MNSR 32 - Structure of Eye and Photoreceptors Flashcards
what type of organ is the eye
sensory
function of eye
converts light energy into electrical signals using photoreceptor cells
name the 6 extraocular muscle that holds the eye in place
4 recti - superior, lateral, medial, inferior
2 oblique - inferior, superior
how is the eye connected to the brain
connected to brain by optic II cranial nerve
goes from back of the eye - innervates muscle to move and focus the eye
name the 2 fibrous layers of the eye
sclera
cornea
sclera
avascular
white and opaque outer layer
gives shape and structure, strength and protection
cornea
in sclera layer at the front of the eye
transparent region
allows light in the eye
provides 2/3 of human eyes focusing power
are the chances of the body rejecting a cornea in a cornea transplant high? why or why not?
the chances of it getting rejected are low - no blood vessels
second layer of the eye
uvea - vascularised
features of uvea
rich in blood vessels to provide oxygen and nutrients
features and function of choroid
contains blood vessel - to provide oxygen and nutrients
rich in melanin
light rays won’t get detracted in the eyes
function of ciliary body
ring shaped muscle surrounding the pupil
alter the shape of lens
3rd layer of eye
sensory tunic
2 layers in sensory tunic
epithelial layer - outer pigmented layer
neural layer - inner light sensitive, contains photoreceptors
where is aqueous humour found
between cornea and the lens
where is vitreous humour
- found in between lens and retina
macula
back of the eye in the retina
large conc of photoreceptor cells - gives high res. colour vision
damage to macula can lead to ..
macular degeneration
how is blindspot created?
optic disk in retina that is the entry point for blood vessels and nerves w/o photoreceptor cells
histology of the retina
outer pigmented epithelial layer is thin and contains a lot of melanin
inner neural layer contains 3 neurons - photoreceptors, bipolar cells and ganglion cells
2 photoreceptor cells
rods - slender and numerous
cone - less numerous and broader body
where are cones found in the retina?
in the centre
location of rods in retina?
periphery
why do we fail to see colour in dim light?
cones - for colour, have low sensitivity in dim light
2 lateral interneurons and their function
horizontal - help w/ passing of light photoreceptor to bipolar
amacrine - - pass light from bipolar cells to ganglion cells
histology of retina
go back to it in slide 12
max scotopic vision rods
maximal at 507 nm - greys and silver
max. photopic vision- cones
555
are eyes fully or slowly adapted
slowly take 30-60 minutes to be fully adapted
what is rhodopsin and what is its function?
protein opsin + cofactor 11 cis retinal
photon - 11 cis retinal -> 11 trans retinol -
change in conformation of membrane as cofactor leaves
activates opsin sends stimulus to nerve
what makes rhodopsin sensitive to light
11 cis retinal derived from 11-trans-retinol, vitamin A
deficiency of vitamin A can lead to…
A deficiency of vitamin A leads to night blindness and eventual deterioration of the outer segments of the rods
visual cycle
go back to it slide 17
what does colour vision require for good visual detail?
require good illumination for good visual detail - photopic vision
fovea
small depression in retina contains only cones
ratio of rods to cones of each 900,000 optic fibres
follows that on average 140 rods and 6 cones converge on each optic fibre
wavelength to pick up blue red and green cones
blue - 400 - 530 nm
green cone - 440 - 610
red cone - 580 - 690 nm
who introduced the colour vision theory and later expanded the theory
Thomas Young
Expanded later by the German physiologist von Helmholtz
Young - Helmholtz or Trichromatic theory
The theory proposed that there are three different types of cone in the retina sensitive to blue, green and red light respectively
cones to perceive the colour orange and yellow
red and green cones
cones to perceive the colour white
all red, green and blue cones
what muscles in the eye control horizontal movements|?
Horizontal movements are controlled entirely by the medial and lateral rectus muscles
what muscles control vertical movement?
the superior
inferior rectus muscles,
2 oblique muscles.
unconscious eye movement relates to what reflex
vestibule ocular reflex - relates to ear vestibular nerve
how do muscles move in response to bright light?
pupillary sphincter contracts and reduces pupil size
how do muscles move in response to dim light?
pupillary dilator contracts, increases pupil size
what tool is used to test a a persons ability to distinguish colour and therefore detect colour blindness
Ishihara colour cards
