19 - Vision Flashcards
5 Major Classes of neuron in the Retina
Ganglion Cells Amacrine Cells Bipolar Cells Horizontal Cells Photoreceptor Cells (Rods/Cones)
3 Nuclear Layers of the Retina
Outer Nuclear Area
Inner Nuclear Area
Ganglion Cell Layer
Layers of the Retina (Inner to Outer)
Ganglion Cell Layer Inner Plexiform/Synaptic Layer Inner Nuclear Layer Outer Plexiform/Synaptic Layer Outer Nuclear Layer Pigment Epithelium
Photoreceptors
Rods (Low light conditions)
Cones (Daylight, color vision, high accuity)
Photoreceptors - Rods
Low Light Conditions
Photoreceptors - Cones
Daylight Conditions, Color
Ganglion Cell Layer
Final output of the Retina, sends signal to the optic disc
Horizontal Cells, Bipolar Cells, Amacrine Cells
Transduce the signal
How many photoreceptors are in the optic disc?
- There is a blind spot there.
Ganglion Cells
Circular
Smaller in the region of the Fovea (high visual accuity)
Larger towards the periphery
Have an antagonistic center-surround organization
2 Major Classes of Ganglion Cells that serve the same Photoreceptor Cells in parallel
M-Type Ganglion Cells
P-Type Ganglion Cells
A-Type Ganglion Cells
Large receptor fields
Respond to the gross aspects of the visual image and its movement.
P-Type Ganglion Cells
Much smaller receptor fields
High visual accuity
Color vision
Synapses from which cells are contained in the Outer Plexiform/Synaptic Layer?
Photoreceptors, Bipolar and Horizontal
Synapses from which cells are contained in the Inner Plexiform/Synaptic Layer?
Bipolar, Amacrine & Ganglion
What is the purpose of pigment epithelium
Preventing any photons not absorbed by the neurons from being reflected back and distorting the image.
Pathway for Visual Perception
Optic Disc Optic Nerves Optic Chiasm Optic Tract Lateral Geniculate Nucleus (Relay) Optic Radiations V1
Synonyms for the Primary Visual Cortex
Striate Cortex
V1
Brodman’s Area 17
Banks of the Calcarine Fissure
Inferior Portion of the Retina - Represents
Contralateral Visual Field
Inferior Portion of the Retina - Pathway
Optic Disc Optic Nerves Optic Chiasm Optic Tract Lateral Geniculate Nucleus (Relay) Meyer's Loop Optic Radiations V1
Ganglion Cell Axons NOT involved in image processing (therefore not synapsing in the LGN) - Targets
Superior Colliculus (Eye Movement, Visuomotor Reflexes)
Pretectal Area/Nuclei (Pupillary Reflexes)
Suprachiasmatic Nucleus of the Hypothalamus (Circadian Rhythms)
What is contained in the Left Optic Tract?
Left Temporal Hemiretina
Right Nasal Hemiretina
What is contained in the Right Optic Tract?
Right Temporal Hemiretina
Left Nasal Hemiretina
Which fibers decuss at the Optic Chiasm?
Both Nasal Hemiretinas
Brachium of the Superior Colliculus
Bypasses the Lateral Geniculate Nucleus, rides on top of the Medial Geniculate Nucleus.
Target = Either Superior Colliculus or Pretectal Area/Nucleus
Pathway for consensual pupillary light reflex
Melanopsin-Containing Ganglion Cells (Retina)
Optic Nerve
Optic Chiasm
Optic Tract
Pretectal Nuclei (SYNAPSE) in the rostral part of the Superior Colliculus
Edinger-Westphal Nuclei (Bilaterally, contralateral courses through posterior commissure) - SYNAPSE
Occulomotor Nerve
Ciliary Ganglion - SYNAPSE
Smooth Muscle of the Pupillary Sphincter
Where is the Edinger-Westphal Nucleus?
Within the Occulomotor Nucleus (III)
What happens in the Edinger-Westphal Nucleus?
Incoming signals synapse on preganglionic parasympathetic fibers headed out with III.
Anisocoria
Pupillary asymmetry
Cause of anisocoria in humans
Lesions of the motor projection to the periphery
How many layers of nuclei are in the Lateral Geniculate Nucleus?
6
Which nuclei within the LGN receive input from the contralateral nasal hemiretina?
6
4
1
Which nuclei within the LGN receive input from the ipsilateral temporal hemiretina?
2
3
5
Magnacellular Component
Large Cells
Nuclei 1 & 2 (Most Ventral) in the LGN
Input = M-Type Ganglion Cells
Parvocellular Component
Smaller Cells
Nuclei 3, 4, 5 & 6 (Most Dorsal) in the LGN
Input = P-Type Ganglion Cells
Stria of Gennari
Defined by line in Lamina 4B (myelin stain)
Determines where Area 17 spans
Adjacent to Stria of Gennari, you find
Area 18
Secondary Visual Cortex
Extrastriate Cortex
Visual Cortex (V1) on Nissl Stain - Layer 1
Few Cells
Visual Cortex (V1) on Nissl Stain - Layer 2, 3 & 4a
High Density of Cells
Output = Extrastriate Cortex
Visual Cortex (V1) on Nissl Stain - Layer 4b
Stria of Gennari
Visual Cortex (V1) on Nissl Stain - Layer 4c
Many Cells (Two sublaminae - input from LGN)
Visual Cortex (V1) on Nissl Stain - Layer 5
Few Cells
Output = Superior Colliculi, Pons, Pulvinar
Visual Cortex (V1) on Nissl Stain - Layer 6
High Density of Cells
Output = LGN & Claustrum
Ultimate target of input from Inferior Retina
Inferior bank of the Calcarine Fissure
Ultimate target of input from the Superior Retina
Superior bank of the Calcarine Fissure
What is represented by the most posterior regions of the Calcarine Fissure?
The center of the visual field (Fovea)
What is represented by the most anterior regions of the Calcarine Fissure?
The periphery of the visual field
V1
Area 17
V2
Area 18
V3, V4
Area 19
V5
Area 19 - Middle Temporal Area (MTA)
Posterior Parietal Cortex
“Where” Pathway
Inferior Temporal Cotex
“What” Pathway
“Where” Pathway
V5 to Parietal Lobe
“What” Pathway
V4 to Temporal Lobe
Lesion on the Optic Nerve causes
Unilateral blindness
Lesion on the Optic Chiasm causes
Bitemporal Hemianopsia
Lesion in the Optic Tract causes
Homonymous Hemianopsia
Lesion in the Lateral Geniculate Nucleus causes
Homonymous Hemianopsia
Lesion in the proximal Optic Radiations causes
Homonymous Hemianopsia
Lesion in Temporal Lobe (extending into Meyer’s Loop) causes
Quadrantanopia of the contralateral superior quadrant
Lesion in the Primary Visual Cortex
Homonymous Hemianopsia (with Macular Sparing)
Why is the macular area sometimes spared form the homonymous hemianopsia resulting from a lesion in the primary visual cortex?
The fovea contains an incredibly dense population of fibers, and it’s hard to get rid of ALL their targets with one lesion.
Trauma to the Visual Pole causes
Homonymous Hemianopsia (of Macular Area)
