visual pathways

Question 1

what is vision?

Answer 1

detecting and interpreting patterns of electromagnetic radiation to make sense of the world

differences in intensity and wavelength (colours)

Question 2

how did eyes evolve?

Answer 2

sequence of improvements for detecting directions and forming an image

Question 3

how do the eyes respond to darkness?

Answer 3

SCN instructs production of melatonin to promote sleep

keep circadian clock accurately timed

Question 4

what are M1 and M2?

what do they do?

what do their axons form?

Answer 4

photosensitive retinal ganglion cells which detect light so affect sleep-wake cycle

send action potentials to the brain

axons form optic nerves

Question 5

what does exposure to blue light do?

Answer 5

increases alterness and stimulation of cognitive functions

e.g from a phone screen

Question 6

what is melanopsin?

Answer 6

light-sensitive receptor molecule

Question 7

what does vision require?

Answer 7

forming and processing an image in the eye

Question 8

what do rod and cone cells form in the retina?

Answer 8

an array

Question 9

steps of image processing?

Answer 9

light passes through cornea, acqueous humor, lens and vitreous humor on the way to retina

refracted at each boundary

accommodation of lens to focus image

Question 10

role of lens?

Answer 10

focus image

Question 11

role of iris?

Answer 11

aperture to control light entering

Question 12

role of photoreceptors?

Answer 12

pixels to register image

Question 13

role of glass body, macula and pigment?

Answer 13

filtering media

Question 14

role of cornea?

Answer 14

filter to protect lens

Question 15

role of eye lid?

Answer 15

lens cover for when not in use

Question 16

role of tears?

Answer 16

cleaning mechanism

Question 17

role of retinal interneurons?

Answer 17

processing algorithms

Question 18

relationship between closeness of object and lens shape?

what is the process of changing strength of lens?

Answer 18

nearer the object, the stronger the lens needed to form a focussed image so becomes larger

accomodation

Question 19

alternative names for near and far sightedness?

Answer 19

near: myopia
far: hyperopia

Question 20

what does the fovea do and what is it ?

Answer 20

collects info about the visual scene

central portion of retina with most photreceptors and so center of our gaze

Question 21

eye movements when making a cup of tea?

Answer 21

saccades in anticipation of next movement

moved to particular locations when eyes engaged in visual search and more precise if know where objects were

eyes disengaged from fixating before an action was completed

Question 22

what can movement be described as?

Answer 22

combination of 3 directions of translation and 3 directions of rotation

yaw - rotation around z axis
roll - x axis
pitch - y axis

Question 23

what are saccades?

Answer 23

move eye very quickly to new position between periods of gaze stabilisation (fixation) to scan scene across whole field of view

direct fovea to collect info about the visual scene

Question 24

what are smooth pursuit movements?

Answer 24

slower and keeps a moving stimulus on fovea

Question 25

what is Optokynetic nystagmus?

Answer 25

brings eye back from a peripheral to more central position after it has followed a large-scale moving stimulus

Question 26

what is

Vestibulo-ocular movements?

Answer 26

compensate for the movement of the head by moving the eye the same distance but in the opposite direction in order to maintain a constant field of view

Question 27

where does conscious and automatic control of eye movements come from?

Answer 27

conscious - cortical frontal eye fields (FEF)

automatic - superior colliculus

Question 28

what are 3 similarities between rod and cone receptors?

Answer 28

both detect light in basically the same way

both recover rapidly from change

have graded responses

Question 29

difference between rods and cones?

Answer 29

cones

• specialised for vision during the day
• smaller than rod cells and contain less photopigment per cell
• situated in fovea

rod cells

• specialised for vision during the night as have high sensensitivity to dim light
• larger than cone cells and contain large amounts of photopigment
• don’t use central fovea (no rods in fovea only periphery) as acuity (clarity) sacrificed for high sensitivity

Question 30

what does light cause in receptor membrane?

Answer 30

hyperpolarisation (decrease in membrane potential) of receptor membrane (not depolarisation)

Question 31

what is opsin?

Answer 31

light-sensitive protein in membrane of photoreceptors (photopigment)

Question 32

difference between cones and rods in terms of opsins?

Answer 32

cone opsins differ in wavelength-specific affinity to light (as 3 classes of cones and opsin) so only 1 opsin type expressed per cone

all rods express the same type of opsin

Question 33

what activates G protein?

Answer 33

conformational change in rhodopsin

Question 34

what does activated rhodopsin cause?

Answer 34

activates messenger (transducin)

causes Na channels to close

membrane therefore becomes more polarised

Question 35

what are the major 2 pathways for vision?

what are they?

Answer 35

1. Geniculate-striate pathway - 90% of retinal projections
2. Extrageniculate pathway

projections from retina to other brain areas

Question 36

what is the role of the extrageniculate pathway?

Answer 36

via superior collilculus

important for eye movements and visual attention

Question 37

what does the high density of cones in V1 tell us?

Answer 37

that more processing power is required for info originating from the fovea

requires higher acuity

Question 38

what does damage to V1 cause?

Answer 38

cortical blindness

Question 39

what is visual transduction?

Answer 39

process by which light is converted into electrical signals in rod, cone and photosensitive genglion cells in the retina of the eye