Visual System Flashcards
Black Pigment Epithelium
- behind the retina, nourishes photoreceptors and absorbs stray light
Photoreceptor location
Rods and cones are in front of the pigment epithelium
Ganglion cells
- connected to photoreceptors by interneurons
- (retinas output neurons), closest to the lens and front of the eye
Tapetum Lucida
lies behind the retina and reflect light back (improved detection of dim lights) (alligator eye reflection )
Rhodopsin (gpcr)
-Darkness- inactive, cGMP high, ion channels open
- Light (bleaches rhodopsin), opsin decreases cGMP, closed Na channel, hyper-polarization of the cell.
- G protein is transducin, Stimulates phosphodiesterase (PDE), breaks down cGMP.
- thousands of rods converge on a single ganglion (poor spatial resolution)
Color Vision
Cones
- Blue (Short wave)
- Green (Middle Wave)
- Red (long wave)
- less convergence (improved spatial resolution)
Central Fovea
No convergence, midget system; one cone to one ganglion(Highest Spatial Res.)
- Cones are concentrated in the fovea
Macular Degeneration
affects the central retina
Retinitis Pigmentosa
Progressive Disease affects mainly rods, leads to night blindness and tunnel vision
Retinal Ganglion cells
EDGE DETECTION
Transient Ganglion Cells
respond to onset or offset of a light stimulus, sensitive to small changes.
Sustained ganglion cells
respond for the duration of the light stimulus, sensitive to color, light intensity, and form.
Intrinsically Photosensitive Sensitive Ganglion Cells
have melanopsin photopigment and are sensitive to blue light
- light responses are slow but very prolonged
- control pupillary responses and circadian rhythms.
Ganglion Cell Projections
- most project to the Lateral geniculate nucleus (LGN) in thalamus then to the primary visual cortex (V1)
- some project to the superior colliculus that control eye movement
LGN
P and M cells in different layers
- P - sustained cells (give you a picture)
-M - Transient cells (cells in motion)
