Visual pathway Flashcards
What are the 3 layers of the eye ball?
Sclera
Choroid
Retina
What structure is in line with the visual axis?
Macula
What does the Macula contain?
It contains Con cells that are invovled in high acuity vision
What nerve controls the ciliary muscle?
The Ps branch of occulomotor nerve via the ciliary ganglion.
Post ganglion axon innervates the spincter pupilae via V1
What does the retina contain?
Photoreceptors
Does the optic disc contain photoreceptors and what is it attached to?
It does not contain photoreceptors it is a blind spot of the eye.
Connected to the optic nerve that goes to the optic chiasma
What two layers can the retina be divided into?
The non neuronal layer ( pigmented) or the neuronal layer ( photoreceptors)
What is the actions of the non neuronal layer of the retina?
It contains pigmented layer that sits against the choroid of the eye ball and is light absorbing. It absorbs any photons not absorbed by the photoreceptors to prevent blurred vision.
It also maintains metabolic activity of the photoreeptors which it surrounds by melanin filled microvilli
Finally it supplies the photoreceptors with capillaries
What does the neuronal layer contain?
Contains photoreceptors, bipolar and ganglion neurones
What does the bipolar neurone connect?
It connects the photoreceptors to the ganglion cells
What do the axons of the ganglion cells form?
The axons of the ganglion cells form the optic nerve at the optic disc
What is the location of the optic disc in relation to the fovea?
It is slightly medial
What interconnects the photoreceptors, bipolar and ganglion cells?
Interneurones: horizontal and amacrine
Where are the horizontal and amacrine interneurones situated?
The horizontal is between the photoreceptors and the bipolar cells
The amacrine is between the bipolar and amacrine cells
What is the function of the interneurons?
They modulate transmission by turning off and on the photoreceptors –> control the acuity of vision.
What is the change of energy at the interneurons?
Photochemical reaction occurs that see’s the transmission of transudece light enery to electricle energy.
There is a change in action potential
What is odd about the retina and direction of light?
The light has to get throug the mesh of support to get to the photoreceptors
What is abnromal about cranial nerve 1 and 2?
They are part of the CNS not the PNS
THe optic chiasma is attached to the floor of the hypothalamus which is a outgrowth of the diencephalon
What is the eye balls a outgrowth of?
The diencephalon
What is the route of the visual pathway? Retina to cortex?
1st and 2nd order are within the retina
First order unlike the others is very short –> Bipolar cells
2nd order: Ganglion cells the axons extend out of the retina into the optic disc where it forms the optic nerve.
The optic nerve ( formed within the CNS) goes to the lateral geniculate nucleus of the thalamus –> relay nuclei
The 3rd order is the optic radiate –> Goes from the thalamus to the primary visual cortex
What surrounds the optic nerve and eye ball as a consequence of being a outgrowth of the CNS?
It is surrounded by meninges as the optic nerve extends to the eye ball.
Has the same layers and structure with CSF in the subarachanoid space
What is the consequence if there is a rise in ICP of the CSF surrounding the eye ball and optic nerve?
Papilloedema
How does Papilloedema arise?
There is a increase in CSF pressure which causes the compression of central retinal veins which prevents venous drainage of the eye.
This causes the swelling of the optic disc and therefore the compression of the optic nerve as well as that is surrounded by the menigines
What is the symptoms of increase CSF pressure in the eye?
Blurred vision, drowsiness, head ache and vomiting
Where is the primary visual area?
The occipital lobe
The calcarine sulcus
What seperates the occipital and parietal lobe?
The parietooccipital sulcus
What sits above and below the calcarine sulcus?
Striate cortex –> upper and lower bank of the calcarine sulcus
Where is the visual assoication cortex?
It is the pre straite area and above and below the upper and lower bank of the calcarine sulcus
Do you see the Calcarine sulcus mainly in the lateral or medial surface of the brain?
The medial surface
What are the two visual fields?
Temporal and nasal Temporal is (lateral) Nasal ( down the middle)
If you are looking left the light will hit what part of the left and right eye?
It will hit the nasal part of the left eye and the temporal part of the right eye
If you are looking dead straight where will the light hit?
The macula
If you are looking right the light will hit what part of the left and right eye?
The light will hit the nasal retina part of the right eye and the temporal retina part of the left eye
From what direction does information cross to the contralateral side?
The information coming from the left or right temporal field
Is the nasal fibers and temporal fibers run contralaterally or ipsilaterally?
