vision iii (transdution) Flashcards
1
Q
outer and inner segments for rods and cones
A
outer segment
- contains photopigments
- transduction of light energy into receptor potential occurs here
inner segment
-contains the nucleus, golgi complex, and mitochondria
2
Q
rods
A
- outer segment is rod-shaped
- dim light –> sensitive to light
- black and white vision
- contain single photopigment –> percieved input in grey tones
- peripheral vison –> located in peripheral zone of retina
- pathways converge, causing fuzzy, indistinct images
- 20 rods: 1 cone
3
Q
Cones
A
- outer segment is cone-shaped
- need bright light for activation (have low sensitivity)
- color vision: have 3 photopigment (red, greed, blue)
- many shades of color- overlap of wavelength domains
- dense in fovea centralis (sharpest vision and best color perception)
-nonconverging pathways for detailed, hi res image
4
Q
photoreceptor cells
A
- vulnerable to damage
- degenerate if retina detaches
- destroyed by intense light
- outer segment renewed every 24 hr
- tips fragment off and are phagocytized
5
Q
photopigments
A
- 2 parts: opsin and retinal
- opsin = 3 types in cones; 1 in rod
- retinal = light absorbing part
- rhodopsin = photopigment in rods
absorption of light by a photopigment leads to structural changes
6
Q
Rhodopsin
A
- deep purple pigment of rods
- 11-cis-retial + opsin
- 3 steps of rhodopsin formation and breakdown (happens in discs and triggers elec impulse)
- pigment synthesis
- pigment bleaching
- pigment regeneration
7
Q
pigment synthesis
A
rhodopsin forms and accumulates in dark
8
Q
pigment bleaching
A
when rhodopsin absorbs light, retinal changes to all-trans isomer
-retinal and opsin separate (rhodopsin breakdown)
9
Q
pigment regeneration
A
- all-trans retinal converted to 11-cis isomer by retinal isomerase
- rhodopsin regenerated in outer segments
- rod regeneration takes much longer than cones
10
Q
Light transduction reactions
A
- light activated rhodopsin activates G-prot transducin (NOT A TYPO)
- Transucin activates photodiesterase (PDE) which breaks down cGMP to GMP
- in the dark, cGMP holds channels of outer segment open –> Na and Ca depolarize cell
- In light cGMP breaks down, channels close, cell hyperpolarizes
- hyperpolarization is sigmal
11
Q
phototransduction in cones
A
- similar process as in rods
- cones are far less sensitive to light, so it takes more light to activate cones
- also regenerate faster
12
Q
Function of Glutamate
A
- glutamate is released by photoreceptors all the time
- glutamate inhibits bipolar neurons
- more glutamate will hyperpolarize bipolar membrane (IPSP)
- glutamate is not released by photoreceptors when the photoreceptors are hyperpolarized
- less glutamate will depolarize bipolar cell membrane (EPSP), leading to AP in ganglion cells
13
Q
Info-processing in retina
A
- photoreceptors and bipolar cells only generate graded potentials (EPSPs and IPSPs)
- when light hyperpolarizes photoreceptor cell, glutamate isn’t released, so bipolar cells depolarize, releaseing NTs onto ganglion cells, which can now generate APs which are tranmitted in optic nerve to brain
14
Q
different wiring for rods and cones
A
rods
- many rods: 1 bipolar cell
- many bipolar cells: 1 ganglion neuron –> convergence
- spatial summation (unclear about source of activation)–> vision not as clear
Cones
- 1 cone: 1 bipolar cell: 1 ganglion neuron
- higher visual acuity of a small area of visual field
15
Q
Light and Dark Adaptation
A
- light adaptation: dark to light = faster
- dark adaptation: light to dark = slower
- cones regenerate rapidly whereas rhodopsin regenerates more slowly
