Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BIO2034 Animal Function > Sensory physiology- photoreception > Flashcards

Sensory physiology- photoreception Flashcards

1
Q

What are the 4 major types of animal eyes?

A

Flat sheet
Convex
Cup-shaped
Vesicular

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Describe the flat sheet eye

A

Contain a layer of photoreceptor cells that form a primitive retina
Provide some sense of light direction and contrast
The pigment layer contains shading pigment that helps provide directional information by shading light coming from some directions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the cup-shaped eye

A

Retina is folded to form a narrow aperture

Similar to pinhole camera where resolution is poor and image is dim

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe the convex eye

A

Photoreceptors radiate outwards from the base forming a convex light-gathering surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe the vesicular eye

A

A lens is inserted into the pinhole aperture
Lens collects light from multiple sources and retracts it thus focusing it onto the retina
The lens is able to change shape allowing it to focus on objects

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the structure of the human eye

A

Light entering the eye passes through the cornea, the aqueous humour, the pupil, the lens, and the vitreous humour before striking the retina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe the parts of the retina

A

The fovea and the choroid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the fovea?

A

A pit in the retina which provides the clearest vision

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the choroid?

A

The vascular layer of the eye which supports the retina with blood

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe the process of accommodation

A

The lens is connected to the round ciliary body (muscle) by fibres called zonules
When the ciliary muscle is relaxed, the zonules are stretched thereby flattening the lens
When accommodated to a nearby object, the ciliary muscle contracts thereby relaxing the zonules and the lens will have a rounder shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is visual acuity?

A

Clarity of eyesight

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the 2 main factors that affect visual acuity?

A

Optical and retinal factors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Give an example of an optical variable of visual acuity

A

The diameter of the pupil (smaller=higher acuity)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Give an example of a retinal variable of visual acuity

A

The density of photoreceptors and retinal ganglion cells and their ratio

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Where is acuity at its max?

A

In the foveal centre and decreases rapidly towards the periphery

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe the structure of eagles eyes

A

The eyes occupy 50% of the skull
The eagle can voluntarily alter the curvature of its lens and cornea thus changing focus
Oxygen is supplied through a structure called the pecten which increases the visual acuity by allowing more rods and cones to be packed in
Have 4-5x the visual acuity of humans
They have 2 foveae per eye to allow for monocular vision
A trench of cones between these foveae allow for horizon scanning without moving the head
They can spot an ant from a ten-story building

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the purpose of the pigmented epithelium in the retina in vertebrates?

A

To absorb the light to prevent photo-oxidative stress

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Where are the photoreceptors located?

A

In the deepest layer of the retina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the photoreceptors connected to?

A

Bipolar cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the bipolar cells connected to?

A

Ganglion cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are the 4 important components for signal processing in the retina?

A

Horizontal cells and amacrine cells

Bipolar cells and ganglion cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What does the retinal pigment epithelium do?

A

Provides metabolic and supportive functions to the photoreceptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What does the outer nuclear layer contain?

A

The photoreceptor cell bodies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What does the outer plexiform layer contain?

A

It’s where the photoreceptor, horizontal, and bipolar cells synapse

25
Q

What does the inner nuclear layer contain?

A

It’s where the bipolar, amacrine and retinal ganglion cells synapse

26
Q

What does the retinal ganglion cell layer contain?

A

The retinal ganglion cell bodies

27
Q

What does the optic nerve layer contain?

A

The ganglion cell axons travelling to the optic disc

28
Q

Describe the organisation of the retina is cephalopods

A

A single layer of photoreceptor cells and supporting cells
Light strikes the photoreceptors directly without passing through multiple layers
No interneurons thus no signal processing in the retina

29
Q

Did the cephalopod and vertebrate eye evolve independently?

A

Yes

30
Q

Describe rods

A

Contain many photopigments and are very sensitive

31
Q

Describe the conditions and results of light hitting rods

A

Active under dim light and can’t discriminate colours

32
Q

Describe cones

A

Less photopigment

33
Q

Describe the conditions and results of light hitting cones

A

Can detect colours and active under stronger light

34
Q

What is the photopigment in rods called?

A

Rhodopsin

35
Q

What is the light receptor in rods called?

A

11-cis retinal

36
Q

How does 11-cis retinal work?

A

It absorbs a photon of light and rotates to form all-trans-retinal

37
Q

What is rhodopsin in its constituent parts?

A

11-cis retinal and the protein opsin

38
Q

Where is rhodopsin located?

A

In the membrane disks of the rod photoreceptors

39
Q

Describe the state of vertebrate photoreceptor cells when unstimulated

A

Vertebrate photoreceptor cells are depolarised when unstimulated

40
Q

Describe the state of vertebrate photoreceptor cells when stimulated with light

A

They are hyperpolarised

41
Q

What does a stronger light stimulus do to the membrane potential in vertebrate photoreceptor cells?

A

A stronger light stimulus leads to a more negative membrane potential

42
Q

When do photoreceptor cells release transmitter?

A

In the dark

43
Q

What is the transmitter photoreceptor cells release?

A

Glutamate

44
Q

Describe the process of transduction

A

In the absence of light Na+ channels are open and create a depolarising dark current
Rhodopsin absorbs light energy
This activates a G protein (transducin) that activates PDE
Activated PDE hydrolyses cGMP causing Na+ channels to close and the cell to hyperpolarise

45
Q

What is a receptive field?

A

Where 1 bipolar cell is connected to more than one photoreceptor in the retina

46
Q

What is the benefit of receptive fields in the retina?

A

There are many more photoreceptors than neurons in the retina

47
Q

What are the 2 types of receptive fields?

A

OFF and ON centre

48
Q

How are OFF and ON centre receptive fields categorised?

A

By the type of retinal ganglion cells beneath the photoreceptor layer

49
Q

Describe ON centre, OFF surround RGCs

A

They respond to light stimuli in the photoreceptors surrounding the centre of the receptive field

50
Q

Describe OFF centre, ON surround RGCs

A

They respond to light stimuli in the photoreceptors at the centre of the receptive field

51
Q

How are ON and OFF centre RGCs physiologically distinct?

A

They respond to light falling on their receptive field differently

52
Q

How are ON and OFF centre RGCs anatomically different?

A

The dendrites branch out in separate sub-layers of the retina and they receive synaptic inputs from different subclasses of bipolar cells

53
Q

Where do the signals from the RGCs go?

A

They remain segregated in the retina and thalamus and then merge in the primary visual cortex

54
Q

Describe lateral inhibition in an ON centre RGC

A

The action potentials arrive at the lateral geniculate nucleus (LGN) in the thalamus
Light hitting a photoreceptor in a receptive field leads to hyperpolarisation of all photoreceptors that receive a photon
In an ON centre RGC, if there is a concentration of light at the centre of the receptive field, negative feedback signals in the horizontal cells depolarise the surrounding photoreceptor cells and further hyperpolarise the centre cell
Combining lots of these RGCs emphasises edges over block colour

55
Q

What is the mach band effect?

A

The combined effect of lateral inhibition across multiple receptive fields emphasises edges
The contrast at the edges of each neighbouring band is increased
The illusion makes the bands appear slightly concave

56
Q

Why do we need multiple cone receptors?

A

Multiple cone receptors are an evolutionary advantage to allow better discrimination between objects

57
Q

What wavelengths of EM radiation can humans detect?

A

Between 350nm and 750nm

58
Q

How many colours can humans detect?

A

10 million

59
Q

What is trichromatic colour vision

A

Only have 3 specialised cones- blue, green and red

BIO2034 Animal Function (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions