Visual System

Front 1

Visual Pathway

Back 1

1. ganglion cells of retina
2. optic nerve
3. Optic chiasm
4. Optic tract
5. LGN
6. Geniculocalcarine tract (visual radiation)
7. Visual cortex

Front 2

Ganglion cells of retina

Back 2

- form optic nerve
- nasal contralateral LGN
- temporal hemiretina ipsilateral LGN

Front 3

Optic Nerve

Back 3

TRANSECTION: causes ipsilateral blindness with no direct pupillary light reflex

Front 4

Optic Chiasm

Back 4

- decussation of the nasal hemiretinas & non-crossing temporal hemiretinas
- project fibres to suprachiasmatic nucleus of the hypothalamus
1. midsagittal transection or pressure (often pituitary tumour)
2. Bilateral lateral compression (ofteen due to calcified ICAs

Front 5

Optic Tract

Back 5

projects to ipsilateral LGN, pretectal nuclei, superior colliculus

Front 6

LGN

Back 6

6 layered
1,4,6 recieved crossed fibres
2,3,5 uncrossed
- LGN recieved input also from layer VI striate cortex (BA 17).
PROJECTS through optic radiation to layer IV of 1o visual cortex

Front 7

Optic Radiation (Geniculocalcarine tract)

Back 7

have 2 divisions
1. UPPER division; to upper banks of calcarine (cuneus) represents superior retinal quadrants
- lesion of both sides causes an lower altitudinopia
2. LOWER division; loops from LGN anteriorly (meyer's loop) then posteriorly to terminate in the lower calcarine sulcus, the lingual gyrus. Input from lower retinal quadrants

Front 8

Visual Cortex

Back 8

BA 17
- has a retinotopic organsiation
1. posterior area recieves macular input (central vision)
2. Intermediate area; paramacular input (peripheral input)
3. anterior area receives monocular input

Front 9

Pupillary Light Reflex

Back 9

1. afferent CNII
2. Efferent CNIII
A. ganglion cells of retina project bilaterally to pretectal nuclei
B. Pretectal nucleus of midbrain project via posterior commissure crossed and uncrossed fibres to EWN
C. EWN preganglionic PS neurons to ciliary ganglion
D. Ciliary ganglion- postganglionic PS fibres innervate sphincter muscles of iris

Front 10

Pupillary Dilation Pathway

Back 10

1. Hypothalamus neurons of paraventricular nucleus project directly to the ciliospinal center (T1-2) of the intermediolateral cell column of the spinal cord
2. Cliocpinal center of Budge projects preganglionic sympathetic fibres through sympathetic trunk to superior cervical ganglion
3. Superior cervical ganglion projects postgang, through perivascualr plexus of the carotid system to the dilator muscle of the iris. The fibres pass through the tympaic cavity, cavernous sinus and superior orbital fissure.

Front 11

The near reflex & Acommodation Pathway

Back 11

A. cotical visual pathways from BA 17 tp BA 19 (assoc. cortex)
B. BA 19 projects through corticotectal tract to superior colliculus & pretectal nucleus
C. these 2 then project to CNIII complex involving
1. rostral EWN, pupil constriction
2. caudal EWN, contraction of ciliary muscles (INC. refreactive lens power)
3. Medial rectus subnucleus mediates convergence

Front 12

Ciliary Muscles and Suspensory Ligaments

Back 12

because the ciliary muscle is a sphincter, when it contracts it gets pulled closer to the pupil and thus relaxes the suspensory ligmanets and allows the lens to take its natural shape

Front 13

Cortical & Subcortical Centers for Ocular Motility

Back 13

A. frontal eye fields
B. Occipital eye fields
C. Subcortical centre for lateral conjugate gaze
D. Subcortical center fro vertical conjugate gaze

Front 14

Frontal Eye Fields

Back 14

A. frontal eye fields= post. part of middle frontal gyrus (BA 8). regulates Saccadic eye movements
STIMULATION: causes contralateral deviation of the eyes (away form the lesion)
DESTRUCTION: causes transient ipsilateral conjugate deviation of the eyes

