BMS11004 WEEK 8 - TUESDAY Flashcards
retina, phototransduction, image formations
what is importance of vision
detect prey, predator, mates
communication
name 3 words which describe light
visible electromagnetic radiation
what is wavelength
distance between peaks/troughs
what is frequency
number of waves per second
what is amplitude
difference between wave peak and trough
how does electromagnetic light travel
straight lines/rays until interact with atoms/molecules
what 3 ways can light rays interact
reflection, absorption, refraction
describe reflection
hits wall, and bounces off
describe absorption of light ray
hits wall, it is absorbed by wall
photoreceptors and pigmented epithelium of retina
describe refraction of light ray
hit wall, is bend and leaves at diff angles
bends due to difference in speed of light through different media
explain monocular vision
one eye either side of head, large visual field = prey
explain binocular vision
eyes facing out front of head, allow measurements of depth perception = predator
what does the pupil do
let light inside eyes
what does iris do
contain muscles that controls amount of light entering eye
what does cornea do
glassy, transparent covering of pupil and iris that refracts light
what does sclera do
continuous with cornea, forms tough protective wall of eyeball to give it its shape
what does extraocular muscles do
move eyeball, controlled by oculomotor nerve (cranial nerve III)
what does optic nerve do
carries axon from retina to brain (cranial nerve II)
what does retina do
contain sensory receptor cells and afferent neurons
what does lens do
suspended by zonal fibres (suspensory ligaments) which are attached to ciliary muscle, enabling lens stretch
what is opthalmoscopes
shine light into eye and look at back of eye
what is optic disk/blind spot
origin of blood vessels and optic nerve, cannot sense light
what is macula
close to midline of nasal retina and temporal retina, for central vision
devoid of large blood vessels to improve vision quality
what is fovea
retina is thinnest here, area of highest visual acuity
when not using fovea, side area of visual field = peripheral vision
where should light rays be focused
onto retina, ideally onto fovea
where do refraction occur
at cornea = 80%
lens 20%
what determines degree of refraction
difference in refractive indice between 2 media, and angle at whicb light hits interface between 2 medias
outline refractive index
measure of speed of light within it
light moves quicker through air than cornea due to increased density of cornea
what cause refraction by cornea
light arrive at cornea via air, but cornea is mainly water and light travel slower water>air due to higher density, so cause refraction
outline focal distance
distance from refractive surface to convergence of parallel light rays
if light hits cornea directly perpendicular, what happens
move straight through onto retina
explain refraction of light of images for distant/close objects through the cornea
distant = almost parallel light ray so cornea provides sufficient refraction to focus them onto retina
closer = light ray not parallel, require additional refraction to focus them onto retina, provided by fattening of lens
what does rounding of lens allow for focusing objects
increases refractive power to focus closer objects onto fovea
explain when eye is emmetropic
when lens is flat and focusing on distant objects
what is farsightedness (hyperopia)
eye too short and near objects focused behind retina, not enough refraction
how can we fix farsighedness/hyperopia
convex glasses, make light coming from near object parallel
explain shortsightedness/myopia
eye too long so distant objects focused before retina, too much refraction
sees close up but not far away
how is myopia fixed
concave lense
what muscles contract to allow lens changing
contraction/relaxing ciliary muscles
how is light focused onto retina converted into neural or electrical activity
photons pass through ganglion or bipolar cells before reaching photoreceptors, absorbed by pigmented epithelium
name main retinal cell
ganglion cells
bipolar cells
photoreceptors
name other retinal cells
amacrine cells (modulate info transfer between ganglion cells, bipolar
horizontal cells (modulate info transfer between photoreceptors, bipolar)
describe what ganglion cell do
output from retina
explain what bipolar cells do
connect photoreceptors to ganglion cells
explain what photoreceptors do
sensory transducers (rods and cones)
outline the duplicity theory of photoreceptors
can’t have high sensitivity and resolution in single receptor so needs separate system for monochrome and colour = rod, cone
outline structure of rod photoreceptors
greater number of disk
higher photopigment conc
1000x more sensitive to light than cones
what type of vision does rod enable
enable scotopic (low light) vision = night time
low visual acuity/resolution
explain structure of cone photoreceptors, what type of vision they allow
fewer disks, used during daylight (photopic), enabling colour vision
high visual acuity/res, low sensitivity
when are rods and cones used together
in intermediate (mesopic) light
does fovea contain more cones/rods, and what does this allow?
most of cones, no rods, allow low convergence on retinal ganglion cells so better for higher res vision
what is convergence, sensitivity and resolution like on central retina
low convergence
low sensitivity
high resolution
what is convergence, sensitivity, resolution like on peripheral retina
high convergence
high sensitivity
low resolution
