Transcript Slide 1
VISUAL SYSTEM Key points Relations of neural retina to other structures in the eye Knowledge of types of photoreceptor and their distribution across the retina Foveal versus peripheral retina Knowledge of the different cell types that make up the retina There are different types of retinal ganglion cell – thus parallel outputs from the retina and beyond…. Central visual pathways – projections to LGB and other subcortical visual structures Organization of visual fields – partial decussation at optic chiasm, binocularity, topography Projection to primary visual cortex – optic radiations Effects of lesions on visual function Reading Nolte (4th Ed), pgs 397-431 Crossman and Neary, pgs 129-133 Fitzgerald, pgs 189-196, 201-202 Kiernan (7th Ed), pgs 364-381 Pritchard and Alloway, pgs 283-315 The human eye Mouse retinal wholemount NB Retina and optic nerve are derived from the neural tube – are of CNS origin Photoreceptors rods cones LIGHT light light Cone photopigments 130 million rods – monochromatic – high sensitivity – convergence 7 million cones – colour – central retina – high acuity – photopic vision 1 million retinal ganglion cells per eye – efferent cell Retinal circuitry rod Photoreceptors cone ONL OPL Horizontal cells Bipolar cells INL light Amacrine cells IPL Ganglion cells GCL output signals There are different classes of retinal ganglion cell: On/off cells, large and small receptive fields, sustained versus transient responses, monochromatic versus colour……(etc!!) Visual Pathways • Retina (rods, cones, fovea) – bipolars – ganglion cells - optic nerve • Chiasm (nasal fibres cross) • Optic tract – suprachiasmatic nuclei (diurnal rhythms) – pretectum (for eye movements) – superior colliculus (new objects, co-ordination of eye and head/neck movements) – lateral geniculate body of the thalamus (to cortex) Visual fields and central visual pathways in the human Lateral geniculate nucleus human monkey Visual topography – maps Control of Eye Movements • Medial longitudinal fasciculus connects all the cranial nerve nuclei (III, IV, VI) together • Descending cortical input • Input from superior colliculus • Input from ascending cervical proprioception Optic Reflexes Pupillary constriction (Edinger-Westphal) due to light (consensual…both eyes at once) On accommodation - convergence Classes of RGC • CAT – On/off cells – sustained X/transient Y – not much colour • MONKEY – On/off – Parvo (P) colour (red/green) and form – Magno (M) motion Monkey area 17 (V1) Ocular dominance stripes in layer IV Last Slide