Eye Flashcards
monocular visual field
area of space visible to one eye
- subdivided into two halves, the hemifields, nasal and temporal hemifields
- contains a blind spot, located within the temporal hemifield
Vision in the visual field center
- operates best under high illumination.
- has good visual acuity and color sensitivity
- ten times better than in the field periphery
- function of photopic (light-adapted) subsystem
Vision in the peripheral visual field
- is more sensitive to dim light
- operates under low illumination.
- has little color sensitivity, poor spatial acuity
- function of the scotopic (dark-adapted) subsystem
‘blind spot” in the visual field
optic disc (formed by the retinal ganglion cell axons that are exiting the retina), located nasal to the fovea region of the retina
devoid of receptor cells, composed mostly of optic nerve layer.
Type P retinal ganglion cells
- are color-sensitive object detectors.
- outnumber M-ganglion cells, 100: 1
- makes synaptic contact with one/a few cone bipolars
- has a small concentric receptive field
- produces a sustained, slowly adapting response that lasts as long as a stimulus is centered on its receptive field.
- produces weak responses to stimuli that move across its receptive field.
Type M retinal ganglion cells
color-insensitive motion detectors.
The rapidly adapting responses of Type M ganglion cells are best for signaling temporal variations and movement of a stimulus.
- much larger than P ganglion cells
- synapses with many bipolar cells
- has a large concentric receptive field
- is more sensitive to small center-surround brightness differences
- responds with a transient, rapidly adapting response to a maintained stimulus.
- responds maximally, with high discharge rates, to stimuli moving across its receptive field.
The axons of the M and P retinal ganglion cells travel…
- in the retina optic nerve fiber layer to the optic disc where they exit the eye.
- Most of the axons terminate in the lateral geniculate nucleus of the thalamus.
What produces high visual acuity in the central visual field?
Low convergence of cones to cone bipolar cells and low convergence of these cone bipolar cells to P-retinal ganglion cells produce high visual acuity in the central visual field.
visual acuity and color vision are greatest in—
visual acuity and color vision are greatest in the central visual field.
the image of the central visual field is projected onto
the fovea.
the cones are concentrated in ______, whereas the rods predominate in the ______ retina.
Cones—-fovea,
rods– predominate in the peripheral retina.
What feature of cones and bipolar cells support higher visual acuity in the central visual field.
high packing density of cones, low convergence of cones + bipolar cells in the macula support higher visual acuity in the central visual field.
these 3 cell types are responsible for photopic, light-adapted vision in the central visual field:
- the foveal cones,
- macular bipolar cells
- P-retinal ganglion cells
What is the basis for poor visual acuity/high light sensitivity of scotopic vision?
higher convergence of rods + peripheral bipolar cells, then peripheral bipolar cells+ amacrine cells = basis for the poor visual acuity + high light sensitivity of scotopic vision.
Bipolar cells
do not generate action potentials.
- respond to glutamate from photoreceptors with graded potentials (hyperpolarizing/ depolarizing).
- two types of bipolar cells:
- OFF bipolar cells— depolarized by glutamate. Detect dark objects in a lighter background
- ON bipolar cells— hyperpolarized by glutamate. detect light objects in a darker background.
