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BMS11004 > W8 Visual ystem ( eye retine, phototransduction) Auditory system > Flashcards

W8 Visual ystem ( eye retine, phototransduction) Auditory system Flashcards

1
Q

What does Vision allow us to do?

A

Detect pray/predator/mates/communicate

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2
Q

What is involved in analysing the visual word

A

1/3 of the human neocortex

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3
Q

What does light has?

A

a wavelength: distance between peaks or troughs.
a frequency: number of waves per second
an amplitude: difference between wave peak and trough

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4
Q

Refraction (light and the environment, optics)

A

Refraction occurs becasue the speed of light differs between mediums (slow through water than air)
The greater difference in speed in the two media the greater the angle of refaction.

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5
Q

Electromagnetic light

A

Travels in straight lines, known as rays, until it interats with atoms and molecules.
3 ways of interaction: Reflection, Absoption and refraction

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6
Q

Example of Absoprtion (electromagnetic light)

A

Photoreceptors and pigmented epithelium of retina

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7
Q

Example of Refraction (electromagnetic light)

A

Used by comea to form images on the retina

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8
Q

Eye position can vary with species

A

Monocular vs binocular vision: field of view/depth of perception/predator vs prey

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9
Q

Pupil and Retina (light)

A

appear black due to heavy pigment at back of the eye. Reflected light appears bright red hwen light is shined due to blod vessels on surface of the retina.

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10
Q

Pupil - Function

A

Lets light inside the eye

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11
Q

Iris - Function

A

contains muscles which ocntrol the amount of light entering the eye.C

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12
Q

Cornea - Function

A

glassy, transparent covering of the pupil and iris that refracts light.

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13
Q

Sclera - Function

A

Continuous with cornea, forms the tough, pretective wall of th eeyeball to give it its shape.

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14
Q

Extraocular muscles - Function

A

Move the eyeball, controled by oculomotor nerve

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15
Q

Optic nerve - Function

A

carries axons from retina to brain

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16
Q

Optic disk

A

origin of blood vessels and optic nerve, cannot sense light (blind spot)

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17
Q

Macula

A

Region of retina for central vision, devoid of large blood vessels to improve vision quality

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18
Q

Fovea

A

Retina is thinnes there and is the area of highest visual acuity

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19
Q

Zonal fibers

A

Suspensory ligaments which are attached to the ciliary muscle, enabling stretching of the lens

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20
Q

Lens

A

Spherical obejct, it is strenghts as it is attached to zonal fibers, they can be tighter or not depending on the ciliary muscle

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21
Q

Two diffferent solution - Eye

A

Viterous humor
Aqueous humor

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22
Q

What is Image formation

A

Light rays must be focused onto the retina (fovea)
Refraction occurs at the cornea (80%) and less (20%)

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23
Q

Degree of refraction is determined by

A

Difference in refractive indices betweween the two media. The angle at which light hits the interface between these two media.

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24
Q

Refractive index

A

essentially a measure of speed of light within it – so light moves quicker through air (1.0003) than the cornea (1.376) due to the increased density of the cornea.

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25
Q

Refraction by the cornea

A

occurs when light hits at an angle, light arrives at the cornea through air, but the cornea is mainly water.
Refraction occurs, light travels more slowly through water than air due to higher density.

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26
Q

Focal distance

A

Distance from refractive surface to vonvergence of parallel light rays.

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27
Q

Accommodation by the lens

A

Distant objects: almost parallel light rays, cornea provides sufficient refraction to focus them on the retina.

Closer Objects: light rays are not parallel, require additional refraction to focus them on the retina, rpovided by the fatterning of the lens.

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28
Q

Len - elasticity

A

Len has natural elasticity so if not stretched it will become more spherical.

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29
Q

Problem with focusing

A

eye is emmetropic when less is flat and we are focussing on a distant object

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30
Q

Laminar organisation of the retina

A

Layers organized in reference to center of the eye i.e. photoreceptors are in the outer layer. Outer layer of the retina (is closest to the inside of your head).

31
Q

Light - neural activity

A

Light focused on the retina must now be converted into neural activity. Light mus tpass through ganglion cels and bipolar cells before it reaches the photoreeptors.

32
Q

Light absorbtion through the retina

A

Light that asses throught the retina is absorbed by the pigmented epithalami.
Nuclear layers contain cell bodies, plexiform layers are regions where synaptic connections occur.

33
Q

Retina - Ganglion cells

A

output from retina

34
Q

Retina - Amarcrine cells

A

Modulate iformation transfer between GCs adn BCs

35
Q

Retina - Bipolar cells

A

connect photoreceptors to ganglion cells.

36
Q

Retina - Horizontal cells

A

Modulate information transfer between photoreceptors and BCs

37
Q

Retina - Photoreceptors [Short definition]

A

Sensory transducers both rods and cones

38
Q

Photoreceptors

A

Both have membraneous disk, inner segments: lots of mitochondria. Only graded potentials in photoreceptors.

Membranous disks contain light-sensitive photopigments that absorb light

39
Q

Duplicity theory

A

Can’t have high sensitivity and high resolution in single receptor. Seperate systems for monocrome and color

40
Q

Rod photoreceptors

A

Greater number of disks.
Higher photopigment concentration. 1000 times more sensitive to light than cones.

