Topic 5 - The Eye Flashcards
What is the conjunctiva
Thin membrane lining the inside of the eyelids and covering the sclera
What is the function of the conjunctiva
Lubricates and protects tissues at the front of the eye, prevents foreign bodies entering the eye
What is the function of the sclera
Protects the eyeball against mechanical damage
What is the sclera
Tough outer layer that encloses the eye, except the front
What is the cornea
Transparent front part of the eye continuous with the sclera
What is the function of the cornea
Allows the passage of light while refracting it
What is the iris
The coloured part of the eye - it contains circular and radial muscles
What is the function of the iris
Controls the size of the pupil to adjust the amount of light entering the eye
What is the pupil
A gap within the iris - appears black
What is the function of the pupil
Allows light to enter the eye
What is the aqueous humour
Transparent watery fluid filling the front part of the eye
What is the function of the aqueous humour
Maintains the shape of the front chamber of the eye
What is the lens
Transparent and elastic Ovoid structure held in place behind the cornea
What is the function of the lens
Changes shape to adjust focusing of light onto the retina
What is the ciliary body
Structure which supports the lens and contains circular muscle
What is the function of the ciliary body
Contraction or relaxation of the circular muscle control the shape of the lens
What are suspensory ligaments
Strong ligaments which connect the ciliary body to the lens
What is the function of suspensory ligaments
Transfers tension in the all of the eyeball to the lens to make it thinner
What is the vitreous humour
Transparent, jelly-like material filling the rear part of the eyeball
What is the function of the vitreous humour
Maintains the shape of the rear part of the eyeball and supports the lens
What is the retina
Inner layer of the wall of the eyeball contains light-sensitive cells
What is the function of the retina
The light-sensitive cells initiate impulses in associated neurones when appropriately stimulated
What is the fovea
The region at the back of the retina that is rich in cones
What is the function of the fovea
A region with high visual activity that allows colour vision
What is the choroid
A layer of pigmented cells at the back of the eyeball behind the retina
What is the function of the choroid
Contains blood vessels which supply the retina; prevents reflection of light within the eyeball
What is the optic nerve
A bundle of sensory nerve fibres which leave from the back of the eye
What is the function of the optic nerve
Transmits impulse from the retina to the optic centre at the back of the brain
What is the blind spot
Region where optic nerve leaves inside of eyeball and so contains no light-sensitive cells
What is the function of the blind spot
A region, which if light strikes it, is not sensitive to light
What happens to the eye in bright light
Circular muscles contract and the radial muscles relax, making the iris widen and therefore making the pupil get narrower. The pupil is small to limit the amount of light passing through
What happens to the eye in dim light
Circular muscles relax and radial muscles contract, widening the pupil to allow more light to reach the retina and provide maximal stimulation of the light-sensitive cells
Where is light refraction adjusted to a single point on the retina
The lens
What is accommodation
The ability to adjust focusing
How is light accommodated to the retina from a far object
The ciliary muscles are relaxed, meaning pressure is transferred via the suspensory ligaments to the lens, pulling it into a thin shape
How is light accommodated to the retina from a near object
The circular muscles contract, closing the aperture around the lens and releases any tension from the eyeball, meaning the lens adopts a fatter shape
What are the two receptors to light in the retina
Rods and cone cells
Where are rods and cones found
Cones are concentrated in the fovea at the centre of the retina
Rods are mainly found around the periphery of the retina
What do rod cells synapse with
Each bipolar neurone and many bipolar cells connect with each neurone of the optic nerve
What do cone cells synapse with
A single bipolar neurone and a single neurone of the optic nerve
What is the difference in light sensitivity between rods and cones
Rods are sensitive to dim light
Cones are sensitive to bright light
What is rhodopsin
The pigment found in rods which is composed of opsin and retinal
What happens when light strikes rhodopsin
Changes occur and rhodopsin breaks down into retinal and opsin
How is a generator potential created
When the membrane potential of a rod cell is changed
What does a generator potential cause
A change in the membrane potential of the neighbouring bipolar neurone, with which the rod cell synapses. The bipolar cell releases transmitter substance into its synapse with a neurone of the optic nerve
Why are rod cells sensitive
Because rhodopsin absorbs light readily and is more easily broken down and because retinal convergence enables the input of many rods to be added together
Why does summation occur
Because generator potentials have an additive effect in stimulating bipolar neurone while transmitter substance from bipolar neurones is added to reach the threshold needed to initiate an action potential in the neurone of the optic nerve
What is a consequence of retinal convergence
The brain cannot distinguish which rod of a group sharing the same optic nerve fibe has been stimulated
What is dark adaptation
When almost all of the rhodopsin is entirely bleached by bright light
What is iodopsin
The pigment found in cone cells
Which is broken down more readily, Rhodopsin or Iodopsin
Rhodopsin
What is high visual acuity
When the brain is able to distinguish between points that are close together
Why do cones not exhibit convergence
As one cone associates with one neurone of the optic nerve
What gives high visual acuity in the eye
Each cone cell stimulated will generate an impulse to the brain
What are the three forms of iodopsin, and what is this theory called
Red, Blue and Green
This forms the basis of the trichromatic theory of colour vision
How is pure red light broken down
It is broken down by red iodopsin and only the red cones will fire impulse to the brain, which is interpreted as red
How is yellow light broken down
Some of the red iodopsin and some of the green iodopsin and so both red and green cones fire impules to the brain, which is interpreted as yellow
What is colour perception dependant on
The relative proportions of the different types of cone that are firing impules
Why do prey have their eyes positioned one opposite sides of their head
To give them a wide field to view, to facilitate the detection of potential predators
Why do predators have eyes positioned on the front of their head
To use both eyes to view an object, to allow more accurate judgement of distance
What is stereoscopic vision
The brain being able to create a 3D image
