3. LIGHT AND VISION Flashcards
1
Q
- Where does a person’s knowledge about the world around it come from?
A
- from its sense
2
Q
- What did Democritus (a Greek philosopher) propose with regards to vision?
A
- he believed that we sensed the external world by means of small, faint copies of objects that are transmitted from the objects to us
3
Q
- What idea did Johannes Muller propose in 1825 with regards to senses?
A
- he believed that the stimuli reaching our organs produce responses in sensory nerves
- different nerves evoke different types of sensations
4
Q
- What can the brain differentiate between?
A
- it can differentiate between light and sound
- this is because the different energies stimulate different nerves
5
Q
- Which system in the body do human beings depend on the most?
A
- the visual system
- the visual system provides us with the richest variety of environmental input
(colour, movement, spatial depth perception are all processed simultaneously)
6
Q
- What is the most studied and best understood of our senses?
A
- the visual system
- our knowledge of the anatomy and coding mechanisms from the visual receptor
- through the central pathways
- into the cerebral cortex
- is better studied than any other sensory system
7
Q
- What percentage of sensory receptors of the whole body are in our eyes?
A
- 70%
8
Q
- What part of the brain is needed to get involved in order to perceive or recognize something?
A
- nearly half of the cerebral cortex needs to get involved
9
Q
- Which sense is considered the dominant sense?
A
- vision
10
Q
- What is light?
A
- it is a form of electromagnetic energy
11
Q
- Which points does the electromagnetic spectrum range from?
A
- it ranges from y-rays to AM waves
12
Q
- What is the visible part of the electromagnetic spectrum range?
A
- it is very small
- it ranges from about 400 nanometers to a little over 700 nanometers
13
Q
- List the forms of light waves on the electromagnetic spectrum from the weakest (longest) to the strongest (shortest).
A
- Radio waves
- Microwave
- Infrared
- Visible
- Ultraviolet
- X-Ray
- Gamma Ray
14
Q
- What filters out much of the energy arriving from the Sun?
What does this result in?
A
- the Ozone layer of the Earth’s environment does this filtering
- it results in 4/5 of the solar radiation reaching the surface of the earth to consist of wave lengths within the visible spectrum
15
Q
- What is the sclera of the eye?
A
- it is the tough outer coat that protects the eyeball
- it is the white outer wall of the eye
- it is a tough fibrous tissue that extends from to the cornea to the optic nerve at the back of the eye
16
Q
- What is the Choroid?
A
- it is the vascular layer of the eye
- it contains the blood vessels that nourish the inner parts of the eye
17
Q
- What is the Cornea?
A
- it is the front portion of the eye
- it is a convex shape
- it bulges outside
- light enters through the cornea
18
Q
- What is the Iris?
A
- it is located just behind the cornea
- it regulates the amount of light that enters the eye
- it does this by adjusting the size of the pupil
19
Q
- What is the pupil?
A
- it is the hole in the middle of the iris
20
Q
- What does the pupil do with regards to the intensity of light entering the eye?
A
- it increases or decreases
21
Q
- What happens when a high intensity of light enters the eye?
A
- the pupil size decreases
22
Q
- What happens when low intensity light enters the eye?
A
- the pupil size increases
- the pupil size can also increase when you are excited or sexually aroused
23
Q
- What is the eye lens made up of?
A
- it is made up of a transparent jelly like substance
- this substance is made up of proteins
24
Q
- How is the eye lens held in position?
A
- it is held in position by the ciliary muscles
- the suspension ligaments
25
Q
- What is the role of the ciliary muscles and the suspensory ligaments?
A
- they adjust the focal length of the eye
- this is so that we can see distant and nearby objects clearly
26
Q
- What is accommodation?
A
- the ability of the eye to focus on distant and nearby objects
- it does this by changing the focal length
27
Q
- What is the Aqueous humor?
A
- it is a viscous (stick) liquid
- it is filled in the area between the cornea and the eye lens
- it prevents the eye from collapsing due to the changes in the atmospheric pressure
28
Q
- What is the Retina?
A
- it a the delicate membrane
- it has a large number of light- sensitive cells
- it is situated at the back of the inner eye
29
Q
- What are the two types of light-sensitive cells?
A
- rod cells
- cone cells
30
Q
- What are rod cells?
A
- they are cells that respond to the intensity of light
31
Q
- What are cone cells?
A
- they are cells that respond to the colour of the objects
32
Q
- What is found in the middle of the retina?
A
- a tiny dimple
- this is know as the fovea or the fovea centralis
33
Q
- What is the fovea?
A
- it is the center of the eyes sharpest vision
- it is the location of the most colour perception
34
Q
- What is present in the Fovea?
A
- the maximum number of cones
35
Q
- What kind of image is formed on the retina when we look at an object?
A
- an inverted real image of the object is formed
36
Q
- Which signals are generated by the cells in the eye?
Where are they sent to and how are they sent?
A
- electrical signals are generated by the cell in the eye
- they are sent to the brain through the optic nerve
37
Q
- What is the Optic Disk also known as?
A
- the blind spot
- this is where all of the axons of the ganglion cells exit the retina
- these ganglion cells form the optic nerve
38
Q
- What is the blind spot?
