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visual pathway.pptx
The visual pathway begins with light entering the eye and stimulating the retina. Optic nerve fibers carry signals from the retina to the optic chiasm, where fibers from the nasal retina cross to the opposite side. The fibers then continue along the optic tracts to the lateral geniculate bodies and on to the primary and secondary visual cortices via the optic radiations. The visual cortex is located in the occipital lobe and is responsible for visual perception and recognition.
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visual pathway.pptx
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- 2. Key points Thevisual pathways; Anatomical considerations Arrangement of fibers Clinical implications on visual field and binocularity.
- 3. Optic nerve Optic chiasma Optictract Lateral geniculate body Optic radiations Visual cortex
- 4. Optic nerve parts ofoptic nerve o Intraocular (1mm) o Intraorbital (25mm) o Intracanalicular o (6-9mm) o Intracranial (10- 16mm)
- 5. Intraocular part Passesthrough sclera, choroid and appears in eye as optic disc. Intraocular portion is of 1.5mm which expands to 3mm just behind eye because of myelin sheath.
- 6. Intraorbital part Extendsback from eyeball to optic formaina. Covered by dura, arachnoid and pia. Central retinal artery enters nerve on its inferomedial aspect about 10mm behind eyeball. Some fibers of superior rectus and medial rectus are adherant to its sheath so painfull ocular movement in retrobulbar neuritis.
- 7. Intracanalicular part About6-9 mm long. The optic nerve passes through the optic canal surrounded by its three meningeal sheaths. Close relation to sphenoid and ethmoid sinus.
- 8. Intracranial part 10-16mm length Above cavernous sinus and converges with its fellow to form chiasma Covered by pia only.
- 9. Optic chiasma o Flattenedstructure measuring 12mm horizontally , 8mm anterio-posteriorly. o It lies over diaphragma sella o Nerve fibers arising from nasal halves of the two retinae decussate at the chiasma
- 10. Optic tracts Boundlesof nerve fibers running outwards and backwards from postero-lateral aspect of optic chiasma Consist of temporal fibers of retina of same eye and nasal half of opposite eye Each optic tract end in LGB.
- 11. Lateral Geniculate Body Oval structures situated at termination of optic tract Each LGB consist of six layers of neurons alternating with white matter. Each body is split into 6 laminae Fibers from ipsilateral temporal retina end in lamina 2,3,5 Contralateral nasal retina end in lamina 1,46 These 6 lamina divide LGB into 2 portions.
- 13. ” “ Functions ofLGB • Relay station to relay visual information from optic tract to visual cortex • To gate transmission of signals to visual cortex
- 14. Optic radiations Extendfrom LGB to visual cortex. Fibers of optic radiation spreads out fanwise to form medullary optic lamina. Superior fibers of radiation (which subserve inferior feild) proceed directly posteriorly through parietal lobe.
- 15. Inferior fibers ofradiation (which subserve superior field) first sweap anteriorly in meyers loop around anterior tip of temporal horn of lateral ventricle and then into temporal lobe.
- 16. VISUAL CORTEX LOCATION: LOCATEDON MEDIAL ASPECT OF OCCIPITAL LOBE. AREAS: THERE ARE TWO MAIN AREAS.
- 17. VISUAL CORTEX 1. PRIMARYVISUAL CORTEX: Brodmann’s area 17. 2. SECONDRY VISUAL CORTEX: Brodmann’s area 18 and 19. BLOOD SUPPLY: Posterior cerebral artery,middle cerebral artery.
- 18. VISUAL CORTEX PRIMARY VISUALAREA: Occupies the walls of calcarine sulcus,extends onto the cortex above and below the sulcus. Recognised by its thinness and white line or striae in grey matter.
- 19. VISUAL CORTEX SECONDARY VISUALAREA: These areas surround the primary visual area on medial and lateral surfaces. These are non striate. Shows 6 layers.
- 20. VISUAL CORTEX FUNCTIONS OFSECONDARY VISUAL CORTEX: Enables individual to recognize what he/she saw. Integrates the 2 halves of visual field. Controls EOM muscles for smooth pursuit of targets.