(40) The Visual System Flashcards
What part of the brain in responsible for visual perception?
occipital cortex
What part of the brain in responsible for visual memory?
parietal an temporal
What part of the brain in responsible for visual reflexes?
brainstem and spinal cord
What part of the brain in responsible for circadian rhythm
pineal gland and dienchephalon
what focuses the incoming light from objects we see to create a crisp image
fovea
What happens to the light from an object after it enters our eye to get to the retina?
refracted by cornea inverted through pupil refracted by lens projected onto fovea fovea focuses/fine tunes light light hits retina
how is the image of the object we are seeing oriented on the fovea in our eye?
inverted and smaller
*due to refraction by cornea and lens
What muscle controls lens refraction and how it is innervated
cilliary muscle via sympathetic and parasympathetic control
protective later to the retinal and choroid
sclers
choroid provides blood flow and nutrients to….
photoreceptors and RPE cells = OUTER retina
describe the circulation in the fovea
there is NONE = no blood vessels bc blood distorts the image
describe the cellular organization of the retina
photoreceptor cell bodies lie in outer nuclear layer and project to outer flexiform layer where they synapse with bipolar cells who’s cell bodies are found in the inner nuclear layer. these bipolar cells project to ganglion cells in the ganglion layer. the ganglion cell projections coalesce to form the optic N
provides the barrier between the retina and the choroid
retinal pigmented cells
support the photoreceptor by providing nutrients
RPE
What are the interneurons that lie in the retina and what cells do they synapse with and what is their function?
horizontal (outer plexiform layer) –modulate photoreceptors and bipolar cells
amacrines (inner plexiform layer) –modulate bipolar cells
what form the blind spot?
optic N entry into retina
how are the retinal cells arranged in the fovea?
radially to minimizes distortion of the image
Macular degeneration results when blood vessels damage the ____ and break through to grow into the ___ region of the eye
RPE and macular region
2 main functions of the RPE
- provide barrier between retina and choroid
2. eat outer rod segments every 10 days (prevents macular degeneration/drusen production)
function of rods
produces black and white vision
what is the spherule?
synapse of rods with bipolar cells and horizontal interneurons
which cones are carried on X chromosome
M and L
what is the purpose of the photoreceptors
abs photons and convert it into electrical signal
what is the response that rods and cones have to light
hyperpolarize
**only sensory cells that hyperpolarize in response to a signal, all others depolarize
describe the bichem that is going on in a photoreceptor that allows for a photon to be converted into an electrical signal
light converts cis retinal to trans retinal which activates rod opsin-rhodopsin which converts GDP to GTP which activates PDE. active PDC lowers cGMP levels which closes the cGMP-gated ion channel (Ca and Na). no cations coming in = hyperpolarization = electrical signal that is the visual response
how is the hyperpolarized state of the photoreceptor reversed?
decreased Ca levels activate guanyl cyclase and inhibits PDE which increases cGMP and allows the cations (Ca and Na) channels to reopen
how is the trans retinal converted back to cis retinal so that another photon can activate it
active rhodopsin-GTP is dephosphorylated back to GDP and allows all the trans to go back to cis
**rhodopsin kinase P-rhodompsin which binds arrestin to make the moleucle inactive untl the photon shows up
At the bipolar ganglion cell synapse, ______ cells detect major changes in activity levels
amacrine
cones and rods have thier own bipolar cells. which ones are found in the periphery and which ones are centrally?
periph = rods
cones = central
what cells help converve the signals from multiple rod photoreceptors to fewer rob bipolar cells? (i.e. convergence)
horizontal cells
what ganglion cells are found in the periphery and receive most of their input from rods
alpha-ganglion cells
alpha ganglion cells project to _____ and function to….
magnocellular layer of lateral geniculate nucleus and function to determine the location of object in space
what ganglion cells are found in the central retianl and receive most of their input from cones
beta ganglion cells
beta ganglion cells project to _____ and function to….
parvocellular region in lateral geniculate nucleus to define color and texture
the foves has (rods, cones, or both)
cones
what ganglion cells decussate in the optic chiasm
only nasal fibers
left visual field is processed by what side of the cortex
right
M pathway originates in the ______ cells and projects to lateral geniculate layers _____ then to layer ____ in the cortex. This pathway relays ____ info
originates in magnocellular ganglion cells
layer 1-2 in LGN
4C-alpha in cortex
space information
P pathway originates in the ______ cells and projects to lateral geniculate layers _____ then to layer ____ in the cortex. This pathway relays ____ info
originates in parvocellular ganglion cells
layer 3-6 in LGN
4C-beta in cortex
form information
high glc causes damage to what cells in the eye
retinal epiptheral cells and pericytes and neurons
**damage activates growth facotrs
what vasculature is damaged in diabetic retinopathy vs macular degeneration
DR = retinal AMD = choroid
how is vision field loss compared in DR and AMD
DR = central AMD = all vision
how is dry AMD different than wet AMD
Dry more common than wet
dry has less vision loss and is usually unilateral while wet is bilateral
dry has drusen and wet sometimes foes
What are the treatments for AMD
Avastin and Macugen injections that block vasculature growth they halt progression and do not reverse*
