Flashcards in Neuro Deck (155)
Where are cones the most present as opposed to rods?
At foavae cones are most present, and then most rods around fovae
What are the major funtions of the retinal pigment epithelium?
spatial buffering of ions in the subretinal space
reisomerization of all-trans retinal
outer segment renewal
secretion of growth factors for maintenance and structural integritiy of retina
What are the two suppliers of blood ot the retina?
inner retina from central retinal artery, and the choroid artery from the short posterior cillary atery from the cillary artery systems
What are the anatomical fovaeal specializations?
Avascular zone, excavation of inner retinal neruons, foveal pit, high cone desnity, absence of rods
What is an important difference between rods and cones withthe amount of light?
Rods "saturate from light and cones do not, and at room light rods are usually saturated
WHat do photoreceptors in response to light?
What is the photopigment used?
Made up of a chromophore (11-cis retinal) and a protein component which normally absorbs light at 375 nm
Where do rods most strongly absorb light in the spectrum?
in the blue-green area
How does phototransduction occur?
isomerization of chromophore (11-cis to trans)
opsin activates transducin
transducin activates PDE
PDE converts cGMP to GMP
Low cGMP closes ion channels
cone hyperpolarizes (inward flux of Ca2+ and Na+)
What is the mechanism by which viagra can cause visual disturbances?
It is a PDE inhibitor, leading to vasodilation
results n an increase in cGMP
results in an opening of cyclic-nucleotide-gated ion channel and thus depolarization of the cell
All photreceptors act in the same way by hyperpolarizing which causes them to waht?
Release less neurotransmitter
When a cone is depolarized at the off center position it releases what neurotransmitter?
Activiity of a single cone gives rise to what?
2 parallel pathways, by connecting two different bipolar cell types,an ON CENTER type
and an OFF CENTER type
glutamate hyperpolarizes the ON center bipolar and depolarizes teh off center bipolar
Bipolar cells in the retina talk to what cells?
Amacrine cells which provide lateral connections
Ganglion cells produce action potential
What are the two types of ganglion cells?
parasol ganglion cells-large with large receptive field projecting to magno layer
midget ganglion cells project to parvo layers and are smaller celsl with smaller receptive fields but are more sustained
What are photoreceptors interconnected by?
Elaborate system of inhibitory interneurons called horizontal cells, whhich havea reciptrocal inhibitory synaptic relationship
What is achromatopsia?
Autosommal recessive disesase where cones cannot hyperpolarize in response to light
A tumor that presses onto the side of the optic chiasm tends to alter what field of vision?
The lateral field, "blinder"
Where is the majority of V1 located?
Inside the calcarine
What is teh result of a unilateral optic nerve lesion?
Blindness in affected eye only
What is the result of lesion of the optic chiasm?
Causes bitemporal hemianopia b/c it interrupts the fibers from nasal portion of retina
What is the result of unilateral optic tract lesion?
Causes contralateral homonymous hemianopia because it interrupts fibers from temporal portions of the retina on the ipsilateral side and the nasal portion on the opposite side
What is the result of unilateral lesion of optic radiation in anterior temporal lobe (Meyer's loop)
leads to contralateral upper quadrantanopia
What is the result of unilateral lesion of optic radiation in the parietal lobe?
Leads to contralateral lower quadrantanopia
What is the role of occipital lobe lesion?
Can lead to homonymous hemianopia. B/c the optic radiation fans out widely before entering visual cortex, lesionso f the occipital lobe tend to spare foveal vision.
What is the result of lesion of cortical areas of occipital pole?
Represents the macula and characterized by a homonymous hemianopic central scotoma.
What is teh central pathway for teh light reflex?
What is pretectal area?
connects chiasm to edinger-westphal nuclei; and visceral
Edinger-westphal nucleus of the midbrain givves rise to waht?
preganglionic parasympathetic fibers, which exit the midbrain with oculomotor nerve and synapse with post-ganglionic neurons at cilary ganglion