Visual Pathways Menini

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Ganglion Cells

Central artery of Retina

Optic Chiasm

Anterior Communicating artery
Anterior Cerebral artery

Optic Tract

Anterior Choroidal artery

Lateral Geniculate Nucleus (Thalamus)

Thalamo-geniculate artery

Optic Radiations
Occipital Cortex

Middle Cerebral artery
Posterior Cerebral artery

Monocular Blindness

Ganglion Cells
Optic Nerve

Bitemporal Hemianopsia

Optic Chiasm

Contralateral Homonymous Hemianopia

Optic Tract
LGN

Contralateral superior or inferior quadrantanopia

Optic Radiations
Occipital Cortex

Name the cells from where the optic nerve originate. Where are these cells located?

Ganglion cells are found in the ganglion cell layer (closest to the vitreous humor) of the retina

List the places in the CNS where the optic nerve fibers terminate.

Most optic nerve fibers (80%) synapse on the Lateral Geniculate Nucleus of the thalamus, then go on to the primary visual cortex.

superior colliculus (10%)
pretectal area (5%)
SCN of the hypothalamus (5%)

How do we call the fiber tracts transmitting visual information from thalamus to cortex? What is the anatomical relationship between these fibers and the lateral ventricles?

These fibers are the optic radiations

The optic radiations leaving the LGN enter the white matter to sweep over and lateral to the atrium and temporal horn of the lateral ventricle and then back toward the primary visual cortex in the occipital lobe. As they do so, these axons fan out over a wide area, forming the optic radiations.

Where is the primary visual cortex located? Indicate the lobe of the brain, the Brodmann's area and the specific location.

The primary visual cortex lies alongside the calcarine fissure in the occipital lobe in Brodman's area 17.

Fibers leave the retina at the optic disk located medial to the posterior pole of the eye. This area represents a blind spot. Why?

There are no photoreceptors at the optic disc to allow the ganglion cell axons to exit the eye.

At the optic chiasm the nasal fibers traveling with each optic nerve cross over the midline and join the contralateral temporal fibers. Where in the retina do the fibers in the optic tracts come from?

Right optic tract: Left nasal retina and Right temporal retina

Left optic tract: Right nasal retina and Left temporal retina

What part of the visual field is represented in each optic tract?

Right optic tract: Left Temporal field and Right Nasal field = left visual field in the binocular representation

Left optic tract: Right Temporal field and Left Nasal field = right visual field in the binocular representation

Axons of the LGN neurons will form 2 pathways that head towards the visual cortices. What parts of the retina are represented in Meyer's loop?

The lower nasal retina of the contralateral eye and the lower temporal retina of the ipsilateral eye

What parts of the visual field are represented in the Right Meyer's loop?

The left upper quadrant of the visual field of both eyes

Which of the 2 optic radiation pathways terminates in the superior bank of the calcrine sulcus?

The upper portions of the optic radiations project to the superior bank of the calcarine sulcus. Upper bank lesions thus cause contralateral inferior quadrant defects.

What parts of the calcarine sulcus are devoted to foveal representation?

The region of the fovea is represented near the occipital pole. Despite its small retinal area, because it is the region of highest density of photoreceptors and ganglion cells correspondingly high visual acuity, the fovea has a disproportionate cortical representation, occupying about 50% of the primary visual cortex. The fovea and mostly the foveola provides one to one connection between cones and ganglion cells.

What parts of the visual field are represented in the superior bank of the calcarine sulcus of one side?

Contralateral inferior quadrants.

What visual deficit would be present in a patient with a lesion of the left optic tract?

A right homonymous hemianopia

What visual deficit would be present in a patient with a pituitary tumor compressing the fibers of the optic chiasm?

A bitemporal (heteronymous) hemianopsia

What visual deficit will be present in a patient with a lesion of the right Meyer's loop?

Left upper quadrantanopsia

What deficit will be present in a patient with a lesion of the right lateral geniculate nucleus?

Left homonymous heminanopsia

Blindsight

Can indicate direction of movement in blind visual field. Extrastriate pathways intact

Motion Blindness

Lesion in Middle Temporal Area

Color Blindness or Achromatopsia

Damage to Area V4 on the Ventral Temporal Lobe

Visual agnosia

Lesion of Ventral Object Area

Visual neglect

Damage to the posterior parietal cortex

Ballint's Syndrome

-Lesion of parieto-temporal junction
-Deficit of spatial attention
-Difficulty to scan a complex visual scene or identify moving objects
-Patients have optic ataxia, ocular apraxia, and simultanagnosia

Optic Ataxia

Inability to reach an object in space under visual guidance or point to a target

Ocular Apraxia

Difficulty in directing the gaze towards an object through saccades

Simultanagnosia

Inability to perceive more than one object in the visual field simultaneously

Right Optic Tract

Left Visual Field

Left Optic Tract

Right Visual Field

Nasal Retina

Temporal area of visual field

Temporal Retina

Nasal visual field

80% of Retinal Output

LGN

Layers 1, 4, 6

Receive info from nasal fibers of the contralateral eye

Layers 2, 3, 5

Receive info from temporal fibers of the ipsilateral eye

LGN Retinotopy

-Each layer has a complete retinotopic map
-Each point in space is represented 6 times
-Fovea is over-represented in the LGN

Meyer's Loop

-Inferior tract
-Goes to the inferior bank of Calcarine sulcus
-Upper visual field quadrants

Direct Tract/Superior pathway

-Goes to the parietal lobe to reach the occipital cortex
-Goes to superior bank of Calcarine sulcus
-Lower visual field quadrants

Fovea

Posterior half of both superior and inferior banks of calcarine sulcus

Central retinal fibers

have an overrepresentation in the different layers of LGN

Stria of Gennari

Myelinated fibers in Lamina IV B of the Calcarine cortex

Ocular Dominance Column

Neurons:
-react to color
-able to communicate laterally with the next column and see binocular space
-cells with complex receptive fields that allow them to have orientation selectivity
-sense movement and have direction selectivity

Visual Processing - 3 Channels

-Motion
-Shape
-Color

Dorsal Pathway

Parietal Lobe
"Where"

Ventral Pathway

Temporal Lobe
"What" - Color, shape, identity

Lateral Occipital Complex Area (LOC)

Shapes of objects
Lateral surface of occipital lobe

Fusiform Face Area (FFA)

Face recognition
Ventral surface of temporal lobe

Parahippocampal place area (PPA)

Localize and identify places
-houses, landmarks, indoor and outdoor scenes

Prosopagnosia

-Don't recognize family, friends, or self in the mirror
-Bilateral lesions in lateral occipital cortex, inferior temporal lobe, and fusiform gyrus

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