Chapter 9: The Eye Flashcards
Fovea
densely packed cones
cones have three types of opsin (red, green blue) –> color vision
one cone –> one bipolar –> one ganglion cell
area of highest acuity
Peripheral retina
more rods than cones
rods: more photopigment=rhodopsin, more sensitive to light
convergence of rods to ganglion cells
greater sensitivity but lower acuity
Light transduction: G protein coupled neurotransmitter receptor
Stimulus: transmitter
Receptor activation: change in protein conformation
G protein response: Binds to GTP
Second messenger change: INCREASE second messenger
Ion channel response: increase or decrease conductance
Light transduction: photopigment
Stimulus: Light
Receptor activation: change in protein conformation
G protein response: binds GTP
Second messenger change: DECREASE second messenger
Ion channel response: DECREASE Na+ conductance
Transduction of light by rods
- Light activates (bleaches) rhodopsin
- Transducin, the G-Protein, is stimulated
- Phosphodiesterase (PDE), the effector enzyme, is activated
- PDE Activity reduces the cGMP level
- Na+ channels close, cell membraine hyperpolarizes
look at page 306: laminar organization of the retina
Ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, outer nuclear layer, layer of photoreceptor outer segments, pigmented epithelium
Path of light
Photoreceptors, bipolar cells, ganglion cells
Generic receptive field
the part of the sensory surface that, when stimulated, causes a neuronal response
Visual receptive field
the area of the retina that, when stimulated, causes a neuronal response in visual pathway
OFF bipolar cells
hyperpolarized when light is shined onto a cone
OFF bipolar cells
hyperpolarized when light is shined onto a cone
have ionotropic glutamate receptors: hyperpolarization means one less neurotransmitter released means more hyperpolarization
ON bipolar cells
depolarized when light is shined onto cone
g-protein-coupled (metabotropic) receptors
Receptive field surround
surrounding area of retina, input via horizontal ceclls
Receptive field surround
surrounding area of retina, input via horizontal cells
on center ganglion cell pathway
center of cone glutamate (transmitter) mGluR6 (receptor) On center bipolar cell depolarized Glutamate AMPA, kainate, NMDA on center ganglion cell
off center ganglion cell pathway
cone
AMPA kainate (receptor)
off center bipolar cell hyperpolarized
off center ganglion cell
off center ganglion cell pathway
cone
AMPA kainate (receptor)
off center bipolar cell hyperpolarized
off center ganglion cell
Mtype ganglion cells
5%
movement
Ptype ganglion cells
90%
more detailed form
Every sensory system has:
- primary area in cortex
- relay nucleus in thalamus
- surface where transduction occurs
Frequency of light
number of waves per second
amplitude
difference between wave trough and peak
Visible light higher vs lower energy
higher energy is blues
lower is reds
reflection
bouncing of rays off of surface (page 296)
depends on angle at which light ray strikes surface
absorption
transfer of light energy to a particle or surface
refraction
forms images in eye
the bending of light rays that travel from one transparent medium to another
Pupil
opening of eye, allows light to enter and reach retina
iris
contains two muscles to make it larger and smaller when it contracts
cornea
glassy transparent external surface of eye, is continuous with sclera
sclera
the white of the eye
forms tough wall of eyebrow
has three extraocular muscles that move eyeball in orbit
eye’s orbit
eye socket in skull
conjunctiva
membrane that folds back from inside of eyelids and attaches to sclera
optic nerve
carries axons from retina, exits from back of eye, passes through orbit, and reaches base of brain near pituitary gland
optic disk
where optic nerve fibers exit retina
blind spot because there are no photoreceptors
blind spots
optic disk, where large blood vessels exit because they cast shadows on retina
macula
central vision, part of the retina, high quality of central vision because there are no blood vessels
fovea
dark spot; retina thinnest here; center of retina
aqueous humor
watery fluid that nourishes cornea; between cornea and lens
lens
transparent; located behind iris
ciliary muscle
forms ring inside eye, attachment site of ligaments
vitreous humor
more viscous jelly-like fluid, in between lens and retina, keeps eyeball spherical
focal distance
distance from refractive surface to the point where parallel light rays converge
depends on curvature of cornea
tighter curve=shorter focal distance
accommodation
refractive power bringing rays into focus on retina by changing shape of lens
ciliary muscle contracts and swells in size (inside ring smaller and decreasing tension, lens becomes rounder and thicker, increases curvature of lens, increasing refractive power)
strabismus
eye disorder: imbalance in extraocular muscles of two eyes, eyes point in opp directions
cataract
eye disorder: clouding over of lens
glaucoma
progressive loss of vission assocsiated with intra ocuar pressure, pressure in aqueous humor
glaucoma
progressive loss of vision associated with intra ocular pressure, pressure in aqueous humor
retinitis pigmentosa
progressive degeneration of photoreceptors, loss of peripheral and night vision, tunnel vision
macular degeneration
losing central vision
visual acuity
the ability of the eye to distinguish between two points near each other
visual angle
measurement by distance across retina in terms of degrees
most direct pathway for visual information
photoreceptors to bipolar cells to ganglion cells
laminar organization
cells are organized in layers
ganglion cell layer
innermost retinal layer; cell bodies of ganglion cells
inner nuclear layer
contains cell bodies of bipolar cells, horizontal cells, amacrine cells
outer nuclear layer
cell bodies of photoreceptors
inner plexiform layer
contains synaptic contacts between
bipolar
amacrine
ganglion cells
outer plexiform layer
photoreceptors make synaptic contact with bipolar and horizontal cells
layer of photoreceptor outer segments
light sensitive elements of retina; embedded in pigmented epithelium
photopigments
light sensitive disk membranes absorb light in the outer segment
rod photoreceptors
long, cylindrical outer segment with many disks
way more rods than cones
cone photoreceptors
shorter, tapering outer segment with fewer membranous disks
color
duplex retina
how rods and cones are two complementary systems in one eye
scotopic conditions
nighttime lighting
rods
photopic conditions
daytime lighting
cones
therefore much greater spacial sensitivity on central retina
mesopic conditions
intermediate light levels (indoor lighting, outdoor traffic lighting at night)
both rods and cones
rods or cones in the fovea?
most cones in fovea; no rods in fovea
photoreceptors
convert/transduce light energy
hyperpolarize in response to light
light reduces cGMP, Na+ channels close, more negative, hyperpolarization
rhodopsin
photopigment in rods; bleaching, which stimulates G protein transucin, etc
rods more sensitive to light because cascade for transduction–>amplification
young-helmholtz trichromacy theory
theory of color vision
red green and blue light make white, all colors seen through these three