Front 15

Occipital eye fields

Back 15

BA 18,19
- for involuntary smooth pursuit & tracking movements
- Stimulation causes contralateral conjugate deviation

Front 16

Subcortical centre for lateral conjugate gaze

Back 16

in abducent nucleus of pons
INPUT: contralateral frontal eye field
PROJECTS: to ipsilateral LR and contralateral MR via MLF

Front 17

Subcortical centre for vertical conjugate gaze

Back 17

in midbrain @ posterior commissure
- called rostral interstitial nucleus of MLF and is assoc. with parinauds Syndrome

Front 18

Ocular motor palsies and pupillary Syndromes

Back 18

Front 19

Internuclear Opthalmoplegia

Back 19

- damage to MLF
- causes MR palsy on attempted lateral conjuagte gaze
- & monocular horizontal nystagmus in the abducting eye
- convergence is normal
- common in MS

Front 20

One & a half syndrome

Back 20

consists bilateral lesions of the MLF & a unilateral lesion of the abducent

Front 21

Argyll Robertson Pupil

Back 21

absence of miotic reaction to light (both direct & consensual) with preservation of a miotic reaction to near stimulus (accomodation-convergence)
- occurs in syphilis and diabetes

Front 22

Relative Afferent (marcus Gunn) pupil

Back 22

lesion of optic nerve, afferent of pupil reflex

Front 23

Transtentorial herniation

Back 23

due to INC. supratentorial pressure (tumor, hematoma..)
1. pressure forces the parahippocampal uncus through tentorial incisure
2. the impacted uncus forces the contralateral crus cerebri aganist the tenotch) and puts pressure on the ipsilateral CNIII and post. cerebral aa.
a. ipsilateral hemiparesis
b. fixed and dilated pupils, ptosis & down & out eye (pressure on CNIII)
c. Contralateral homonymous hemianopia (due to compression of the post. cerebral a. which irrigates the visual cortex)

Front 24

Papilledema (choked disk)

Back 24

- non-inflammatory congestion of the optic diskdue to INC. intracranial pressure
- common cause brain tumor, subdural aematoma or hydrocephalus
- MAY cause bilateral enlarged blind spots. Often assymmetric and greater on the side of the supratentorial lesion

Front 25

Adie's Pupil

Back 25

large tonic pupil that reacts slowly to light but not to near (light-near dissociation)
- Fq seen in females with absent knee or ankle jerks

Front 26

Retinal Layers

Back 26

1. ganglion cells: (magnocellular + parvocellular)
2. Bipolar cells: link interneurons
3. Photoreceptors: light sens. RODS and CONES
4. Amacrine cells/Horizontal cells: interneurons
5. Pigment epithelium: light abs. (strongly adhere to the choriod but loosely to the photoreceptors so potential for retinal detachment)

Front 27

Location of retinal detachment

Back 27

- pigment epithelium

Front 28

Magnocellular

Back 28

large cells for MOTION

Front 29

Parvocellular

Back 29

medium sized; deal with colour

Front 30

Where is the one place light directly hits the photoreceptors?

Back 30

fovea centralis

Front 31

Macula Lutea

Back 31

area full of ganglion cells that have been pushed away from the fovea centralis

Front 32

Macular degeneration

Back 32

the central retina degenerates first so DEVASTING effects
unlike glaucoma where the periphery is first to go

Front 33

View through opthalmoscope

Back 33

Front 34

LGN Functions

Back 34

• 3 BIG jobs
(1) STREAMS: what function? Magn and parvo
(2) TOPOGRAPHY: where located? MAP
(3) LATERALITY: which eye? • each layer driven by one or other eye
- ipsilateral/contralateral inputs

each LG maps the contralateral visual field (so the right picture ends up on the contralateral brain all together)

