Dorothy FarrarOccipitallappen
The occipital lobe is part of the cerebrum and functions as the visual center in the brain . It is the smallest of the four parts of the cerebrum and is also known as the occipital lobe due to its location in the skull.
Definition
The occipital lobe, in German spelling occipital lobe, is located at the back of the cerebrum. The cerebrum is part of the central nervous system and is the largest of the five brain areas.
It consists of frontal lobes , parietal lobes, temporal lobes and occipital lobes. The occipital lobe is the smallest of these four parts of the brain and is located at the back of the head. It is part of the visual system and is responsible for processing visual stimuli.
Anatomy
The occipital lobe nestles against the rear skin bone (Os occipitale). This anatomical location also gave the occipital lobe its name. Below it borders on the cerebellar tent (tentorium cerebelli), from the front it is bordered by the parietal lobe, the lobus parietalis. The parietal lobe and occipital lobe are separated by the sulcus parietooccipitalis, a cerebral groove.
Anatomically, the occipital lobe can be divided into two areas. First, there is the primary visual cortex. This corresponds to Brodmann’s area 17. The area of the primary visual cortex has numerous stripes in its structure. That is why the area is also called area striata.
The striata area is on the middle, inward-facing side of the cerebral hemispheres. The visual association cortices V2 to V5 form the second area of the occipital lobe. Since this secondary visual cortex is located directly next to the striata area, it is also known as the parastriata area.
The arterial supply of the occipital lobe takes over the Arteria cerebri posterior. The venous outflow of blood takes place via the superficial veins of the brain, the venae superficiales ascendentes cerebri and the venae superficiales descendentes cerebri. From there, the venous blood flows into the superior sagittal sinus and via other sinus vessels finally into the internal jugular vein, which leads out of the skull.
Function
The visual stimuli of the retina are processed in the primary cortex of the two occipital lobes. Each of the lobes is responsible for specific areas of the retina. The processing of the visual impulses of the right half of the retina of both the left and the right eye takes place in the right occipital lobe.
The signals from the left half of the retina of both eyes are assigned to the left occipital lobe. The primary visual cortex is arranged retinotopically. This means that each point on the retina is assigned an area in the visual cortex. So if a point on the retina is next to a certain other point, then this point is also next to exactly this other point in the occipital lobe.
The place of sharpest vision on the retina is called the fovea centralis. The fovea centralis of the retina is about 1.5 millimeters in diameter. In the occipital lobe, the mapping of visual impulses to the central fovea occupies almost 80% of the primary cortex. This enables fast processing of what the eye is currently focusing on.
The secondary visual cortex is formed by the visual association cortices. In the secondary visual cortex, the visual impressions gained are compared with already known sensory impressions. In the secondary visual cortex, the interpretation and recognition of the processed patterns from the primary visual cortex takes place. The impressions are put together and thus allow the perception of space, movement and colour.
Nerve pathways run from the secondary visual cortex to other parts of the cerebrum, where they are linked to experiences. This makes it possible for people to recognize things and people. Connections with the angular gyrus link what is seen with language. The secondary visual cortex is also connected to the frontal lobe and thus has an influence on eye movements.
Diseases
- Scott
- cortical blindness
- visual agnosia
- Dyslexia
- Alexie
The symptoms of failure of the primary and secondary visual cortex differ depending on the location. Unilateral damage in the area of the primary visual center leads to visual field defects. This loss of visual field is also known as a scotoma.
With unilateral damage, a contralateral scotoma occurs. Cortical blindness occurs when both visual centers are completely destroyed. Although the retina and visual pathways are functional, the patient is completely blind.
The reflexes of the eyes remain intact, only the visual information recorded by the eyes can no longer be processed in the brain. The patients see nothing despite healthy eyes.
When there is a defect in the secondary cortex, those affected can see, but cannot recognize or give meaning to what is perceived. This processing disorder of visual stimuli is also called mental blindness or visual agnosia.
Forms of mental blindness are also reading disorders (dyslexia) and the complete inability to read (alexie). Primary and secondary cortex failures can be caused by hemorrhage, head injury and trauma, or by infarction.
Hello and welcome to my Health Guide & Encyclopedia! My name is Dorothy Farrar, and I'm the founder and main author of this platform.
My passion for health and wellness started at a young age when I became interested in the connection between the food we eat and the way we feel. This fascination led me to study nutrition and dietetics in college, where I learned about the importance of a balanced diet and the impact of various nutrients on the body.