Occipital lobe

The occipital lobe ( Germanized spelling: occipital lobe ) or occipital lobe (Latin occipital lobe ) is the posterior portion of the cerebrum and the smallest of the four lobes of the brain. As part of the visual system to process the visual stimuli, which is why he is the visual center of the brain.

Anatomy

The occipital lobe is located on the occiput. He sits on the cerebellum from which it is separated by the cerebellum tent. Forward it borders on the parietal lobe ( parietal lobe ), from which it is separated by the parieto-occipital sulcus, and the temporal lobe ( temporal lobe ), to which no clear boundary is visible.

The occipital lobe is divided by the calcarine sulcus, above which the cuneus lies and below the lingual gyrus. The occipital lobe contains the primary and secondary visual cortex ( visual cortex).

Blood supply

The occipital lobe is mainly supplied from the posterior cerebral artery. The blood outflow via the ascending (venae superficiales ascendentes cerebri) and descending (venae superficiales descendentes cerebri) superficial veins of the brain. The ascending veins carry blood to the superior sagittal sinus, the descending into the transverse sinus, the sinus and the superior saggitalis passes. The transverse sinus passes the blood eventually in the internal jugular vein, which leads out of the skull.

Functions

Primary visual cortex

Is located on the side facing the center of the body ( medial ) side of the occipital lobe of the so-called calcarine sulcus, the calcar avis einsenkt as in the dorsal horn ( Cornu posterior ) of the lateral ventricles. On both sides of the sulcus is the primary visual cortex corresponding to the Brodmann area 17. This area has a typical six-layer structure of the neocortex. Striking feature of the visual cortex is an additional nerve fiber band in the lamina IV ( inner nuclear layer ), which is referred to as Gennari or Vicq- d'Azyr Strip. This is macroscopically visible and the reason why the area also striate area ( " striped area " ) is called.

In each of the occipital lobe, the visual pulse temporal ipsilateral and nasal contralateral retina ( retinal ) can be processed, that is, the right occipital lobe, the signals of the respective right-hand half of the retina in both eyes to be processed, the left occipital lobe for the signals of the left-hand retinal halves both responsible eyes (See visual system and visual pathway ). Here, each point on the retina is a small area in the visual cortex associated ( retinotopische arrangement ). The fovea centralis, which is the site of sharpest vision of the retina takes according to their importance in relation to other areas of a about 80% of the visual cortex. The information processing is carried out in so-called " cortical columns ", ie superimposed cell aggregates. It can be found here also cell groups that appeal to certain patterns (eg lines of certain orientation) and filter out this information from the quasi overall impression (so-called "feature extraction ").

Secondary visual cortex

The secondary visual center belongs to the association areas of the brain and corresponds to Brodmann's areas 18 and 19 This area is also Area parastriata named because it is adjacent to the area striata. Here the processed samples from the primary visual cortex known sensations are compared and thus interpreted and recognized. From the secondary visual cortex running tracks in other cortical areas of the brain, such as the angular gyrus to link to the language, or in the frontal lobes, where the eye movement is coordinated.

Pathology

Failures of the visual pathway may result in all involved structures, such as by hemorrhage, infarction, trauma. This following may result:

  • Primary visual center: Unilateral lesions in this area lead to the contralateral visual field loss.
  • Destruction of both primary visual centers ( the anatomically close to each other and only through the interhemispheric fissure ( longitudinal fissure ) are separated ) leads to cortical blindness. The typical reflections of the eye will be kept. The information of the eye run virtually only into the void.
  • Secondary visual center: Disturbances in this area relate to the identification and linking of what is seen ( psychic blindness, also visual or visual agnosia ). Things are thereby certainly looked, but can not be named. This includes the reading disorders ( dyslexia ) or the inability to read ( alexia ).
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