occipital lobe
The occipital lobe (Germanized spelling: occipital lobe ) or occipital lobe ( lat. Lobus occipitalis ) is the rearmost part of the cerebrum and the smallest of the four brain lobes. As part of the visual system, it processes the visual impulses, which is why it is the visual center of the brain.
anatomy
The occipital lobe rests against the occiput . It sits on the cerebellum , from which it is separated by the cerebellar tent. To the front it borders on the parietal lobe ( lobus parietalis ), from which it is separated by the sulcus parietooccipitalis , and the temporal lobe ( lobus temporalis ), to which no clear border can be seen.
The occipital lobe is divided by the calcarin 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 occurs via the ascending ( superficiales ascendentes cerebri veins ) and descending ( superficiales descendentes cerebri veins) superficial veins of the brain. The ascending veins carry the blood into the superior sagittal sinus , the descending veins into the transverse sinus , into which the superior sagittal sinus also merges. The transverse sinus eventually directs blood to the internal jugular vein that leads out of the skull.
Functions
Primary visual cortex
On the ( medial ) side of the occipital lobe that points towards the middle of the body, there is the so-called sulcus calcarinus , which sinks into the posterior horn ( cornu posterius ) of the lateral ventricle as a calcar avis . The primary visual cortex , which corresponds to Brodmann area 17, is located on both sides of the sulcus . This area has a six-layer structure typical of the neocortex . A noticeable feature of the visual cortex is an additional nerve fiber band in lamina IV (inner granular layer), which is known as the Gennari or Vicq d'Azyr stripe. This is macroscopically recognizable and the reason why the area is also called Area striata ("striped area", striary cortex).
The visual impulses of the temporal ipsilateral and the nasal contralateral retina ( retina ) are processed in each occipital lobe, i.e. the signals of the right half of the retina of both eyes are processed in the right occipital lobe, the left occipital lobe is for the signals of the left halves of the retina eyes responsible (See visual system and visual pathway ). A small area in the visual cortex is assigned to each point on the retina ( retinotopic arrangement ). The fovea centralis , i.e. the point of sharpest vision of the retina, takes up about 80% of the visual cortex in accordance with its importance compared to the other areas. The information processing takes place in so-called "cortical columns", that is in superimposed cell groups. There are also cell clusters that respond to certain patterns (e.g. lines with a certain orientation) and filter this information out of the overall impression (so-called "property extraction").
Secondary visual cortex
The secondary visual center belongs to the association centers of the brain and corresponds to the Brodmann areas 18 and 19. This area is also called the area parastriata (extrastrial cortex) because it is adjacent to the area striata. Here, the processed patterns from the primary visual cortex are compared with known sensory impressions and thus interpreted and recognized. Paths run from the secondary visual cortex to other cortical areas of the cerebrum, for example to the angular gyrus for connection to language, or in the frontal lobes, where eye movement is coordinated.
pathology
Failures of the visual pathway can occur in all structures involved, e.g. B. bleeding , heart attack , trauma . This can result in the following disorders:
- primary visual center:
- Unilateral damage in this area leads to contralateral visual field defects .
- Destruction of both primary visual centers (which are anatomically close together and are only separated by the interhemispheric fissure ( fissura longitudinalis )) leads to cortical blindness . The typical reflexes of the eye are retained. The information from the eye is virtually nothing.
- secondary visual center:
- Disturbances in this area affect the recognition and connection of what is seen ( soul blindness , also optical or visual agnosia). Things are perceived, but cannot be named. This also includes reading disorders ( dyslexia ) or the inability to read ( alexia ).
Web links
- Gray´s_Anatomy_Brain
- Clear image with the most important parts of the brain (including sulci, gyri and lobes)
Individual evidence
- ↑ Federative Committee on Anatomical Terminology (1998). Terminologia Anatomica . Stuttgart: Thieme.
- ↑ Martin Trepel: Neuroanatomy. Structure and function . 3. Edition. Urban & Fischer Verlag, Munich 2004. (p. 226).
- ↑ Martin Trepel: Neuroanatomy. Structure and function . 3. Edition. Urban & Fischer Verlag, Munich 2004. (p. 227).