Front 35

LGN Organistion

Back 35

inferior retina - lateral LG
superior retina - medial LG
central retina - caudal LG
peripheral retina - rostral LG

green= contralateral
red= ipsilateral

Front 36

Primary Visual Cortex

Back 36

• banks of calcarine sulcus (band of Gennari)
• faithful projection from LG (same but different)
- topography
- streams
- register

inferior retina - inf bank V1
superior retina - sup bank V1
central retina - caudal V1
peripheral retina - rostral V1

Front 37

NON-IMAGE FORMING PATHWAY

Back 37

- unconscious vision and other details
Suprachiasmatic (Sch) - time-keeper (circadian)
Pretectum (Pre) - pupillary reflex (II,III)
Superior Colliculus (SCol) - attention, avoidance
Pulvinar (Pul) - attention, integration (see, touch, hear)
Secondary Visual Cortex (V2-V5) - orientation, colour, motion
(adds a little more visual detail)

Front 38

Visual Cortical Functions

Back 38

V5 - motion detection: a life in photographs
V5a - face recognition: facial agnosia
V4 - colour, colour edges: colour blind
V2,V3 - orientation
V1 - conscious vision, topography: blindsight (some residual vision)

Front 39

Phtotoreceptors

Back 39

light shuts down cation conduction

Front 40

Rod Cell Functioning

Back 40

high cGMP in the dark (inward Na & Ca) and countered by K thus called the dark current
- depolarised photoreceptr releases glutamate
- depolarisation around -40mV

light closes the membrane cGMP channels, however the outwards K is still there, thus hyperpolarisation, thus realising less glutamate

Front 41

Rhodopsin

Back 41

protein highly expressed in outer membrane...
-7TMD (like a GPCR)
- protein part syn by golgi body of cell
- VitA part
- pigment eplithilium, provides retinal the photosensitve part of the retina

Front 42

Photon effect on the retinal...

Back 42

Front 43

Step 1

Back 43

Front 44

Step 2

Back 44

AMPLIFICATION: one photon to one rodopsin, then this interacts with many G-proteins, then it will act to many cGMP decreasing its conc.

Front 45

Bipolar Cells

Back 45

Front 46

Cone vision

Back 46

aka day light
OFF_ respond with hyperpolarisation
ON_ respond with depolarisation

then the glutamate released has different effects depending by whom its released

Front 47

Cone ON

Back 47

mGluR6

Front 48

Cone OFF

Back 48

AMPA/KA receptors

Front 49

Parallel Processing of INFO

Back 49

ON; optimised to INC. in intensity light
OFF: for dec. in light intesity

and they both work to allow better discrimination
PARALLEL processing of info; 2 different channels carring info separately

Every single point in the retina hit by a light source is covered by every different physiological type of ganglion cell. Thus, each point is simultaneously analysed with regards to its contrast, colour, movement as well as other characteristics. Parallel processing of visual information starts in the retina

Front 50

Types of Ganglion cells

Back 50

•Local contrast detectors
•Direction selective neurons
•Local Edge Detectors and Orientation Detectors
•Fast motion detectors
•Luminosity Detectors ("tonic units")

Front 51

intrinsically photosensitive Retinal Ganglion Cells

Back 51

express melaopcin (express light irrespective of the photoreceptors)
- they have their own photpigment making them sens. to light

so photoreceptors arent the only light sens cell in the eye

•Encodes ambient light levels
•Sets the biological clock
•Regulates activity and melatonin levels
•Adjusts pupil diameter.

so this is important that people that are blind still have connections with the SCN (suprachiastmaitic nucleus) and they go free running no longer sync with the external envirnoment

Front 52

Back 52

visual illusion; maach bands
- 8 uniform vertical strips of grey, however when u look at them the left edge looks lighter than the right edge
- because our eyes are optimised to extract info about contrast so it enhance the contrast at the edges (lateral inhibition - that occurs at the retina)

Front 53

Zone of Inhibition

Back 53

increase in activity when close and decrease when adjacent and nothing when far away (this is the receptive fields (excitatory center, with an inhbitory surround- anatgonist functions)

Front 54

Function of horizontal cells

Back 54

horizontal cells use inhibtory NT to modulate inhibotry stuff along the pathway

- important in things like inhibition zone and contrast definition