The Central Visual System

Front 1

What is the retinofugal projection?

Back 1

The neural pathway leading away from the eyes towards the brain stem.

Front 2

Optic nerves

Back 2

1. Exit left and right eyes at optic disks.
2. Travel through fatty tissue behind the eyes in their bony orbits.
3. Pass through holes in base of skull.

Front 3

Optic chiasm

Back 3

The optic nerves from both eyes = the chiasm.
-The axons originating from the nasal retinas cross from one side to the other.

Front 4

Decussation

Back 4

-The crossing of fiber bundles from one side of the brain to the other.

Front 5

Why does is there only partial decussation at the optic chiasm?

Back 5

Because only the nasal retinas cross (not the temporal, superior, or inferior retinas)

Front 6

What is the visual hemifield?

Back 6

-Half of the visual field (e.g. right and light)

Front 7

Binocular visual field

Back 7

-The area of the visual field viewed by both eyes.
-Central portion
-The left visual hemifield is viewed by the right hemisphere and the right visual hemifield is viewed by the left hemisphere.

Front 8

What is the importance of the lateral geniculate nucleus (LGN)?

Back 8

-Most optic tract axons innervate at the LGN of the dorsal thalamus.
-The neurons here give rise to axons that project to the primary visual cortex.

Front 9

Optic tracts

Back 9

After decussation, the axons of the retinofugal projection form these, which run under the pia along the lateral surfaces of the diencephalon.

Front 10

What is optic radiation?

Back 10

-The LGN gives rise to axons which travel to the primary visual cortex. This projection is called optic radiation.

Front 11

Superior colliculus

Back 11

-10% of ganglion cells in the retina project to this part of the midbrain tectum.
-

Front 12

Retinotectal

Back 12

-Projections from the retina to the superior colliculus.

Hint 12

optic tectum

Front 13

True or false? Different types of retinal information are received in the same area of the LGN.

Back 13

False. Various inputs from the right and left eye are segregated into the 6 layers of the LGN.

Front 14

On what layer do ipsilateral inputs synapse?

Back 14

2, 3, and 5

Front 15

On what layer to contralateral inputs synapse?

Back 15

1, 4, and 6

Front 16

What are the ventral layers of the LGN called and why?

Back 16

Magnocellular LGN layers, because they contain larger neurons.

Front 17

What are the dorsal layers of the LGN called and why?

Back 17

Parvocellular LGN layers, because they contain smaller neurons.

Front 18

Koniocellular layers

Back 18

-Contain tiny neurons lying just ventral to each layer of the LGN.
-Receive input from nonM-nonP types of retinal ganglion cells.
-Project to visual cortex

Front 19

Describe the importance of nonretinal inputs to the LGN.

Back 19

-80% of excitatory synapses come from the primary visual cortex.
-Also from neurons in the brains stem whose activity is related to alertness and attentiveness.
-LGN is more than a simple relay from retina to cortex - it is the first site in the ascending visual pathway where what we see is influenced by how we feel.

Front 20

Primary Visual Cortex

Back 20

-Brodmann's Area 17
-Occipital lobe
-Also called V1 and striate cortex.

Front 21

What is retinotopy?

Back 21

-Mapping of vision on certain structures in the brain.
-Similar to tonotopy, somatotopy.

Front 22

Cytochrome oxidase

Back 22

-Mitochondrial enzyme used for cell metabolism.
-Organized in blobs.
-Interblob regions
-Blobs receive direct LGN input from the koniocellular layers, as well as parvocellular and magnocellular input from the layer IVC of striate cortex.

Front 23

Magnocellular Pathway

Back 23

-Begins with M-type ganglion cells in the retina
-Cells project axons to the magnocellular layers of the LGN.
-These layers project to IVB.
-The pyramidal cells in IVB have binocular receptive fields of the simple/complex type.
-Object motion/guidance of motor actions

Front 24

Parvo-interblob pathway

Back 24

-Originates with P-type ganglion cells of the retina, which project to the parvocellular layers of the LGN.
-The parvocellular LGN sends axons to layer IVC(beta) of striate cortex.
-Fine object shape

Front 25

Cortical Modules

Back 25

-2 x 2 mm chunk of cortex
-Sufficient because it contains all the neural machinery required to analyze the participation of this point in oriented and/or colored contours viewed through either eye.
-necessary because its removal would leave a blind spot for this point in the visual field

Hint 25

Necessary/Sufficient

Front 26

Why is the striate cortex also called V1?

Back 26

-"Visual Area 1"
-First cortical area to receive information from the LGN.

Front 27

General definition for Dorsal and Ventral Streams

Back 27

-Dorsal: Serve the analysis of visual motion and the visual control of action.
-Ventral: Involved in perception of the visual world and the recognition of objects.

Front 28

Area MT

Back 28

Also known as V5
-receives retinotopically organized input from a number of other cortical areas, such as V2 and V3, and it also is directly innervated by cells in layer IVB
-Neurons have large receptive fields hat respond to stimulus movement in a narrow range of directions.

Front 29

Area MST

Back 29

-Cells selective for linear motion, radial motion, and circular motion.

Front 30

Area V4

Back 30

-In Ventral Stream
-Receives input from the blob and interblob regions via V2
-Larger receptive fields than cells in striate cortex
-Orientation and color selective
-Shape/color perception

Front 31

Area IT

Back 31

-Ventral Stream
-Inferior temporal lobe
-Colors/abstract shapes
-Perception/memory