The Visual System Flashcards
Neural component of the eye.
- designed to transduce a photon of light into something the nervous system will recognize (action potential)
- transduced through chemical reactions into action potentials
Primary (only) purpose of non-neural eye components.
refract (bending) photons of light
Non-neural components of the eye.
cornea, aqueous chamber, lens, vitreous chamber/fluid, neural retina, fovea/macular region, ciliary muscle and lens, iris
How does the cornea receive nutrients?
tears (avascular - CN VII damage can cause cornea to dry out)
Attach lens to ciliary muscles.
zonular ligaments
This helps maintain the shape of the eye.
vitreous chamber
Fovea Centralis
where all photons of light are refracted to, greatest acuity
Macula Lutea
surrounds fovea centralis, yellowish in color b/c of protein lutein (filters out ultraviolet light and helps to protect the eye)
Retina is an extension of the ___________.
diencephalon (thalamus, hypothalamus, etc.)
What occurs when the ciliary muscle fibers are relaxed?
suspensory ligament/zonular ligament are taught, pulling on lens to elongate lens for focusing on distance vision
What occurs when the ciliary muscle fibers are contracted?
narrows aperture, allowing suspensory ligaments to be relaxed, thickening/rounding the lens for focusing on near vision
Iris (two series of muscles)
circular: sphincter pupilli (parasympathetic)
radially orientation: dilation of iris (sympathetic)
Visible light
between 400-700 nm in wavelength
Round muscle around the border of the iris.
ciliary muscle (CN III)
Connect the photoreceptor cells to the retinal ganglion cells (output cells).
bipolar cells
Photoreceptor cells
Rods (1) and Cones (3: red, blue, green)
These cells spread info laterally rather than vertically.
Horizontal Cells and Amacrine Cells
Superficial: optic fiber layer
axons of retinal ganglion cells
Ganglion cell layer
cell body of retinal ganglion cells
Inner plexiform layer
synapses are occurring between amacrine and bipolar cells with ganglion cells
Inner nuclear layer
cell heavy with cell bodies of bipolar cells, horizontal cells, and amacrine cells
Outer plexiform layer
cell free layer! synapses for horizontal, bipolar cells, and photoreceptor cells
Outer nuclear layer
contains cell bodies of rods and cones
Inner segments and Outer segments
contains photoreceptors
Series of blood vessels that feed the deeper structures of the eye.
choroid plexus
Retinal Layers
optic fiber layer–>ganglion cell layer–>inner plexiform layer–>inner nuclear layer–>outer plexiform layer–>outer nuclear layer–>inner segments and out segments–>pigment epithelium–>choroid
Foveal pit
- marks the center of the fovea, in the center of the macula lutea
- greatest concentration of photoreceptors, bipolar, to ganglion cells (1:1:1 relationship)
- creates your greatest visual acuity
- prone to degenerative diseases
Right visual world
Left Temporal Retina
Right Nasal Retina
Left visual world
Right Temporal Retina
Left Nasal Retina
The greatest acuity is in which field?
macular field
Nasal retinas
in each eye will cross midline at the decussation/optic chiasm to go back to the lateral geniculate body
Two locations for optic nerve fibers to synapse.
superior colliculus (visual tracking), lateral geniculate body (most fibers synapse here)
Two loops of optic radiations.
Baum’s Loop: medially located - fibers from superior retina carry information from the inferior part of the visual field
Meyer’s Loop: laterally located- fibers from inferior retina carry information from the superior part of the visual field
Lesion of the optic nerve.
Lose total vision in ipsilateral eye, both temporal and nasal retina (anopsia), more loss of vision in the peripheral field
Lesion of the optic chiasm.
pituitary tumors are common, and can cause lesions in the optic chiasm; loss of nasal retina of both left and right side, resulting in tunnel vision; no peripheral vision (heteronymous hemianopsia)
Lesion of the optic tract.
with a right lesion loss of temporal retinal on right side and nasal retina on left side, so you lose the entire left hemifield; Homonymous hemianopsia
Lesion of optic radiations (Meyer’s and Baum’s loops)
loss of upper (Meyer) or lower (Baum) quadrant depending of what portion of the loop is involved; Quadrantanopia
Lesion at striate cortex.
Loss of both upper and lower quadrant; Called macular sparing (loss of vision is not a complete hemifield, but a notched hemifield); Will have central vision
Two types of cells of the lateral geniculate body.
Large Cells: Magnocellular
Smaller denser pact cells: Parvocellular
Laminas in the LGB.
1, 4, 6 lamina get info from contralateral eye
2, 3, 5 lamina get info from ipsilateral eye
Geniculo-cortical inputs
- as info goes from LGB it goes within various parts of optic radiations, back to VI and segregated into ocular dominance columns
- throughout VI we have columns of cells that layer: right eye, left eye, right eye, etc.
17, 18, 19 brodmann’s areas
17: V1
- takes up cuneus and lingual portions
- macular region will be most posterior and the rest of the eye is represented more anterior in area 17
18 & 19:
- wrap around to the lateral surface
- visual Processing areas, where the what/whys/knowledge is added
Area 17
V1 primary visual cortex
Area 18
V2, V3, V3a
Area 19
V4, V5 Association Cortex
Line of Gennari
gives the striate cortex its name (only place to see the line)
Visual processing - 3 types of cells
Each type of cell will respond best to a bar/point of light in a specific orientation; simple, complex, hypercomplex
Retinal Physiology
1) Certain types of photoreceptor cells will respond to specific photons of light, starts a chain reaction that leads to an action potential
2) In some cases retinal ganglion cells will only respond to a bar of light
3) On-Centers and Off Surrounds Cells
light will only be “turned-on” in the on-centers
helps to see contrast
4) Off-centers and On Surround Cells, when light hits this cells you would see stimulus, stop, stimulus (creating contrast)
Orientation columns and response to light.
Certain cells only respond to certain orientation, or bar of light, or bar of light moving in a particular fashion; all are composed in these orientation columns, alternating between information from the Left and Right Eye; Columns next to each other have interconnections for communication
Within the visual cortex there is also some segregation of information depending on if the information is coming from?
rods or cones
Rods info (Fast, black and white vision):
goes to retinal “Y” ganglion cells; those axons will go to magnocellular of LGB, those axons travel via optic radiations to Layer 4 of the visual cortex
Cone info (Very accurate, color vision):
Retinal type “X” cells receive cone info, synapse in the parvocellular region of LGB and come in and synapse in cells in Layer 4 of visual cortex
Visual streams hypothesis.
- separation of information of the inferior portions of the temporal lobe (ventral stream), putting what or meaning to the visual information
- 2nd pathway (dorsal stream) into the parietal lobe that puts the where or how on the information we see
Visual Agnosia
Lesions of the “what” (ventral stream) pathway will cause pt. not be able to recognize the object, but could describe it (doesn’t know it’s a pencil, but knows it is long, yellow, etc)
What happens when you shine a light into a pt.’s eye?
- some info comes into the pretectal area of midbrain, and synapses on edinger-westphal nucleus (both ipsilateral and contralateral)
- causes the pupil to constrict, and also the contralateral pupil will constrict
- If the contralateral pupil doesn’t constrict, the contralateral pathway from pretectal area to edinger-westphal has been broken
