Biochemistry and Physiology of Phototransduction Flashcards
Just the high yield bit of the phys and biochemistry.
Lack of LRAT and RPE65 in the retinoid cycle can lead to what?
Retinitis Pigmentosis
Mutations in what can lead to macular degeneration?
ABCA4 (normally works to remove all-trans retinal deriviatives from photoreceptors)
Xerophthalmia
most common type?
What are bitot spots?
abnormal dryness of the conjunctiva and cornea of the eye with inflammation and ridge formation
,most common type is night blindness usually due to low vit. A leading to insufficient rhodopsin
gross, foamy plaques on conjunctiva (build up of keratin)
Red Green blindness
X linked recessive
What is the role of Ca+ in the rhodopsin signaling
what activates Gt and what does that lead to?
by controlling the rate of cGMP synthesis, Ca+ levels govern the rate by which the system is restored.
Gt activation by light activates cGMP PDE
Where is LRAT and RPE65 made?
retinal pigmented epithelium
Signal Transduction
photons induce isomerization of the cis-retinal to trans retinal
decreased cGMP means Na channels close causing hyperpolarization (from all the K leaving the cell) nd this causes the Ca channels to close
decreased Ca in the photoreceptors causes a decrease in Glutamate
light=less glutamate=hyperpol.
Vitamin A
retinol, retinoic acid, retinal
def. in vit A can lead to night blindness as well as epithelial problems
night blindness is due to a decrease in vit. A as it decreases rhodopsin, making it harder to see in the dark
Dark Current (phys part of lecture)
stimuli–>photons (light) –> hyperpolarize cells–> decrease glutamate
no stimuli–> no photons (dark) –> depolarizes cells–>increase in glutamate release
ON-Bipolar cells
express mGluR6 receptor (inhibitory)
increase glutamate means the channel will be inhibited
dark–>increased glutamate–>mGluR6 is activated–>increase Ca2+ –>hyperpolarization–>little glutamate released by bipolar cells
Off Bipolar cells
No mGluR6 receptor
Express non-NMDA receptor
increase in glutamate means increase in activation
Function of the lateral geniculate nucleus
converge on a single pt, focus on distant object, map out space, detect movement
Function of Superior Colliculus
creates a map of visual space, coordinates head and eye movement to visual targets
Function of Pretectum
reflex control of pupil and lens
Function of hypothalamus
drives light-dark entrainement of neuroendcorine function and other circadian rhythms
