Bb W3 Physiology Of The Visual System

Front 1

What would be considered the box and window of the eyes

Back 1

Scalera and cornea

Front 2

Characteristics of the sclera

Back 2

- opaque
- protects the eye
– Ankers extrinsic muscles
– Continues with dura where the optic nerve enters

Front 3

Characteristics of the cornea

Back 3

– Transparent
– lets light enter the eye
– Many nerve endings [pain receptors]

Front 4

What are the three layers of the ocular apparatus

Back 4

– Outer layer
– Middle layer [Uvea]
– Inner layer

Front 5

What are the components of the outer layer

Back 5

– Schlera
– Cornea

Front 6

What are the components of the middle layer

Back 6

– Choroid
– Ciliary body
– Suspensory ligament
– Lens
– Iris
– Pupol

Front 7

Function of Choroid

Back 7

– Pigmented layer
– Reduces light scatter within the eye

Front 8

Which structures are part of the focus mechanism

Back 8

– Ciliary body [smooth muscle, maintains tension on the ligaments and changes SHAPE of lens]
– Suspensory ligament [Extends from ciliary body to the lens]
– Lens [Acellular, vascular translucent structure, changes FOCAL LENGTH]

Front 9

Which structures are part of the aperture mechanism

Back 9

Shutter = Iris [Pigmented part of the eye between the cornea and the lens]
Aperature = Pupil [Regulates amount of light entering eye]

Front 10

What are the components of the inner layer (retina)

Back 10

– Retinal pigment epithelium
– Retina [photoreceptors and neurons]

Front 11

Describe the outer pigmented layer of the retina

Back 11

Absorbs light and prevented from scattering

Front 12

Describe that inner neural layer of the retina

Back 12

Contains photoreceptors [Rods and cones] and neuron [bipolar cells, amacrine cells and ganglion cells]

Front 13

Blood supply to eye and it's divisions

Back 13

Ophthalmic artery
– Posterior ciliary arteries: supplies outer Redknot and optic disc [choroidal circulation]
– Central retinal artery: Supplies inner retina

Front 14

Scotopic vision: characteristics

Back 14

– photoreceptors = rods
– High sensitivity in dark
– Saturate as light increases
– Low spatial resolution

Front 15

Low versus high spatial resolution

Back 15

Low: input from MANY rods are summated by one bipolar, so cells can't easily tell where input is coming from

High: each con synapses with ONE single bipolar self

Front 16

Phototopic vision: characteristics

Back 16

– Photoreceptors: cones
– Best in bright light
– Adapt to background to give wide dynamic range
– Color vision
– High spatial resolution

Front 17

Three types of cones + wavelengths of each

Back 17

Classified based on type of photo pigment [opsin]
– R (long - 564nm peak sensitivity)
– G (medium - 534nm)
– B (short - 420nm)

Front 18

Components that make up photo pigments

Back 18

– Opsin
– Retinal [vitamin a derived molecule]

Front 19

Describe steps of photo transduction

Back 19

1) Light [a photon] converts 11– cis-retinal to all-trans-retinal causing a change in shape of the photo pigment
2) Activation of the 100 molecules a G-protein transducin
3) Each transducin will activate a cGMP phosphodiesterase molecule
4) Each phosphodiesterase breaks down 1000 molecules of cGMP
5) Closure of sodium channels in the cell membrane
6) Hyperpolarization of cell

Front 20

Distribution of photoreceptors in the fovea

Back 20

– Center of retina
– Highest resolution
– Only cones

Front 21

Distribution of photoreceptors in the periphery

Back 21

– Both rods and cones
– Decline with increasing eccentricity

Front 22

What is the physiological blind spot

Back 22

Area on retina with no photoreceptors called the optic disc.
– Located near optic nerve entry

Front 23

What is the three neuron relay

Back 23

photoreceptor --> bipolar cell --> retinal ganglion cell --> lateral geniculate nucleus (LGN) and optic radiation

Front 24

Characteristics of bipolar cells

Back 24

– Separate bipolar cells for rods and cones
– Receive input from horizontal and amacrine cells in the retina

Front 25

Signal transduction from photoreceptor to bipolar cell

Back 25

1. hyperpolarization of photoreceptor decreases release of glutamate
2. OFF cone bipolar cells are hyperpolarized by this decrease
3. ON cone bipolar cells are depolarized
4. result is a graded excitatory postsynaptic potential (EPSP)
5. release of glutamate and activation of retinal ganglion cell

Front 26

ON versus OFF bipolar cells

Back 26

ON cells are inhibited by glutamate, hence light which reduces glutamate release causes ON cells to become active --> EPSP

