the eye Flashcards
func of the eyelid
protection against mechanical damage
squinting prevents excessive entry of light
blinking spreads tears and removes irritants
func of tear glands
secrete tears to remove irritants
lubricate conjunctiva and moisturise the eye
func of eyelash
shields the eye from irritants
func of the iris
pigmented layer of muscular tissue
consists of radial and circular muscles which control the diameter of the pupil and light which enters the eye
func of pupil
hole in the centre of the iris which allows light to enter the eye
func of conjunctiva
mucus membrane covering sclera
func of cornea
refracts light rays (has the most refractive power)
func of sclera
protects against mechanical injury, allows attachment of eye muscles to enable movement, maintains shape of eyeball
func of choroid
black pigmented layer which prevents internal refraction of light
rich in blood vessels to transport o2, nutrients, waste products
func of retina
innermost light-sensitive layer on which images are formed
contains photoreceptors, connected by nerve fibers from optic nerve
func of fovea
pit in retina where images are focused
contains cones but no rods
permits detailed coloured vision
func of blind spot
point in retina where optic nerve exits eye
no photoreceptors, insensitive to light
func of optic nerve
transmit nerve impulses from photoreceptors to brain
func of vitreous humour
transparent jelly like substance
maintains shape of the eye
refracts light onto retina
func of lens
shape/thickness can be changed to refract/focus light onto the retina
func of ciliary body
contains ciliary muscles that control the curvature and thickness of lens
func of suspensory ligament
attaches lens to ciliary body
func of aqueous humour
clear watery fluid that supplies nutrients to cornea and lens
maintains convex shape of cornea
refracts light into pupil
rods vs cones
provide b&w vision vs coloured vision
dim light vs bright light
found in places other than fovea vs conc at fovea
peripheral vision vs fine details (respond quickly and able to perceive rapidly changing images)
light sensors vs colour sensors
func rhodopsin in rods
allows sensitivity to light
bleached under bright light, regenerated in absence of light
pupil reflex (bright)
circ musc contract
radial musc relax
pupil diameter decr
amount of light entering decr
pupil reflex (dim)
circ musc relax
radial musc contract
pupil diameter incr
amount of light entering incr
reflex arc (pupil reflex)
- incr/decr in light intensity was detected by photoreceptors in the eyes
- nerve impulses generated, carried by sensory neurone in optic nerve, passed over a synapse to a relay neurone in the brain
- relay neurone would pass the impulse to an outgoing motor neurone across another synapse
- the motor neurone would bring the impulse to the motor end plates in the circular and radial muscles in the iris, causing them to contract/relax respectively
- the pupil constricts/dilates, incr/decr amount of light entering to fall on the fovea of the retina
focusing/accommodation: distant
ciliary muscles: relax
suspensory ligaments: taut
lens: thinner, less convex
focal length: incr
focusing/accommodation: near
ciliary muscles: contract
suspensory ligaments: slacken
lens: thicker, more convex
focal length: decr
properties of images focused on the retina
vert inverted, laterally inverted, diminished
reflex arc (focusing)
- inverted image is formed on the retina
- photoreceptors are stimed
- nerve impulses generated are transmitted through the optic nerve to the optic centre of the brain
- brain interprets the info and forms an upright image
