CENTRAL VISUAL PATHWAY Flashcards
The eye is a fluid-filled sphere enclosed by 3 layers of tissue:
Sclera: Outermost layer
Choroid: Intermediate layer
Retina: Innermost layer
Which fluid compartement is in the anterior chamber and is a watery liquid
aqueous humor
describe vitrous humor and function
a thick gelatinous substance. It fills the space between the back of the lens and the retina. It maintains the shape of the eye and supplies nutriments to surrounding structures
what is the sclera and what does it become in front of the eyes
white fibrous tissue forming the outermost layer of the eye. At the front of the eye, it becomes the Cornea
what is the cornea
a transparent tissue that separates and protects the eye from the external environment and allows light rays into the eye.
what is the coroid
capillary bed that nourishes the retinal cells
what is the cilary body
a ring of tissue that encircles the lens and consists of a muscular and vascular part
what is the ciliary muscle
controls the shape of the lens. Connected to the lens by the Zonule fibers.
what is the ciliary process
produces the aqueous humor in the anterior chamber
what is the iris
coloured portion of the eye seen through the cornea, contains 2 sets of muscles that contract and to adjust the size of the pupil
what is the lens
Lens refracts (bends) light rays coming into the eye and generates a focused image on the surface of the retina.
what is the accomodation of the lens
dynamic changes in the refractive power of the lens to form a shape image on the retina. These changes are made by the contraction of the Ciliary muscle.
what happen with lens with distant vision and near vision
Distant vision: lens becomes thin and flat. Less refractive power.
Near vision: lens becomes thick and round. Most refractive power
what is emmetropia
: In the normal eye, the lens has a right accommodation level, the image is focused right on the retina.
what is myopia
the lens does not accommodate enough, the image is focused in front of the retina. Hard to see distant objects. Corrected by convex (converging) eye glasses.
what is hyperopia
the lens over accommodate, the image is focused beyond the retina. Hard to see a nearby objects. Corrected by concave (diverging) eye glasses
what is the retina
the innermost layer of the eye.
The retina is considered a part of the Nervous System. It contains neurons that are sensitive to light and convert visual information to electrical signal and transmit it the brain
Photosensitive (photoreceptor) neurons:
rods and cones
which one btw rods and cones make the color vison
cone
which one create bright light and which one night vision
bright: cone
night: rods
which one produce periphery vision and which one produce center vision
rods: peri
cone: center
which produce low resolution and which one high resolution accuracy
cones: high
rodds: low
what are the 5 classes of neurons of retina
photosensitive
bipolar
ganglion
horizontal cell
amacrine cell
which neuron regulate the activity of photosensitive
horizontal cell
which cell make the Lateral communication between neurons
amacrine cells
what are the 2 classes of ganglion cells
on center cell
off-center cell
role of on-center cells
active to light spot in center and silent to dark spot in center.
role of off-center cells
silent to light spot in center and active to dark spot in center.
which cells also have on-center and off-center cells
bipolar cells
The activity of the On-center/Off-center ganglion cells is controlled by
multiple interactions between the photosensitive cells (cone/rod), bipolar cells and at horizontal cells.
how is the image convert on the retina
the image is inverted top to bottom and reversed right to left.
what is the visual field
part of word seen by the eye. It can be divided to 2 hemi-fields:
right visual hemi-field is seen by
the right nasal retina & left temporal retina.
left visual hemi-field is seen by
): seen by the left nasal retina & right temporal retina.
qhat is the binocular visual field
Visual fields of both eyes overlap in the central portion of the visual field =
60% of the optic nerve fibres crosse at the
optic chiasma to the opposite side of the brain
40 % of fiber goes where
stay on the same side (ipsilateral) of the brain.
Fibres from the nasal retina project to the
contralateral side of the brain (i.e. crosse the optic chiasm).
Fibres from the temporal retina project to the
ipsilateral side
after the optic chiasma, the optic fiber form what
optic tract
The majority of optic fibres terminate in the
Lateral Geniculate Body (LGB) in the thalamus.
neuron from LGB form what and terminate where
Neurons from the LGB form the optic radiation and terminate in the striate cortex (occipital cortex).
neuron from LGB form what and terminate where
Neurons from the LGB form the optic radiation and terminate in the striate cortex (occipital cortex).
role of hypothalamus, pretectum, superior colliculus
Hypothalamus: regulation of circadian rhythms (biological clock).
Pretectum: control of the pupillary light reflex.
Superior colliculus: orienting the movements of head and eyes (see the vestibular system).
role of visual cortex
processes the basic of the sensory information sent by the retina (e.g. place back the inverted image to its original position, binocular vision, 3D image, ect)
which info have a large representation in th visual cortex
Sensory information from the central region of the retina (macula, fovea) have a large representation in the visual cortex. the central region of the retina sends the large portion of sensory information to the visual cortex.
what is the name of the 6 cellules layer in striate cortex
“Cytoarchitecture”;
geniculate neuron are mono or bicular
monocular
The lateral geniculate nucleus (LGN) receives input
both eye
LGN input remain segreated where
in layer 4 of the striate cortex (ocular dominance columns). Here also the neurons are still monocular.
in which state the image from both eye are converge onto a single image
Layer 4 neurons send their outputs to other cortical layers; it is at this stage that the images from both eyes converges onto a single image (cyclopean representation of the external world = binocular vision).
role of Dorsal pathway (where pathway
projects to the parietal lobe. Responsible of spatial aspect of vision (e.g. analysis of motion, positional relationship between objects…ect).
