The Eye Flashcards
Label the eye
See notes
Should include
-cornea
-iris
-lens
-pupil
-sclera
-choroid
-retina
-blind spot
-optic nerve
-suspensory ligaments
-ciliary body/ muscle
-conjunctiva
In which layer does most refraction of light occur?
The cornea
Which structure is responsible for refracting light rays so that they are focused on the retina?
The lens
What is accommodation?
The reflex action during which the lens thickness is adjusted so that light rays are always focussed on the retina
How does the eye focus on a distant object?
-The light rays are parallel so do not need much refraction
-So, the ciliary muscles relax while the suspensory ligaments become taut (tension from wall of eyeball is transferred through suspensory ligaments to the lens)
-Lens is pulled thinner giving it less refractive power
How does the eye focus on a near object?
-The light rays are diverging so need more refraction
-So, the ciliary muscle contracts while the suspensory ligaments slacken
-Allowing the lens to spring back to its normal thicker/ fatter shape which has greater refractive power
Where are the photoreceptor (photosensitive) cells found and what are their names?
The photosensitive cells are called rods and cones and they are found the retina, the cones being more concentrated in the central fovea and the rods more concentrated towards the peripheries
Why is it important that the right intensity of light enters the eye and reaches the retina?
Too little light will mean the photoreceptor cells are not stimulated enough to form an image and too much light may damage the photoreceptor cells, again preventing an image from being formed
Describe the pupil reflex in bright light
-The circular muscles of the eye contract (circular relax)
-Pupil dilates (becomes wider)
-More light rays enter the eye
Describe rod cells
-They contain the light sensitive pigment, rhodopsin
-The pigment molecules are packed into the large surface area provided by the membrane disks in the outer segment
-There are many mitochondria present in the inner segment, which provide ATP for the regeneration of the pigment
-Rod shaped
Describe cone cells
-They contain the light sensitive pigment, iodopsin
-The pigment molecules are packed into the large surface area provided by the membrane disks in the outer segment
-There are many mitochondria present in the inner segment, which provide ATP for the regeneration of the pigment
-Cone shaped
How is sensitivity (ability to see in dim light) achieved in the rod cells
-Each rod cells synapses with several bipolar cells-RETINAL CONVERGENCE (decreases visual acuity)
-So that when dim light hits several rods, the generator potentials (depolarisation) from the rods SUMMATE to reach the threshold for setting up a generator in the bipolar neurone
-Also, the pigment,rhodospin, breaks down easily to retinal and opsin (it bleaches) when exposed to low levels of light and is easily regenerated
How is high visual ACUITY, the ability to see highly precise colour vision of high resolution, achieved during the day?
-Each cone cell synapses with one bipolar cell in a 1:1 relationship
-Each cone cell, when stimulated, provides its own discrete image in vision, resulting in high resolution
-Also, the pigment, iodopsin breaks down less readily and will only produce a generator potential in bright light
-This vision will be in
