sense organ Flashcards
human eye
names some receptors
- photoreceptors
- chemoreceptors
- thermoreceptors
- mechanoreceptors
- exteroceptors
- interceptors
function of the eyelids?
control the amount of light entering the eye
function of the eyelashes?
protection form entering dust particles
what is the conjuctiva?
- thin transparent membrane covering the exposed part of the eye
- lubricated by tears
what happens to extra tears?
- drains down into the nasolacrimal duct
where is the eyeball locates?
in a socket (orbit) present in the skull held by 6 extrinsic muscles
what are the layers that make up the walls of the eye?
-sclera
- choroid
- retina
what is the sclera?
- tough, fibrous, white layer
- forms a transparent bulge at the front of the eye called the cornea
- denser medium than air causing light rays to refract upon entering
what is the choroid?
-network of blood capillaries
- pigmented black (no internal reflection)
- froms ciliary body and iris
what is the ciliary body?
contains ciliary muscles which alters the thickness of the lens
what is the retina?
- photoreceptors
- images formed on the retina
- nerve ending to the optic nerve sending impulses to the brain
- two types of photoreceptors
what is the iris?
disc shaped structure with a round hole (pupil) in the center
what are the types of photoreceptors in the eye?
rods and cones
what is the function of the optic nerve?
sending impulses to the brain once photoreceptors are stimulated
amount of rods in the retina?
120 million
what are the rods used for?
night/scotopic vision
name of the pigment used for night vision?
vision purple
where is vision purple located?
in the rods
what happens to vision purple when it comes in contact with light?
it gets bleached
function of the cones?
responsible for light vision (color vision)
what are the types of cones?
red, blue and green
amount of cones in the retina?
5 million
what is the fovea?
point in the retina where visual activity is the highest
how many cones are present in the fovea?
2000
how does light enter the eye?
through the pupil
what is the role of the ciliary body?
focusing and accommodation
what is the function of the lens?
transmit light, focusing it on the retina
what are the chambers of the eyeball?
2 chambers
- small one known as aqueous humor filled with a watery liquid
- large one has a jelly like fluid called vitreous humor
keep the eyeball firm
describe the lens
transparent, biconvex and crystalline
which vitamin assists in the formation of vision purple?
vitamin A
what does the deficiency of vitamin A cause?
night blindness
which photoreceptor absorbs light of diff wavelenghts?
cones, which enables us to see diff colours and a complete spectrum
what is the yellow spot (fovea centralis)?
a shallow, yellow depression located in line with or on the optical axis of the lens
what is the blind spot?
over the optic nerve where it enters the eye/ no photoreceptors found here
what is the position of the ciliary body when seeing a distant object?
ciliary muscles relaxed
suspensory ligaments tightened
lens pulled thin
what is the position of the ciliary body when seeing a close object?
ciliary muscles tightened
suspensory ligaments slackened
lens allowed to bulge
