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BMS153 NEUROSCIENCE > the eye > Flashcards

the eye Flashcards

1
Q

where are the photoreceptors found

A

back of retina

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2
Q

cones for

A

perceive colour under norma lighting conditions

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3
Q

rods for

A

allow to see in dim light but not perception of colour

more of these than cones

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4
Q

fovea

A

no rods but many cones
5 million

provides highest acuity vision, and thus is at the centre of our gaze

retina is thinnest here

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5
Q

when light hits photoreceptors (cascade)

A

it interacts with photopigment

propagates the signal to bipolar cells which connect photoreceptors to ganglion cells

which leave the eye in a large cluster at the optic disc

after leaving the retina the ganglion cell fibres are called the optic nerve
(which carries visual into to visual cortex)

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6
Q

optic disc

A

no photoreceptors
so the retina cannot process visual info here - natural blind spot

origin of blood vessels and optic nerve, cannot sense light (no photoreceptors) lets blood vessels in and optic nerve in and out

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7
Q

other two types of cells in the retina

A

horizzontal and amacrine cells

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8
Q

horizontal cells

A

receive input from multiple photorepceotrs
integrate signalling from different populations of photorecpeot cells

make adjustments to the signals that will be sent to bipolar cells

and regulate acticivty in photoprepctos cells themsleves

Horizontal cells – input from and output to photoreceptors, output to bipolar cells

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9
Q

amacrine cells

A

reveice signals from bipolar cells and are involved in the regulation and integration of activity in bipolar and ganglion cells

Amacrine cells – input from bipolar cells, influence ganglion cells, bipolar cells and other amacrine cells

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10
Q

layers of nerve cells

A

ganglion cell layer

inner plexiform layer
inner nuclear layer
outer plexiform layer

outer nuclear layer

layer of photoreceptors

pigmented epithelium

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11
Q

bipolar cells

A

connect photoreceptors to ganglion cells

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12
Q

ganglion cells

A

output from retina

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13
Q

membranous discs in photoreceptors contain

A

light sensitive photopigments that absorb light

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14
Q

duplicity theory

A
  • can’t have high sensitivity and high resolution in single receptor
  • thus separate systems for monochrome and colour
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15
Q

rods structure

A

greater number of discs

higher photopigment conc

1000 times more sensitive to light than cones

vision in low light (scotopic)

low visual acuity /resolution

~92 million rods in each human retina

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16
Q

cones structure

A

fewer discs

used during daylight (photooptic)

enable colour vision

lower sensitivity

high visual acuity/resolutions

~5 million cones in the human retina

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17
Q

mesopic conditions

A

intermediate light conditions

both rods and cones used

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18
Q

central retina

A

low convergence and high resolution

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19
Q

peripheral retina

A

high convergence and low resolution

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20
Q

rod photopigment

A

rhodopsin

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21
Q

cone photopigments

A

three varieties of opsin (S, M and L

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22
Q

retinal ganglion photopigments

A

melanopsin

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23
Q

relative absorbance of human photo pigments

A

lower wave length to higher wave length

S cones
melanopsin
Rods
M cones 
L cones
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24
Q

phototransduction in the dark

A

rods are depolarised
due to influx of Na+
known as the dark current
maintained by cGMP (cyclic guanosine monophosphate)

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25
Q

phototransduction in the light

A

cGMP levels are decreased
Na+ channels close
Na+ influx is prevented
Rods are hyper polarised

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26
Q

refraction

A

Refraction occurs because the speed of light differs between mediums e.g. slower through water than air. The greater the difference in speed in the two media, the greater the angle of refraction. Refraction occurs towards a line that is perpendicular to the border.

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27
Q

absorption

A

transfer of light energy to a particle or surface
occurs in some retinal cells
Refraction

28
Q

light

A

Electromagnetic light travels in straight lines in a vacuum, known as rays, until it interacts with atoms and molecules

29
Q

PUPIL

A

lets light inside the eye

30
Q

iris

A

contains schinter muscles to control size

31
Q

cornea

A

glassy transparant covering the pupil and iris

32
Q

sclera

A

continuous with cornea forms the wall of the eyeball- protects it by coping with pressure

33
Q

extaocular muslces

A

move the eyeball (controlled by cranial nerve 3 ocular motor nerve and cranial nerve 4 tropclial nerve and abducens cranial nerve 6

34
Q

conjunctiva

A

membrane underneath eyelids that attached to the sclera (gets infected)

35
Q

optic enrve

A

carries axons from retina to brain

36
Q

strabismus

A

imbalance in the extracoular muscles

estropia- convergence of eyes (cross eyes)

exotropia - divergence of eyes wall-eyed.

