Visual System Flashcards
What are the three layers that comprise the eye?
Sclera, choroid, retina (from outermost to innermost)
What are the two fluid compartments of the eye?
Aqueous humous & vitrous humor
What is the function of the aqueous humor?
supplies the nutrients to surrounding structures (present in anterior chamber)
What is the function of the vitrous humor?
maintains the shape of the eye and supplies nutrients to surrounding structures (present in space between back of lens and retina)
What is the difference between the sclera and cornea?
Sclera is a white fibrous tissue that forms the outermost layer of the eye. It becomes the cornea at the front of the eye. The cornea is a transparent tissue that separates and protects the eye from external environment and allows light in
What is the choroid?
Capillary bed that nourishes the retinal cells
What is the ciliary body?
a ring of tissue that encircles the lens. Consists of muscular and vascular part
What does the ciliary muscle do?
Controls shape of lens. Connected to lens by zonule fibers
What do the ciliary processes do?
produce the aqueous humor in anterior chamber
What is the iris?
Coloured portion of the eye seen through the cornea. Contain 2 sets of muscles that contract and to adjust size of pupil
What does the lens do?
it refracts light rays coming into the eye and generates a focused image on the retina
What are accommodations of the lens and how do they happen?
changes in refractive power of lens to form a sharp image on the retina. The changes happen thanks to the contraction of the ciliary muscle
What happens to the lens during distant vision?
Lens becomes thin and flat. Less refractive power
What happens to the lens during near vision?
lens becomes thick and round. More refractive power
What is emmetropia?
Normal vision, proper accomodation
What is myopia?
the lens over accommodates (i.e. high refractive power), the image is focused in front of the retina. Hard to see distant objects. Corrected by concave (converging) eye glasses.
What is hyperopia?
the lens does not accommodate enough (i.e. weak refractive power), the image is focused beyond the retina. Hard to see a nearby objects. Corrected by convex (diverging) eye glasses.
What is the retina?
Innermost layer of eye. Considered part of nervous system. Contains light sensitive neurons. Converts visual info into electrical signal to transmit to brain
What are the photosensitive neurons?
Rods and cones
List the characteristics of Rods.
Rod shaped, 120 million, located in periphery, dim light (highly sensitive to light, night vision), low resolution, pigments: rhodopsin, type of cells: monochromic (absorbs white color), no color vision.
List the characteristics of cones.
Cone-shaped, 8 million, center (fovea), bright light (low sensitivity to light, day vision), high resolution, pigments: iodopsin, porphyropsin, cyanopsin, 3 types of cell: S-cones (blue), M-cones (green), L-cones (red), color vision
What are the five classes of neurons in the retina?
Photosensitive, bipolar cells, ganglion cells, horizontal cells (regulate photosensitive activity), amacrine cells
What are the 2 classes of ganglion cells?
on-center cells and off-center cells
What do the on-center cells respond to?
Active to light spot in center and silent to dark spot in center
What do the off-center cells respond to?
Silent to light spot and active to dark spot in center
what other class of neurons has on and off center cells?
Bipolar cells
What control the activity of the on-center/off-center ganglion cells?
The multiple interactions between the photosensitive cells, bipolar cells and horizontal cells
What are the horizontal cells thought to regulate?
Regulate the amount of transmitter that the photosensitive cells release onto bipolar cell dendrites
How is the image perceived on the retina?
it is inverted top to bottom and reversed right to left
How can the visual field be divided?
into right visual hemi-field and left-visual hemi-field
The right visual hemi-field is seen by what part of the retina?
the right nasal retina and left temporal retina
The left visual hemi-field is seen by what part of the retina?
The left nasal retina and right temporal retina
What is the binocular visual field?
Visual fields of both eyes overlap in the central portion of the visual field
What forms the optic nerve?
axons of the ganglion cells
What happens to the optic fibres at the optic chiasm?
60% of the optic fibre crosses to the opposite side of the brain, 40% stays on the same side of the brain
Fibres from the nasal retina project to which side of the brain?
The contralateral side
Fibres from the temporal retina project to which side of the brain?
The ipsilateral
What do the optic fibres form after the optic chiasm?
the optic tract
Where do the majority of the optic fibres terminate in?
In the lateral geniculate body (LGB) in the thalamus
What do neurons in the LGB form and where do they terminate?
Neurons from the LGB form the optic radiation and terminate in the striate cortex (occipital cortex)
What other midbrain areas do the axons of ganglion cells project to?
Hypothalamus (regulation of circadian rhythm), Pretectum (control of pupillary light reflex), superior colliculus (orienting the movements of head and eyes)
What is the visual cortex?
Visual cortex= striate cortex= primary visual cortex = V1= Brodmann’s area 17
What does the visual cortex do?
Processes the basic of the sensory info sent by retina (places back the inverted image to its original position)
How much representation does the sensory information from the central region of the retina have in the visual cortex?
Large representation
Are the geniculate neurons monocular or binocular?
Monocular
Are the neurons in layer 4 of the striate complex still monocular?
yes
At what stage does the images from both eyes converge into a single image?
When layer 4 neurons send their output to other cortical layers
The primary visual cortex projects to what other cortex areas?
The extrastriate cortex which is involved in complex visual perception
The dorsal pathway projects to what?
Projects to the parietal lobe. Responsible of spatial aspect of vision
The ventral pathway projects to what?
projects to the temporal lobe. Responsible for object recognition
