32: Visual System Physiology Flashcards
Where are rods and cones the most dense?
Cones: fovea
Rods: eccentricity of about 20 degrees
How is glutamate inhibitory in bipolar cells?
Glutamate is an EAA, but is only excitatory with NMDA, AMPA, and Kainate receptors
Receptive field pattern for photoreceptors, bipolar cells, and ganglion cells
Photoreceptor: size of a photon on retina
Bipolar cell: more complex with center of field responding different than surroundings
Ganglion cell: extremely complex, visual fields are rectangular
Achromatopsia
Inability to process or differentiate colors
Unilateral lesion of V4 visual area
May be unnoticed by patients
Which two columns of the primary visual cortex span all six layers?
Ocular dominance columns, blobs
Copying objects, naming objects, and facial recognition: in same area or specialized areas?
Specialized areas -> damage to one area can occur without damage to another
Melanopsin ganglion cells
1-3% of ganglion cells that can directly sense light
How do melanopsin ganglion cells work?
They express melanopsin, which is sensitive to blue light
What process are melanopsin ganglion cells involved in?
Regulation of circadian rhythm
What do melanopsin ganglion cells project directly to?
Hypothalamic suprachiasmatic nucleus, the NE effector in the pineal gland that produces melatonin rhythmically
If a pt is blind from photoreceptor loss but still has ganglion cells, what happens?
Still have a pupillary light reaction to bright blue light -> can maintain circadian rhythm
Lens becomes more yellow with age… what is the effect of that?
Spectrum of blue light absorption decreases over the years, which can cause sleeping issues in older people
What can blue light do?
Treat SAD, increase alertness and cognition, but can also disrupt sleep behaviors when exposure is prior to sleep
