Visual pathways and perception Flashcards
where is the optic chains in relation to the pituitary
- The optic chiasm is immediately above the pituitary
what does a pituitary tube cause
It causes bilateral loss of peripheral receptive fields
where does the optic nerve synapse and become a 2nd order neurone
- in the optic tract in the lateral geniculate nucleus
what does the lateral geniculate nucleus project into
The lateral geniculate cells project into the optic radiation into the primary visual cortex(area 17) and then into the visual association cortex
what supplies the axon of the optic nerve
Retinal ganglion cells supply the axons that constitute the optic nerve (
what pathway mediates visual perception
- the lateral geniculate occipital cortex pathway
where do some other optic nerve fibres project into
some optic nerve fibres project to the superior colliculi in the midbrain
what do the superior colliculi do
- they are necessary from tracking an object
- they connect to the medial longitudinal fascicule which links and synchronises with the oculomotor nuclei
if you have damage to the superior colliculus pathway what happens
Damage to the superior colliculus pathway means that a patient has difficulty tracking a moving object
what is another name for the superior colliculi
- optic tectum
where do some fibres from the retina project into
Some fibres from the retina project to the pretectal nuclei and then bilaterally to the Edinger-Westphal nuclei
How is the pupillary light reflex caused
- Parasympathetic preganglionic fibres project from the Edinger-Westphal nuclei to the ciliary ganglia in the orbit behind each eye.
- From here postganglionic fibres enter the eye and act on sphincter muscles around the pupil to constrict it.
- This is the pupillary light reflex - this reflex is bilateral so both eyes are affected
where do the axons from the cells in the lateral geniculate go
- Axons from cells in the lateral geniculate nucleus project to the visual cortex via the optic radiation.
- The axons from the lateral geniculate cells project anteriorly and then posteriorly along the side of the posterior horn of the lateral ventricle eventually to reach the occipital cortex.
What is Meyers loop
- Fibres in the optic radiation mediating vision from the upper quadrants loop more anteriorly around the side of the lateral ventricle
- this is Meyers loop
- on the other hand fibres from the lower quadrants travel more directly back to the visual cortex
describe strokes and Meyer’s loop
Strokes or tumors can sometimes selectively damage Meyer’s loop on one or other sides of the brain
both eyes….
contribute to both visual fields
- the The left visual field projects to the right visual cortex and vice versa.
How can both eyes contribute to both visual fields
- The nasal hemiretina from the left eye projects to the right visual cortex
- the temporal hemiretina from the right eye projects to the same right visual cortex - this is because the temporal hemiretina do not cross over the chiasmata whereas the axons from the nasal hemiretina do
- Both hemiretinae view objects in the left visual field.
what the lesions in the visual system
1 Partial optic nerve lesion: Ipsilateral scotoma*
2 Complete optic nerve lesion Blindness in that eye
3 Optic chiasm lesions: Bitemporal hemianopia
4 Optic tract lesions: Homonymous hemianopia
5 Damage to of Meyer’s Loop:
Homonymous upper quadrant anopia (axons are arranged with upper part of visual field anterior)
6 Optic radiation lesion:
Homonymous hemianopia
7 Visual cortex lesion
Homonymous hemianopia
(Macular sparing)
