Vision Flashcards
sclera
The white part of the eye
Optic nerve
the axons carrying information from the retina to near the pituitary gland
macula
the part of the retina for central vision
fovea
dark spot on the retina. This is the thinnest spot of the retina
cornea
The part of the eye near the iris which maintains the eyes refractive power
ganglion cells
cells firing action potentials in response to light. Ganglion cells are the only source of output from the retina
photoreceptors
the only light sensitive cells in the retina
laminar organization
The layerized structure of the visual system cells
two types of photoreceptors
cones and rods. Rods are more sensitive to light than cones
rhodopsin
a receptor protein activated by light
How is a signal amplified in transduction
by using a biochemical cascade process
biochemical cascade by light energy
activation of rhodopsin by light causes the g-protein to exchange GDP for for GTP which in turn activates the enzyme phosphodiesterase (PDE). PDE breaks down cCMP and shuts the dark current
dark current
cGMP gates a sodium channel causing an inward Na+ current and depolarization
ON and OFF cells
ON cells are depolarized by light whereas OFF cells are depolarized by lack of light
classification of ganglion cells
appearance, connectivity and electrophysiological properties
Two major types of ganglion cells
M-type and P-type. P stands for parvo “small”, M form Magno “large”. about 5% are non-M-non-P
Neurotransmitter used by ganglion cells
glutamate
V1
visual area one, the striate cortex
functions of the ventral stream
thought to be involved in the perception of the visual world and the recognition of objects
Area MT
an area of the dorsal stream specialized in processing object motio. Receives input at least from V2 and V3.
Neurons in area MT have large receptive fields, almost all cells are direction-selective unlike areas in other parts of the dorsal stream or ventral stream.
MST
an area sensitive to linear motion, radial motion and circular motion
The ventral stream
a progression of areas from V1, V2, V3 running ventrally toward the temporal lobes. Specialized in for the analysis of visual attributes other than motion.
Area V4
Neurons in V4 have larger receptive fields than cells in the striate cortex. Many cells are orientation selective and color selective.
It appears that this area is important for shape recognition and color perception.
Achromatopsia
A rare syndrome resulting in the loss of color vision. Associated with cortical damage in the occipital and temporal lobes. V1, LGN intact . Suggest color processing in ventral stream. No clear link to V4.
