalamus pad (Fig. 4.2.27).

The external geniculate nucleus consists of the dorsal and phylogenetically older 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 fit into 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 asymmetric cone with a rounded top (Fig. 4.2.25-4.2.28). The horizontal section shows that the lateral geniculate body is connected anteriorly with the optic tract, laterally 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. The cushion of the thalamus is adjacent to the nucleus of the lateral geniculate body from above, anterio-laterally - temporopontine fibers and the posterior part of the internal capsule, laterally - Wernicke's area, and on the inside - the medial nucleus (Fig. 4.2.27). Wernicke's area is the innermost part of the internal capsule. It is in it that visual radiance begins. The fibers of the optic radiation are located on the dorsolateral side of the nucleus of the external geniculate body, while the fibers of the auditory tract are located on the dorsomedial side.

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 provided the basis for the long held view that 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. 9. 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.