Visual Pathways Flashcards
Cornea
Clear protective outer layer.
Iris
Thin circular structure that controls diameter of the pupil; defines eye color.
Pupil
Hole in the center of the iris that allows light to enter.
Lens
As light passes through the cornea, the lens refraction occurs to form the image on the retina.
Vitreous body
Clear, gel-like structure between the lens and retina.
Retina
Layer of cells lining the back wall inside the eye; it senses light and sends signals to the brain so you can see.
Fovea
Region of the retina with the highest visual acuity.
Macula
An oval region that surrounds the fovea; relatively high visual acuity.
Optic disc
Region where the axons leaving the retina gather to form the optic nerve; no photoreceptors.
Optical properties of the lens _____ and _____ the projection of the visual image on the retina.
Invert and reverse
Two classes of photoreceptors in retina:
Rods and cones
Rods
More numerous than cones; main function is for vision in LOW lighting conditions. They do NOT detect color, andy have relatively poor spatial and temporal resolution.
Cones
Less numerous; highly represented in the fovea (visual acuity); detects colors, and has relatively high spatial and temporal resolution.
Layers of the retina (outermost to innermost)
Photoreceptor layer, outer nuclear layer, outer plexiform layer, inner nuclear layer, inner plexiform layer, then ganglion cell layer.
Photoreceptors synapse on _______ cells.
Bipolar
Bipolar cells synapse on ___________ cells.
Ganglion
Axons of the ganglion cells sent into ________ _______.
Optic nerve
True or False: photoreceptors and bipolar cells fire action potential.
False
True or False: ganglion cells do not fire action potentials.
False
What are the two types of interneurons in the layers of the retina? What do they each modulate?
Horizontal and amacrine cells; horizontal cells modulate photoreceptor and bipolar cell synapses, and amacrine cells modulate bipolar cell and ganglion cell synapses.
What are the two classes of center-surround bipolar and ganglion cells?
On-center cells and off-center cells
What are the two types of retinal ganglion cells?
Parasol and midget cells
Describe parasol cells.
Large cell bodies, large receptive (dendritic) fields, respond best to gross stimulus features and movements, large diameter fibers, and project to magnocellular layer of the lateral geniculate nucleus of the thalamus.
Describe midget cells.
Small cell bodies, small receptive (dendritic) fields, more numerous, sensitive to fine visual details and to colors, smaller-diameter fibers, and project to parvocellular layers of the lateral geniculate nucleus of the thalamus.
Describe midget cells.
Small cell bodies, small receptive (dendritic) fields, more numerous, sensitive to fine visual details and to colors, smaller-diameter fibers, and project to parvocellular layers of the lateral geniculate nucleus of the thalamus.
The optic tract wraps around what structure in the brain?
Midbrain
Optic tract supplies what two pathways?
Geniculate and extrageniculate pathway
Geniculate pathway synapses where?
In lateral geniculate nucleus of the thalamus
Extrageniculate pathway synapses where?
Synapses in the superior colliculus and pretectal areas of the midbrain.
Function of the geniculate pathway.
Visual discrimination and perception.
Function of the extrageniculate pathway.
Direct visual attention and eye movement towards stimuli.
