Central Visual Pathways and the Perceived Visual Field
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Where is vision processed?
In the occipital cortex
Where does cross over of visual information occur?
At the optic chiasm
In which species do all the fibres cross over at the optic chiasm?
Fish and birds (excluding birds of prey)
Information travels from the optic chiasm, along the optic tract, to the ...?
Lateral geniculate nucleus
Which nerves control the ocular muscles?
Oculomotor, trochlear and abducent (CNs III, IV, and VI)
Sympathetic/parasympathetic supply is associated with the oculomotor nerve (CN III)?
Parasympathetic - therefore damage to CN III can result in dilation of the eye
What is the difference between central and subcortical visual pathways?
Central pathways involved the visual cortex whereas subcortical pathways do not
What type of blindness is associated with central/subcortical pathways?
- Central - central blindness
- Subcortical - peripheral blindness
What is the dazzle reflex?
Blink or moving head away from sudden illumination of eyes
Which test involves the visual cortex: the menace response or pupillary light reflex?
The menace response
Why will the menace response not be present in younger animals?
As the menace response has to be learned - it is a response not a reflex
Which nerve is responsible for the blink caused during the menace response?
The facial nerve (CN VII)
What can do to test an animals vision? What elements are we testing?
- Menace response, observation in environment, visual tests e.g. dropping cotton wool
- Optic nerve (CN II), Optical cortex and associated effector systems
What can we do to test pupil size? What elements are we testing?
- Low light levels to stimulate pupil dilation. Testing optic nerve afferent (CN II), brainstem, autonomic supply to the eye (CN III - oculomotor nerve)
- Pupillary light reflex. Testing Optic nerve afferent (CN II), brainstem, autonomic supply to the eye (CN III)
What elements does the menace response test?
Optic nerve afferent, facial nerve efferent and cortex
How do we test facial sensation? What elements are we testing?
- Stimulate skin of the face to try and get facial twitching or head movement
- Trigeminal nerve afferent (CN V) and facial nerve efferent (CN VII)
Which tests can be used to test cortical/subcortical visual pathways?
- Cortical - menace
- Subcortical - pupillary light reflex, dazzle reflex
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