The occipital The occipital lobes Occipital lobe - Mahidol University

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23/06/54corpus callosum (Latin: tough body), also known as the colossalcommissure, is a wide, flat bundle of neural fibers beneath the cortex in theeutherian brain at the longitudinal fissure. It connects the left and right cerebralhemispheres and facilitates interhemispheric communication. It is the largest whitematter structure in the brain, consisting of 200–250 million contralateral axonalprojections.The posterior portion of the corpus callosum is called the splenium; theanterior iscalled the genu (or "knee"); between the two is the truncus, or "body", of the corpuscallosum. The part between the body and the splenium is often markedly thinnedand thus referred to as the "isthmus". The rostrum is the part of the corpus callosumthat projects posteriorly and inferiorly from the anteriormost genu, as can be seenon the sagittal image of the brain displayed on the right. The rostrum is so named forits resemblance to a bird's beak.Thinner axons in the genu connect the prefrontal cortex between the two halves ofthe brain. Thicker axons in the midbody of the corpus callosum and in the spleniuminterconnect areas of the premotor and supplementary motor regions and motorcortex, with proportionally more corpus dedicated to supplementary motor regions.The posterior body of the corpus communicates somatosensory informationbetween the two halves of the parietal lobe and visual center at the occipital lobeCorpuscallosumCorpuscallosumOccipital lobe lesions• Irritative lesions –seizure– Seizure symptoms: visual hallucinations,consisting of unformed flashes of light andcolors• Destructive lesions– Visual field defects (homonymous field defects)– Psychic blindnessOccipital lobe epilepsy• Seizure symptoms– Visual hallucinations and/or illusions– Blindness or decreased vision– Pallinopsia or image repetition (a visual limage isreplayed again and again)– Sensation of eye movements16
23/06/54Occipital lobe epilepsy• Seizure symptoms (cont.)– Eye pain– Involuntary eye movement to one or other side– Nystagmus or eye jerking to one or other side– Eyelid fluttering• 4 major types of visualfield defects– Altitudinal field defects– Central scotoma– Bitemporal hemianopia– HomonymoushemianopiaVisual field defectsVisual field defectsTypes of visual field defects• Altitudinal field defects = loss of vision aboveor below the horizontal plane• Central scotoma = loss of central vision• Bitemporal hemianopia = loss of vision at thesides• Homonymous hemianopia– Loss at one side in both eyes– Sites of lesion: behind optic chiasmNormalvisual fieldBitemporalhemianopiaPictures from WikipediaTypes of visual field defectsTypes of visual field defectsNormalvisual fieldNormalvisual fieldBinasalhemianopiaPictures from WikipediaLefthomonymoushemianopiaPictures from Wikipedia17
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The occipital The occipital lobes Occipital lobe - Mahidol University

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