Chapter 10: The Central Visual System Flashcards
Retinofugal Projection:
neural pathway that leaves the eye (retina), beginning with the optic nerve
What are the components of the retinofugal projection (in order)?
optic nerve
optic chiasm
optic tract
The optic nerves exit the left and right eyes at the […], travel through the […] behind the eyes in […]., then pass through holes in the floor of the skull.
optic disks; fatty tissue; bony orbit
The optic nerves from both eyes combined to form the […].
optic chiasm
What occurs at the optic chiasm?
the axons originating in the nasal retinas cross from one side to the other
Where is the optic chiasm located?
lies at the base of the brain, just anterior to where the pituitary gland dangles down
Decussation:
crossing of a fiber bundle from one side of the brain to the other
After partial decussation at the optic chiasm, the axons of the retinofugal projections form the […].
optic tracts
Optic tracts run under the […] along the lateral surfaces of the […].
pia; diencephalon
Visual hemifield:
objects appearing to the left or right of the visual midline
Binocular visual field:
central portion of both visual hemifields viewed by both retinas
Lateral geniculate nucleus (LGN):
a thalamic nucleus that relays information from the retina to the primary visual cortex
Optic radiation:
projection from LGN to cortex
Lesion anywhere in the […] projection from eye to […] to visual cortex cause blindness in humans.
retinofugal; LGN
What would happen if there was a transection in the following areas:
Left optic nerve
Left optic tract
Optic chiasm midline
LON– blind in the left eye only
LOT– blindness in the right visual field as viewed in either eye
OPM– blindness results in regions of the visual field viewed by the nasal retinas
Superior colliculus:
This is also called …
structure in the midbrain that receives direct retinal input and controls saccadic eye movement
optic tectum
Projections from the retina to the superior colliculus are often called the …
retinotectal projection
The […] nuclei, located in the dorsal thalamus, are the major targets of the two optic tracts.
right and left lateral geniculate
What is the arrangement of each LGN?
Describe this arrangement:
six distinct layers of cells
like a stack of six pancakes, bent around the optic tract (like bent around the knee)
What sends synaptic input to LGN neurons?
Where do these neurons project to?
retinal ganglion cells
project an axon to primary visual cortex via optic radiation
What axons synapse on the LGN cells (3)?
- M-type
- P-type
- nonM-nonP ganglion cells
Right LGN receives information about the […].
left visual field
The LGN is the gateway to the […] and therefore is conscious […] perception.
visual cortex; visual
In the right LGN, the right eye:
What types of axons synapse on the LGN cells?
In what layers of the LGN does this occur (there’s six).
ipsilateral
2, 3 ,and 5
In the left LGN, the right eye:
What types of axons synapse on the LGN cells?
In what layers of the LGN does this occur (there’s six).
contralateral
1, 4, and 6
What layers of the LGN contain large cells? small cells?
L: 1 and 2 (ventral)
S: 3-6 (dorsal)
Magnocellular LGN layers are the LGN’s […].
Parvocellular LGN layers are the LGN’s […].
ventral; dorsal
Where do the P-type ganglion cells in the retina project to?
Where do the M-type ganglion cells in the retina project to?
parvocellular LGN
magnocellular LGN
A thing […] layer is ventral to each of the six LGN layers.
koniocellular
Given the LGN layer and cell type, determine the retinal output.
Layer: 6
LGN cell type: parvocellular
G: P-type
E: contralateral
Given the LGN layer and cell type, determine the retinal output.
Layer: 5
LGN cell type: parvocellular
G: P-type
E: ipsilateral
Given the LGN layer and cell type, determine the retinal output.
Layer: 4
LGN cell type: parvocellular
G: P-type
E: contralateral
Given the LGN layer and cell type, determine the retinal output.
Layer: 3
LGN cell type: parvocellular
G: P-type
E: ipsilateral
Given the LGN layer and cell type, determine the retinal output.
