VISION Flashcards
how are mecahno receptors activated
mechanical deformation in nerve endings
how are thermo receptors activated
temp
how are chemo receptors activated
chemicals in enviro
what energy is required to activate photo receptors
photon energy
what do osmo receptors regulate
osmolarity of body fluids
what are AP s of nociceptors interpreted as
pain
what receptors are involved in hearing
meachno receptors
what mechanical deformation occurs in mechano receptors for hearing
bending of hair
what receptors are involved in vision
photo receptors
what is sensory perception
converting en from outside of body into form that body can interpret
what form of en can body interpret
AP s
what is adequate stimulus
particular type of energy that sensory ending responds to
what must all energy be converted to
- electrochemical energy (AP s)
- change in mem potential
what is primary transduction process
conversion of one form of energy / event to electrochemical energy
what is primary transduction process for vision
photons of light converted to AP
what is primary transduction process for hearing
- sound waves in air get converted to sound waves in fluid
- sound waves in fluid cause bending of hair
- bending of hair opens channels
- opening of channels changes mem potential
what is generator potential
stimulus that causes depolarization or hyper polarization in sensory nerve
graded
when is generator potential hyper polarizing
if K + leaves cell
what is generator potential proportional to
strength of stimulus
what determines how many stimuli can be discriminated
- range
2. stimuli
VISION what does range of visual system depend on
the wavelengths visible to humans
VISION what is sclera
white fibrous part of eye
VISION what is cornea
clear continuation of sclera
VISION what is conjunctiva
thin protecting mem covering cornea
VISION what is most powerful part of light focusing system
cornea
VISION where does light get partially focused
cornea
VISION what is anterior chamber
small chamber behind cornea
VISION what is anterior chamber filled with
aqueous humor
VISION what secretes aqueous humor
ciliary body
VISION what drains aqueous humor
canal of schlemm
VISION where is canal of schlemm
where cornea and sclera join
VISION what is posterior chamber
chamber behind anterior chamber
VISION what is posterior chamber filled with
aqueous humor
VISION where is crystalline lens located
behind anterior chamber
VISION what are characteristics of lens
- convex
2. elastic
VISION what does fluid filled anterior chamber allow cornea and lens to do
act as single optical unit
VISION what is cornea analogous to
coarse adjustment
VISION what is lens analogous to
fine adjustment
VISION where is vitreous chamber located
behind lens
VISION what is vitreous chamber filled with
vitreous humor
VISION what is the function of vitreous humor
maintain shape of eye
VISION what does fibrous tissue and fluid in eye allow
deformation without breaking
VISION where is retina located
back of eye
VISION what kind of layers of cells does retina contain
- receptor cells
2. processing cells
VISION where is choroid layer located
behind retina
VISION what is choroid layer composed of
layer of pigment cells
VISION what do pigment cells contain
melanin
VISION what does melanin absorb
light not absorbed by receptor cells to prevent light scatter
VISION what would light scatter result in
blurred image
VISION what is accommodation
process by which curvature of lens increased
VISION when does accommodation occur
during near vision
VISION what holds lens in place behind iris
suspensory ligaments
VISION what are suspensory ligaments attached to
ciliary muscles
VISION what are ciliary muscles
sphincter like muscles
VISION what happens when ciliary muscle relaxes
- tension on suspensory ligaments increases
- lens flattens
- distance vision (unaccomodated)
VISION what happens when ciliary muscle contracts
- tension on suspensory ligaments decreases
- lens roundens
- near vision (accomodated)
VISION what is refraction
deflection of light from straight path when passing from one medium to another
VISION what is focal distance
distance from refractive surface to point where parallel light rays converge
VISION what is refractive surface
cornea
VISION what is refractive power
reciprocal of focal distance
VISION what is unit for refractive power
diopter
VISION what is refractive power of cornea
42 dioptewrs
VISION what does refractive power of cornea mean
parallel light striking surface of cornea will be focused 2.4 cm behind it
VISION what is 2.4 cm behind cornea
retina
REFRACTIVE ERRORS what is myopia
nearsightedness
REFRACTIVE ERRORS what causes myopia
eyeball too long
REFRACTIVE ERRORS what is hyperopia
farsightedness
REFRACTIVE ERRORS what is cause of hyperopia
eyeball too short
REFRACTIVE ERRORS in myopia where is image focused
in front of retina
REFRACTIVE ERRORS in hyperopia where is image focused
behind retina
REFRACTIVE ERRORS how is myopia corrected
- concave / neg lens
- moves focal point back
REFRACTIVE ERRORS how is hyperopia corrected
- convex / pos lens
- moves focal point forward
REFRACTIVE ERRORS what is presbyopia
lens stiffening
REFRACTIVE ERRORS what causes presbyopia
age
REFRACTIVE ERRORS what does presbyopia result in
decreased ability to focus for close up vision
REFRACTIVE ERRORS why is there decreased ability to focus
- lens loses flexibility
- lens loses ability to accomodate
REFRACTIVE ERRORS what is astigmatism