Enable vision in low light (scotopic) conditions i.e. at night-time. Low visual acuity/resolution

41
Q

Cone photoreceptors

A

Fewer disks.
used during daylight (photopic) conditions. Enable color vision, high visual acuity/resolution.
Low sensitivity

42
Q

Where are the cones and rods located

A

Mainly in the fovea

43
Q

Central retina

A

low convergence, low sensitivity, high resolution

44
Q

Peripheral retina

A

high convergence, high sensitivity, low resolution

45
Q

Scotpopic condition (wavelenght/visual)

A

night time. Rode photopigments (rhodopsin) most sensitive

46
Q

Photopic condition (wavelenght/visual)

A

Day-time. Cone photopigments:
3 cones: defined by what type of opsins they have Short (S): blue spectrum of light. Medium (M) cones, yellow, Long (L) cones.

High sensitivity to ligh tin middle and long cones => photopic ocndition is closer to 550m wavelenghts.

47
Q

Retinal ganglion photopigment

A

Melanopsin, sensitive to blue light

48
Q

Unusual photoreceptor cell property

A

Unusual cell property: photoreceptors are hyperpolarized by light. Photoreceptors are depolarized at rest.

49
Q

Rods (phototransduction)

A

dark/night-time.
cGMP-gated non-selective cation channels are open in the dark allowing a Na+ influx known as the dark current to depolarizes photoreceptors.

To maintain the Na gradeint, Na/K pump are found in the inner segment that removes Na in exchange for K.

50
Q

light’s affect on cGMP

A

Light dereases cGMP levels, closing the channels and preventing Na+ inflx, hypoerlarizing photoreceptors.

51
Q

Phototransduction (molecular level - rods)

A

Rhodopsin is activated by light. Stimulates the G-protein, transducin, to become transducin GTP.

The α subunit activates the enzyme phosphodiesterase (PDE). PDE reduces cGMP levels, closing Na+ channels
Signal amplification occurs as this is an enzyme cascade

52
Q

Saturation of resposne in bright light (differences in rods adn cones)

A

Rods cannot process bright light, they become saturated.Rhodopsin is bleached. cGMP levels are so low that noa dditional hyperpolarisation can occur.

Cones are not saturated as easily, so they are used in bright light.

53
Q

Ligth adaptation

A

Ohotoreceptors initially hyperpolarise greatly. Photoreceptors gradually depolarise with continued bright light.

54
Q

Does light adaptation require calcium?

A

In the dark: Ca2+ normally enters cells and blocks guanylyl cyclase. This reduces cGMP production, so closes some ion channels.
The CGMP keep broken down in the light, so you are getting less calcium.

In the light: Channels are shut so Ca2+ cannot enter cells. Block on guanylyl cyclase is released. More cGMP produced = more channels open.

55
Q

Why does calicuim mediates light adaptation?

A

to continued light stimulation

56
Q

Classification of bipolar cells

A

Based on bipolar response to glutamat.
Hyperpolarise: Off bipolar cells.
Depolarises: On biplar cells.

57
Q

Photoreceptors hyperpolarise to whaat?

A

Light, reduce glutamate release

58
Q

Receptive field - Retinal Ganglion cells

A

Will only fire action potentials when specific areas of retina are illuminated

59
Q

Biplar cells are organised how?

A

They have a center surround organization.
Take the information from multipole photoreceptors but not only they receive information from center organization.

60
Q

What is sound?

A

Particles of air moving back and forwards, hitting eachother.

61
Q

Rarefied air

A

low density

62
Q

Compressed air

A

High density

63
Q

What are the properties of sound?

A

Intenisty: Air pressure increases when there are more particles around and decreases when less air.
Air is compressed when pressure increase.

Frequency: Number of compressed or rarefied patches of air that pass by our ear each second, expressed as Hz.

64
Q

Phsyiological ranges of requency and intensity for humans

A

The Louder the sound is the air pressure difference between the compression and rarefied air is bigger

65
Q

Human hairing range

A

20Hz to 20,000 Hz

66
Q

Outer ear -

A

Helps know where the sound comes from. (behind/infront or below/above)

67
Q

Ossicles

A

Air filled with 3 ossicles (little bones)
Malleus, incus, stapes

68
Q

How does the middle ear transfer sound?

A

The oval would barely move if it was moved directly by sound due to the air fluid interface, as fluid has a greater inertia (impedance).
Impedance matching – air and water have different impedances: tendency of each medium to oppose movement brought about by a pressure wave.

69
Q

Ossicles amplify sounds

A

Exerts ~20 times more pressure on the oval window than on the tympanic membrane. Overcomes the greater impedance of cochlear fluid.

70
Q

What are hair bundles

A

are made of stereocilia and are located at the top (apical) part of the hair cells. Stereocilia connected by tip links.
Fluid moves in the air, the stereocilia move around.

Lechanoelectrical transducer channel, opens and depolareised hair cells: positive going in.

71
Q

Stapes moves outwards

A

Basilar membrane moves upwards, hair cells depolarise

72
Q

Stapes move inwards

A

Basilar membrane moves downards, hair cells hyperpolarise

73
Q

IHCs

A

Primary sensory receptors

BMS11004 (12 decks)

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