BIOL 428 Central Visual Pathways

How does light information travel from the retina to the primary visual cortex?

1. Photoreceptors

2. Bipolar Cells

3. Ganglion cells

4. Lateral Geniculate Nucleus

5. Striate Cortex

What are the targets of regions for retinal ganglion axons?

• optic chiasm

• LGN

• Suprachiasmatic Nucleus of Hypothalamus

• Pretectum

Optic Chiasm

visual information from same visual field of both eyes travels to the opposite side of the brain

Lateral Geniculate Nucleus

Region in the thalamus where ganglion cells synapse with neurons traveling to visual cortex

Suprachiasmatic Nucleus of Hypothalamus

controls regulation of circadian rhythms. Retinal ganglion cells innervating the SCN use melanopsin as a photopigment. Helps overcome jet lag

Pretectum

Bilateral Effect: retracts retina/pupil when light is too bright. Postgangionic parasympathetic activate neurons in Eidinger-Westphal nucleus.

How does Binocular visual information come together at the optic chiasm?

information from both eyes but same visual field goes to the opposite side of the brain

Monocular peripheral vision

visual information captured by the ends of the nasal retina

Where is information integrated along the visual pathway?

Visual information remains segregated through the LGN and combines at the ocular dominance columns of the visual cortex

Ocular Dominance Columns

Columns througout V1 cortex layers that combine left and right eye information

How are visual maps organized in the LGN

different layers on each side contain the contralateral visual field information. Layers alternate what eye they process

How are visual maps organized in the V1

information arrives at layer 4. Information is spread to other layers with some segregation and ocular dominance columns

How are retinal visual maps reflected on visual cortex

information are flipped and reflected. Size is directly disproportionate relative to visual field

Stereopsis

sensation of depth resulting from binocular vision

types of binocular neurons that offset point of focus

Far Cells, Near Cells and Tune Cells

Far cells

discharge to retinal disparities beyond the point of focus

Near cells

discharge to retinal disparities in front of the point of focus

Tune Cells

discharge at the point of focus

What light stimuli/signals do cortical neurons respons to?

neurons can be selective to different edges/ movement

Simple cells

neurons in striate cortex with orientation preference

Complex cells

neurons sensitive to direction of motion, spatial and temporal frequency, patterns and colors

Cortical layers

Has spiny and smooth neurons

receive and organize visual map information from LGN

Spiny neurons

cortical layer neurons with dendritic spines

• pyramidal

• stellate

Pyramidal neurons

most common spiny cortical neurons

where do pyramidal neurons project to

they project to other cortical regions

where are pyramidal neurons found

layer 4 but not in 4C

what kind of neurotransmitter do pyramidal neurons release

glutamine

where are stellate neurons found and where to they project to

glutamatergic spinous neurons common in layer 4C and project to the other layers

Smooth/ Aspinous dendritic neuron

local axonal harbors that release GABA for cortical inhibition

Cortical columnar response forms—

visual maps in the primary visual cortex

How does cortical columar response work?

different light orientations create different responses from veritcal or oblique activation

Different ganglion cells of the LGN

• Parvo (p-type)

• Magno (m-type)

• Konio (k-type)

Parvo P-type ganglion cells

LGN ganglion cells with small fields, high spatial resolution, color sensitive and sustained responses

Magno M-type ganglion cells

LGN ganglion cells with large fields, large diameter axon, sensitive to contrast, depth, and movement

Konio K-type ganglion cells

LGN ganglion cells with soem aspects of color (S-wave), and fine-caliber retinal axons

In what layers are Parvo cells?

LGN layers 3-6

In what layers are magno cells?

LGN layers 1-2

In what layers are Konio cells?

All LGN layers

Where do Parvo cells axons terminate?

striate layer 4C(alpha)

Where do Magno cells axons terminate?

striate layer 4C(beta)

Where do Konio cells axons terminate?

striate layers 2 and 3

What are the extrastriate regions?

V2-V4 and medial temporal area (V5)

Medial temporal area (MT)

neurons that respond selectively to direction of a moving edge

V4 are selective to

color

Dorsal Pathway

spatial vision; mostly includes Magno (M-type) cell pathways

Ventral Pathway

object recognition; mostly includes Parvo (P-type) cell pathways

What extrastriate cortex does the ventral pathway go to?

V4

What extrastriate cortex does the dorsal pathway go to?

Medial temporal area