46 & 47 Physiology of visual sensation

Question 1

What is the unit of power and what is its equation?

Answer 1

power = 1/focal length (diopter)

Question 2

What is focal length?

Answer 2

The length between the focal point (fovea) and the lens

Question 3

The higher the refractive power, the shorter/longer the focal length.

Answer 3

shorter

Question 4

How is accommodation achieved when a person switches to view a near object?

Answer 4

• lateral geniculate nucleus > blurred image perceived in visual cortex > recognised as out of focus > signals from cortex to brainstem at Edinger-Westphal nucleus > signals to ciliary ganglion > ciliary muscles contract > zonular fibers slacken > lens rounded

Question 5

What is the range of accommodation?

Answer 5

Near point - far point

Question 6

In presbyopia, the range of accommodation increases/decreases because?

Answer 6

decreases;

the near point is too far

Question 7

What happens to the near point and far point in myopia?

Answer 7

both too near ;

far point too near is the culprit

Question 8

What lens shall be worn in myopia?

Answer 8

Concave lens

Question 9

When should convex lens be worn?

Answer 9

Hyperopia / Presbyopia

Question 10

What happen to the near point and far point in hyperopia?

Answer 10

near point too far

far point too far (but can be compensated by accommodation

Question 11

Which are the 5 major layers in the retina?

Answer 11

1. Outer nuclear layer
2. Outer plexiform layer
3. Inner nuclear layer
4. Inner plexiform layer
5. Ganglion cell layer

Question 12

In the ______________ layer, retinal ganglion cells make synaptic contacts with bipolar cells and amacrine cells.

Answer 12

inner plexiform

Question 13

In the inner plexiform layer: retinal ganglion cells make synaptic contacts with __________ and __________.

Answer 13

Bipolar cells and amacrine cells

Question 14

Light passes through the layers before/after reaching the photoreceptors.

Answer 14

before

Question 15

Information is modulated by ______________ cells in the ___________layer and are relayed to bipolar cells, then the retinal ganglion cells.

Answer 15

horizontal;

outer plexiform

Question 16

Connection of cone to ganglion cell results in small/big receptive field, and low/high visual acuity.

Answer 16

small; high

Question 17

Multiple rods converging to a single ganglion cell result in a small/big receptive field, and low/high visual acuity.

Answer 17

big; low

Question 18

Photoreceptors have an outer segment which contain the _________________ located on a stack of membranous discs.

Answer 18

photosensitive pigment

Question 19

Rods contains ____________ which contributes to its high sensitivity to light.

Answer 19

rhodopsin

Question 20

Cones contains ___________ thus they have lower sensitivity to light.

Answer 20

Iodopsin

Question 21

Cones are chromatic because?

Answer 21

They have multiple types of iodopsins

Question 22

Which type of photoreceptors have higher convergence of retinal ganglion cells?
This results in lower/higher spatial resolution.

Answer 22

Rods;
Cones: one receptive field connect to one retinal cell only ;
lower

Question 23

Which type of photoreceptors is shorter, thicker and tapered?

Answer 23

Cones

rods: long, thin, cylindrical

Question 24

Single pigment system cannot differentiate colours because both _________ and _____________affects the response.

Answer 24

wavelength and intensity

Question 25

Humans have 3 types of cones, which type is much fewer in number than the other 2?

Answer 25

Blue cones

Question 26

Give the 4 possibilities of color weakness.

Answer 26

1. Absence of cones 2. Just one cone available (monochromatism) 3. 3rd cone missing (dichromatism) 4. Abnormality in photopigment (anomalous trichromatism)

Question 27

Red-green color weakness is more/less common than blue color weakness, and is more frequent in males/females.

Answer 27

more; males

Question 28

Subtypes of common colour weakness can be tested with the ______________.

Answer 28

Ishihara chart

Question 29

In the absence of light, the membrane is _______________ due to _______________. __________ pump maintains the concentration gradient

Answer 29

depolarised; high level of Na+ current flowing into the outer segment.; Na/K+ pump

Question 30

In bright light, the membrane is more _____________, because _________________.

Answer 30

hyperpolarized,; | the Na+ channels are closed

Question 31

Give the flow of events happening when light is shone on the retina.

Answer 31

Light activates transducin (G-protein) > activates cGMP phosphodiesterase > break down cGMP > Na+ channels close > membrane hyperpolarization > less glutamate release

Question 32

The Na+ channels in the membrane is kept opened by?

Answer 32

cGMP

Question 33

Glutamate is inhibitory to ___________ cells.

Answer 33

On center bipolar cells

Question 34

Glutamate is excitatory to _____________ cells.

