Brainscape's Knowledge GenomeTM

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


See full index

Neuroscience > The Visual System 1 & 2 > Flashcards

The Visual System 1 & 2 Flashcards

1
Q

importance of vision

A

detect prey, predators, mates
communicate
more than 1/3 neocortex involved in analysing visual world

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

light and eye

A

EM radiation that is visible
light has:
a wavelength - distance between peaks and troughs
a frequency - number of waves per second
an amplitude - difference between wave peak and trough

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

light and environment

A

optics
EM light travels in straight lines - rays - until it interacts with atoms and molecules
interact in 3 ways: reflection, absorption and refraction

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

pupil

A

lets light inside

black as all light absorbed

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

iris

A

contains muscles which control amount of light entering eye

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

cornea

A

glassy

transparent covering of pupil and iris that reflects light

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

sclera

A

continuous with cornea

forms tough proctective wall of eyeball to give shape

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

extraocular muscles

A

move eyeball

controlled by oculomotor nerve (CN III)

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

optic nerve

A

CNII - sensory

carries axons from retina to brain

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

opthalmoscope

A

to see blood vessels
optic disk - blind spot, origin of blood vessels and optic nerve, cannot sense light
macula - region of retina for central vision, devoid of large blood vessels to improve visual quality
fovea - retina is thinnest here and is area of highest visual acuity

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

cross section of eye

A

retina - contains sensory receptor cells and afferent receptors
lens - suspended by zonal fibres - ligaments - which are attached to ciliary muscle, enabling stretching of lens
2 solutions in eye:
aqueous humor - provides cornea with nutrients
vitreous humor - provides structure and pressure outwards

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

image formation

A

light rays must be focussed on retina - ideally fovea

refraction occurs at: cornea - 80%, lens - 20%

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

degree of refraction determined by

A

difference in refractive indices between the 2 media

angle at which light hits the interface between 2 media

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

refraction by the cornea

A

light arrives through air but cornea is mainly water
light travels mroe slowly through water than air due to hgiher density = refraction occurs
distance from refractive surface to convergence of parallel light rays = focal distance

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

accommodation by the lens

A

distant object
- almost parallel light rays
- cornea provides sufficient refraction to focus them on retina
closer objects
- light rays arent parallel
- requires additional refrection to focus them on retina
- provided by the fattening of the lens

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

rounding of lens:

A

increases refractive power to focus closer objects on fovea

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

problems with focussing

A

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

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

farsightedness

A

eye is too short
near objects are focussed behind retina
not enough refraction

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

nearsightedness

A

eye is too long
distant objects are focussed before retina
too much refraction

20
Q

eye summary

A

cornea focus most of light on fovea of retina due to power of refraction
closer objects require additional refraction achieved by accommodation of lens which is regulated by contraction and relaxation of ciliary muscle

21
Q

laminar organisation of retina

A

light focused on retina must now be converted into neural activity
light must pass through ganglion cells and bipolar cells before ti reaches photoreceptors
light that passes all the way through retina is absorbed by the pigmented epithelium

22
Q

layers of retina

A

ganglion cell layer - inner layer, action potentials
inner layers - graded potentials
pigmented epithelium - outer layer

23
Q

cells of retina

ganglion

A

output from retina

24
Q

cells of retina

amacrine

A

modulate info transfer between ganglion cells and bipolar cells

25
Q

cells of retina

bipolar cells

A

connect photoreceptors to ganglion cells

26
Q

cells of retina

horizontal cells

A

modulate info transfer between photoreceptors and bipolar cells

27
Q

cells of retina

photoreceptors

A

sensory transducers, both rods and cones

28
Q

photoreceptors

A

membranous discs contain light sensitive photoreceptors that absorb light
lots of mitochondria - active transport to balance depolarisation

29
Q

phototransduction occurs in:

A

rod

30
Q

duplicity theory

A

cant have high sensitivity and high resolution in single receptor
separate systems of monochrome and colour

