M3 L6 Flashcards
whats the retinofugal projection?
the neural pathway that carries visual information away from the retina to the brain.
Retina —> Optic nerve —> optic chasm —> optic tract —> thalamus —> visual cortex
Role of the optic nerve in the retinofugal projection?
The optic nerve (cranial nerve II) carries visual information from each eye to the brain.
Role of the optic chasm in the retinofugal projection?
At the optic chiasm, fibers from the nasal (inner) part of each retina cross over to the opposite side, while temporal (outer) fibers stay on the same side.
Role of the optic tract in the retinofugal projection?
The optic tract is the continuation of the fibers from the nasal part of the retina after the chiasm, now reorganized so that each hemisphere processes visual input from the opposite visual field.
What is binocular vision?
the area both eyes can see at the same time.
What does the nasal retina see?
The nasal retina (inner part of the retina) captures the outer edges of the visual field.
- sees the image of the same side
- ex: looking at the left side from the center is your left nasal retina
What does the temporal retina see?
The temporal retina (outer part of the retina) captures the central part of the visual field.
- sees opposite side
- ex: left side viewed by right temporal
What is the left side of the binocular field captured by?
- The left nasal retina (inner part of the left eye)
- The right temporal retina (outer part of the right eye)
What is the right side of the binocular field captured by?
- The right nasal retina (inner part of the right eye)
- The left temporal retina (outer part of the left eye)
Which retina is contralateral and which is ipsilateral?
Nasal retina is contralateral to brain
* The nasal retinal fibers (from the inner part of each eye) cross over at the optic chiasm and go to the opposite (contralateral) hemisphere
Temporal retina is ipsilateral to brain
* The temporal retinal fibers (from the outer part of each eye) do not cross and stay on the same (ipsilateral) side of the brain.
- FIBERS ARE CONTRALATERAL NOT WHAT THEY ACTUALLY SEE
What happens if one eye isn’t working?
- We lose binocular vision (depth perception)
- Lose peripheral vision on affected side
- DO NOT lose central vision bc it will be compensated with the other eyes temporal resina + memory (false vision)
What is the optic radiation?
bundle of white matter fibers that carries visual information from the lateral geniculate nucleus (LGN) of the thalamus to the primary visual cortex (V1) in the occipital lobe.
Not all visual signals go straight to the visual cortex—some take alternate routes for specific functions. What are they?
Hypothalamus (small amount) → Regulates sleep and wakefulness (circadian rhythms) based on light exposure.
Pretectum (Midbrain) (small amount) → Controls pupil size (pupillary light reflex) and basic eye movement.
Tectum (Superior Colliculus) → Helps control head and saccadic eye movements (quick eye shifts to focus on objects).
The Lateral Geniculate Nucleus
* what is
* where is
* how arranged
* what do
* where receive signals from
- acts as a relay center for visual information
- Located in the dorsal thalamus
- arranged into 6 layers
- Sends information to the visual cortex
- from brainstem and visual cortex
The Lateral Geniculate Nucleus
- Which layers contain small neurons and what are they called?
Layers 3, 4, 5, and 6 contain small neurons (parvo cellular neurons)
The Lateral Geniculate Nucleus
- Which layers contain large neurons and what are they called?
Layers 1 and 2 contain large neurons (magnonellualr neurons)
- bc magnum is large
What layers do axons from the nasal retina synapse on?
Axons from nasal retina synapse on axons in layers 1, 4, and 6
Right nasal to left LGN - synapse on opposite side
What layers do axons from the temporal retina synapse on?
Axons from temporal retina synapse on axons in layers 2, 3, and 5
Right temporal to right LGN - synapse on same side
How does the LGN receive input from the eyes?
The LGN receives input from both eyes, but it keeps signals from each eye separate with contralateral and ipsilateral.
What layers is contralateral input processed in for the LGN
Contralateral input (opposite eye) is processed in layers 1, 4, and 6.
What layers is ipsilateral input processed in for the LGN
Ipsilateral input (same-side eye) is processed in layers 2, 3, and 5.
What are the two types of ganglion cells that project to the LGN? Ad where do they send input to?
1) M-type (Magnocellular) ganglion cells
* Process motion and brightness.
* Send input to LGN layers 1 and 2.
2) P-type (Parvocellular) ganglion cells
* Process fine detail and color.
* Send input to LGN layers 3-6.
What are the two divisions of the LGN?
Magnocellular layers (1-2)
Parvocellular layers (3-6)
what is the Koniocellular Layer? function?
thin layers found between the M and P layers in the LGN.
Receive input from the nonM–nonP types of retinal ganglion cells and also project to the visual cortex
define receptive field
The area on the retina that trigger the firing of certain ganglion cells
What is Retinotopy
An organization whereby neighboring cells in the retina feed information to neighboring places in their target structures (ganglion cells, LGN, and striate cortex)
What do ON-center retinal ganglion cells respond to?
respond best to small circular spots of light surrounded by darkness.
What do Simple cells in V1 (primary visual cortex) respond to
respond best to elongated bars of light, meaning they detect edges and orientation.
