Vision Flashcards
Two organizational principles of V1
Topographical mapping and foveal magnification
Receptive fields maintain antagonistic center around, produced by combining outputs of LGN cells
Simple V1 cortical cells
Respond to stimuli shaped like bars or edges that have a particular slant or orientation (particular angle)
Simple V1 cortical cells
Processed in left hemisphere (not just right eye)
Right VF
Processed in right hemisphere (not just left eye)
Left VF
What does the dark do to photoreceptors?
Depolarizes. More glutamate
What range does the left eye see?
1-8
What wavelength causes the max response in middle cones?
530 nm
When the light entering the eye is focused in front of the retina and stint objects can’t be seen sharply. Near sightedness
Myopia
How does the lens accommodate for near objects
Convex shape
Function similar to horizontal cells
Amacrine cells
How does the lens accommodate for far objects
Concave shape
Blind spot is created by this
Optic disk
Two types of this cell: diffuse (peripheral) and midget (fovea)
Bipolar cells
Represents brightness
Amplitude
Hardening of the lens. The capsule that encircles the lens becomes less elastic as well. Harder to focus on close things. Old sight
Presbyopia
Receptive fields replicate the info passed to them by the bipolar cells. Max response to dots of specific size. Sensitive to contrast
Ganglion cells
Colored area. Contains muscles that control the pupil
Iris
Most detail and best perception of color in this type of vision
Central vision
Long cone defect
Protoanomalous
Transparent disk that uses accommodation to focus light rays for near of far distances
Lens
Part of environment registered on retina
Visual field
No short cone
Tritanope
Integrate info from photoreceptors close to one another and communicate through graded potentials with bipolar cells
horizontal cells
Why is the cell depolarized in the dark?
Sodium channels are kept open by cGMP. Na+ is allowed in in the dark
Organizational principle of V1. Locations on retina and LGN correspond to locations in V1
Topographical mapping
How many cells in the visual cortex
200 million
Receives input from M ganglion cells. Respond best to large, fast moving objects
Magnocelluar LGN layers
What is light?
Particle and a wave. Moving waves of photons
How many other cortical areas participate in visual processing other than V1?
At least 12
How many ganglion cells are there and what does this mean for how they respond to photoreceptors?
1 million. They respond to many photoreceptors
What are the wavelengths for the visible light spectrum?
400-800 nm
Shows preferred stimulus size and orientation but not location within the visual field. Sensitive to unidirectional movement
Complex V1 cortical cells
What is akinetopsia? What is it associated with?
Cant process motion. Dorsal stream
No medium cone
Deuteranope
How do on center and off center cells work?
On center = light in center: depolarized. Light in surround: hyperpolarized.
Off center = Light in center: hyperpolarized. Light in surround: depolarized
How does light need to behave in complex V1 cortical cells?
It must be moving and in a certain direction
Four parts of a hyper column
Orientation columns, ocular dominance column, movement, and color
Back opening that lets in light
Pupil
Optic nerve target that is the pacemaker for circadian rhythms. Regulates sleep/wake cycles and receives small numbers of retinal axons
Suprachiasmatic nucleus in hypothalamus
Represents color or shades of gray
Wavelength
What type of potentials are produced by photoreceptors?
Graded potentials, not AP
Why is it harder to focus when you get older?
The lens hardens
Has 6 distinct stacked layers, keeps input from each eye separate, modifies flow of info based on levels of alertness
Lateral geniculate nucleus in thalamus
Larger receptive fields with no off regions
Complex V1 cortical cells
What happens to the shape of retinal when it is exposed to photons?
It straightens
What does having more types of cones cause?
A poorer ability to discriminate colors, it does not make it better
Receive input from P ganglion cells. Respond best to fine spatial details of stationary objects
Parvocellular LGN layers
What wavelength causes the max response in rods?
502 nm
What range does the right eye see?
2-9
What does bright light lead to?
