Visual System Flashcards
what structures make up the optical part of the eye?
iris, cornea, lens, colliery muscles and zonular fibers
what is the function of the optical portion of the eye?
regulation of amount of light entering the eye, refraction
what structures make up the neural part of the eye?
retina an doptic nerve
what is the function of the neural part of the eye?
phototransduction and signal transduction
what are the intraocular structures of the eye?
choroid, sclera, aqueous and vitreous humorist, cilliary body, canal of schlemm
function of choroid
contains blood vessels
function of sclera
protective connective tissue
function of aqueous and vitreous humour
fill anterior and posterior eye cavities
function of the optic nerve
bundle of axons that transmit information to visual cortex and subcortical areas
the choroid provides nutrition to the __
retina
structure of the iris
fibrovascular structure with embedded circular and radial muscles and central pupil
what causes pupil to constrict?
contraction of circular muscles
what causes pupil to dilate?
contraction of radial muscles
iris muscles are under the control of a __
reflex arc
myopia is also known as
shortsightedness
what causes myopia?
long egg eyes that are too long to allow lens to focus distant objects on the retina
hyperopia is also known as __
farsightedness
what causes hyperopia?
eye to short to focus near objects on the retina
what is presbyopia?
loss of lens elasticity with age, becomes less spherical
what is an astigmatism?
irregular curve of cornea/lens, causing light to be detracted unevenly and resulting in a blur
what is cataract?
opaque lens caused by the accumulation of pigments, causing less light to be absorbed
refraction is carried out by __ and __ . What % does each contribute?
cornea 75% and lens 25%
what is accommodation?
adjustment of lens convexity by colliery muscles, allowing images both near and far to be focused on the retina
what is the cornea?
transparent structure at anterior of eye
lens can change its power by ___ muscles attached to ___fibers
colliery; zonular
what lens type is used to correct myopia
concave
what type of lens is used to correct hyperopia
convex
a convex lens adds __ power
refractive
when the colliery muscles are relaxed, the zonular fibers are __ and the lens is __, leading to what change in refractive power?
tightened, less convex, less refraction
when the colliery muscles are contracted, the zonular fibers are __ and the lens is ___, leading to what change bin refractive power?
loosened, more spherical, increased refraction
the fovea contains only
cones
the fovea lacks a __ cell layer
bipolar ganglion
why does the fovea lack a bipolar ganglia layer?
allows for more direct light without it
the fovea is the site of greatest visiual __
acuity
t/f there is convergence in the fovea
false
the peripheral retina contains mostly __
rods
the density of cones decreases with increasing distance from the __
fovea
in the peripheral retina there is convergences between ___ and __ as well as __ an __
rods and bipolar cells; bipolar cells and ganglion cells
what is theistic disc?
area where retinal ganglion axons bundle to form the optic nerve
there are not __ in the blindspot (optic disc)
photoreceptors
cones allow for __ vision
colour
rods allow for ___ vision
low-light
___ are the site of phototransduction
photoreceptors
what are the 3 types of higher-order sensory neurons involved in vision?
- bipolar cells
- ganglion cells
- inhibitory interneurons
bipolar cells are excited or inhibited by __ , ___, ___ and ___
rods, cones, action potential, nT release
ganglion cells are activated (result in ap) when __
excitatory signal from bipolar cells
what are the only neurons to enter the retina?
ganglion cells
ganglion cells die in __ and __
glaucoma and macular degeneration
what are the 2 types of inhibitory interneurons and where they are located
- horizontal cells (between photoreceptors)
2. amacrine cells (between bipolar and ganglion cells)
lateral inhibition increases__ an __
contrast and acuity
light enters the retina by the __ cells
ganglia
___ are the only cells to create action potential and carry information from the retina out through the optic nerve to the cortex
ganglia
t/f cones are not as sensitive as rods and require more light to function
ture
what is the purpose of the pigment epithelium at the back of the retina?
to absorb stray light
what is phototransduction?
turning light into the release of NT (neuronal response )
what is the NT in the eye?
glutamate
how does light provoke a neuronal response?
- photoreceptors transduction it to glutamate
- bipolar cells detect glutamate resulting in graded potentials
- graded potentials cause release of glutamate to ganglion cells
- ganglion cells detect glutamate and if depolarization is large enough, an cation potential will happen
photoreceptors have membrane stacks called __ in the outer segment
disks
disks contain __
photopigment
what is photopigment?
proteins with covalently bound light-absorbing retinal cofactor
what photopigment is found in rods?
rhodopsin
what photopigments are found in cones?
opsins (red, green, blue)
rhodopsin absorbs light from what range?
blue to orange
light leads to the isomerization of __ and the activation of __
retinal; opsins
what is the isomerization of retinal?
conformational change from cis to trans
light-activated trans-retinal dissociates from ___ and is converted to __ before re-binding to __
opsin; cis-retinal; opsin
describe the process of phototransduction in the dark
cGMP is constantly made by guanylyl, cGMP gated ion channels open, persistent depolarization and constant NT release
describe the process of phototransduction in light
conformational change of retinal, activation of transducer G protein, degradation of cGMP, close ion channels, hyperpolarization, decreased NT release
the retina has 2 kinds of bipolar cells ___ and __
ON and OFF
ON bipolar cells have __ receptors
inhibitory metabotropic glutamate
light leads to ___ of ON bipolar cells and a ___ in NT and action potential
depolarization; increase
ON bipolar cells synapse onto __ ganglion cells
ON
darkness leads to ___ of ON bipolar cells and a ___ in NT and action potential
hyper polarization; decrease
ON bipolar cells synapse onto
ON ganglion cells
OFF bipolar cells have __ receptors
excitatory inotropic glutamate receptors
light leads to __of OFF bipolar receptors
hyper polarization
OFF bipolar cells synapse onto __
OFF ganglion cells
due to lateral inhibition, light in the receptive field periphery leads to ___ of ON bipolar cells and ___ of OFF cells
inhibition; activation
lateral inhibition is caused by the influence of neighbouring ___ cells
horizontal
activity of bipolar cells is not only affected by the photoreceptors that synapse directly to them, but also by __
surrounding horizontal cells
retinal ganglion cell axons form the ___ that travels to the neurons in the __ and ___
optic nerve and tract; thalamus; visual cortex
what us decussation?
axons from ganglion cells in nasal half of retinas cross the optic chasm so that the right visual field is presented to the left visual cortex
t/f the temporal half of ganglion neurons do not decussate
true
retinal ganglion travel to the midbrain to control changes in ___ in response to illumination and to control movements of ___, __ and__
pupil size, illumination; eye, head, neck
nasal halves of the retina receive info from the __ side
epsilateral
temporal halves of the retina revive info from the __ side
contralateral
