Visual Pathway Flashcards
What is the central visual pathway?
The main pathway for conscious site
Where do the axons from the nasal half of retina go when the reach the chiasm?
They cross to the contralateral optic tracts
Where do the axons from the temporal half of retina go when they reach the chiasm?
They continue ipsilaterally
Where do 90% of fibres from optic tracts synapse?
The lateral geniculate nucleus of the thalamus
What do the other 10% of fibres from optic tract form?
The superior brachium
Where does the superior brachium pass to?
The superior colliculus
Where do the optic radiation neurons arise?
The lateral geniculate nucleus
Where do the optic radiation neurons pass to?
Primary visual cortex on medial surface of occipital lobe
Where does the upper loop of the optic radiation pass through?
The parietal lobe
Where does the upper loop of the optic radiation terminate?
The superior margin of the calcarine sulcus
Where does the lower loop of the optic radiation pass through?
The temporal lobe
Where does the lower loop of the optic radiation terminate?
The inferior margin of the calcarine sulcus
What are the four main layers of the retina?
The pigment, photoreceptor, bipolar and ganglion layers
What is the function of the pigment layer?
Absorbs light and prevents reflection
What do the bipolar cells represent?
1st order neurons for this pathway
What are the ganglion cells?
2nd order neurons
Outline the pupillary light reflex pathway
- Light generates impulses that pass to pretectal nucleus in midbrain
- interneuorns connect pretectal nucleus to accessory occulomotor nuclei
- Fibres cross to contralateral nucleus via posterior commissure
- Parasympathetic fibres from accessory occulomotor nuclei travel with occulomotor nerve to ciliary ganglion
- Fibres synapse in ciliary ganglion and pass into eyeball via short ciliary nerves
- Terminate in sphincter pupillae muscle of iris
- sphincter pupillae constrict iris
Outline reading aloud pathway
- Visual images travel to LGN
- Travel to visual cortex via optic radiation
- From calcarine sulcus, information is moved to association cortex
- Transferred to dominant hemisphere via corpus callosum
- Visual phrase passed from occipital lobe to angular gyrus in inferior parietal lobule
- Transfered to Wernickes area
- Transfered to Broca’s area in frontal lobe via arcuate fasiculus
What does the saccadic system allow for?
Voluntary direction of gaze
What does the pursuit system allow for?
Subject to follow moving object
What does optokinetic system allow for?
Restores gaze despite movements from outside world
What is the function of vestibulo-occular reflex system?
corrects movement of head to preserve stable visual image of world
What is the function of the accommodation reflex?
Allows focussing on close objects
How does accomodation occur?
- Same pathway utilised as pupillary reflex, with exception that ciliary body also entrained
- Contraction of ciliary body releases tension in suspensory ligaments of lens- lens thickens due to own elasticity, causing increased refraction of light
What do axons of the ganglion nerve form?
The optic nerve
