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visual pathway
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- 2. Begins at theoptic disc Pierces tunic of eyeball 3mm nasal to posterior pole
- 3. Visual Pathway • Eacheyeball act as camera ;it perceives the images & relay the sensations to the brain(occipital cortex) via the VISUAL PATHWAY.
- 4. VISUAL PATHWAY comprises of: OpticNerve Optic Chiasma Optic Tract Lateral Geniculate Body Optic Radiations Visual cortex
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- 6. OPTIC NERVE • 2nd cranialnerve. • 47-50 mm in length. • Starts from optic disc & extends upto optic chiasma where the two nerves meet. • Backward continuation of nerve fibre layer of retina which consist of axons originating from ganglion cells. • Contains the afferent fibres of light reflex • Has 4 parts : 1)intraocular (1mm) 2)intraorbital (30mm) 3)intra canalicular (6-9mm) 4)intracranial (10mm)
- 7. Schematic representation ofvisual pathways
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- 9. Receptors: 1. Rods 2. Cones Neurons: 1.First order: bipolar cells 2. Second order: ganglion cells 3. Third order: LGB Visuo-striate area (17): Both walls of calcarine sulcus involving Cuneus and lingual gyrus
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- 12. OPTIC CHIASMA • AFLAT MASS OF PARTIALLY DECUSSATING FIBRES WHICH LIES AT THE JUNCTION OF THE ANTERIOR WALL AND FLOOR OF THE 3RD VENTRICLE • ONLY NASAL RETINAL FIBRES CROSS OVER . • THEY JOIN THE FIBRES FROM THE OPPOSITE TEMPORAL RETINAS • THESE FIBRES FORM THE OPTIC TRACTS.
- 13. 1. OPTIC NERVE (STUMP) 2. 0PTIC CHIASMA 3.OPTIC TRACTS
- 14. VisualVisual PathwayPathway Optic chiasma: 1. Junctionof the floor and the anterior wall of the third ventricle 2. Rests on the diaphragma sellae 3. Wilbrand’s loop
- 15. OPTIC TRACTS • Cylindricalbundle of nerve fibres. • Run outwards & backwards from posterolateral aspect of optic chiasma ,between tuber cinereum & anterior perforated substance to unite with cerebral peduncle. • Fibres from temporal half of retina of same eye & nasal half of opposite eye. • Posteriorly each ends in Lateral Geniculate Body.
- 16. VisualVisual PathwayPathway Optic tracts: 1. Medialroot Gudden’s commisure 2. Lateral root a. LGB b. Superior colliculus & pre-tectal nucleus c. Supra-chiasmatic nucleus
- 17. VisualVisual PathwayPathway Lateral geniculate body: 1.Part of meta-thalamus 2. Connected to superior colliculus via superior brachium 3. Cells arranged in six layers
- 18. OPTIC RADIATIONS (Geniculo- CalcarinePathway) • From LGB to the occipital cortex. • Pass forwards then laterally through the area of wernicke as optic peduncles. • Anterior to lateral ventricle ,traversing the retrolenticular part of internal capsule,medial to auditory tract. • Its fibres then spread out fanwise to form medullary optic lamina. • Inferior fibres subserve upper visual fields & sweep anteroinferiorly in meyer’s loop & temporal lobe to visual cortex. • Superior fibres subserve inferior visual field proceed posteriorly through parietal lobe to visual cortex.
- 19. VisualVisual PathwayPathway Optic radiation: 1. FromLGB to striate area of visual cortex (17) 2. Passes through the retro- Lentiform part internal capsule 3. Meyer’s loop
- 20. Primary Visual Cortex???? •Area 17 • located in the occipital lobe in the calcarine fissure region extending to the pole • large representation in visual cortex for the macula (region for highest visual acuity) • receives the primary visual input BY Muhammad Ramzan Ul Rehman Nishtar Ken 20
- 21. primary VISUAL CORTEX • FROMTHE LATERAL GENICULATE NUCLEUS, THE FIBRES PASS BY THE OPTIC RADIATIONS TO THE PRIMARY VISUAL CORTEX. • IT IS LOCATED IN THE CALCARINE FISSURE AREA OF THE MEDIAL OCCIPITAL LOBE. (BRODMANN’S AREA 17 OR V1)
- 22. Secondary Visual Areas •visual association cortex (area 18, 19) • responsible for analyzing the visual information • area for 3 dimensional position, gross form, and motion • area for color analysis BY Muhammad Ramzan Ul Rehman Nishtar Ken 22
- 23. VISUAL CORTEX • Locatedon the medial aspect of occipital lobe, in & near calcarine fissure.
- 24. Retinal Projections to SubcorticalRegions • suprachiasmatic nucleus of the hypothalamus – control of circadian rhythms?? • pretectal nuclei – pupillary light reflex – accommodation of the lens • superior colliculus – rapid directional movement of both eyes BY Muhammad Ramzan Ul Rehman Nishtar Ken 24
- 25. The Autonomic Nervesto the Eyes 25
- 26. The Autonomic Nervesto the Eyes • The eye is innervated by both parasympathetic and sympathetic neurons. • Parasympathetic fibers arise in the Edinger- Westphal nucleus, pass in the 3rd cranial nerve to the ciliary ganglion. – Postganglionic fibers excite the ciliary muscle and sphincter of the iris. • Sympathetic fibers originate in the intermediolateral horn cells of the superior cervical ganglion. – Postganglionic fibers spread along the corotid artery and eventually innervate the radial fibers of the iris. 26
- 27. Control of PupillaryDiameter • miosis: decreasing of pupillary aperture due to stimulation of parasympathetic nerves that excite the pupillary sphincter muscle • mydriasis: dilation of pupillary aperture due to stimulation of sympathetic nerves that excite the radial fibers of the iris 27
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- 29. Visual reflexes • Light reflexor pupillary reflex: When light is shown to one eye, normally the pupils of both eyes constrict. - Direct light reflex: The constriction of pupils upon which light is shown is called direct light reflex. - Indirect or consensual: The constriction of pupil on the other eye even though no light is shown
- 31. Pathways of directand indirect light reflexes (v.imp.) BY Muhammad Ramzan Ul Rehman Nishtar Ken 31
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- 34. ACCCOMODATION REFLEX • Whenthe eyes are focussed from a distant to near object, three reactions take place • 1. Constriction of pupils • 2. thickening of lens due to contraction of ciliary muscles • 3. Convergence of both eye balls These three reactions together constitute Accommodation or near reflex
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