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BMS153 NEUROSCIENCE > the eye > Flashcards

the eye Flashcards

(66 cards)

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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
phototransduction in the light
cGMP levels are decreased Na+ channels close Na+ influx is prevented Rods are hyper polarised
26
refraction
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.
27
absorption
transfer of light energy to a particle or surface occurs in some retinal cells Refraction
28
light
Electromagnetic light travels in straight lines in a vacuum, known as rays, until it interacts with atoms and molecules
29
PUPIL
lets light inside the eye
30
iris
contains schinter muscles to control size
31
cornea
glassy transparant covering the pupil and iris
32
sclera
continuous with cornea forms the wall of the eyeball- protects it by coping with pressure
33
extaocular muslces
move the eyeball (controlled by cranial nerve 3 ocular motor nerve and cranial nerve 4 tropclial nerve and abducens cranial nerve 6
34
conjunctiva
membrane underneath eyelids that attached to the sclera (gets infected)
35
optic enrve
carries axons from retina to brain
36
strabismus
imbalance in the extracoular muscles estropia- convergence of eyes (cross eyes) exotropia - divergence of eyes wall-eyed.
37
macula
region of retina for central vision, devoid of large blood vessels to improve vision quality because nothing distorts vision
38
aqueous humour
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
the lens
is suspended by zonal fibres (ligaments) which are attached to the ciliary muscles
40
vitreous humour
a viscous fluid, keeps the eyeball spherical
41
disorders of the aqueous humour
cateracts glaucoma
42
cateracts
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
glaucoma
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
image formation
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
refraction by the cornea
light arrives at the cornea though air but the cornea is mostly water light travels more slowly through water than air-- refraction occurs
46
focal distance
distance from the refractive substance (the cornea) to where the parallel light rays converge.
47
light rays from distant objects
are almost parallel by the time they reach the eye
48
light rays from nearer objects
are not parallel, therefore require additional focussing power to focus them on the retina
49
far point
ciliary muslces relax, zonal fibres stretch, lens flattens
50
near point
ciliary mscles contract, less tension in zonal fibres, lens beomces more pserhical
51
how to increase refractive power
rounding of the lends ir has natural elasticity, so if not stretched it will become more spherical
52
hyperopia
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
myopia
``` 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
emmetropic
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
pupillary light reflex
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
globe luxation
eye ball pop out
57
3 wall layers
fibrous layer (contains connective tissue, white 'sclera', outermost part vasucular inner- transparent cornea window at front into eye
58
walls of middle vascular layer contain
posterior choroid (membrane that supplies all layers with blood)
59
anterior layer
ciliary body\ring of muscles tissue that surrounds lens
60
retina's 2 layers
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
ganglion cell
goes on to form optic nerve cranial nerve 2) carries input to thalamus and then visual cortex
62
cones
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
rods
``` 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
after image
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
how is light reflected from objects only 3 meters from the eyes, focussed on the retina
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
how does the lens become more spherical
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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