Task 2 Flashcards
(44 cards)
1
Q
Visible light - Definition
A
Visible light: energy within the electromagnetic spectrum that humans can perceive
- humans can perceive wavelengths from 400 to 700 nanometers
2
Q
The Eye
- Cornea
A
- light enters eye through cornea
- no blood vessels (=transparent) —> photons d not get reflected/absorbed
3
Q
The Eye
- Lens
A
- no blood supply (=transparent)
- control process (accommodation) to prevent blurring
4
Q
The Eye
- Retina
A
- contains photoreceptors responsible for receiving image from lens and send it to the brain through the optic nerve
- brings light into focus
- detects light and communicates to brain the aspects of light related to objects in the environment
5
Q
The Eye
- Iris
A
- gives eye distinctive color
- controls size of pupil and the amount of light that reaches the retina
- pupillary light reflex: automatic expansion or contraction when level of light increases or decreases, that allows either more or less light to enter the eye
- attached to ciliary muscles
6
Q
The Eye
- Pupil
A
- circular opening in the middle of the iris
- responsible for letting light in and to get it to the lens
7
Q
The Eye
- Aqueous Humor
A
- fluid that fills space behind the cornea
- supply of oxygen and nutrients to cornea and lens
- removes waste from cornea and lens
8
Q
The Eye
- Vitreous Humor
A
- gel-like fluid that fills the vitreous chamber
- vitreous chamber: longest part of journey through eyeball
- light refractor: to reach retina, light goes through vitreous chamber, where it is refracted by vitreous humor
9
Q
The Eye
- Fovea
A
- part in center of retina responsible for producing the highest visual acuity and point of fixation
- specialized for seeing fine detail, reading and identifying objects
- only two cones in the fovea
10
Q
The Retina
- Fundus
A
- back layer of the retina
- only place where veins and arteries can be seen directly
11
Q
The Retina
- Optic Disc
A
- point where arteries and veins responsible for feeding the retina, enter the eye
- point where axons of ganglion cells leave the eye via the optic nerve
- contains no photoreceptors
- blind spot: area in retina where there are no receptors
12
Q
The Retina
- Photoreceptors
A
- light-sensitive receptors in last layer of retina — must be close to pigment epithelium and other neurons
- help transducing light energy to neural energy
- capture light and initiate seeing by producing chemical signals
13
Q
The Lens
- Accommodation
A
- change in lens‘ shape that occurs unconsciously when ciliary muscles tighten and increase curvature of lens
- eye constantly adjusting focus with this process
14
Q
The Lens
- Persbyopia
A
condition that occurs when a person gets older, where the distance of the near point increases
- because lens hardens with age and ciliary muscles become weaker
15
Q
The Lens
- Myopia
A
(Nearsightedness) —> people are unable to see distant object clearly
- reason: myopic optical system brings parallel rays of light into focus at point in front of retina
16
Q
The Lens
- Hyperopia
A
(Farsightedness) —> people are unable to see nearby objects clearly
- focus point —> located behind retina because eyeball is too short
17
Q
Retinal Information Processing
A
Retina contains 5 major classes of neurons: photoreceptors, horizontal cells, amacrine cells, bipolar cells, and ganglion cells
18
Q
Photoreceptors
A
human retina consists of two types of photoreceptors - rods and cones - with different shape, function and distribution
19
Q
Photoreceptors
- Rods
A
- sensitive photoreceptors that can only be activated by a single photon
- depolarized at night - specialized for night vision
- releases inhibitory neurotransmitter at night
- photogigment Rhodopsin
- only one type
- high convergence, low acuity and high light sensitivity (=slow response)
- slow regeneration of pigments
20
Q
Photoreceptors
- Cones
A
- mostly present in fovea
- specialized for daylight and vision because of low sensitivity but high acuity
- need light in order to be activated
- three photopigment:
- S-cones: blue
- M-cones: green
- L-cones: red
- receptive fields bigger than those of rods
- little convergence, high acuity and low light sensitivity (=respond fast)
21
Q
Photoreceptors
- Third Type
A
- contains melanopsin — photopigment sensitive to ambient light
- involved in adjusting circadian clock
22
Q
Characteristics of Photoreceptors
A
- information passed to bipolar cells via graded potential
- consist of an outer segment, inner segment, and synaptic terminal
23
Q
Light Transduction by Receptors
A
- Photoactivation
- activation by light that initiates a chain of biochemical events that lead to an overall hyperpolarization of the cell - Hyperpolarization
- increase in membrane potential —> makes inner membrane surface more negative than outer one - Closing of calcium channels at synaptic terminal
- Decrease of glutamate concentration
- signals bipolar cell, that rod captured photon; hyperpolarization in photoreceptors causes depolarization in bipolar cells
24
Q
Horizontal Cells
A
- produce inhibitory neurotransmitter GABA
- form lateral connections between photoreceptors and cause lateral inhibition
- important for center-surround organization of ganglion receptive fields and for perception of visual contrast
- in contact with nearby photoreceptors and bipolar cells
25
Amacrine Cells
- many different types, produce different neurotransmitters, mostly inhibitory
- found in inner synaptic layer where they connect bipolar cells with ganglion cells
- present in cone and rod pathway, thus, it sometimes combines input from these pathways
- involved in contrast enhancement and temporal sensitivity, detection of movement and temporal sensitivity
26
What is Lateral Inhibition?
