FINAL EXAM Lecture 12 Visual System Flashcards
The eyeball is made up of 3 concentric layers:
1.
2.
3.
- Outer, fibrous layer
- Middle, vascular layer (uvea)
- Retina
The outer, fibrous layer of the eye is made up of:
1.
2.
- Sclera - White
- Cornea - Transparent
The middle, vascular layer ( _____ ) is made up of:
1.
2.
- ________; contains a _______ in most domestic animals. (Absent in the pig)
- Iris
- Ciliary body
- Choroid; Tapetum Lucidum
Retina = _____ _____ of the eyeball
The ______ ______ of the retina lines the Iris, _____ ______ and ________.
The functional ____ ____ of retina lines the fundus to the level of the ora serrata.
Consists of ___ histological layers, including retinal ganglion cells, which give rise to the _____ ______.
Inner Layer
Pigmented Epithelium; Ciliary Body; Choroid
Optic Part
10; Optic Nerve
_____ _____ ______:
Formed by the retinal pigmented epithelium & the endothelium of retinal capillaries, which lie within the nerve fiber layer of the retina.
Breakdown of the barriers leads to _________
Blood Ocular Barrier
Uveitis
Fundus:
________ part of the eye consisting of:
1.
2.
3.
Can be observed with an opthalmoscope
- Appearance of ____ ____
- Appearance of ________
- Reflectivity of ______ _________
- _________ attachment
Interior
- Retina
- Choroid
- Optic Disk
- Optic Disk
- Vasculature
- Tapetum Lucidum
- Retina
Embryonic Development of the Retina
The retina develops from the ___ ___ of the _______, and the optic nerve is histologically a _____ tract. The optical part of the retina develops from the inner wall of the optic cup.
The outer wall becomes the _____ ______ layer.
Optic Cup
Diencephalon
CNS
Pigmented Epithelial
Histological Organization
______ histological layers are recognized in the optic part of the retina:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
10
- Pigmented Epithelium
- Rods & Cones
- External Limiting Membrane
- Outer Nuclear Layer
- Outer Plexiform Layer
- Inner Nuclear Layer
- Inner Plexiform Layer
- Ganglion Cell Layer
- Optic Nerve Fibers
- Internal Limiting Membrane
Retina Organization
Light must penetrate _____ of the layers to reach outer segments of rods & cones where ______ are absorbed. Processes of ______ ______ cells surround the outer segments of rods and cones.
_________ axons of ganglion cells run to the ______ _____ and then exit the eyeball as _______ axons that comprise the _____ ______.
Photoreceptor cells are absent at the ____ _____ (blind spot). Retinal vessels enter at the disc and course along the retinal surface.
The area ______ (visual streak) of the retina has highest visual acuity.
8; photons
pigmented epithelium
Nonmyelinated; optic disc; myelinated; optic nerve
Optic Disc
Centralis
______________ transduce light energy to neural electrical activity. They are excited ( ______ ) in the _____ and inhibited ( ______ ) by _______.
Photoreceptors
Polarized; dark
Hyperpolarized; light
_____ _____ receive input from photoreceptors and synapse on ____ ____ (as well as some amacrine cells).
These are depolarized (ON) or hyperpolarized (OFF) in response to light.
Bipolar cells
Ganglion Cells
Ganglion Cells:
Their axons leave the ____ and form the ____ _____.
Unlike all other retinal cells, ganglion cells generate _____ ______.
Their rate of firing is increased or decreased by ______ stimuli.
Retina; Optic Nerve
Action Potentials
Visual
Horizontal cells:
are always ________. They have complex interactions with _________ and modulate the activity of _____ ____ indirectly.
They are primarily responsible for ______ inhibition (inhibition of cells as a result of activity in a neighboring cell).
inhibitory
Photoreceptors; Bipolar cells
Lateral
Amacrine Cells:
are often _____ neurons that make synaptic contact with ____ & _____ ______.
Some respond to the onset.offset of light, others are responsive to direction of light movement. The optic nerve contains _____ axons, which synapse on amacrine cells to provide brain control of ______ activity.
There are ____ different populations of amacrine cells with respect to morphoology and neurotransmitters released.
inhibitory; bipolar; ganglion cells
efferent; retinal
30
Radial Glial Cell
AKA _______ ________
Modified astrocytes which provide ______ and _______ support. Like astrocytes they take up excess ions and neurotransmitter molecules to maintain homeostasis. Processes of these cells form the internal and external limiting membranes.
Mueller Cells
Structural
Metabolic
Transduction of Visual Signals by Photoreceptors
There are two populations of photoreceptors: ____ & ___.
