vision Flashcards
chemoreceptors
- oxygen, pH, various organic molecules such as glucose
mechanoreceptors
- pressure (baroreceptors), cell stretch (osmoreceptors), vibrations,, acceleration, sound
photoreceptors
- photons of light
- rods and cones
thermoreceptors
varying degrees of heat
transduction
- stimulus energy converted into information processed by nervous system
– Ion channels or second messengers initiate membrane potential change
adequate stimulus
- form of energy to which a receptor is most responsive
threshold
- minimum stimulus
receptor potential (graded potential)
- change in sensory receptor membrane potential
receptive field
- the physical area where a stimuli activates a neuron
– Primary sensory neuron and secondary sensory neuron - Receptive fields frequently overlap
neighboring fields experience what
convergence
size determines sensitivity
– Two-point discrimination test: gives you a perception of how far something is
- test peripherals too
– Sensitive areas have smaller receptive fields: think color
– Less sensitive areas have larger receptive fields
- large receptive fields = black and white
cones and rods
- cones = pick up color
- rods = black and white
vision
– Light reflected from objects in the environment are translated into a mental image
- based on graded potential
3 steps to vision
- Light enters the eye, and the lens focuses the light on the retina
- Photoreceptors of the retina transduce light energy into an electrical signal
- Neural pathways from retina to brain process electrical signals into visual images
anatomy of the eye
- Lens focuses light
– Suspended by ligaments called zonules - Two chambers in the eye
– Anterior chamber
▪ In front of the lens filled with aqueous humor covered by cornea
– Vitreous chamber
▪ Behind the lens, filled with vitreous body (humor) - Sclera
– Outer wall of eye consisting of connective tissue
light is modified
– Pupil modulates quantity of light and depth of field
– Focused on retina by changes in the lens
light is directed to the retina
– Photoreceptors transduce light energy into electrical signal
neural pathways process electrical signals into visual images
– Optic disk (blind spot) is location where neurons join into the optic nerve
– Optic nerves cross over in the optic chiasm
– Neurons synapse in lateral geniculate body in thalamus
– Optic tracts end at the visual cortex in the occipital lobe
what kind of reflex is pupillary reflex?
- consensual reflex
eye and vision
- light enters the pupil
- dilation = gets more light
- constrict = less light
lateral and medial
- L= same side
- M= opposite
- left lateral vision = left side of the brain
- right medial vision = left side of brain
optics describe what?
- light behavior and properties
focal point
- point where light rays converge
focal length
- distance from the center of lens to the focal point
light entering the eye
- refracted or bent at the cornea and lens
– Lens is modified to have focal point land on retina by ciliary muscles
accommodation
- process of the eye adjusting lens shape to keep objects in focus
– Near point of accommodation is the closest distance at which the lens can focus an object
myopia
- focal point falls in front of the retina
hyperopia
- focal point falls behind the retina
presbyopia
- loss of accommodation
astigmatism
- distorted images usually caused by a misshapen cornea
phototransduction
- converts light energy into electrical signals
what do pigment epithelium absorb?
- light that escape the photoreceptors
where do most acute vision occur?
- at the fovea and macula (visual field)
photoreceptor cells
- pass sensory information to bipolar cells which pass information to ganglion cells
– Ganglion cells form the optic nerve which leaves the eye at the optic disk (blind spot)
optic disk
- no photoreceptors
- called blind spot
is vision graded potential?
- yes
- strength –> lots of light coming at it –> lots of stimulus
do cones and rods share basic structure?
- yes
- outer, inner, and basal segments
what do rods and cones contain?
– Rods contain rhodopsin
– Cones contain three pigments primary excited by red, green, and blue light.
▪ Color-blindness defect in one or more cones
rhodopsin
– Opsin – protein (GPCR) embedded in rod membrane disks
– Retinal – vitamin A derivative
▪ Light-sensitive pigment, undergoes conformation change
– With light, opsin no longer binds to retinal –> blecahing
cyclic-nucleotide gated (CNG) channels
– Open when cGMP is present
– Rod is depolarized –> release of glutamate onto bipolar cell
transducin – G protein
– Light stimulates to start cascade that reduces availability of cGMP
▪ CNG channel closes, rod no longer depolarized –> no glutamate
what do photoreceptor cells converge in?
- bipolar neurons
what do multiple bipolar neurons converge onto?
- one ganglion cell
horizontal cells
- synapse with photoreceptors and bipolar cells
amacrine cells
- modulate information between bipolar and ganglion cells
ganglion cells have visual receptive fields
– Round center
– Doughnut-shaped surround
– Use contrast to interpret visual information
– M cells vs. P cells
binocular zone
– The central portion of the visual field where the visual field of each eye overlap
– Processed to give 3D vision
monocular zone
– Visual field of only one eye
projected and processed info is highly organized
– Topographical organization
