Chp 50-52 (Optic of Vision, Neuro function of Retina) Flashcards
Define Eye
- Organs of the Visual system
- Detects light and convert it into electro-chemical impulses in neurons
- Regulates the light intensity through a diaphragm, focuses it through an adjustable assemly of lenses to form an image-convering the image to electrical signals and transmits these signals to the brain.
NOTE: the eye is not shaped like a perfect sphere
The Wall of the Eye consists of 3 concentric layers:
- outer layer- (cornea, conjunctiva, sclera)
- Middle layer- (Iris,Ciliary body, choroid plexus)
- Inner Layer- (retina)
Discuss the anatomy of the Eye in detail:
- Eye is made up of 3 coats or layers
- spaces of the eye are filled with the aqueous humor antriorly (between cornea and lens)
- the vitreous body= a clear jelly-like substance composed of water and proteins = behind the lens, filing the entire posterior cavity.
- the lens is suspended to the ciliary body by the suspensory ligament (zonule of zinn) made up of hundreds of fine transparent fibers which transmit muscular forces to change the shape of the lens for focusing.
What is the average normal intraocular pressure and does it remain constant?
- 15mm Hg, with a range from 12 to 20 mm Hg
- Intraocular pressure remains constant in the normal eye, usually within + or - mm Hg of its normal level.
Define Glaucoma and normal range of intraocular pressure:
is a group of eye conditions that damage the optic nerve. This damage is often caused by pathologically high intraocular pressure in the eye.
Pressure rises acutely to 60 to 70 mm Hg.
NOTE: pressure rising above 25 to 30 mm Hg can cause loss of visoin when maintaing for long periods due to compression on the axons of the optic nerve
what changes the curvature of the lens and what is this process called?
changing of the Curvature of the lens is carried out by the Ciliary Muscles surrounding the lens.
This process is calld “Accomodation”
In children the refractive power of the lens of the eye can be increased voluntarily from _____ to _____
20 diopters to 34 dipters
Fun Fact:
how many estimated suspensory ligaments are attached radially around the lens, pulling the lens edges toward the outer circle of the eyeball?
70 Ligaments
light energy enters the eye through what anatomical structure?
Through:
cornea
pupil
then lens
T or F
The lens shape is changed for near focus (accomodation) and is controlled by the Ciliary Muscle.
True
Name the light sensitive cells of the Retina
Photoreceptors: Cones and Rods
Photons of light falling on the light-sensitive cells of the retina are converted into what?
Converted into electrical signals that are transmitted to the brain by the optic nerve and interpreted as sight and vision
What type of Nerves control “accomodation”?
Parasympathetic Nerves
The ciliary muscle is controlled almost entirely by what nerve signals?
Parasympathetic Nerve signals
Parasympathetic nerve signals are transmitted to the eye through what cranial nerves?
Through Cranial Nerve III from the third nerve nucleus in the brain stem
Define Emmetropia
Normal Eye
Define Presbiopia
- the loss of accommmodatin by the lens
- lens begins to lose its intrinsic elastic properties and becomes less responsive and unable to focus on near objects (corrected with bifocal lens)
Define Myopia
- Nearsightedness
- due to an eye that is elongated from front to back causign light rays to focus in front of the retina (corrected with concave lens)
Define Hyperopia
- Farsightedness
- due to an eyeball that is too short from top to bottom, causing light rays to focus behing the retina (correction with a convex lens)
Define Astigmatism
-caused by substantial difference in the curvature over different planes through the eye, resulting light rays entering the eye form diffent directions are focused at differnt points (corrected with the use of cylindrical lens)
Define Cataracts:
- Condition comonly affecting the eye(s) of older people
- A cloudy or opaque area or areas in the lens
- some of the lens fibers become denatured
- the same protein coagulate to form opaque areas in place of normal transparent protein fibers
- Condition correction= surgical removal of the lens replaced by a powerful Convex Lens in front of the eye
The “Retina” contains what 2 major types of light-sensitive photoreceptor cells used for vision?
name and what are they responsible for?
-Rods = are mainly responsible for black and white vision and vision in the Dark
-Cones = responsible for Color Vison
Rods are responsoble for?
Contain what type of pigment?
- responsoble for low-light monochrome vision (black and white)
- Contain pigment “Rhodopsin” (visual Purple) which is sensitive at low light intensity but saturates at higher (photopic) intensities
Note: distibution is not present fovea and blind spot
Note: Rod density is greater in the peripheral retina than in the central retina
Cones are responsible for?
where are they mostly found?
- responsoble for color vision
- require brighter light to function
- 3 types of cones (red,green,blue)
- mostly concentrated in and near the fovea
Photochemistry of Vison:
the outer segment of the rod that projects into the pigment layer of the retina has a concentration of ____% of the ____ ____ pigment called _____ or visual purple.
40%
Light sinsitive pigment
Rhodopsin
Rhodopsin is composed of what proteins?
