Visual System Flashcards
The fact or phenomenon of light being deflected in passing obliquely through the interface between one medium and another through a medium of varying density
Refraction
First site of refraction as light enters eye; is this refraction variable?
Cornea; not variable (accounts for 2/3 of light bending)
The second site of refraction in the eye is the ___ which adds a variable amount of bending. Variability depends on curvature, which is under physiological control. The ______ the structure above, the more refraction there is; the ______ the structure, the less refraction
Lens; rounder; flatter
Increasing curvature of the lens = ciliary muscle ______, which alows suspensory ligaments to ______. The lens assumes a more _____ shape; this is used for ______ vision
Contracts; loosen; rounded; near
Decreasing curvature of the lens = ciliary muscle ______, causing suspensory ligaments to _______, thus causing the lens to _____; used for ____ vision
Relaxes; tighten; flatten; far
Condition in which lens becomes stiffer in aging, loss of elasticity
Presbyopia
The near response of the eyes requires what 3 events?
Contraction of ciliary muscles
Convergence of eyes
Constriction of pupil
Path of light from entry to eye to activation of photoreceptor
Ganglion cells Amacrine cells Muller glia Bipolar cells Horizontal cells Rods/cones
What are the 3 vertically oriented cell-types in the retina?
Receptor cells (rods/cones) Bipolar cells Ganglion cells (subtype melanopsin ganglion cells)
Which type of photoreceptor is associated with convergence, dim light, and sensitivity but NOT acuity?
Rods
[cones have less convergence, but maximized acuity]
Rod/cones constantly release NT ________; this release is at its highest in the _____, and lowest when there is _______ (hyperpolarization of cells)
Glutamate; dark; light
In differentiating ON-centers from OFF-centers:
Activation of a photoreceptor in the center of an ON-center bipolar cell’s receptive field causes ______
Activation of the periphery of this bipolar cell’s receptive field causes ________
The opposite is true for OFF-center cells
Depolarization
Hyperpolarization
[so for OFF-center cells, activation of a photoreceptor in the center causes hyperpolarization while activation in the periphery causes depolarization]
________ bipolar cells increase their discharge rate to luminance increments in the receptive field center
______ bipolar cells increase their discharge rates to luminance decrements in the receptive field center
ON-center
OFF-center
The glutamate receptor in depolarizing bipolars is a GPCR that _____ cGMP-gated ion channels similar to light transduction in photoreceptors.
Channels _____ when less glutamate is present
Closes
Open
Describe activity of an ON-center bipolar cell by a cone photoreceptor in the dark
- Glutamate would activate a Gi GPCR-metabotropic receptor on the ON-center cell
- Results in a decrease in cation influx into bipolar cell
- Cell is hyperpolarized
Describe activity of an ON-center bipolar cell in the light
- Light decreases presence of glutamate
- Less activation of metabotropic receptor
- Less Gi signaling
- Increase in cation influx
- Cell depolarization
When the bipolar cell is activated, it releases glutamate to depolarize ______ cells which also have ON-center and OFF-center varieties. These cells then become the fibers of the _____
Ganglion; optic n
Many rods converge on one _______bipolar cell, which connects to a rod-bipolar cell and a rod-amacrine cells, which function as interneurons releasing ____ or ______. These then connect to a cone-bipolar cells, then to a ganglion cell
ON-center; glycine; GABA
Overall function of ON- and OFF-center cells
Help us increase the ability to detect edges and sharpen our vision
ON-center cells tell us where something is
OFF-center cells tells us where something ends
Direct targets of the retina
Lateral geniculate body Superior colliculus Pretectum Hypothalamus Accessory optic nuclei (AON)
Signals from the 2 eyes are kept apart in the LGB. What are the functions of the LGB?
Control motions of the eyes to converge on point of interest
Control focus of the eyes
Determine relative position of objects to map them in space
Detect movement relative to an object
There are 6 layers to the primary visual cortex. Layers I, II, and III allow for networking between VI and other areas of the cortex.
Layer ___ receives input from the LGB
Layers ___ and ___ are main output layers; LGB, thalamus, subcortical regions
IV
V; VI
Slab of cells that preferentially respond to input from one eye or the other
Ocular dominance columns
Organized region of neurons that are excited by visual line stimuli of varying angles, oriented perpendicular to cortical surface
Orientation columns
_____ exist in primary visual cortex as an organized region of neurons that are sensitive to color and assemble into cylindrical shapes
Blobs
The arrangement of neurons in columns and blobs is not nearly as linear or rectangular as previously depicted but they are mapped into the following stuctures:
The ____ of ocular dominance columns
The ______ of orientation columns
Cytochrome oxidase stain shows ______
Stripes
Swirls
Blobs
Major job of primary visual cortex VI
Identify edges and contours of objects
Major job of primary visual cortex V2
Depth perception
Major job of primary visual cortex V3a
Identification of motion
Major job of primary visual cortex V4
Complete processing of color input
The dorsal pathway in visual processing arises from _____ and is responsible for completing motor acts based on visual input (tracking an object)
V3
Which pathway of visual processing is primarily involved in interpreting images and facial recognition?
Ventral pathway