A
- it is a small region in the retina
- it is where the optic nerve enters the eye
- it is insensitive to light
39
Q
- What happens when an individual has just been hit with a blinding flash light beam?
A
- the light hits the posterior retina
- it spreads from the photoreceptors to the bipolar cells
- these bipolar cells are just beneath the photoreceptors
- this light continues to spread to the ganglion cells
- this light then generates action potentials within the ganglion cells
40
Q
- What do the axons of the ganglion cells do?
A
- they weave together
- this creates the thick ropey optic nerve
( this is also known as the cranial nerve) - this optic nerve leaves through the back of the eyeball
41
Q
- What does the optic nerve carry?
Where does it carry it to?
A
- the optic nerve carries the impulses up to the thalamus
- it then goes to the brains visual cortex
42
Q
- What is the thalamus?
A
- it is the massive gray matter located in the forebrain
43
Q
- What are the functions of the thalamus?
A
- the thalamus have several functions
- such as relaying sensory signals
(including pain and visual perception)
44
Q
- What is the occipital lobe of the mammalian brain associated with?
A
- it is associated with visual processing
- it contains most of the anatomical region of the visual cortex
45
Q
- What is the primary visual cortex?
A
- the Broadmann area 17
- also known as V1 (Visual one)
46
Q
- Where are the cone and the rod photoreceptors located?
What do they do?
A
- they are located near the retina center
- they detect fine detail in colour
47
Q
- When do cones hit their activation thresholds?
A
- they hit them in bright conditions
- this is because cones are not very sensitive
48
Q
- What are some characteristics of rods?
A
- they are more numerous
- they are more light sensitive
- they cannot pick up on real colour
- they only register a grayscale of black and white
- they are situated around the edges of retinas
- they rule the peripheral vision
PERIPHERAL VISION:
the ability to see things where you are not directly looking
49
Q
- How many cones are there roughly in the human eye?
A
- about six to seven million
50
Q
- What are some characteristics of cones?
A
- they are less sensitive to light than the rod cells in the retina
- they allow the perception of colour
- they are able to perceive finer details and more rapid changes in images
- this is because their response time to stimuli is faster than that of rods
51
Q
- How many types of cones are there?
Name them
A
- there are three types:
1. S- Cones
2. M- Cones
3. L- Cones
52
Q
- What is each type of cone sensitive towards?
A
- they are sensitive to visible wavelengths of light
- these wavelengths of light correspond to short- wavelengths, medium- wavelength and long-wavelength light
53
Q
- What do these three types of different cones have?
A
- they have different types of photo receptors
- they have different types of response curves
- they respond to a variation of colour in different ways
54
Q
- What is trichromatic vision?
A
- it is vision that involves three independent channels for conveying colour information
- these channels are derived from the three different types of cone cells in the eye
55
Q
- What does genetic mutation vary with regards to trichromatic vision?
A
- genetic mutations result in the three pigments responsible for detecting light to have variations in their exact chemical compositions
- different individuals will have different cones with different colour sensitivity
56
Q
- What is colour blindness/colour vision deficiency?
A
- it is an inherited and rarely acquired eye condition
57
Q
- What causes colour blindness in an individual?
A
- it is a result of the destruction of cone cells from diseases
58
Q
- What is the most usual form of colour blindness?
A
- Daltonism
- it was named after John Dalton
- he found out about this condition at the age of 26
- this was when he accidentally understood that his grey jacket was actually dark red
59
Q
- What is colour blindness the general name for?
A
- it is the general name for all deficiencies related to the ability to see different colours
- it can manifest itself in several ways
(some colour blind people cannot distinguish from shades of red)
(others cannot distinguish between shades of purple or green)
60
Q
- What is the most unusual form of colourblindness?
A
- Monochromacy
- people suffering from it see most of the world in black and white
- this is a condition of almost total colourblindness
- this is when two or more of the light sense cones do not work
61
Q
- What percentage of Red-Green colour blindness affects men?
A
- 7-10%
62
Q
- What percentage of Red-Green colour blindness affects women?
A
- 0.4%
63
Q
- How does Red-Green colour blindness genetically occur in men?
A
- most men get the gene from their grandfather on their mother’s side
- it is a genetic mutation on the X chromosome
- this means that they will have this characteristic in their phenotype if it occurs in their genotype
- they will then experience colour blindness
64
Q
- Why does Red-Green colour blindness genetically not occur in women that often?
A
- women have two X chromosomes
- some women will have one X chromosome with the genetic mutation on it
- their other X chromosome will not have a genetic mutation on it
- this will override the phenotype of Red Green colour blindness
- the condition will not manifest itself
65
Q
- What is Achromatopsia?
A
- this is a rare condition
- it is the inability to see the world in any other colour except black and white
66
Q
- What is tetrachromatic vision?
A
- people with this condition have four or more types of cones
- this occurs when someone (almost always a female) has a fourth type of cone cell
- these people have a more intense vision
67
Q
- Label the eye diagram below.
A
- Conjunctiva
- Iris
- Lens
- Pupil
- Cornea
- Conjunctiva
- Sclera
- Optic Disc
- Optic Nerve
- Macula
- Retina
- Choroid
- Ciliary Body
- Vitreous Body
- Anterior Chamber