-this substance is a combination of the protein “Scotopsin” the carotenoid pigment 11- cis retinal
The primary visual cortex lies in the ____ ____ area, extending forward from the ____ ____ on the medial aspect of each occipital cortex (area #17)
- Calcarine Fissure Area
- occipital pole
Name the Layers of Retina from the outside to the inside:
(total of 9)
(1) pigmented layer,
(2) layer of rods and cones projecting to the pigment,
(3) outer nuclear layer containing the cell bodies of the rods and cones,
(4) outer plexiform layer,
(5) inner nuclear layer,
(6) inner plexiform layer,
(7) ganglionic layer,
(8) layer of optic nerve fibers, inner limiting membrane
(9) inner limiting membrane
Rods and Cones (photosensors) are found in which layer of the eye?
What else can be found in this layer?
Under the Pigmented epithelium
The outer layer
Additional: Outer layer of Granular Cells
What type of cranular cells are present in the “Inner Layer” of the eye ?
- Horizontal cells
- Bipolar Cells
- Amacrine Cells
- Ganglion Cells
What can be found in the Nerve Fiber layer of the Eye?
Optic Nerve
What is the importance of Foveal Region of the Retina ?
- Is important for ” Acute and Detailed Vision”
- fovea is a minute area in the center of the retina,
- is composed almost entirely of cones
- these cones have a special structure that aids their detection of detail in the visual image.
T or F
the photochemicals in the cones have almost exactly the same chemical composition as that of rhodopsin in the rods.
the only difference is that the protein portions, or the opsins-called photopsins in the cones - are slightly different from the scotopsin of the rods.
True
What is the chemical composition found in the rods?
The Proten portion is known as?
Chemical composition Rhodopsin
Protein Scotopsin
Protein portion of the photochemcals known as Photopsin is found in the ?
And is the only difference found in the chemical compositon “protein portion” as that of Scotopsin of the ?
Cones
Rods
Name the Color pigments of Cones
These color pigments show peak absorbencies at light wavelents of…provide each
- Red (570)
- Blue (445)
- Green (535)
The absorbtion curve for the Rhodopsin of the Rods shows a peak at ______ nanometers .
505 nanometers
Name the different neuronal cell types :
- Photoreceptors
- Horisontal cells
- biporal cells
- amacrine cells
- ganglion cells
Photoreceptors
The photoreceptors: rods and cones
-which transmit signals to the outer plexiform layer,
where they synapse with bipolar cells and horizontal cells
Horizonatal Cells
The horizontal cells,
which transmit signals horizontall in the outer plexiform layer from the rods and cones to bipolar cells
Bipolar cells
The bipolar cells
transmit signals vertically from the rods, cones, and horizontal cells to the inner plexiform layer, where they synapse with ganglion cells and amacrine cells
Amacrine cells
amacrine cells,
which transmit signals in two directions,
either directly from bipolar cells to ganglion cells
or horizontally within the inner plexiform layer
from axons of the bipolar cells to dendrites of the ganglion cells or to other amacrine cells
Ganglion cells
ganglion cells,
which transmit output signals
from
the retina through the optic nerve into the brain
describe the Visual pathway
The visual nerve signals leave the retinas through the optic nerves.
At the optic chiasm, the optic nerve fibers from the nasal halves of the retinas cross to the opposite sides, where they join the fibers from the opposite temporal retinas to form the optic tracts. The fibers of each optic tract then synapse in the dorsal lateral geniculate nucleus of the thalamus, and from there, geniculocalcarine fibers pass by way of the optic radiation (also called the geniculocalcarine tract) to the primary visual cortexin the calcarine fissure area of the medial occipital lobe
Visual fibers also pass to several older areas of the brain: describe
(1) from the optic tracts to the suprachiasmatic nucleus of the hypothalamus, presumably to control circadian rhythms that synchronize various physiologic changes of the body with night and day;
(2) into the pretectal nuclei in the midbrain, to elicit reflex movements of the eyes to focus on objects of importance and to activate the pupillary light reflex;
(3) into the superior colliculus, to control rapid directional movements of the two eyes;
(4) into the ventral lateral geniculate nucleus of the thalamus and surrounding basal regions of the brain, presumably to help control some of the body’s behavioral functions.
The primary visual cortex lies in the ____ ______area, extending forward from the ____ ____on the medial aspect of each occipital cortex.
This area is the terminus of ____ ______ signals from the eyes.
calcarine fissure area
occipital pole
direct visual signals .
The fovea is responsible for the highest degree of
What ?
Visual Acuity
- macula is the region that the retinal fovea transmits its signals.
- Based on retinal area, the fovea has several hundred times as much representation in the primary visual cortex as do the most peripheral portions of the retina
What is the Secondary visual area called and where can it be found?
visual association areas
-lies lateral, anterior, superior, and inferior to the primary visual cortex.
Most of these areas also fold outward over the lateral surfaces of the occipital and parietal cortex.
Secondary signals are transmitted to these areas for analysis of visual meanings.
The secondary visual areas, also called visual association areas, lie lateral, anterior, superior, and inferior to the primary visual cortex..
These Secondary signals are transmitted to these areas for analysis of WHAT?
visual meanings