31
Q

rod photoreceptors

A 
greater number of discs
higher photopigment concentration
1000x more sensitive to light than cones
enable vision in low light (scotopic)
low visual acuity/resolution
32
Q

cone photoreceptors

A 
fewer discs
used in daylight (photopic)
colour vision
high visual acuity/resolution
lowr sensitivity
33
Q

retinal structure varies with region

A

fovea contains most of 5 million cones and no rods

34
Q

central retina

A

low convergence, low sensitivity and high resolution

35
Q

peripheral retina

A

high convergence, high sensitivity and low resolution

36
Q

absorbance spectra in humans

A

rod photopigment = rhodopsin, in dark conditions (scotopic) optium wavelength of light = 500nm
cone photopigment = three varieties of opsin - Short cones, Medium and Long cones, in light conditions optium = 560nm
retinal ganglion photopigment = melanopsin

37
Q

photoreceptors are hyperpolarised by light

A

resting pot = -30mv (in dark)
in a rod in the dark - molecule called cGMP - free in cytoplasm, capable of binding to channel in cell membrane and it opens - intracellular ligand = causes pore to open and Na comes in known as dark current. = depolarises photoreceptors
K channels further up cells to stop over depolarisation
in light - channels are shut, light decrease cGMP levels closing channels and preventing Na influx = hyperpolarisation as K channel doesnt shut

38
Q

phototransduction

A

5-7 photons can evoke a sensation of light in humans
in membrane of disc molecules like rhodopsin live
e.g. rhodopsin is made of an opsin (GPCR) and retinal
opsin varies in each cones
retinal stays the same
light comes in and makes retinal change confirmation which changes opsin
leads to activation of transducin (G protein mage of a, b, g subunits)
in membrane also = phosphodiesterase
wehn transducin is activated, alpha subunit moves to actiate phophodiesterase and it becomes activated
so cGMP gets broken down to GMP = changes amount of open channels in membrane
in dark Na moves in through cGMP channel, but since no GMP - channel closes - in light

39
Q

signal amplification

A

1 photon being absorbed by rhodopsin can lead to 1,400 molecules of cGMP being broken down = 1,000,000 Na ions not moving in

40
Q

saturation of responses in bright light

A

rods cannot process bright light as they become saturated easily
rhodopsin becomes bleached, cGMP levels are so low that no additional hyperpolarisation can occur
cones are not saturated easily, so are used in bright light
on a graph - saturation peak around -65 but plateu becomes longer

41
Q

light adaptation

A

photoreceptors initially hyper polarise greatly

photoreceptors gradually depolarise with continued bright light

42
Q

light adaptation requires calcium

A

in the dark:
Ca normally enters cells and blocks guanylyl cyclase from making more cGMP
this reduces cGMP production, so closes some ion channels
in the light:
channels are blocked due to signalling cascade
Ca cant enter cell
guanylyl cyclase isnt inhibited so cGMP can start binding to channels and opening them
this causes membrane potnetial to return to depolarised level

43
Q

downstream of photoreceptors

A

there are different types of bipolar cells
bipolar cells have complex receptive fields
have on and off bipolar cells

44
Q

on and off bipolar cells

A

classified based on responses to glutamate
photoreceptor hyperpolarises to light = reduced glutamate release
some bipolar cells hyperpolarises = OFF bipolar cell e.g. switched off by light
some depolarise = ON bipolar cell e.g. switched on my light

45
Q

bipolar cells use different receptors

A

OFF uses ionotropic glutamate receptors, when glutamate binds, pore opens and positive ions move into cell = why they depolarise in dark
ON uses metabrotropic cells, in dark release glutamate and binds to inhibitory metabotropic receptor = hyperpolarises, in light = less activation of inhibition

46
Q

the receptive field

A

retinal ganglion cells will only fire action potentials when specifc areas of the retina are illuminated

Neuroscience (21 decks)

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