Ch 50 B Flashcards
Who has the most simple light-detecting organs? What is it?
Planarians
Pair of ocelli called eyespots
What is negative phototaxis?
when animals move away from light
What are compound eyes composed of? What are its benefits?
Ommatidia
Effective at detecting movement
Have excellent color vision
What changes the diameter of the pupil?
iris
What controls how much light enters?
Pupil
How many lens do vertebrates have?
single lens
What is the choroid?
What is its function?
Thin, pigmented layer
Provides nutrients and blood
Where is the choroid located?
outside the retina
What is the Retina?
a layer of photoreceptors cells and glial cells within the eye
What is the lens?
a transparent disk of protein
What is in front of the lens and is clear and watery
aqueous humor
What is behind the lens and is jellylike?
Vitreous humor
When light enters and strikes the retina it reaches?
Rods and cones
(Photoreceptors)
Where does the neurons of the retina then relay visual information to?
Optic nerve and brain
What lacks photoreceptors and doesn’t detect light
Optic disk
Human two main types of photoreceptor cells
Rods: sensitive light but no color
Cones: provide color vision
light absorbing pigment bound to a membrane protein opsin
Retinal
Rhodopsin
visual pigment
contains retinal and opsin
What does absorption of light cause?
shape change in retinal
What does the transduction of visual information to the nervous system begin with?
conversion of cis-retinal to trans-retinal (from light)
What is the process of converting trans-retinal to cis-retinal called?
bleaching
What activates rhodospin?
Trans-retinal
What does rhodopsin activate?
G protein (transducin) which activates phosphodiesterase which leads to hydrolysis of cyclic GMP
What is the function of Cyclic GMP in the eye?
In the dark binds sodium ion channels and keeps them open
What happens with cyclic GMP breaks down? (3)
1) Na channels close
2) Causes hyper polarizes the cell
3) Signal Transduction pathway usually shuts off again as enzymes convert retinal back to the cis form
Processing of visual information begins
Retina
Rods and cones continually release the neurotransmitter? into what?
Glutamate into synapses with neurons called bipolar cells
What happens when light strikes the rods and cones? (very general)
They hyperpolarize shutting off their release of glutamate
What does the decrease in glutamate cause?
Change membrane potential of bipolar cells
What is lateral inhibition
When a rod or cone stimulates a horizontal cell and the horizontal cell then inhibits more distant photoreceptors and bipolar cells
What does lateral inhibition help?
Helps enhances contrast
What is a receptive field?
the cones and rods defined by a single ganglion
What causes sharper images?
A smaller receptive field
Where do the optic nerves meet at?
At the optic chiasm near the center of the base of the cerebral cortex
Where do sensations of visual fields from each side of the brain go to?
The opposite side of the brain
What do mammals that are nocturnal have high proportion of
They have high proportions of rods and don’t see vivd colors during the day
What are the three types of cones
Red
Green
Blue
What are RGB pigments are called
photopsins
How are photopsins formed?
formed when retinal binds to three distinct opsin proteins
Where do abnormal color vision results from?
Mutations in the genes for one or more photospin proteins
what is focusing?
changing shape of the lens
What is the fovea?
Center of the visual field and contains no rods but a high density of cones
What are the 2 types of accommodation?
1) near vision
2) distance vision
explain near vision accommodation (3)
1) ciliary muscles contract
2) suspensory ligaments relax
3) lens becomes rounder
explain distance vision accommodation (3)
1) ciliary muscle relax
2) suspensory ligaments
3) lens becomes flatter
