Neurophysiology - L8 Flashcards
Rods
Used when in dark. Low threshold. Low acuity.
No color
Scotopic Vision
Scotopic Vision
The vision from the rods.
Cones
Higher Threshold. High acuity. See in color
Photopic Vision
Photopic Vision
The vision from the cones
The Fovea
An indentation in the retina in which cones are packed. This is the reason why we see better in the center of our vision.
Rods are seen more on the sides
Why Rods and Cones are at the back of the eye
That is where the blood supply is and the rods and cones need a ton of energy and metabolites
Four Interneurons (and functions) within the eyes
Bipolar Cells - Connect Receptor to ganglion Cells
Ganglion Cells - Are the outward cells first spot of the action potential (afferent)
Amicrine Cells - inhibitory cell
Horizontal Cells - Connects the cells to cross talk..
Reason Why Signal does not degrade in the bipolar cells of the eye
The distance is so small and so the gap of bipolar cells is not that big of a deal
Rod/Cone Structure
Discs are location of the photopigments.
Inner Segment - Has mitochondria nucleus and NT spot
How we adjust for Large range of intensity of light
1) Adjust shutter diameter (Use Iris to change pupal)
2) Divide into rods and cones
3) Adaptation - photoreceptors channels will be reduced
Dark Adaptation - is when you go in to the dark
Light Adaptation - is when you go in to light and adjust
The Two Parts of Color Vision (subunits)
Chromophore - Derivitive of Vitamin A. 11-cis-retinal
Opsin - 7 transmembrane units and is the receptor
There are four different opsin
rods have one and cones have three
Short, Medium, and Long-Wave Opsin
Short - 420 blue
Medium - 530 Green
Long - 560 Red`
Path of Transduction in the eye
When light goes on PHOTOISOMERIZATION happens and 11-cis retinal chromophore goes to all-trans retinal
Retinal then seperates from opsin. causing activation of Gi g protein
Thus activating a PDE which hydrolyzes cGMP and causes closing of Na channel and hyperpolarization
Bleaching Adaptation
When the retinal seperates from opsin it cannot go again. You need energy to put it back on. so this seperation causes bleachin
Calcium Importance of the Sight Transduction
On the membrane we have calcium and sodium important. That is activated by cGMP (and this inhibited by the light pathway)
*There is also a Na / K, Ca counterporter.
When cGMP is hydrolyzed when you see light. Then the Ca and Na stop going in to the cell.
But Calcium keeps going out.
Thus the decrease in cellular Calcium stimulates guanylyl cylcase to increase cGMP to reopen the cGMP gated channel (to let sodium in)
