Lecture 7 Flashcards
High Convergence in the periphery
Multiple rods will synapse on diffuse bipolar cells
-Multiple bipolar cells will synapse on parasol ganglion cells
Low Convergence in the fovea
Single cone cells will synapse on single midget bipolar cells, which will synpase on single midget ganglion cells
High Degree of Convergence in periphery
-Greater light sensitivity
-Less acuity in periphery
Optic Chiasm Structure
-Located in front of the hypothalamus
-Site where half of the optic nerve fibers from each eye decussate to the contrelateral brain hemisphere
-Enables visual corticles to process information from the contrelateral visual field, not the contrelateral eye
Temporal Retina
Oriented towards the contrelatera visual field; no decussation required
-Closer to side of head
Nasal Retina
Oriented towards the ipsilateral visual field; decussates to transmit visual information to the contrelateral hemisphere
-Closer to center of head
-This is the side of the retina that crosses over
Optic Tract
-Retinal projections beyond the optic chiasm are called the optic tract
-Approximately 90% of optic tract nerve fibers synapse in the lateral geniculate nuclei (LGN) of the thalamus
Lateral Geniculate Nucleus (LGN)
Located in the thalamus; anatomically divided into 6 layers
Magnocellular Layers (1-2)
-Input from parasol retina ganglion cells
-Process peripheral vision
Parvocellular Layers (3-6)
-Input from midget retinal ganglion cells
-Process central vision
Konicellular Layers
-Located in intralaminar regions of the LGN
-Specialized for colour perception due to sensitivity to wavelength and low light sensitivity
Optic Radiations and Primary Visual Cortex (V1)
-LGN axons from optic radiations that project to the primary visual cortex (V1) in the occipital lobe
-Right visual cortex processes stimuli from the left visual field (both eyes), and vice versa
Retinal Projections to the Superior Colliculus (SC)
-10% of retinal outputs bypass the LGN and project to the superior colliculus (SC)
-SC has a retinotopic layout of the contrelateral visual field
Blindsight Phenomenon
-Seen in patients with damage to the primary visual cortex
-Un conscious visual perception
-Patients respond to visual stimuli without conscious awareness
-Can accurately guess line orientation, object movement, and spatial location
-Comes from the 10% of retinal outputs that bypass LGN
Retinotopic Mapping
The spatial organization of the visual field is preserved in the brain, with neighbouring areas of the retina mapping onto neighbouring areas of the primary visual cortex (V1) in a point-by-point manner
Cortical Space in V1
More space is dedicated to central vision compared to peripheral vision
Fovea
Higher density of ganglion cells than the peripheral retina
LGN (asymmetry)
Twice as many parvocellular layers as magnocelluar layers
Cortical Magnification
V1 further amplifies the total number of neurons devoted to central vs. peripheral vision where the central 10 degree of the visual field (1% of the total visual field) occupies 50% of V1’s surface