OFF cells are excited by glutamate --> no EPSP

Front 27

Described lateral inhibition

Back 27

– Bipolar cells receive inputs from horizontal and amacrine cells in the retina that create lateral inhibition by light in neighboring regions of the retina --> stronger response by central cell
– This gives rise to the "center surround" receptive field organization evident in the retinal ganglion cells to which bipolar cells project

Front 28

Two most important types of retinal ganglion cells

Back 28

– Magnocellular RGC (LARGE)
– Parvocellular RGC (small)

Front 29

Characteristics of magnocellular RGC

Back 29

– Large cell bodies and long dendrites
– Large receptive fields
– Low spatial resolution
– Respond transiently to onset and offset a flight [high temporel resolution]

Front 30

Characteristics of parvocellular RGC

Back 30

– Small cell bodies
– Short dendrites
– Small receptive fields
– High spatial resolution
– Sustained response to onset of light [low temporal resolution]

Front 31

What is color oponency

Back 31

Some cones prefer to be fired by red colours, but will still fire less strongly for green objects.
What is important is to compare what is going on in green cone vs red cone.
Any one cone by itself can’t tell you what colour is out there, it only tells the colour by comparing what is going on with another cone (in that region) with a different wavelength

Front 32

Central scotoma

Back 32

–slicing of arching fibers coming from retina towards optic disc
– As fovea is located in the center of eye, this will create a blind spot in the areas from which the fibers originated

Front 33

Ceca-Central scotoma

Back 33

– Cutting of fibers coming from fovea almost at entrance to optic disc
– Would result in merging of physiological blind spot with pathological blind spot

Front 34

(Nasal) Arcuate defect

Back 34

– Severing of fibers that have a rainbow arch shape
– Arch starts from one spot and moves nasally
– Would present a problem in your Temporel visual field

Front 35

(Temporal) Wedge Defect

Back 35

– Fibers leaving blank spot and moving superiorly are cut
– Will result in a wedge defect on your lower visual field

Front 36

Describe the path of fibers leaving the RGC and moving towards the brain

Back 36

– RGC gather together at the optic disc to form the optic nerve
– Optic nerves pass into the cranium through the optic canal
– Converge above the pituitary at the optic chiasm
– Axons from the nasal half of each retine (temporal hemifeild) decussate in this structure
– Optic track continues from Arctic has, but now each tract presents information from the contralateral nasal hemifield of each eye
– Track terminates in the LGN

Front 37

Is that optic nerve part of the peripheral or central nervous system?

Back 37

- Optic nerve is actually component of the central nervous system
- it's myelin is produced by oligodendrocytes

Front 38

Possible destinations for axons traveling in the optic nerve

Back 38

– Striate cortex
– Preoptic nucleus
– Superior caliculus
– Nucleus of the optic tract and accessory optics system
– Suprachiasmatic nuclei

Front 39

Role of preoptic nuclei

Back 39

Pupil light reflex
(pretectal nuclei in midbrain)

Front 40

Role of superior caliculus

Back 40

Guide rapid eye and head orientation [mediates reflective eye movements]

Front 41

The role of nucleus of optic tract and accessory optics system

Back 41

Supplement vestibular information innkeeping gaze stable

Front 42

Role of suprachiasmatic nuclei

Back 42

Diurnal regulation of homeostasis [regulates sleep/wake cycles]
Located in hypothalamus

Front 43

Bilateral hemianopia

Back 43

– Caused by lesions in the optic chiasm
– Almost always due to compression by a mass, often a pituitary tumor

Front 44

Homonymous hemianopia

Back 44

– Caused by lesions of the optic tract
– Usually partial
- Usually incongruous [different and extent between the two arts]

Front 45

What would be observed in an endoscopy in loss of supply to inner retinal artery

Back 45

If you lose blood supply to central retinal artery you will lose supply to inner retinal layer resulting in grayness with cherry red spot

Front 46

Describe the layers of the lateral geniculate nucleus

Back 46

– 4 where Parkthrough cellular RGC axons terminate
– 2 where magnocellular RGC terminate
– Organize in` alternation

Front 47

Cortical input to LGN

Back 47

LGN is modulated by cortical input, which may refine perception and mediate effects of visual attention

Front 48

Retinotopic (spatial) arrangerment

Back 48

– Central field in lateral aspect of mid radiation
– Lower field in upper radiation
– Upper field in lower radiation

Front 49

Meyer's loop

Back 49

Forward growth of the anterior horn of the lateral ventricle during development has displaced the lower fibers [from the upper retina] anteriorly, to form the Meyer's loop

Front 50

Magnocellular information from CONTRALATERAL eye terminates in which layer of the LGN

Back 50

1

Front 51

Magnocellular information from IPSILATERAL eye terminates in which layer of the LGN

