physiology of light Flashcards
what is the pupil
opening where light enters the eye
what is the sclera
white of the eye
what is the iris
gives colour to the eye
what is the cornea
glassy transparent external surface to the eye
what is the optic nerve
bundle of axons from the retina
when the eye collects light where does it focus to
the retina
what is a unique feature about how the eye perceives images
it is inverted
ERROS OF REFRACTION
what is emmetropic
normal eye
ERRORS OF REFRACTION
what is presbyopia
as you get older the lens harden and the cilia muscles weakens, causing a decreased ability in accomodation
what is hyperopia
far saightedness
what is myopia
near sightedness
in addition to the cornea and the lens, the pupil contributes to the optical functioning of the
eye
PUPILLARY LIGHT REFLEX
the pupils continuously adjust to what
different light levels
PUPILLARY LIGHT REFLEX
the pupils can be described as consensual
what does this mean
both pupils react similarly and simultaneously
PUPILLARY LIGHT REFLEX
circular (constrictor) muscles act to _____ pupil size
decrease
PUPILLARY LIGHT REFLEX
circular (constrictor) muscles act to decrease pupil size under what control
parasympathetic
PUPILLARY LIGHT REFLEX
radial (dilator) muscles act to _____ pupil size
increase
PUPILLAR LIGHT REFLEX
radial (dilator) muscles act to increase pupil size under what control
sympathetic
what is the visual field
amount of space viewed by the retia when the eye is fixated straight ahead
what is visual acuity
ability to distinguish two nearby points
what is visual acuity determined by
largely by photoreceptor spacing and refractive power
what cells are involved in the pathway for signal transmission and what order to they transmit in
photoreceptors -> bipolar cells -> ganglion cell s
what do horizontal cells receive input from
and what do they project to
photoreceptors
photoreceptors and bipolar cells
what do amacrine cells receive input from
and what do they project to
bipolar cells
project to ganglion cells, bipolar cells, and other amacrine cells
what cranial nerve is the optic nerve
CNII
what is transduction the converting of
converts electromagnetic radiation to neural signals
what are the two types of photoreceptors
cones and rods
what are the 4 main regions of a photoreceptor
outer segment
inner segment
cell body
synaptic terminal
light converts 11-cis retinal to what
all-trans retinal
what enzyme converts all trans retinal back to 11-cis retinal
isomerase
what is rhodopsin made of
opsin and 11 cis retinal
MOLECULAR PATHWAY OF LIGHT
What happens when all trans retinal activates transducin
decrease in cGMP
MOLECULAR PATHWAY OF LIGHT
what happens when there is decreased cGMP
closure of cGMP gated Na+ channels
MOLECULAR PATHWAY OF LIGHT
MOLECULAR PATHWAY OF LIGHT
what happens whem there is the closure of cGMP-gated Na+ channel
lowered entry of Na+ results i hyperpolarisation
the dark current opens in what light setting
in the dark
the dark current channels closes in response to what
light
the dark current channel is permeable to what ion
Na+
the dark current channels keeps the Vm of photoreceptors what charge
positive
what facilitates high acuity
distribution of rods and cones
what light setting are rods good for seeing in
dim light
what light setting are cones good for seeing in
normal daylight
in the ON/OFF pathways, when is glutamate inhibited
in the on pathway
what are the only cells in the eye that can produce action potentials
ganglion cells (some amacrine)
RETINAL PROCESSING
lateral inhibition is by what cell
horizontal cells
CENTER-SURROUND ORGANISATION IN THE RETINA
horizontal cells interconnect a group of ‘surround’ neurons. It samples the total amount of excitation in that surround and responds by releasing what
GABA
CENTRE-SURROUND ORGANISATION IN THE RETINA
If there is low surround, then there is ____ GABA released
less
what are the two types of ganglion cells
M-type
P-type
what are the differences between the M type and P type ganglion cells
M type: large receptive fields, transient activation
P type: smaller receptive fields, sustained activity, colour sensitive
what does LGN stand for
lateral geniculate nuceli
what are the two types of LGN
magnocellular LGN
parvocellular LGN
INPUTS TO THE STRIATE CORTEX
magnocellular LGN neurons project to what layer
Layer IVCalpha
INPUTS TO THE STRIATE CORTEX
Parvocellular LGN neurons project to what layer
IVCbeta
INPUTS TO THE STRIATE CORTEX
Koniocellular LGN axons project to what layer
what layer do they bypass
by pass layer IV to make synapses in layers II and III
in the striate cortex, most neurons in layer III are what
binocular
vision for perception
the ventral pathway projects to where in the brain
projects to occipitotemporal ass cortex
vision for action
the dorsal pathway project where in the brain
project to parietao occipital ass cortex
what is Hebb’s postulate
neurons know that they are around others of the same eye