The nasal fibers run contralaterally
The temporal fibers run ipsilaterally
What part of the cerebral hemisphere does the left and right half of visual field go to?
The left half of the visual field goes to the right cerebral hemisphere
The right half of the visual field goes to the left cereberal hemisphere
What bank fo the calcarine sulcus does upper and lower vision field go to?
The upper vision field goes to the lower bank of the calcarine sulcus
The lower vision field goes to the upper bank of the calcarine sulcus
Where does center visual axis (macule) go to?
The occipital pole
What is the route of the pathway from the LGN of the thalamus to the upper and lower banks of the calcarine sulcus?
They take different pathways to the banks.
There is a upper and lower visual field pathway.
What is the Meyers loop?
Due to the position of the inferior horn of the lateral ventricle the lower visual field pathway has to loop around the inferior horn which is called the Meyer’s loop
How can vision be disrupted?
Damage to the vision pathway between the retina and the cerebral cortex
What is the name of localised patches of blindness?
Scotoma
What is anopia?
Referes to the loss of one or more quadrants of visual field
What is hemianopia?
When there is loss of half the visual field
What is the name of the condition when you loose quater of your visual field?
Quadrantanopia
What is heteronymous?
Visual loss that is different on each side
What is homonymous?
Visual field loss that is similar on each side
What is homonymous heminopia?
It is the loss of half of your visual field on the similar side of each side
What is monocular blindness?
Complete blindness in one eye
In monocular blidness where is the lesion?
Lesion of the optic nerve
Lesion of the optic chiasma will cause what type of visual field loss?
Heteronymous hemianopia
It is visual loss in the outer half of both the right and left eye
What is homonymous hemianopia and what is the cause?
Is loss of vision on the same side of both eyes
Caused by a lesion of the optic tract–> complete lesion
How do you get homonymous quadratanopia?
Damage to one of the fibers in the optic radiation
10% of optic tract don’t go to the LGN but to another structure. What structure is this?
10% take a medial root to the pre tectal area in the mid brain in front of the colliculus.
Involved in pupillary light reflex
What is the pupil light reflex?
The ability for both eyes to dilate or constrict depending on the level of the light the retina recieves
What two cranial nerves are invovled in the pupil light reflex?
Afferent (sensory) root = optic nerve and tract
Efferent (motor) root = occulomotor nerve
What are the two components of the pupil light reflex?
Direct component –> shine light in a eye and the same pupil constricts
Consensual component –> shine light in one eye and the opposite pupil constricts
What are the two nucleis of oculomotor nerve?
Oculomotor nuclei
Edinger Westphal nuclei
What are the functional characteristics of Rod cells?
Highly sensitive to light ( specialised for night vision)
High photopigment, capture a large amount of light
High amplification
Low temporal resolution ( slow response)
More sensitive to scattered light
What are the functional characteristics of Cone cells
Low sensitivity to light ( specialised for day vision) Less photopigments than rod cells Low amplification High temporal resolution ( fast acting) More sensitive to direct light
What are the functional characteristics of rod system?
Low acuity, not found in the fovea and invoveld in converent pathway
Achromatic only one type of rod cell
What are the function characteristics of cone system?
High acuity and found in the Fovea. Invovled in divergent pathway
Trichromatic, has 3 different types which have different wavelength preference
What is the fiber that transfers information from the primary visual area ( straite cortex) to the secondary visual area ( prestraite area)?
Short assoication fibers
Macula vesion goes to what part of the occipital?
The occipital pole
Where would there be damage if there was homonymous heamianopia ( with macula sparing)
There would be damage to the optic radiate not going to the occipital pole
If there was bilateral central scotoma what part of the visual pathway would be damaged?
The ocipital pole would be cut
If you were going to have homonymous hemianopia ( with macula sparing) where would be the lesion?
The lesion would cut the optic radiate of both optic tracts but the occipital pole would remain intact.
What nuclei does the optic nerve in the pre tectorial area synapse with?
The Edinger- Westphal nucleus on the ipsilateral and contralateral side
If you damage the optic nerve of a eye would it stll be able to constrict?
Yes it would be because the occulomotor nerve is still intact and the other eye can cause the constriction to happen
If there was damage ot the occumulotor nerve of one of the eyes would that eye be able to constrict?
No it would not be able to constrict as there is no way of getting PS information to the eye and therefore the eye would be slightly dilated as there as the sympathetic input is unopposed
