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Where is vision processed?
In the occipital cortex
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Where does cross over of visual information occur?
At the optic chiasm
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In which species do all the fibres cross over at the optic chiasm?
Fish and birds (excluding birds of prey)
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Information travels from the optic chiasm, along the optic tract, to the ...?
Lateral geniculate nucleus
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Which nerves control the ocular muscles?
Oculomotor, trochlear and abducent (CNs III, IV, and VI)
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Sympathetic/parasympathetic supply is associated with the oculomotor nerve (CN III)?
Parasympathetic - therefore damage to CN III can result in dilation of the eye
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What is the difference between central and subcortical visual pathways?
Central pathways involved the visual cortex whereas subcortical pathways do not
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What type of blindness is associated with central/subcortical pathways?
- Central - central blindness
- Subcortical - peripheral blindness
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What is the dazzle reflex?
Blink or moving head away from sudden illumination of eyes
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Which test involves the visual cortex: the menace response or pupillary light reflex?
The menace response
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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
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Which nerve is responsible for the blink caused during the menace response?
The facial nerve (CN VII)
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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
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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)
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What elements does the menace response test?
Optic nerve afferent, facial nerve efferent and cortex
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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)
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Which tests can be used to test cortical/subcortical visual pathways?
- Cortical - menace
- Subcortical - pupillary light reflex, dazzle reflex
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