Unit 5 Lecture 38 Flashcards
What is the sensory surface of the eye?
retina
What is the bending of light rays?
Refraction
When does refraction occur?
Occurs when light passes from one medium (air) into another (water)
Where does most refraction take place?
Cornea
What is the purpose of the lens?
critical ‘fine tuning’ of refraction
What happens when bright light goes into the eye?
The pupil gets SMALLER bc CIRCULAR muscles of iris contract
What nervous systems control the constriction and dilation of the eye?
constriction= Parasympathetic NS
dilation = sympathetic NS
What happens when normal light goes into the eye?
Iris muscles relax and the pupil is normal
What happens when dim light goes into the eye?
The pupil get BIGGER (dilates) bc RADIAL muscles of the iris contract
What is the function of the iris
regulates light entry
How does the eye see images from long distances?
In parallel rays
How does the eye see images close up?
In non-parallel rays
What happens to light when it enters a new medium?
bends (refracts)
Where does the eye make an image when the object is far away?
Plane of the retina
Where does the eye make an image when the object is up close?
Behind the retina
What objects look out of focus?
Close up things
How does the eye focus things up close?
Accomodation
Define accomodation
The change of lens shape to see things up close
Steps of accomodation
- Lens gets round
- Entering angle of light increases
- Light gets more bent so the image falls on retina
How does the lens become more round?
Suspensory ligaments loosen up -> less tension on lens
Define presbyopia
Can’t see things up close because the lens tightens with old age and can’t get round
Define emmetropia
Eyes without vision problems
Define hyperopia
short eyeball
What happens with hyperopia?
Image falls behind retina
Define myopia
Long eyeball
What happens with myopia?
Image falls in front of retina
The retina is made of many what?
layers
What are the layers of the retina?
- Ganglion cell layer
- Neuron layers
- Photoreceptor later
Function of the ganglion cell layer
carries signals to the brain
Function of the neuron layers?
Processes photoreceptor signals
What are the 2 cell types in the photoreceptor layer?
Rods and cones
What is a rod?
Processes black and white, VERY sensitive, dim light
What is a cone?
Color vision, not as sensitive, bright light
What is the path of light through the retina?
Ganglion Cell L -> Neuron L -> Photoreceptor L
What is the path of visual data processing?
Photoreceptor L -> Neuron L -> Ganglion Cell L
Characteristics of rods
- sensitive to light
- Black and white
- @ periphery of retina (whole back of eye but the macula)
- LARGE receptor field
- senses movement
Characteristics of cones
- Not sensitive
- COLOR
- @ macula lutea (circle on retina)
- SMALL receptor field
- differentiates wavelength
What is the light receptor in rods called?
Rhodopsin
What is Rhodopsin made of?
opsin and retinal
Explain rod phototransduction
- Light photon absorbed in retinal
- Opsin is activated -> breaks down”chemical messenger” cyclic GMP (cGMP) that keeps Na+ channels open
- cGMP-gated sodium channels close
- Rod hyperpolarizes
- Glutamate is NOT released
What is glutamate?
a popular neurotransmitter in the brain
What are the two “halves” of the eye?
Nasal and temporal
What half of the eye has the larger receptor density
Temporal…. that’s the side with the blind spot