37
Q

macula

A

region of retina for central vision, devoid of large blood vessels to improve vision quality because nothing distorts vision

38
Q

aqueous humour

A

watery fluid that provides nutrients to the cornea and lens

normally produced by the ciliary body and absorbed by the canal of Schlemm (between cornea and sclera)
contains nutrients e.g. glucose

39
Q

the lens

A

is suspended by zonal fibres (ligaments) which are attached to the ciliary muscles

40
Q

vitreous humour

A

a viscous fluid, keeps the eyeball spherical

41
Q

disorders of the aqueous humour

A

cateracts

glaucoma

42
Q

cateracts

A

clouding of the lens

can occur due to changes in the composition of the aqueous honour (lack of nutrients)

increased with age, smoking, diabetes mellitus

treament- artificial lens

43
Q

glaucoma

A

slowed uptake of aqueous humour to the canal of scheme leads to elevated intracellular pressure

causes compression of the optic nerve and reduced bloody supply to the retina

leads to a progressive loss f vision from periphery inwards

44
Q

image formation

A

light rays have to focus on the retina

achieved by refractive powers of the cornea- 80% of toal refraction

the lens- 20% of total refraction

higher the refractive index the slower the light will travel through

45
Q

refraction by the cornea

A

light arrives at the cornea though air but the cornea is mostly water

light travels more slowly through water than air– refraction occurs

46
Q

focal distance

A

distance from the refractive substance (the cornea) to where the parallel light rays converge.

47
Q

light rays from distant objects

A

are almost parallel by the time they reach the eye

48
Q

light rays from nearer objects

A

are not parallel, therefore require additional focussing power to focus them on the retina

49
Q

far point

A

ciliary muslces relax, zonal fibres stretch, lens flattens

50
Q

near point

A

ciliary mscles contract, less tension in zonal fibres, lens beomces more pserhical

51
Q

how to increase refractive power

A

rounding of the lends

ir has natural elasticity, so if not stretched it will become more spherical

52
Q

hyperopia

A

far sightedness, can’t see up close

resolved with a convex lens in front (can straighten out the light rays giving enough refractive power)

53
Q

myopia

A 
eyeball too long, 
short-sightedness 
cannot see far away
light rays are too parallel 
so converge before the retina

too much refractive power for size of eye ball
resolve by making eyes more divergent

54
Q

emmetropic

A

is a state in which the eye is relaxed and focused on an object more than 6 meters or 20 feet away. The light rays coming from that object are essentially parallel, and the rays are focused on the retina without effort.

55
Q

pupillary light reflex

A

Iris regulates light levelsPupillary constrictor (smooth circular muscle)Pupillary dilator (smooth radial muscle)

Enables us to adjust to changes in light intensity
Consensual light reflex i.e. occurs in both eyes even if only one is stimulated

56
Q

globe luxation

A

eye ball pop out

57
Q

3 wall layers

A

fibrous layer (contains connective tissue, white ‘sclera’, outermost part

vasucular

inner- transparent cornea window at front into eye

58
Q

walls of middle vascular layer contain

A

posterior choroid (membrane that supplies all layers with blood)

59
Q

anterior layer

A

ciliary body\ring of muscles tissue that surrounds lens

60
Q

retina’s 2 layers

A

1) outer layer- pigmented, absorbs light so doesn’t scatter around the eye ball

2) inner neural layer- contains photoreceptors
bipolar cells
ganglion cells

bipolar- syanpses at both ends- 1 end synapses with photoreceptor and other with ganglion cell

61
Q

ganglion cell

A

goes on to form optic nerve cranial nerve 2)

carries input to thalamus

and then visual cortex

62
Q

cones

A

sit near retina centre
detect fine details and colour

1) red 2) green 3) blue

only really reach their activation threshold in bright conditions

fewer compared to rods

each get their own personal ganglion cell
v detailed colour vision
carries inputs to thalamus and then visual cortex

63
Q

rods

A 
more numerous
more light sensitive 
only register scale of black and white
edges of the retina (rule peripheral vision)
lots connect to one ganglion cell
so brain can't tell which rods are activated 
can't give detail images
general shapes of objects
64
Q

after image

A

bright lights can means photoreceptors can keep sending action potentials even after image is switched off
cones can get tired- can receive some bright stimulus for too long– stop responding

65
Q

how is light reflected from objects only 3 meters from the eyes, focussed on the retina

A

the cornea enables the majority of the refraction and the fattened lens enables the remainder of the refraction that focusses the light onto the retina (generally when objects are less than 9 meters away)

cornea always provides the majority o the refractive power

66
Q

how does the lens become more spherical

A

This is achieved by contraction of the ciliary muscle which leads to slackening of the zonal fibres/suspensory ligament, reducing the pull on the lens and enabling it to assume its naturally spherical shape.

BMS153 NEUROSCIENCE (24 decks)

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