8.1 vision Flashcards
what range of light are the rods and cones senstiive to
400-600 nm
what does a concave lens do? what does a convesx lens do?
- concave: scatters light rays (light is bent away)
Convex: causes light rays to converge, bends like wds a focal point
*image of eye is filled in both vertical and horizontal planes -> but rbain then corrects this
what is the pathway when light enters teh eye?
where in the eye is light reafracted?
Pathway: cornea, aqueous humor, lens, vitreous humor, and the neural layer of the retina to the photoreceptors
light is refracted: at cornea, entering the lens and leaving the lens
*lens curvative and shape are what allow for fine focusing of an image
what is the optic disk
blind spot
- region where optic nerve and blood vessels leave the eye -> no rods and cones in this area
what is the fovea
- region of sharpest vision
- very high conc of cones (colour vision: red, blue and green cone cells)
What is the macula
- centre of the visual field
(sharpes vision bc cones are concentrated here)
Focusing for Distant Vision
- light from disance needs little adjustments for proper focusing (uses sympathetic enrvous system)
- far point of vision: the distance beyond which the lens does not need to change shape to focus (6m)
*when far away have lots of beams coming at you (good parallel lines), -> relaxed lens flattens and iris is fully open
lens if flattened for distant vision, pupil of iris is large, get crisp image at back of eye
Describe focusing for close vision
when clsoer than 6m
- requies accommodation: changing the lens shape by ciliary muscles to increase refractory pwoer (ciliary contract to make lens more bioconvex)
constriction: pupillary reflex constricts pupils to prevent divergent light rays from entering
convergence- medial rotation of eyeball
*parasympathetic regulation, lens buldges for close vision
*light it bent more to focus on fovea
some epopel ahve longer eyes and shorter eyes, what adjustments need to be made>
- Long eye: mypoic
- near sighted
- use a concave lens to bend light less so it can conventrate on the fovea
- Shorter eye: hyperopic
- farsighted
- need to push the focal point up so bend light more
What is photoreceptoion?
what in the eye contains visual pigments
Photoreception - process by which the eye detects light energy
- Rods and cones contain visual pigments (photopigments)
- Rods: elongated, sensitive to dim light
- Cones: better at focusing and detecting colour
what are the 4 main regions of the photo receptor
- Synaptic terminal
- synpases wtih bipolar cells
- Inner Segment
- location of major organelles and metabolic operations
- photopigment synthesis and ATP production
- mitochondria
- location of major organelles and metabolic operations
- Outer sigment
- Vigual pigments in membrane disk
- studed with opsims -> have retinal and opsin embedded in membrane
- Pigment epithelium
- 1 cell thick, supprots rods and cones
- prevents light scattering
Describe the rods
- senstiive to dim light, ebst suited for night vision
- absorb all wave legnths of visible light
- Fuxxy grey, indistinct images
*lots of convergence leading to low sensitivity bc many rods convered to one bipolar cell, and multiple bipolar cells converge to a gnagliion cell
-> decreased resolution
describe retinal
- light absorbing molecule of the visual pigments
- combines with opsins to form visual pigments
- synthesized from vit A
- two isomers: 11-cis and all-trans
*Isomerization of retinal initiates electrical impulses in the optic nerve
describe the excitation of rods
- light comes in @ outer segment of rod
- > causes isomerication off the 11-cis -> all trans
- all trans is then recycled back to 11-cis at the retinal pigment epithelium
Describe the cones
- have pigments that furnish a vividly coloured view and each cone synapses with a single ganglion cell
*causes detailed vision with high resolution
- needs to be bright light for activation
*depending on the opsin will allow to see colour
describe phototransduction
AP ARE NOT GENERATED ONLY GRADED POTENTIALS (EXAM)
- light comes in and hits vidual pigment, activates transducin
- transducin binds, get conversion of 11-cis to the all-trans retinal
- transucin then activates phosphodiesterase
- causes cRMP to break down into GMP
- this reduced the cation channel activity
- NET EFFECT IS CLOSED CATION CHENNEL, TURNS OFF GRADED POTENTIALS
**HYPERPOLARIZATION OF CELL, NEUROREANSMITTER RELEASE DECREASE IN POPORTION TO AMOUNT OF LIGHT
What happens in phototransduction in darkness
- rhosopsin in inactive, cGMP is high and ion channels are open
- get tonic release of neutotransmitter onto bipolar cells
describe recovery phase of transduction
- retinal converted to inactive form, convert all-trans back to 11-cis
- retinal recombines with opsin to form rhodospin
* rods and cones dont recylic retinol by themselves they need help
comparision of signal transmission in retina light vs dark
- No light
- no opsin activated
- photoreceptor depoarized
- Ca2+ channels open, neurotransmitter released
- INHIBITORY NEUROTRANSMITTER
- IPSP in bipolar cell
- no neurotransmieer released
- no excitatory post synaptic postential in ganglion cell
- no action potential
- Light
- optin activated
- photoreceptor is hyperpolarized
- Ca2+ channle slcosed, no neurotransmitter released
- no IPSP, dipolar cells depolarize
- neutrotransmitter released
- get an EPSP in ganglion cell -> action potential
*Ganglion generates AP but rods and cones go graded
Describe adaptation
-
Bright light: going from dark -> light involves
- dramatic decrease in retinal sensitivity -> rod function is lost
- sensitive to dim so inactivated by bright light
- switing from rod -> cone system to gain visal acuity
- mostly all trans retinol (not light sensitive)
- dramatic decrease in retinal sensitivity -> rod function is lost
-
Dark light
- cones stop functioning in low light
- rhodopsin accumulates in dark and retinal sensitivity is resotes (convers all trans-> 11-cis)
describe rential processing: receptive fields of gnaglion cells
- On center off surround feilds
- Stimulated by light hitting the center of the field
- Inhibited by light hitting the periphery of the field
- Off-centre on-surroun fields
- opposite efects
what is the neural pathway for vision
Optic nerve -> optic chiasm -> optic tract -> lateral geniculate body (thalamus) -> visual cortex (occipital lobe)
describe thalamis procesing
- in Lateral geniculate nuceli of thalams (LGN)
- relat informtion on movement
- Segregate the retinal axons in preparation for depth perception
- Emphasize visual inputs from regions of high cone density
- sharpen contract information received by retina
what 3 regions does the LGN project into
- cuperior colliculus
- Suprachiasmatic nucleus (SCN)
0 VIsual cortex (where most info is sent to