- antagonistic neural interaction between adjacent regions of the retina
- important for: visual perception and illusion, perceiving contrast
27
Bipolar Cells
| - Diffuse bipolar cells
Bipolar cells: function as kind of mediator
Diffuse bipolar cells: processes are spread out, so they can receive information from multiple cones
- sensitivity increased by gathering information from many photoreceptors
- visual acuity falls off rapidly with eccentricity
28
Bipolar Cells
| - Midget bipolar cells
Midget bipolar cells: cells in fovea that receive input from single cone and pass it on to single ganglion cell
- in foes: no convergence (high acuity, low sensitivity to light)
29
Ganglion Cells
cells responsible for the process of visual information received from the photoreceptors to the brain (visual cortex) and midbrain (thalamus)
30
Receptive Fields
= region of the retina in which stimuli influence a neuron‘s firing rate; can be either excitatory or inhibitory
- each ganglion cell has its own receptive field:
- ON-Center cell —> cell that depolarizes in response to increase in the light intensity in receptive-field center
- OFF-Center cell —> cell that depolarizes in response to decrease in the light intensity in receptive-field center
31
P Ganglion Cells
- smaller receptive field (do not converge, connected to one photoreceptors)
- sustained firing when light shines on excitatory regions
- transmit information about contrast in retinal image
32
M Ganglion Cells
- bigger receptive fields (converge); more sensitive under low-light conditions
- respond more transiently, with brief bursts of impulse when the spot of teh receptive field is turned on; then, they quickly return to spontaneous state
- transmit information about how this image changes over time
33
Center-Sourround Receptive Fields
= each optic nerve fiber monitors a small area of the retina and together they take in information about what is happening over the entire retina
- Center-surround organization: area in ‚center‘ of receptive field that responds differently to light than area in teh ‚surround‘ of the field
34
Transduction
| + Isomerization
Transduction: transformation of one form of energy into another form of energy, that occurs in the rods and cones
- visual pigments contained in outer segments of these receptors; two parts:
- opsin — large protein
- retinal — small light-sensitive component
- when combined, it results in a molecule that absorbed visible light
- Isomerization: change of shape in retinal that occurs when visual pigment absorbs one photon of light
35
Dark Adaptation
| - Definition
= process of increasing sensitivity in the dark
| - rod and cone receptors adapt to light at different rates because of difference in their visual pigments
36
Dark Adaptation
| - Distribution of Rods and Cones
fovea: only cones
peripheral retina: all of the retina outside of fovea; more rods than cones
blind spot: no receptors
37
Dark Adaptation
| - Measuring Dark Adaptation Curve
Dark adaptation curve shows the function relating sensitivity to light to teile in the dark; begins when lights are turned off
38
Dark Adaptation
| - Visual Pigment Regeneration
= in weak light, there are lots of pigments available; therefore, rods and cones absorb and respond to them as much as they can
39
Neural Convergence and Perception
Convergence = increased sensitivity of the ganglion cells
40
Consequences of Convergence
rods have higher convergence than cones
- takes less light to generate response from individual rod receptor than from individual cone receptor
- rod and cone sensitivity is determined by groups of receptors converging onto other neurons
41
Consequences of Lack of Convergence
cones have better visual acuity because they have less convergence
42
Visual Illusions
| - Lateral Inhibition
lateral inhibition: effect in which illumination of receptors ‚inhibits‘ firing of neighboring receptors; increase in contrast and sharpness when it comes to visual response
43
Visual Illusions
| - Mach Band
- in dark, small light stimulus enhance rods
- rods in center of stimulus transduces ‚light‘ signal to brain
- rods in outside of stimulus transduces ‚dark‘ signal due to lateral inhibition from horizontal cells
- contrast between light and dark create Mach band effect
44
Visual Illusions
| - Hermann Grid
- receptive field at intersection of white cros has more light on inhibitory surround than the one between two black squares
- excitatory center of this receptive field between squares has stronger response than the other one
- receptive fields in central fovea are smaller than in rest of retina
- we do not see a dark area when we look directly at intersection of white cros, but we see it in our peripheral vision
