human eye Flashcards
the eyeball is attached to the eye socket by…
enabling the eyeball to…
- six rectus muscles
- rotate slightly within the socket
State the function of the conjunctiva
thin transparent membrane that protects cornea at the front of eyeball against friction by secreting mucus to keep the eyeball moist
State the structure and function of cornea
- structure: anterior end and transparent portion of sclera forming a small bulge at front of eye
- function: transparent portion of sclera allows light to pass through to reach retina. (most of the) refraction of light into pupil.
State the 3 parts of the wall of the eye and state their functions
- sclera: protects eyeball against mechanical injury
- choroid: contains blood vessels supplying retina with oxygen and nutrients. also pigmented black to prevent internal reflection of light
- retina: contains photoreceptors that detect stimuli
if choroid is other colour, it suggests lack of this pigment to prevent internal reflection
State the function of the optic nerve
hint: how do you state the function of nerves?
transmits nerve impules from photoreceptors to the brain
State the function of iris
consists of circular and radial muscles that controls the size of pupil and hence the amount of light entering the eye.
State the function of pupil
hole in centre of iris that allows light to enter eye
State the function of lens
focuses light rays onto retina by changing shape
State the structure of lens and its significance
transparent, biconvex, and elastic, hence able to change thickness and shape to refract light onto retina
State the function of suspensory ligaments
Holds the lens in postition by attaching lens to ciliary body
State the function of ciliary body
- support the lens
- contains muscles controlling lens curvature
Distinguish the functions of vitreous and aqueous humour
- vitreous : supports the lens; refracts light rays and keep the eyeball firm
- aqueous : maintains the shape of anterior chamber of eyeball; refracts light rays and keep the eyeball firm
Describe the distribution of photoreceptor cells in fovea, blind spot, and other areas of the retina, and briefly describe its implications
- fovea : contains only cones which are densely packed; part of retina most sensitive to light and provides acute colour vision in bright light when images are focused on to it. images are normally focused here
- blind spot : at point of attachment of optic nerve to the eye. no photoreceptor cells. hence no vision when image falls on it.
- other areas of retina : density of rods is much higher than codes; provides vision in dim light
must know how to explain why there even is a blind spot
State the 4 differences between rods and cones
- rods are highly sensitive to low light level while cones are sensitive to high light level
- rods are dispersed in periphery of retina while cones are concentrated in the fovea
- images produced by rods are blurry while images produced by cones are sharp
- images produced by rods are in shades of gray while cones produce coloured images
State the 3 properties of the image formed on retina
- inverted
- reversed
- diminished
Describe pupil reflex for bright/dim light
- increase/decrease in light intensity stimulates photoreceptors in retina to generate nerve impulses transmitted along the sensory nerone in optic nerve to brain
- (if 5~6 marks question depends) in brain, impulses are transmitted across a synapse to relay neurone and across another synapse to motor neurone by the release of neurotransmitters
- nerve impulses are transmitted alng motor neurone to the iris.
- circular muscles of the iris contract/relax
- radial muscles of the iris relax/contract
- to constrict/dilate pupil
- reduce amount of light / allow as much light as possible to enter the eye
- prevents damage to rods and cones of retina / enable us to see more clearly
Describe the process of accomodation for near and distant objects [10m]
light rays reflected off a distant object are almost parallel when entering the eye
ciliary muscles of ciliary body relax, suspensory ligaments become taut
elastic lens becomes thinner, less convex, and less refractive
light rays reflected off nearby objects are divergent when entering the eye
ciliary muscles of ciliary body contract, suspensory ligaments slacken
elastic lens become thicker, more convex, and more refractive
after the lens become more or less refractive, light rays are focused on fovea. photoreceptors are stimulated to generate nerve impulses transmitted along sensory neurone in optic nerve to brain. brain interprets the nerve impulses and the person sees the object
Explain why UV protection is important
blocks UV to prevent cancer OR blocks excessive light to prevent damage to retina
Suggest 2 ways inflammation/damage to choroid of retina affects vision
- impaired nutrient supply to retina distorting vision
- may be internal reflection of light distorting vision
link back to functions of choroid !!
