Photoreception -12.2 Flashcards
What is the percentage of how much vision supplies the sensory information reaching the brain?
80 to 90%
Describe the human eye.
fluid filled hallow ball - 2.5cm in diameter
How many layers does each eye have and what are they?
Three layers
Outer layer - sclera
Intermediate layer - choroid layer
Inner layer - retina
What does the cornea do?
It bends light rays into the eye
What does the choroid do?
Absorbs scattered light and contains blood vessels
What does the pupil do?
It is the opening for light to enter the inner eye?
What does the iris do?
It regulates the amount of light that enters the pupil
- adjusts size of pupil depending on light conditions (adaptation)
What do ciliary muscles do?
They change the shape of the lens in order to focus
What does the lens do?
Focuses light rays on the fovea centralis.
What is the retina?
Thin layer of the eye - contains the photoreceptors - rods, cones, and the fovea centralis
What are rods?
Rods are photoreceptors - they are sensitive to dim light, and allow us to see black and white
What are cones?
Cones are photoreceptors - they are sensitive to different wave lengths of light, allow us to see different colors
Where are cones most concentrated in?
The fovea centralis.
How do the rods and cones send sensory information to the brain?
Through the optic nerve.
What attaches ciliary muscles to the lens?
The suspensory ligaments
What is the anterior chamber?
The area that is Infront of the lens
What is the posterior chamber?
The area that is behind the lens
What is the aqueous humour?
Liquidy, jelly substance
Maintains the shape of the cornea
Provides oxygen and nutrients for surrounding cells
Found in anterior chamber
What causes glaucoma?
When cells in the eye detoriates due to lack of oxygen and nutrients - can lead to blindness
What is the vitreous humour?
Liquidy, jelly substance
Found in the posterior chamber
Helps maintain the shape of the eye ball
Supports surrounding cells
What does the lens do?
They focus light onto the fovea centralis and bend light rays
What are the two main components of the eye that make it bend?
The cornea and the lens.
What is the advantage of lens’ being flexible?
It allows for finer focus when viewing objects.
What happens to a lens, ciliary muscles, and suspensory ligaments when an object is far away?
Lens becomes flat
Ciliary muscles relax
Suspensory ligaments taut
What happens to a lens, ciliary muscles, and suspensory ligaments when an object is nearby?
Lens becomes more rounded
Ciliary muscles contract
Suspensory ligaments relax
What is accomadation?
The ability of the lens to change shape so that it can focus images clearly on the retina
What happens when lens’ age?
They become lex flexible
They become more opaque - hard for light to pass through
What are cataracts?
Grey, white spots on lens’
What is astigmatism?
Uneven curvature at part of the cornea
Light rays cannot bend to meet at the correct focal point
What is 20/20 vision?
When people can see a size 20 letter from 20 feet
What does it mean to be nearsighted?
You can see close images - you cannot see size 20 letter from 20 feet
What is myopia?
Associated with nearsightedness - eye ball is elongated
Focused light falls in front of the retina - instead of on photoreceptors
What can people with myopia do to fix this?
They can wear concave lenses - diverges light so it falls on the retina
Corrective laser surgery - ophthalmologist reshapes cornea
What is hyperopia?
Associated with farsightedness - eyeball is to short
Can see 20 size letter from 20 feet - cannot see close objects
Light rays focus behind the retina
How can you fix hyperopia?
Where convex lenses - bends light rays at a sharper angle
When does vision begin?
When light is focused on the photoreceptors
Where are rods more concentrated?
In the outside edges of the retina
What is responsible for peripheral vision?
Rods
Where are cones more concentrated?
At the fovea centralis - back and centre of retina
Which are more sensitive to light, rods or cones?
Cones - require a lot of light so that the fovea centralis can produce a sharp image
Rods - can be stimulated by a simple photon of light
What are the three types of cones?
Red sensing cones
Blue sensing cones
Green sensing cones
What causes color deficiency (colour blindness)
Caused by lack of deficiency in particular cones (usually red and green)
What light absorbing pigment are rods made from?
rhodspin
What does rhodspin consist of?
retinal, vitmain A derivative, and protein opsin
Describe how rods work to send a neural impulse to optic nerve.
In dark - rods release inhibitory neurotransmitters that inhibit neighboring nerve cells
When rod absorbs light - rhodspin splits into retinal and protein opsin - triggers a chain of reactions - stops the release of inhibitory neurotransmitters
- Allowing the transmission of a neural impulse to the optic nerve
What is the pigment in cones?
Photospin - only reacts to certain wavelengths of light
What are the three main layers of neurons in the retina?
Rod and cone layer
Bipolar cell layer
Ganglion cell layer
What forms the optic nerve?
Axons from the ganglion cells
What Lobe does the optic nerve send visual images?
occipital lobe
What is the area called where the ganglion cells merge to form the optic nerve?
The blind spot - no photoreceptors - incapable of detecting light
What is the complete passage for visual information starting from retina?
Retina - optic nerve - thalamus - occipital lobe of cerebral cortex
What does it mean that the visual image is split in the occipital lobe?
Left optic tract - carries information about the right portion of the visual field
Right optic tract - carries information about the left portion of the visual field
What does it mean that humans have front facing eyes?
We have binocular vision - we both eyes to collect visual information about an object
What is the leading cause of vision loss?
disorders of the retina
What is diabetic retinopathy?
Capillaries to retina burst - spilling blood into vitreous fluid between lens and retina
(Careful regulation of blood glucose can guard this disorder)
What happens as a result from change in consistency of the vitreous fluid?
Retinal detachment - Retina becomes seperated from choroid vessels that supply it with oxygen and nutrients
What is macular degeneration?
Cones are destroyed due to thickened choroid vessels - cannot function like before
Result is blurring or the development of a blind spot in central vision