Greater hyperpolarization
Organizational principle of V1. Central vision has more brain representation than peripheral vision
Foveal magnification
Direct input from single set of photoreceptors
Center
Theory stating color vision is based on exciting one color and inhibiting its opposite
Opponent process theory of color vision
Optic nerve target that projects to primary visual cortex (V1). Visual perception. 90% of retinal axons
Lateral geniculate nucleus in thalamus
No long cone
Protanope
Respond to light falling in receptive fields. Antagonistic center-surrounded organization. Lateral inhibition. Communicate through graded potentials with amacrine and ganglion cells
Bipolar cells
A visual defect caused by the unequal curing of one or more of the refractive surfaces of the eye, usually the cornea
Astigmatism
What path does light take?
It passes through cells then hits the photoreceptors?
Less detail and color perception in this type of vision
Peripheral vision
Six muscles that rotate the eye in all directions
Eye muscles
What are the optical functions of vision?
Capture light and form detailed spatial images
What is the correct term for colorblindness?
Color anomalous
Responds to lines of a single angle for single eye, made of simple cortical cells. Hyper column part
Orientation column
What is the stimulus for vision?
Light
What does light do to rhodopsin and what does it do to cGMP?
Light breaks down rhodopsin, releasing enzymes that break down cGMP
These cells are filled with light sensitive chemicals called photopigments
Photoreceptor cells
Contain lodopsin
Cones
What causes age related macular degeneration
Problems with the macula leading to blurred central vision
Area involved in visual processing towards the top of the head that plays an important role in processing motion. Areas MT and MST
The dorsal stream (where/how)
In this cell, the bipolar cell is depolarized (excite)
On center cell
Composed of opsin and retinal
Rhodopsin
Where does the nasal (central) view of each eye go?
Contralateral (opposite side)
Rods only, no cones or only one type of cones
Monochromats
Circular receptive fields found in retina and LGN are replaced with elongated stripe receptive fields in cortex
Visual cortex (striate cortex)
What happens when enzymes created by light breaking down rhodopsin break down cGMP?
Fewer Na channels remain open and the cell hyperpolarizes
About 50% of these fibers cross to opposite hemisphere at the optic chiasm
Optic nerve
What is the resting potential fo rod outer segments in complete darkness?
-30 mV. Depolarized
Part of the retina where light rays are most sharply focuses
Fovea
Why is the eye extremely sensitive to pain?
Many pain receptors on cornea
What wavelength causes the max response in long cones?
560 nm
Optic nerve target that guides head and eye movement, visual reflexes. Receives 10% of retinal axons
Superior colliculus in midbrain
Three targets of the optic nerve
Lateral geniculate nucleus (LGN) in thalamus, suprachiasmatic nucleus in hypothalamus, and superior colliculus in midbrain
In between layers of LGN
Koniocellular LGN layers
Layers 3-6 of LGN
Parvocellular LGN layers
What is cGMP?
A secondary messenger that keeps sodium channels open in in the dark to allow depolarization
Human have 3 different types: short, medium, and long
Cones
What is prosopagnosia? What is it associated with?
Face blindness. Ventral stream
A membrane on the retina that improves night vision in animals that have it, humans don’t
Tapetum lucidum
Sensitive to dim light in the blue to green range of the EM spectrum (shorter end)
Rods
Defect in one type of cone
Anomalous trichromats
Theory supported by complementary colors and afterimage effects
Opponent process theory
5 steps in the visual pathway
- ) R and L visual field to retina
- ) Optic nerve to optic chiasm to optic tracts
- ) 90% to LGN of thalamus
- ) Optic radiations to primary visual cortex (V1) in occipital lobe
- ) Secondary visual cortices
What does dim light lead to?
Less hyperpolarization
Where does the temporal (outside) view of each eye go?
Ipsilateral (same side)
Where are the genes that produce photopigments?
X chromosome
What does the light do photoreceptors?
