Definition
The visual center, also called the visual cortex, is part of the visual system. It is located in the occipital lobe of the brain and belongs to the central nervous system. This is where information from nerve fibers in the visual pathways arrives, is processed, interconnected, interpreted and coordinated.
Disturbances in the visual pathways and the visual cortex manifest themselves in very different, sometimes characteristic, ways, and range from visual field loss to blindness and the inability to recognize faces or objects, for example. The occipital lobe (Lobus occipitalis) is the occipital lobe of the brain. It is located above the cerebellum in the posterior fossa.
Towards the front it borders on the temporal and parietal lobes. The sulcus calcarinus is a major landmark in the occipital lobe, in this area lies the visual cortex, also called the primary and secondary visual cortex. In order to describe the function of the visual center, the visual pathway preceding this center, i.e. the path from the eye to the brain, must first be briefly described.
On the way from the eye to the brain, the visual impression passes through several nerve cells. The first nerve cell is located in the retina, called rods and cones. The rods are mainly used for light perception, cones are used for color perception.
The second neuron on its way to the brain belongs to the so-called bipolar cells, which are located a small distance in front of the retina in the eye. They transmit the impulses to the ganglion cells, which are also located in the area of the retina. Together with their extensions, they form the optic nerve (optic nerve).
Like the retina, the optic nerve is a part of the brain, even if it is located outside the eye. After entering the cranial cavity, the optic nerves on both sides unite to form the so-called optic chiasma (optic nerve junction). Here, all the fibers that represent the outer (lateral or temporal) visual field cross over to the opposite side, those that represent the inner (medial or nasal) visual field run through the chiasma on their original side.
It is somewhat confusing that the lateral visual field is represented on the medial side of the retina and the medial visual field on the lateral side of the retina. This is due to the fact that the retina is an optical system in which the object being imaged is reduced in size and, more importantly, the reverse is true. This is similar to a camera.
The optic tractus is connected to the optic nerve junction. The left optic tract contains fibers for visual impression from the left inner (medial) and right outer (lateral) visual field, the right optic tract contains fibers from the right nasal and left temporal visual field. The optic tract ends in the lateral geniculate corpus.
This lies in the thalamus. Here the information is switched to the fourth neuron. Prior to this, some fibers go off to the brain stem, which are essential for the control of reflexes.
In everyday life, such a reflex is, for example, the coordination of both eyes when looking to the side: If you look to the left with your left eye, the right eye automatically follows. From the thalamus, the fibers run further than visual radiation (radiata optica) to the visual cortex. The visual cortex is divided into the primary and secondary visual cortex.
The primary visual cortex is the first station for the fibers of the visual path. It is located in the Brodmann area 17 and is also called area striata because of a white stripe it leaves in the gray matter of the brain. When the impulses from the eye reach the primary visual cortex, what is seen is first consciously perceived, but an interpretation of what is seen is not yet possible.
A certain point on the retina corresponds to a certain area in the cortex, this is called retinotopic striation. The fovea centralis, the place of sharpest vision on the retina, takes up 4/5 of the entire primary visual cortex. The primary visual cortex sends fibers primarily into the secondary visual cortex.
This takes up the Brodmann areas 18 and 19. It wraps around the primary visual cortex like a horseshoe. Here the visual impressions are integrated, analyzed, resolved and interpreted according to size, shape, color, distance and much more.
It is now known that areas extending beyond the occipital lobe into the temporal and parietal lobes are also crucial in the secondary processing of visual impulses. For example, what is seen is linked with what is known, so that faces or objects, for example, can be recognized.The secondary visual cortex, in turn, sends fibers to the frontal and parietal lobes, among other places, where centers of vision are located, which, for example, mediate turning or averting the gaze, corrective movements of the eyes, and gaze-following movements. Fibers also draw fibers to the angular gyrus, which is essential for linking what is seen with speech. Furthermore, fibers from the secondary visual cortex draw fibers into the brain stem, which is important for reflex movements in the area of the eyes.
