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Perception > Task 2 the retina > Flashcards

Task 2 the retina Flashcards

1
Q

Waves

A

An oscillation that travels through a medium by transferring energy from one particle or point to another without causing any permanent displacement of the medium

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2
Q

Photon

A

A quantum of visible light, demonstrating both particle and wave properties

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3
Q

Cornea

A

Transparent window to the world (80% of the focus power)

o Has transparent sensory nerve endings to trigger tears or forcing the eyes to close

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4
Q

Aqueous humor

A

fluid that fills the space behind the cornea, supplying nutrients, oxygen and removing waste from the cornea and the lens

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5
Q

Lens

A

Completely transparent, the shape is controlled by the ciliary muscle
o Enables change of focus (20%)

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6
Q

Pupil

A

the dark centre of the iris where light passes into the eye

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7
Q

Iris

A

gives the eye its colour and controls the size of the pupil, and so controls the amount of light that reaches the retina, gets bigger when low light and smaller when bright light

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8
Q

Vitreous humor

A

the transparent fluid that fills the vitreous chamber in the posterior part of the eye, comprises 80% of the internal volume of the eye

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9
Q

Retina

A

A light sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the optic nerve

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10
Q

Fundus

A

The back layer of the retina. The point where the arteries and veins that feed the retina enter the eye, and where the axons of the ganglia cells leave the eye via the optic nerve
 Contains no photoreceptors, so it is blind

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11
Q

Photoreceptors

A

A light sensitive receptor in the retina
 When they sense light they can stimulate neurons in the intermediate layers, including bipolar cells, horizontal cells and amacrine cells

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12
Q

Rods

A

A photoreceptor specialized for night vision (90 mil.) (can’t signal differences in colour) (communicate through diffuse bipolar cells which is the reason for the good low light seeing ability)
• Rhodopsin: visual pigment in rods (mainly in the outer segment)

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13
Q

Cone

A

A photoreceptor specialized for daylight vision, fine visual acuity and colour (4-5 mil.)
• Consist of three different photopigments that differ in the wavelength at which they absorb light most efficiently. This enables them so provide colour signals.

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14
Q

S-cones

A

Short wavelength sensitive cones constitute about 5-10% and they are missing in the centre of the fovea

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15
Q

L-cones

A

long wavelength sensitive cones are the largest part

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16
Q

M-cones

A

Medium wavelength the amount is the half of L-cones

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17
Q

Outer segment

A

The part of a photoreceptor that contains photopigment molecules (visual pigments)

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18
Q

Inner segment

A

The part of a photoreceptor that lies between the outer segment and the cell nucleus

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19
Q

Synaptic terminal

A

The location where axons terminate at the synapse for transmission of information by the release of information by the release of neurotransmitter

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20
Q

Chromophore

A

captures light photons

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21
Q

Melanopsin

A

A photopigment that is sensitive to ambient light and send their information to the superchiasmatic nucleus (SCN) the home of the internal clock

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22
Q

Photoactivation

A

initiates a cascade of biochemical reactions eventually resulting in hyperpolarisation. This reduces the concentration of glutamate, which changes signals to the bipolar cell that the rod has captured a photon

23
Q

Graded potential

A

The amount of glutamate in the photoreceptor-bipolar cells synapse is inversely proportional to the number of photons being observed by the photoreceptors.

24
Q

Fovea

A

A small pit, near the centre of the macula, that contains the highest concentration of cones and no rods. It is the portion of the retina that produces the highest visual acuity and serves as point of fixation
 Under low light conditions the middle part is blind because it only contains cones and not rods

25
Q

Periphery

A

used for detecting and localizing stimuli that we aren’t looking at directly

26
Q

Eccentricity

A

The distance between the retinal image and the fovea

27
Q

Amacrine cells

A

Mostly present in rod pathways between bipolar and ganglion cells. They are able to combine signals from rod and cone pathways. Are important for the detection of small movements

28
Q

Ganglion cell

A

A retinal cell that receives information from photoreceptors via bipolar cells and amacrine cells and transmits information to the brain and midbrain

29
Q

P ganglion cells

A

A small ganglion cell that receives excitatory input from single midget bipolar cells in the central retina and feeds the parvocellular layer of the lateral geniculate nucleus 70% of the ganglion cells (small receptive field) (finer resolution)