Layer: 1 and 2
LGN cell type: magnocellular
G: M-type
E: ipsilateral (1) and contralateral (2)
Koniocellular layers have what type of ganglion cells?
nonM-nonP
What are some other terms to describe the primary visual cortex?
V1
striate
Retinotopy:
an organization whereby neighboring cells in the retina feed information to neighboring places in their target structures
Stellate cells make […] connections while pyramidal cells make […] connections.
local; extended
It is important to remember that only […] cells send axons out of striate cortex.
pyramidal cells
How is the neocortex/striate cortex cell bodies arranged?
- half dozen layers: I-VI with VI being closest to the white matter and the most outward I by the pia
- three layers are combined in layer IV
Layer I of the striate cortex consists of …
axons and dendrites of other cells in other layers
What are the sublayers of the stiate cortex layer IV?
IVA, IVB, IVC
What are the two types of neuronal shapes within the striate cortex? What is also an important neuron to be found in the cortical layers?
- spiny stellate cells
- pyramidal cells
inhibitory neurons (lack spines/shape)
Spiny stellate cells description:
Where can they be found in the striate cortex?
small neurons with spine-covered dendrites that radiate out from the cell body
found in the two tiers of layer IVC (alpha and beta)
Pyramidal cells description:
neurons covered in spines
contain single thick apical dendrite that branches as it ascends toward the pia mater and multiple neurons that extend horizontally
What type of connections do the inhibitory/spine deficient neurons form in the cortical layers?
local connections in all layers
In the LGN, every layer recieves retinal […] and send […] to the […].
afferent; efferent; visual cortex
In the LGN, every layer receives retinal afferents and sends efferents to the visual cortex. In the visual cortex this is different…how so?
only a subset of the layers receives input from the LGN or sends output to a different cortical/subcortical layer
Pretectum:
control size of the pupil, certain types of eye movement
Magnocellular LGN neurons:
large center-surround receptive fields with transient response
Parvocellular LGN cells:
small center-surround receptive fields with sustained response
Primary visual cortex provides […] of the synaptic input to the LGN.
80%
Brain stem neurons provide […] on neuronal activity
modulatory influence
Characteristics of retionotopy (4):
- map of the visual field onto a target structure
- central visual field (fovea) overrepresented in map
- discrete point of light can activate many cells in the target structure due to overlapping receptive fields
- perception is based on the brain’s interpretation of distributed patterns of activity—not literal map
Ocular dominance column:
a region of striate cortex receiving information predominantly from one eye
Radial connections in the cortical layers (3):
- majority of intracortical connections
- extend perpendicular to the cortical surface along radial lines that run across the layers
- from white matter to layer 1
Horizontal connections in the cortical layers (1)?
- axons of some layer III pyramidal cells extend collateral branches
Where do the layer IVC stellate cells project axons to?
Why is this significant?
radially up mainly to layers IVB and III
for the first time, information from the left eye and the right eye begins to mix
IVC neurons type of input vs layers II and III:
IVC– monocular input
L2/3– binocular input
Layer IVC alpha receives […] LGN input, and projects mainly to cells in layer […].
Layer IVC beta receives […] LGN input, and projects mainly to cells in layer […].
magnocellular; IVB
parvocellular; III
In layers III and IVB, an axon may form synapses with the dendrite of […] cells of […] layers.
pyramidal; all
What layers play a key role in visual processing?
How does this information leave to other cortical areas?
What are the two output forms?
layers II and III
leaves layer VI
two distinct populations of neurons in superficial layers: blob and interblob regions
When the striate cortex is stained to reveal the presence of […].
cytochrome oxidase
Cytochrome oxidase:
mitochondrial enzyme used for cell metabolism; not uniformly distributed in the striate cortex
How does cytochrome oxidase appear in a striate cortex cross-section?
colonnade, a series of pillars at regular intervals in layers II/III and V/VI
Blobs:
cytochrome oxidase-rich neurons
