The visual pathway Flashcards
What is the start to end of the visual pathway
ganglion cell axons
Optic nerve
Optic Chiasm
OPtic tract
Lateral geniculate body (LGB)
Optic radiation
Visual cortex
What will happen if a lesion happens along the visual pathway
Visual field loss will occur (note that nasal half of retina sees the temporal part of the obj.)
What is the field of vision
100 temporal
60 nasal
120 central (binocular vision)
60 superior
75 inferiorly
What does the optic nerve contain
Millions of axons derived from the retinal ganglion
What is the optic nerve subdivided into
Intra-ocular (eye)
- retinal surface of optic disc to sclera
Intra orbital (orbit)
- Globe to optic canal
Intracanlicular (canal)
- Passes thr optic canal
Intracranial (head)
- leaves canal to reach optic chiasma
What is the blood supply of the intra ocular portion of the optic nerve
Branches of circle of Zinn-Haller and short posterior ciliary arteries
What is the blood supply of intra orbital portion of optic nerve
Pial plexus of vessels, central collateral arteries (central retinal artery)
What is blood supply of the intracanalicular portion of the optic nerve
Branches from pial plexus
What makes the circle of willis
Anterior communicating artery
Anterior cerebral arttery
Internal carotid artery
Posterior commmunicating artery
posterior cerebral artery
Which nerve fibres cross and do not cross at the optic chiasma
Fibres from nasal half of retina decussate a and cross to opp. optic tract
- partial crossing essential for binocular vision
Fibres from temporal half of the retina do not cross but pass back into the optic tract of the same side
What is the blood supply of the optic chiasma
Branches from the internal carotid artery
Which fibres are the optic tract derived from
Form nasal nerve fibres from opp. side and temporal nerve fibres from same side of the retina
Where do the fibres reach after the optic tract
90% of nerve fibres reach lateral geniculate body
Some distrbuted to
- superior colliculus (eye reflex)
- pretectal nuclues (pupillary reflex)
Describe the LGB
Axons of retinal ganglion cells synapse here in a specific layering pattern
Recives nasal nerve fibre from opp. side and temporal nerve fibres from same side of the retina
What does LGB play a part in
Modify pattern of the strength of retinal signals and plays a part in stereopsis and colour vision
Describe the optic radiation
Arise from LGB to relay messagesto occipital lobe at striate region
What are the two parts of visual cortex
Primary visual cortex (straite cortex)
Secondary visual cortex
Type of cells in the primary visual cortex
Simple, complex and hypercomplex
How does the receptive field differ in the cortex vs the retina
Receptive fields as mapped out in the cortex differs from those in the retina without the concentric circularly symmetrical pattern
How is the perception of edges perceived
Combination by simple and complex cells
Combined action of simple and complex cells provide the neuronal basis of perceiving edges, borders, boundaries and contrasts
What is the function of the primary visual cortex
Detection of lines and borders, orientation of lines lines and borders, line position and length of lines/ detects lines and borders
What is the function of the secondary visual cortex
Interpret signals from primary visual cortex and allows one to recall memory of previous sensory experience/ responsible for visual memory
Extra:
- recognition of objects but not recognition of written or printed symbols of language
- recall of visual memory relating to obj. but not to language symbols