30
Q

M ganglion cells

A

A ganglion cell resembling a little umbrella (because of their spread dendrites) that receives excitatory input from diffuse bipolar cells and feeds the magnocellular layer of the lateral

31
Q

Koniocellular cells

A

A neuron located between the magnocellular and parvocellular layers of the lateral geniculate nucleus. This layer is known as the koniocellular layer. Input from S-cones

32
Q

Receptive fields

A

the region on the retina in which visual stimuli influence neurons firing rate
 Increases when light hits this field and decrease when light hits somewhere else

33
Q

Horizontal cells

A

allows the electrical signal to travel between the receptors, they define the centre and the surrounding of the cell

34
Q

On centre cells

A

A cell that depolarizes in response to an increase in light intensity in its receptive-field centre and decreases when the light hits the surrounding

35
Q

Off centre cells

A

A cell that depolarizes in response to a decrease in light intensity in its receptive-field centre

36
Q

Layout of ganglion cells

A

they have a circle in the middle (antagonistic centre) which reacts exciting and surrounding rings that react inhibiting. This interaction is known as lateral inhibition.

37
Q

Filter

A

Allows the passage of some frequency’s and blocks passage of others
 Each step of the visual system can be considered as a filter which is responsible for extracting a particular aspect of the visual world and passing this aspect on to the next stage

38
Q

Contrast

A

The difference in luminance between an object and the background, or between lighter and darker party of the same object

39
Q

Bipolar cells

A

A retina cell that synapses with either rods or cones (not bot) and with horizontal cells, and then passes the signals (as many as 50) to the ganglion cells

40
Q

Diffuse bipolar cells

A

A bipolar retinal cell whose processes are spread out to receive input from multiple cones (low acuity but high sensitivity to light)

41
Q

Midget bipolar cells

A

receive input from single cones and pass this information to a single ganglion cell. They only exist in the fovea and this is why the image is most clear when it falls in this part of the retina (High acuity but poor sensitivity to light)

42
Q

On bipolar cells

A

A bipolar cell that responds to an increase in light captured by the cones

43
Q

Off bipolar cells

A

A bipolar cell that responds to a decrease in light captured by the cones

44
Q

Emmetropia

A

the condition in which there is no refractive error, because the refractive power of the eye is perfectly matched to the length of the eyeball

45
Q

Myopia

A

When the eyeball is to long, the image will be focused in front of the retina (can be corrected with a minus lens)

46
Q

Hyperopia

A

When the eyeball is to short the image will be focused “behind” the retina (can be corrected with a plus lens)

47
Q

Astigmatism

A

A visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea

48
Q

Accommodation

A

(change in focus) is achieved by contraction of the ciliary muscle, it is attached with tiny fibres
o When muscle is relaxed the eye focuses objects which are far away when it contracts it can focus object closer to the eye, this contraction reduces the tension on the fibres and enables the lens to bulge

49
Q

Presbyopia

A

Old sight where you lose accommodation because of your age which makes it harder to focus on close objects

50
Q

Cataracts

A

loss of transparency

51
Q

Hermann Grid illusion

A

You see the spots in the intersection because higher illumination means higher lateral inhibition so the corridors are surrounded by black fields which reflect less light to the retina → less lateral inhibition so the corridors look white and the intersection where more lateral inhibition is caused by more white fields is seen as grey (inhibition is always 0.1 from the original intensity)

52
Q

Mach Band Illusion

A
  • Receptive field over the bright Mach Band gives stronger response in the centre because part of the surround is in the darker area –> receives less inhibition from the surround than did the centre at the extreme left and right ends
  • Receptive field over the dark band receives more surround inhibition because part of the surround is in the brighter area –> excitatory response is less –> results in our seeing that the area as darker
53
Q

Lateral inhibition

A

enables the signals that reach the retinal ganglion cells to be based on differences in activation between nearby photoreceptors

54
Q

Low light adaption

A

o Your cones will adapt faster when you turn out the light, while the rods continue to adapt because we have so many rods that need new visual pigments, in the end we see better because of the rods

Perception (9 decks)

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