Answer 34

Off center bipolar cells

Question 35

Surround photoreceptors are associated with _________ cell. In dark light, it will cause ___________ to photoreceptor, and more/less glutamate release from the photoreceptor to the __________ cell. The __________ cell in turn release more/less inhibitory NT , causing the on center// off center bipolar cell to __________ respectively.

Answer 35

``` horizontal; depolarization; more; horizontal; horizontal; more; ``` less glutamate release on center: depolarised; off center: hyperpolarized

Question 36

Retinal ganglion cells with small receptive fields (P cells) receiving main inputs from _________ cells are concentrated in the _______.

Answer 36

cones; | fovea

Question 37

Retinal ganglion cells with ________ receptive fields (__ cells)are found more in the periphery.

Answer 37

large; | M

Question 38

What type of retinal ganglion cell is intrinsically sensitive to light ? It plays a role in ____________ by their direct projection to the ___________ nucleus of the hypothalamus, also mediating light reflex.

Answer 38

Photosensitive melanopsin; circadian rhythm; suprachiasmatic

Question 39

State the route of the visual pathway from nerve fibers leaving the eye to the cortex.

Answer 39

> Optic chiasm > cross-over medial bundles > lateral geniculate nuclei > optic radiation > primary visual cortex (V1)

Question 40

_____________ cells project to the parvocellular layers of the lateral geniculate nucleus consisting of small cells.

Answer 40

Retinal P cells

Question 41

M cells project to ____________ layers of the lateral geniculate nucleus consisting of larger cells.

Answer 41

Magnocellular

Question 42

Majority of neurons in primary visual cortex are specialized in detecting ________________ and their _________, and properties like color.

Answer 42

line contrast of specific orientation; | movements

Question 43

Neurons in primary visual cortex are named ________ cells.

Answer 43

Simple and complex

Question 44

Contour detection by the primary visual cortex is achieved by convergence of inputs from the ______________ into _____________.

Answer 44

Lateral genicular nucleus nuerons into one simple cell in V1

Question 45

What are complex cells?

Answer 45

While simple cells respond maximally to a bar at a preferred orientation in a specific location, one type of complex cells have a larger receptive field which are orientation-sensitive but location-insensitive

Question 46

__________________ represents the initial site of analysis of visual images.

Answer 46

Primary visual cortex (V1, area 17)

Question 47

The primary visual cortex projects to the ____________________ for further visual processing, from there to visual association cortex and higher visual areas.

Answer 47

Extrastriae visual cortex

Question 48

What does the dorsal stream detect and via what to reach its final destination?

Answer 48

Where?; | via middle temporal visual area (V5) to the posterior parietal cortex.

Question 49

What is V5? Which pathway is it involved? | Lesion?

Answer 49

``` Middle temporal (MT) visual area; dorsal pathway (where); V5: for analysis of motion, seeing world in series of snapshots ```

Question 50

What will happen with damage to the parietal lobe?

Answer 50

Hemineglect syndrome, tendency to ignore the contralateral side.

Question 51

What does the ventral stream detect and via what to reach its final destination?

Answer 51

What? | via V4 to the inferior temporal cortex

Question 52

Function of fusiform gyrus? | Neurons there have small/large receptor field, therefore?

Answer 52

recognition of face; | large, can code an code different sizes of the faces reflecting different distance from the subject

Question 53

Spatial orientation, depth perception, location of objects is detected in which pathway?

Answer 53

Where pathway | also movement of objects

Question 54

What pathway detects what features of vision?

Answer 54

Color and shape, important in language ability.

Question 55

Describe the flow of events in pupillary reflex.

Answer 55

When light shines onto retina > signals project to pretectal area > Edinger-Westphal nucleus > send out to contract the sphincter muscles > decrease size of pupil

Question 56

Why pupillary reflex is consensual?

Answer 56

Due to the bilateral projection of the pretectal nucleus of one side to Edinger-Westphal nucleus on both sides.

Question 57

Briefly describe what is glaucoma.

Answer 57

Excess aqeuous fluid in anterior chamber of the eye, retinal ganglion cells and axons degenerates, causing tunnel vision then blindness

Question 58

How can cataract be treated?

Answer 58

Lens become cloudy, replacement by artificial lens.

Question 59

What is macular degeneration? Will it cause whole-blindness?

Answer 59

Atrophy of neural tissue or severe haemorrhage diseases at the macula (includes fovea). No, peripheral vision is not affected.

Question 60

_____________ is progressive degeneration of the retina resulting from diabetes mellitus. Blood vessels burst and neural cells die.

Answer 60

Diebetic retinopathy

Question 61

In retinal detachment, _______ becomes separated from the _________.

Answer 61

Retina; choroid