The outer segments of rods & cones contain stacked membranous discs that are continually produced, sloughed, and phagocytized by pigmented epithelium. The discs contain the photosensitive molecule _____ (retinal + protein) that intercepts _____.
Rods & Cones
Rhodopsin
Photons
Transduction of Visual Signals by Photoreceptors
Photoreceptor cells are excited ( _____ ) in the ____ and inhibited ( _______ ) in the _____.
They do NOT generate _____ _____. They repond to ______ stimuli with graded depolarization and hyperpolarization, which results in proportional release of _____ neurotransmitter.
Depolarized; dark
Hyperpolarized; light (photons)
Action Potentials; Visual; Glutamate
Rods; Dim
Cones; Bright Light
Transduction of Visual Signals by Photoreceptors
______ form convergent circuits with bipolar cells, which improves vision in ____ light but at the expensve of image _______.
________ form relay circuits with bipolar cells, which provides good visual detail but requires ____ _____.
Rods; Dim
Cones; Bright Light
Rods
_____ of photoreceptor cells
Widely distributed throughout the retina
Single population all containing _______ (protein + retinal); No ____ sensitivity
Functional in ____ light, response saturates in daylight
Participate in highly _______ circuits (>1,000 rods _____ on one ganglion cell); low spatial resolution
High _______ – can response to a single photon
95%
Rhodopsin; color
Dim
Convergent; Converge
Sensitivity
Cones
_____ of photoreceptor cells
Concentrated in ____ ______
Multiple populations, base on different _______ (color) sensitivities, due to protein differences (Protein + Retinal)
Operate under ____ light conditions
Participate in _____ circuits (few cones per ganglion cell); high spatial resolution
______ sensitivity – need hundreds of photons for a response
5%
Area Centralis
wavelength
Bright
Relay
Lower
_Processing of Visual Stimuli _
Processing of visual stimuli in the retina (and in the visual system in general) is organizerd in a way that optimizes the detection of ________.
This pattern in the visual scene is the type of visual information most useful to the animal.
For example, contrast at the edges of an object defines it shape and motion involves both _____ and ____ contrast.
Contrast
Temporal; Spatial
Vertical and lateral pathways in the retina
Cells in the vertical pathways
( ______ –>_______ _______ –> ______ _____ )
are specialized to detect changes in _________.
______ and _____ ______ that specialize in detecting increases in brightness/illumination (e.g. a bright object on a dark background) are termed “ ____” cells.
These cells that specialize in detecting decreases in brightness/illumination are termed “ _____” cells.
Photoreceptors –> Bipolar Cells –> Ganglion Cells
Contrast
Bipolar & Ganglion CElls
ON
OFF
Vertical & Lateral Pathways in the retina
Cells in the _______ pathways ( _____ and _____ cells) contribute to contrast enhancement.
Lateral
Horizontal & Amacrine Cells
_The detection of contrast is based on the organization of receptive fields _
The ____ _____is the region of the retina that must be illuminated in order to obtain a response in a visual neuron.
_____ ______ of retinal ganglion cells are round and have a _____ and a ______ with _______ properties. Responses in the center are mediated by _______ pathways. Responses in the surround are based on _______ inhibition mediated by ______ pathways.
Receptive Field
Receptive Fields
Center
Surround
Anatgonistic
Vertical
Lateral; Lateral
The detection of contrast is based on the organization of receptive fields
The receptive fields of _______ cells are overlappingso that every point of the retinal surface is analyzed by several on-center and off-center _____ cells.
Center-surround receptive fields are first established at the level of ______ cels and persist at the _____ levels of visual processing (i.e., lateral geniculate nucleus and visual cortex).
Ganglion; Ganglion
Bipolar; CNS
Responses of ON-center and OFF-center ganglion cells
On-center ganglion cells _____ their rate of firing when the center is illuminated and ____ it when the surround is illuminated.
Off-center cells ____ their fire when the center is illuminated and ____ it hen the surround is illuminated.
The firing rate of a ganglion cell is a measure of the ______ between the illumination of the center and the surround.
Increase; Decrease
Decrease; Increase
Contrast
Principles of Visual Processing
The visual system uses ______ ______ to process information abotu different features of the visual scene (e.g. form, motion, color). These originate in the ____ from functionally distinct clases of ganglion cells. 90% of the primate ganglion cells fall into 2 functional classes desginated as ____ (magni, large) and _____ (parvi, small)
Parallel Pathways
Retina
M; P
M cells have _____ receptive fields and signal _____, ____ and _____
P cells have _____ receptive fields and provide information about ____ _____ and _____.