Hyperpolarizes. Less glutamate
Path from photoreceptors
Photoreceptors to horizontal cells to bipolar cells to amacrine cells to ganglion cells to axons of optic nerves
Shape of receptive field elongated (lines not donuts)
Simple V1 cortical cells
What are the neural functions of vision?
Transduce light into neural signals, then relay and process those signals
What are bipolar cells?
One receiving and one transmitting branch
Outer surface of the eye. Curved, transparent dome that initially bends incoming light
Cornea
Medium cone defect (most common)
Deuteranomalous
In this cell, the bipolar cell is hyperpolarized (inhibit)
Off center cell
Area involved in visual processing toward the bottom of the head important for object recognition. Areas V4, IT and fusiform face are (FFA)
Ventral stream (what)
Color theory based on combination of activity in short, medium, and long cones
Trichromatic theory
Also known as primary visual cortex, Brodmann’s area 17, or V1
Striate cortex
Photopic vision (bright light), color, high acuity, high density near fovea, humans have 6 million
Cones
Receive input from bipolar, amacrine cells
Ganglion cells
Missing one type of cone
Dichromats
Layers 1 and 2 of LGN
Magnocellular LGN layers
Contain rhodopsin pigment
Rods
Complex cells in a hyper column
Movement
This energy is abundant, travels quickly, and in straight lines
Electromagnetic energy
How is the eye protected?
Located in bony orbit of the skull, cushioned by fat, eyelids/eyelashes/blinking, and tears produced by the lacrimal gland
Visual pigments made. Contains chromophore to capture photons and an opsin protein
Inner part of photoreceptors
Loss of transparency in the lens that can be solved with silicone implants
Cataracts
Also known as the young-helmholtz theory of color vision
Trichromatic theory
Innermost layer in back of the eye where light is converted to neural impulses. Contains visual interneurons and photoreceptors
Retina
Changing the shape of the crystalline lens to focus on objects of varying distance
Accommodation
Short cone defect
Tritanomalous
How is light wavelength determined in the trichromatic theory?
Total activity across all 3 cones is used
Requires more light the other photoreceptor to respond
Cones
What 3 things can happen when light hits an object?
Reflection, absorption, or refraction
Cytochrome oxidase blobs in hyper columns
Color
Where blood vessels and optic nerve leaves the retina there are no photoreceptors. Compensatory mechanisms
Blind spot
Transparent, gelatinous mass that fills space from cornea to pupil
Aqueous humor of anterior chamber
What percent of males and females have colorblindness?
8% of males an 0.5% of females
Form connections between bipolar, ganglion, and other types of this cell. Play a possible role in processing movement
Amacrine cells
Located at the center of the macula and comes into play with central vision
Fovea
Responds to input from either the L or R eye, but not both. Preferred orientation changes. Hyper column part
Ocular dominance column
Theory supported by color blindness
Trichromatic theory
Contains visual interneurons, photoreceptors, optic disk, macula, and fovea
Retina
Transparent, gelatinous mass that fills space from pupil to retina
Vitreous humor
When light entering the eye is focused behind the retina. Farsightedness
Hyperopia
Ganglion cell axons bundle together and exit each eye through the optic disk, forming this leaving each eye
Optic nerve
Nutrients from epithelium and visual pigment storage
Outer part of photoreceptors
Scotopic vision (dim light), no color, low acuity, high density in the peripheral retina. Humans have 120 million
Rods
Transmits imputes from retina to brain
Optic nerve
Produce APs. Axons leave the eye as the optic nerve
Ganglion cells
What wavelength causes the max response in short cones?
420 nm
Is there more neural activity in the dark or light?
Dark
Indirect input from horizontal cells connected to photoreceptors
Surround
How does a cell know when light is present?
It interprets the reduction of glutamate caused by hyper polarization as light
The happy condition of no refractive error. Perfect vision
Emmetropia