Back 51

2

Front 52

Parvocellular information from CONTRALATERAL eye terminates in which layer of the LGN

Back 52

4, 6

Front 53

Parvocellular information from IPSILATERAL eye terminates in which layer of the LGN

Back 53

3, 5

Front 54

From the LGN where does the information go

Back 54

To the visual cortex via optic radiations

Front 55

Other names for the visual cortex

Back 55

– Striated cortex
– VI
– Calacrine

Front 56

Define: retinotopic

Back 56

Specific for location of stimulus on retina

Front 57

Describes a highly retinotopic representation of the striated cortex

Back 57

– Fovea at the occipital pole/peripheral field just posterior to parieto-occipital fissure
– lower field in upper calacrine bank/ upper field in lower calacrine bank

Front 58

Homonynous superior quadrartanopia

Back 58

caused by lesions in meyer's loop

– Commonly seen after Temporel lobectomy done to treat epilepsy

Front 59

Describe the processing that occurs in the striated cortex

Back 59

Instead of spots of light, information is starting to be represented as linear segments and boundaries
– Cells have preference for lines of a specific orientation
– Lines are organize in a regular array of orientation columns

Front 60

Cortical magnification

Back 60

Refers to the fact that more is devoted to central vision and prayerful vision

Front 61

Described the defects that would occur as a result of lesions in the following areas of the striated cortex:
Occipital pole
Everything but the pool
Superior bank
Inferior bank

Back 61

Occipital pole : Hemi-central scotoma
Everything but the pool: macula sparing hemianopia
Superior bank: inferior quadrantanopia
Inferior bank: Superior quadrantanopia [can be confusing deletions of meyer's loop]

Front 62

Describe the extra-striated cortex

Back 62

- After V1, visual information fence out into large array of additional cortical regions arranged in a hierarchy
– Ascending the hierarchy, information becomes less retinotopic and more specific for other special visual property

Front 63

The extrastriate array can be divided into 2 broad streams

Back 63

WHERE stream: Dorsal [ occipito-parietal]
WHAT stream: Ventral [ occipito-temporal]

Front 64

Role of dorsal stream

Back 64

– Motion processing
– Depth perception
– Visual spatial data for attention
– Eye and hand movement

Front 65

Role of central stream

Back 65

– Color processing
– Object recognition [example words and faces]

Front 66

Define: Akinetopsia

Back 66

Problem seeing motion [rare]

Front 67

Define: Asteropsis

Back 67

Neglect for the opposite side of space

Front 68

Balint's syndrome

Back 68

Ocular motor apraxia = Poor targeting of eye movements to targets

Front 69

Define: Optic Ataxis

Back 69

Misreaching for visual objects

Front 70

Define: Simultangnosia

Back 70

Inability to attend to more than one object at a time

Front 71

Legions of various components of the dorsal stream can cause which disorders

Back 71

- Simultangnosia
- Optic Ataxis
- Balint's syndrome
- Asteropsis
- Akinetopsia

Front 72

Lesions of various components of the ventral stream can cause which disorders

Back 72

- acromatopsia
- agnosia
- alexia

Front 73

Define: acromatopsia

Back 73

Cerebral loss of color vision

Front 74

Define: Agnosia

Back 74

Issues with general visual object identification for example man who mistook his wife for a hat

Front 75

Define: Alexia

Back 75

Impaired recognition of words

Front 76

Conjunctivitis

Back 76

Inflammation of the superficial covering of the sclera
– Most commonly a viral or infectious event
- relatively benign

Front 77

Uvetis

Back 77

– More serious and conjunctivitis
– Associated with systemic diseases like sarcoidosis, RA, MS, tumors, infections, AIDs
– Can be segmental

Front 78

Anterior ischemic optic neuropathy

Back 78

- due to ischemia of the posterior ciliary arteries
- result in a swollen infarcted disk

Front 79

Central renal artery occlusion

Back 79

– Results in a pale retina with a cherry red spot a fovea

Front 80

Opsin mutations

Back 80

- Cause different types of in congenital color blindness
- more prevalent in men
– Signs and symptoms depend on which photoreceptors involved

Front 81

Describe the main types of opsin mutations

Back 81

- cone dystrophy, macular degeneration: central scotoma with poor central daytime vision

- retinitis pimentosa: disease of the rods, cause ring schotomata and nyctalopia (night blindness)

Front 82

Where's the density of rods the greatest

Back 82

Around 20°

Front 83

Where is the density of cones the greatest

Back 83

At 0°

Front 84

Where is their only cones

Back 84

At 0°

Front 85

Where is there predominantly rods

Back 85

From ~5° onwards