The parallel pathways remain separate from retina to cortex.
Larger; Motion, Position, Depth
Small; Fine Detail & Color
______ _____ in lateral geniculate nucleus and primary visual cortext (lost at level of association cortex). In the primary visual cortex representation of the area centralis is graetly enlarged compared to cortical surface area devoted to the rest of the retina.
Retinotopic Mapping
_____ ______: receptive fields become larger and more complex at each level.
Hierarchial Processing
Color Vision
Humans have ____ populations of color sensitive _____. We are trichromatic and can distinguish the range of colors with which you are familiar.
Color vision in dogs is said to be comparable to people are are ____-_____ color blind. Dogs are ______ and seem to see _____ and ____ but not green or orange-red.
All of several horses tested could distinguish ____ and _____ from gray. Some but not all of the horses could also distinguish ____ & ____ from gray.
Nocturnal animals are completeley color blind (rat, hampster, etc.)
3; Cones
Red-Green
Dichromatic
Blue; Yellow
Red; Blue
Yellow; Green
Non-Image Forming Vision
- Mediated by intrinsically photosensitive _____ _____ cells, which contain melanopsin (peak sensitivity in the ____/_____ range of the spectrum)
- Detect _____ light
- Involved in ______ clock
Retinal Ganglion
Blue/Green
Ambient
Circadian
Visual Pathways
Conscious Pathway:
____ –> _____ –> ______
Retina —> Lateral Geniculate –> Cortex
Visual Pathways
Reflex Pathways
Retina –> _______ ______
(eye, ear, and head turning to oreitn to a visual stimulus)
Retina –> _______ _____
(pupil size regulation to compensate for light intensity)
Rostral Colliculus
Pretectal Region
Optic Nerve:
axons from ____ ____ cells
Retinal Ganglion Cells
Optic Chiasm:
decussation of ____ _____axons; depending on species, percentage of axons from the lateral side of each retina do not cross
Optic Nerve
Optic Tract:
axons from both eyes. The optic tract conveys _____ visual field information
contralateral
Binocular Vision:
Important for _____ ______
- Requires visual field overlap so that individual objects can be viewed simulatneously by both eyes.
- “corresponding” ganglion cells in each eye send their axons through the same optic tract
- The visual cortex in one cerebral hemisphere receives info about an object from both eyes. In visual cotex, some columnds monitor stimulation in corresponding loci of the 2 eyes.
Depth Perception
Concious Visual Pathway
Optic tract fibers synapse in the ____ _____ nucleus. Neurons of this nucleus send their axons into the optic radiation of the internal capsule and the nto the primary visual cortex.
Lateral Geniculate Nucleus
Conscious Visual Pathway
The ____ ____ _____ exhibits the typical columnar organization of neocortex. Colums respond to geometric & dynamic elemnts of an image. A cell column within visual cortex becomes excited in response to light-dark boundaries oriented at a certain angle, moving in a certain direction, affecting either or both eyes, etc. Some cell columns are activated by particular colors.
Primary Visual Cortex
Conscious Visual Pathway
The ____ ____, surrounding the primary visual cortex, is required to associated meaning and significance to the elements of the primary image. There are two separate visual integrations:
- A phylogenetically older “____” system that analyzes motion and depth. Damage produces:
Failed ocular pursuit of a moving target
Poor depth perception
Deficient visuall guided movements
deficits in visual attention - A phylogenetically newer “_____” sysmte that analzyes form and color. Damage produces:
Loss of color Vision
Impaired pattern recognition, including face/object recognition
Association Cortex
Where
What
Reflex Visual Pathways
Axons participating in subconscious visual reflexes leave the optic tract and travel in the ______ of the _____ ____ to reach two visual reflex centers, the
- _____ ______
- _______ _______
(Axons also leave the optic tract to reach the hypothalamus)
Brahcium of the Rostral Colliculus
- Rostral Colliculus
- Pretectal Region
Eye, ear and head turning to orient to a sudden, prominent visual stimulus inolves the ______ ______.
Neurons of this send their axons to appropriate motor nuclei via tecto_____ and tecto_____ tracts.
Rostral Colliculus
Tectobulbar & Tectospinal
Pupil size regulation to compensate for light intensity involves the ______ ______, with fiber decussation in the ________ ________.
Axons go to the ________ nucleus of the ________ nerve for pupillary constriction (dilation is achieved by less constriction).
Pretectal Region
Caudal Commissure
Parasympathetic
Oculomotor
The pupillary light reflex is important for diagnosing lesions in the _______ pathways.
Visual
