Lecture 9 - Vision

Question 1

Define sensation

Answer 1

Receiving information about a certain stimulus

Question 2

Define perception

Answer 2

Conscious experience and interpretation of information that was sensed

Question 3

How do receptor neurons detect physical stimuli?

Answer 3

With receptor proteins that are specific to different stimuli

Question 4

Define sensory transduction

Answer 4

Process by which sensory stimuli get transformed into receptor potentials

Question 5

Define receptor potential

Answer 5

Graded change in membrane potential of a sensory neuron caused by sensory stimuli

Question 6

Define sensory neuron

Answer 6

Specialized neuron that detect particular sensory stimuli

Question 7

Do all sensory neurons generate action potentials?

Answer 7

No, not all sensory neurons have axons or generate action potentials, but all of them release neurotransmitter

Question 8

In what fashion do small sensory neurons release neurotransmitter?

Answer 8

In graded fashion, the more depolarized the neuron is, the more neuotransmitter will be released

Question 9

What’s the name of receptor proteins that are sensitive to light?

Answer 9

Opsins

Question 10

Name all opsin proteins used to detect light

Answer 10

Rhodopsin, red, blue, green cone opsins

Question 11

How many opsins does one photoreceptor cell contain?

Answer 11

Each photoreceptor cell can only contain one type of opsin

Question 12

How many photoreceptor cells do humans have?

Answer 12

Four, rod cells that express rhodopsin, and red, green and blue cone cells that express red, green, and blue cone opsins respectively

Question 13

What is a photoreceptor cell?

Answer 13

Sensory neuron responsible for vision. These cells convert electromagnetic energy from visible light into receptor potentials

Question 14

Define Opsin

Answer 14

Light sensitive protein

Question 15

How do opsins gain their sensitivity to light?

Answer 15

By binding to a molecule of retinal

Question 16

What type of receptors are opsins in our eye that transduce visual info

Answer 16

They are inhibitory metabotropic receptors

Question 17

Define retinal

Answer 17

A molecule made from viatmin A that binds to opsin proteins

Question 18

What happens when light reaches retinal?

Answer 18

Retinal reacts to light and changes its shape, launching a signaling cascade of G-proteins

Question 19

How does retinal return to its initial form?

Answer 19

An enzyme comes in and uses ATP to bring the electron to a low energy state, thus forcing retinal to go to its initial state

Question 20

What wavelength is visible light?

Answer 20

Between 380 and 760 nm

Question 21

What are gamma rays and how do they interact with physical matter?

Answer 21

Gamma rays have extremely short wavelength and usually don’t interact with physical matter because of that

Question 22

What happens if gamma rays hit an electron in a body

Answer 22

If an electron is hit by gamma rays, it will leave the atom entirely, creating positively charged ions which are very unstable.

Question 23

What do positively charged ions do to balance themselves?

Answer 23

They will try to grab electrons from neighboring cells, leading apoptosis or blocking of cell destruction, leading to cancer

Question 24

What happenes to electrons in the visible light wavelength?

Answer 24

Photons get absorbed by electrons causing electrons to enter higher energy state

Question 25

What allows us to see ful spectrum of color?

Answer 25

Presence of red, blue and green cone opsins

Question 26

Where are most cone opsins concentrated?

Answer 26

In the center of the eye

Question 27

Where are rods mostly concentrated?

Answer 27

In the peripheral vision

Question 28

How do three cone opsins work?

Answer 28

By relative activation, some opsins are activated less, some more to create a certain color

Question 29

What are three perceptual dimensions of light and color?

Answer 29

Brightness, Saturation (purity in terms of composite wavelength), Hue (color)

Question 30

Define protanopia

Answer 30

Absence of red cone opsins, people with this condition have trouble differentiating color in green-yellow-red spectrum, but have normal visual acuity since red cone cells get filled with green cone opsin

Question 31

Define deuteranopia

Answer 31

Absence of green cone opsins, visual acuity is not affected, since green cone cells get filled with red cone opsins

Question 32

Define tritanopia

Answer 32

Absence of blue cone opsin. Blue cone cells do not compensate for that loss, but visual acuity is not affected since blue cone cells are not sensitive to light

Question 33

Define Achromatopsia and the cause

Answer 33

True color blindness that is usually cause by malfunctioning of G-protein signaling cascade that is shared between all of the opsins

Question 34

What type of cells does fovea mostly contain?

Answer 34

Fovea primarily contains cone cells

Question 35

Why are images in the center of our FOV usually very clear?

Answer 35

In the fovea, there is no compression of information, photorececptors (primarily cones) converge to downstream collections of neurons that do not decrease drastically, ensuring good image quality

Question 36

Why are images less clear in our peripheral vision?

Answer 36

Photoreceptors (primarily rods) converge to fewer and fewer downstream collections of neurons, the information gets compressed leading to poor resoluton, but high detection of light and general shapes

Question 37

What allows to hide the presence of a blind spot and the fact that our peripheral vision is color blind?

Answer 37

Rapid eye movement with the help of psychological processes that complete the images

Question 38

Define Saccadic eye movement

Answer 38

Rapid eye movement that is scattered all over the place

Question 39

Define Pursuit movement

Answer 39

Focused type of eye movement that allows us to keep a clear image of a moving object

Question 40

What is an unusual property that photoreceptors have?

Answer 40

Apart from potassium leak channels, photoreceptors also have leaky sodium ion channels which are open in the dark when cells are at rest. In the dark, sodium constantly enters the cell through these channels depolarizing the membrane to -40mV

Question 41

What do photoreceptors do in the depolarized state?

Answer 41

They continuously release glutamate

Question 42

When are photoreceptor cells more depolarized and release more glutamate?

Answer 42

During the night, for when light hits photoreceptors, opsin receptor proteins change shape and launch a g-protein cascade that hyperpolarizes the cell

Question 43

What are the two types of bipolar cells?

Answer 43

OFF bipolar cells and ON bipolar cells

Question 44

How do OFF bipolar cells function?

Answer 44

They are more depolarized by glutamate since they express ionotropic glutamate receptors. Since photoreceptor cell constantly releases glutamate in the dark, OFF bipolar cells are more active in the dark than light

Question 45

How do ON bipolar cells function?

Answer 45

Bipolar On cells have inhibitory metabotropic glutamate receptors hence they are uncommonly inhibited by glutamate. They are more active in presence of light than darkness

Question 46

What does receptive field refer to?

Answer 46

it refers to the area of visual space where light is capable of changing the activity of a neuron