when cornea or lens is more curved in one plane than another
REFRACTIVE ERRORS what are cornea and lens both involved in
focusing light to retina
REFRACTIVE ERRORS what is result of astigmatism
eye unable to focus light rays to single point causing vision to be out of focus
REFRACTIVE ERRORS what is correction for astigmatism
cylindrical lens
REFRACTIVE ERRORS how is cylindrical lens diff from spherical lens
focus light into a line instead of a point
REFRACTIVE ERRORS what does uneven curvature result in
- difference in refraction
2. point of light seen as line or oval
REFRACTIVE ERRORS what is emmetropia
normal vision
what is fovea
area of greatest visual acuity
what is fovea lacking
blood vessels
RETINA why does retina appear to be built upside down
- first layer of cells light strikes is ganglion cells
- second layer light strikes is receptor cells
RETINA what are ganglion cells a part of
final common pathway
RETINA how are axons of ganglion cells diff from other cells in retina
able to conduct AP
RETINA what happens despite retinal being transparent
- some light absorbed
- some light reflected away
RETINA what is pathway of light once it reaches retina
- ganglion cells (processing)
- bipolar cells (processing)
- receptor cells
- rods
- cones - choroid layer
RETINA what does outer segment of photoreceptors contain
discs
RETINA what do discs contain
visual pigment rhodopsin
RETINA what happens to discs
- shed
- phagocytized by retinal pigment epithelium
- replaced (from bottom to top)
RETINA what are 2 types of receptor cells
- rods
2. cones
RETINA which of receptor cells is more numerous
rods
RETINA what is vision w rods
shades of grey
RETINA what is sensitivity of rods
- high ==> require lower light
- night vision
RETINA what kind of acuity pathways do rods have
low acuity (not a lot of sharp detail)
RETINA what happens to pathways that serve rods
- converge
- multiple rods feeding into fewer bipolar cells
RETINA what is vision w cones
colour
RETINA what is sensitivity of cones
- low ==> require brighter light
- day vision
RETINA what kind of acuity pathways (cones)
high acuity (a lot of sharp detail)
RETINA what happens to pathways that serve cones
- little convergence
RETINA what does little convergence result in
no loss of acuity
RETINA where are cones concentrated
in fovea
DARK in the dark what do receptor cells have a high conc of
cyclic GMP
DARK what does high conc of cGMP allow
- Na channels open
- Na flow into cell
- mem depol
DARK what does mem depol result in
- Ca channels open
- Cell increases release of inhibitory glutamate
- inhibitory glutamate inhibits bipolar cells
DARK what does inhibition of bipolar cells result in
- no AP conducted to ganglion cells
- no AP conducted to optic nerve
- no AP conducted to lateral geniculate nucleus of thalamus
STEPS IN PHOTO RECEPTION what are steps in photo reception
- light strikes 11-cis retinal
- 11-cis retinal converted to all trans retinal
- conformational changes in opsin leads to production of metarhodopsin 2
- metarhodopsin 2 activates transducin G protein
- transducin activates phosphodiesterase
- phosphodiesterase catalyzes conversion of c GMP to 5’-GMP
(cGMP levels decrease) - Na channels close
- hyper polarization decreases release of inhibitory glutamate
what are 2 types of glutamate receptors on bipolar cells
- ionotropic (depolarization)
2. metabotropic (hyper polarizing)
what does decreased release of glutamate result in for ionotropic receptors
- no depol
- hyper polarization
- inhibit bipolar cells
what does decreased release of glutamate result in metabotropic receptors
- no hyper polarization
- depolarization
- excite bipolar cells
LIGHT in light what do receptor cells have low concentration of
cyclic GMP
LIGHT what does low concentration fo cGMP allow
- Na channels close
- no Na flow into cell
- mem hyper polarization
LIGHT what does hyper polarization result in
- Ca channels close
- decrease release of inhibitory glutamate
- bipolar cells not inhibited
LIGHT what does lack of inhibition of bipolar cells result in
- AP in ganglion cell
- AP in optic nerve
- AP in lateral geniculate nucleus of thalamus
what surrounds receptor cells
retinal pigment of epithelium
what is the function of RPE
- absorb light that does not get absorbed by photoreceptors
- transport nutrients and ions to photoreceptors
- required for regeneration of 11-cis retinal
- required for shedding of photoreceptor disks
how is trans retinal converted back to 11 cis retinal
- trans retinal reduced to trans retinol
- trans retinol exits rod and goes to RPE
- trans retinol converted to 11 cis retinol
- 11 cis retinol converted to 11 cis retinal
- 11 cis retinal returns to rod
- 11 cis retinal combines w opsin to form rhodopsin pigment
RECEPTIVE FIELD what is receptive field
area on retina which when stimulated enhances / inhibits activity of bipolar or ganglion cells
RECEPTIVE FIELD how are receptor fields set up
- RF s have areas that excite ganglion cell when stimulated
- RF s have areas that inhibit ganglion cell when stimulated
what is pathway of axons from ganglion closest to nose
- ganglion cell to optic nerve
- optic nerve to optic chiasm
- cross over to opposite side
what is pathway of axons from ganglion closest to temporal lobe
- ganglion cell to optic nerve
- optic nerve to optic chiasm
- do not cross over to opposite side
where does info about L visual field go
R side of brain
where does info about R visual field go
L side of brain