1. Visual Pathways 2 Flashcards
Give the point where the first synapse is made by the optic tract for primary (conscious vision) vs secondary (unconscious vision)?
Primary vision- optic tract makes first synapse at LGN.
Secondary: the first synapse is at the superior colliculus, pretectum or Supra- chiasmatic nucleus (SCN).
Target of fibres in the optic tract thalamus (LGN)?
Vision
Target of fibres in the optic tract pretectum (OPN)?
Pupillary light reflex
Target of fibres in the optic tract of superior colliculus (tectum)?
Eye movement
Target of fibres in the optic tract accessory optic nuclei?
Visual ‘flow’
Target of fibres in the optic tract suprachiasmatic nuclei?
Circadian rhythm
Optic tract is found quite free near the chiasma, expect for?
Except for attachment to the 3rd ventricle wall.
Optic tract moves to?
LGN
LGN is shaped like?
Shaped like a knee- and as fibres move to the LGN they change shape to accommodate what they are going to plug into.
Fibres that move from the optic tract to the tectum produce?
Produce a parallel map of the visual world.
Suprachiasmatic nuclei are respond to?
Respond to a wavelength of light at a particular time (reset body clock).
Geniculate nucleus is dived into?
- Lateral GN
- Medial GN
Role of medial GN?
Auditory
Left LGN receives information from which optic tract that is carrying info from what hemi-field?
Left LGN receives information from left optic tract that is carrying information from the right hemi- field.
Location of LGN in the brain ?
In the middle of the brain- this is called diencephalon.
LGN has how many primary layers?
6 primary layers
Describe how LGN receives information? What are the layers called?
Layers 1 & 2 receive information from magnocellular RGCs.
Layers 3-6 receive information from parvocellular layers. Each layer of the eye receives information from only 1 eye.
Does LGN have binocularity?
NO
Each layer in the LGN only receives information from 1 eye.
The LGN has 6 intervening layers, what are this layers known as?
Koniocellular layers- they receive information from B/Y opponent Retinal Ganglion Cells.
LGN contains information form cells from 3 different layers, name them?
- Parvocellular layer
- Magnocellular layer
- Koniocellular layer
Which cells Parvo or Magno are on/ off?
Parvo
Optic tract is carrying information from both eyes hence, once information reaches LGN processing visual information is…?
Is from hemi-fields
Parvo or Magno which cells are on/off?
Parvo cells can be on/ off
Magno cells are also known as?
Parasol cells
Parvo cells are also known as?
Midget cells
Which cells have large dendritic arteries for blue/ yellow opponent cells?
Konio cells
Describe crossed and uncrossed projection seen in LGN.
If you inject an eye with dye, in the opposite eye in LGN crossed projection is seen. In that same eye you get uncrossed projection.
Crossed projection (contralateral) is in layer 1,4 & 6 and same side projection (ipsilateral) is in layer 2, 3 & 5.
Inputs from the two eyes are kept separate by?
By the LGN
Role of Parvocellular (P)/ Midget cells?
Responsible for detail, spatial contrast and some in colour.
Role of Magnocellular (M)/ Parasol cells?
Largely respond to movement. Also has some response to contrast.
Role of koniocellular?
Koniocellular is a colour channel largely B/Y.
80% of input in the LGN is from?
Is from the visual cortex.
Role of visual cortex?
Role of the visual cortex is feedback, control and mapping.
Role of brainstem?
Role of brainstem is alertness, attentiveness and arousal.
LGN performs well only when you are alert and awake. This is controlled by?
Controlled by RAS (reticular activating system).
Ability to switch attention from topic to topic is controlled by?
Controlled by the cortex.
Optical radiations emerge from?
LGN
Describe the movement of optical radiations?
Optical radiations emerge and fan out from LGN and move to the back of the brain to the occipital lobe.
However, lateral ventricles are in the way but they do not invade the movement of the fibres.
The fibres fibres form a flap and and fan like structure.
Since lateral ventricle comes in the way as optical fibres move from the LGN some fibres will have to come through?
Some fibres come through the temporal lobe.
The lower optical radiations come from?
The lower retina
The lower portion of the radiations which goes through the temporal lobe is called? And where does it terminate?
Is called Meyer’s loop, and this terminates below the calcarine sulus.
Damage to lower optical radiation produces what defect?
“Pie in the sky” defect- this is when upper quadrat of that visual hemi- field is defected/ lost.
Role of Meyers loop?
Responsible for information coming from the upper field and the upper radiations( upper retina) from the lower field.
Meyers loop is carrying information from lower retina meaning it is carrying information from which visual field?
Upper visual field
Visual cortex lies on top of?
Calcarine sulcus at the back of the brain
The lower portion of visual cortex is receiving information from ?
Lower hemi- retina
Calcarine Sulcus that corresponds accurately to?
Horizontal meridian in the retina.
Striate cortex is sometimes referred to as?
Area 17 (Brodmann’s Area 17) or V1 or primary visual cortex.
The visual cortex contains what % of all neurons of the entire neocortex?
10%
What amount of visual cortex is devoted to the fovea?
1/3 to 1/2
All the visual information passes through what before going to V2 and V3?
V1
Why is the cortex striated?
A myelinated layer is present within V1 (It is called line of Gennari). This is where you get the strip. The line separates V1 from V2 that allows you to differentiate between layers and hence, it is called striated. This layer is myelinated hence appears to be white.
Why do nasal RGCs cross at the chiasma?
Allows the visual cortex to receive the same hemispheric visual field from both eyes.
Accessory optic nuclei is divided into?
Left and Right, Up and Down
Middle portion of the brain is called?
What is found in the middle portion of the brain?
It is called diencephalon.
Thalamus found in the middle.
P-cells are neurons located within which layer?
Parvocellular layer
Line of Gennari corresponds to which layer in V1?
4B
Which layer is the input layer in V1? Where does the input come from?
Layer 4 majority and sometimes layer 2.
Input comes from LGN.
Line of Gennari ends with layer what are the 2 advantages of this?
- Makes it easier to identify V1
- Useful when doing elcto- physiological experiments.
What is special about the cells found in all 6 layers in V1?
Each layer has different cells.
These cells have different shapes, sizes and this relates to the fact that each cells processes information in a different manner. This layers can be differentiated by staining and microscopy.
Main output layer in LGN?
Layer 5 & 6
Describe the distribution of layer 4 in V1
Layer 4 is divided into A, B, C.
Layer C is sub-divides alpha and gamma.
Describe the difference in input to 4C beta and 4C alpha?
4C beta: input from parvo
4C alpha: input from magno
Where does koniocellular layer go in V1?
This goes into the colour blob in layer 2.
Once information is out of V1 it follows which 2 paths?
Dorsal & Ventral Pathway
Where does Dorsal & Ventral Pathway end?
Dorsal Pathway: Ends in the temporal lobe.
Ventral Pathway: Ends in the parietal lobe.
Loss of V4 & V5 results to?
Loss of V4: Patients can not see colour.
Loss of V5: Patients can not process motion.
LGN receives 80% of input from?
Visual Cortex
