Download VISUAL SYSTEM Key points Relations of neural retina to other

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
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