3.2-3.3 Vision

Question 1

Eyeball Anatomy: Outer Layer (2)

Answer 1

<ul> <li>Eyeball Anatomy: Outer Layer (1/6th) (2) <ul> <li>Cornea: Transparent to allow light in</li> <li>Sclera: Outer shell to protect eyes</li> </ul> </li></ul>

Question 2

Eyeball Anatomy: Inner Layer (5/6th) (2)

Answer 2

<ul> <li>Eyeball Anatomy: Inner Layer (5/6th) (2) <ul> <li>Neuronal Layer</li> <li>Macula: On the retina, surrounds the fovea and is responsible for central vision (20/20)</li> </ul> </li></ul>

Question 3

Factors limiting visual acuity (2)

Answer 3

Neural factors: How neurons are connected<br></br>Optical factors: How much can light hit neurons (3)<br></br>

Question 4

Optical factors: How much can light hit neurons (3)

Answer 4

1.Pupil Size<div>2. Clarity of Optical Media</div><div>3. Refractive errors (Leads to blurring)<br></br><br></br></div>

Question 5

Optical Factor:Pupil Size (1)

Answer 5

<ul> <li>Pupil Size (1) <ul> <li>Smaller = More Clear</li> </ul> </li></ul>

Question 6

Optical Factors: Clarity of Optical Media (2)

Answer 6

<ul> <li>Clarity of Optical Media (2) <ul> <li>Cataracts (Len opacity)</li> <li>Corneal Opacity</li> </ul> </li></ul>

Question 7

Optical Factors: Refractive errors (Leads to blurring) (4)

Answer 7

<ul> <li>Refractive errors (Leads to blurring) (4) <ul> <li>Myopia (short sightedness, eyeball is too long and light doesn’t focus on the retina)</li> <li>Hypermetropia (long sightedness, eyeball is too short and light doesn’t focus on the retina)</li> <li>Astigmatism (odd shaped eyeball)</li> <li>Presbyopia</li> </ul> </li></ul>

Question 8

Basic Properties of Rods: Vision, Types, Colour, Number, Fovea

Answer 8

<ul> <li>Basic Properties (6) <ul> <li>Night vision (Scotopic)</li> <li>Very sensitive</li> <li>Only 1 type of rod</li> <li>No colour vision</li> <li>100 million (1Cone:20Rod)</li> <li>Absent from the fovea</li> </ul> </li></ul>

Question 9

Basic Properties of Cones: Vision, Types, Colour, Number, Fovea

Answer 9

<ul> <li><ul><li>Cones<br></br></li></ul></li><li><ul> <li>Basic Properties (5) <ul> <li>Day vision (Photopic)</li> <li>3 types: red, blue and green</li> <li>Allow colour vision</li> <li>5 million (1 Cone: 20Rod)</li> <li>Most dense in the fovea (middle of macula)</li> </ul> </li> </ul> </li></ul>

Question 10

Why can photoreceptors respond to light (2)

Answer 10

<ul> <li>Photoreceptors contain photopigments that are activated by light <ul> <li>In cones, the photopigments are 1 or 3 different coneopsins</li> <li>In rods, the photopigments are rhodospin</li> </ul> </li> <li>Opsins bind to vitamin A (all-trans-retinal), which picks up light signals</li></ul>

Question 11

PhototransductionStep 1 (2): Change in Structure

Answer 11

“<ul> <li>When light hits photoreceptors, 11-cis retinal becomes all trans retinal</li> <li>This change in conformation causes a change in rhodopsin, and converts a light signal into an electrical signal<br></br><br></br><img></img><br></br></li></ul>”

Question 12

Phototransduction Step 2 (2): Depolarisation

Answer 12

“<ul> <li>Photoreceptors are depolarized in the absence of light and are hyperpolarized by light (Respond via. changes in graded potentials, not APs)</li> <li>Glutamate is the NT used in photoreceptors (Dark: Release NT all the time; Light: Reduce NT)</li></ul><div><img></img><br></br></div>”

Question 13

PhototransductionStep 3 (2): Dark vs Light

Answer 13

“<ul> <li>In the dark, <ul> <li>cGMP gated Na+ channel has continuous Na+ influx</li> <li>Causes depolarization of the photoreceptor</li> </ul> </li> <li>In the light, <ul> <li>cGMP is broken down into GMP</li> <li>cGMP is no longer present to keep open Na+ channels. Na+ influx ceases and causes hyperpolarisation<br></br><br></br><img></img><br></br></li> </ul> </li></ul>”

Question 14

<br></br>TLDR Summary of Phototrasnduction (4)

Answer 14

“<ul> <li>Light causes a conformational change in retinal, which in turn causes a conformational change in rhodopsin</li> <li>Rhodopsin activates trasducin</li> <li>Transducin activates phosphodiesterase</li> <li>Phosphodiesterase breaks down cGMP, causing closure of Na+ channels and hyperpolarization</li></ul><div><img></img><br></br></div>”

Question 15

Retina: General neuralstructure and function (2)

Answer 15

“<ul> <li>Retina contains many cell types (Light must pass through from ganglion to photoreceptor)</li> <li>Many vascular and supporting cell types around photoreceptors important for keeping them alive</li></ul><div><img></img><br></br></div>”

Question 16

Retina: Pathways and Interactions

Answer 16

”"”Through”” Pathway (3)<br></br>- Photoreceptors (Rods and Cones)<div>- Bipolar Cells<br></br>- Ganglion Cells</div><div><br></br></div><div>Lateral Interactions</div><div>- Horizontal Cells</div><div>- Amacrine Cells</div>”

Question 17

Bipolar Cells: Function, Types

Answer 17

<ul> <li>Synapses with both photoreceptors and ganglion</li> <li>10 types (1 for rods, 9 for cones)</li> <li>Spatial vision and colour vision</li></ul>

Question 18

Define Receptive Field? (1)

Answer 18

<ul> <li>Area of the retina when stimulated, causes a change in ganglion cell membrane potential</li></ul>

Question 19

Types? (4) Ganglion cells. What is the shape of the receptive field?

Answer 19

<ul> <li>Many types (20 Types) <ul> <li>ON: Switch on when light shines in receptive field</li> <li>OFF: Switch off when light shines in receptive field</li> <li>M: Motion</li> <li>P: Colour</li> </ul> </li> </ul>

<div>Hence, ganglion cells respond to light differently, depending on where light falls in receptive field (CONCENTRIC)</div>

Question 20

Function? (1) Ganglion Cells

Answer 20

<ul> <li>Output of retina neurons</li></ul>

Question 21

Action? (1) Ganglion Cells

Answer 21

In response to light, they release glutamate and fire APs (Only cell in the retina that does it)

Question 22

“<img></img>What is the red and green”

Answer 22

Red: Horizontal Cells (Input and Output: Both photoreceptors)<div><br></br></div><div>Green: Amacrine Cells (Input: Bipolar & Output: Bipolar and Ganglion)</div>

Question 23

Horizontal Cells: Function, Action, Response

Answer 23

<ul> <li>Lateral inhibition of the retinal through pathway <ul> <li>Receive input from photoreceptors</li> <li>Output to other photoreceptors</li> </ul> </li> <li>Uses GABA</li> <li>Respond to light by hyperpolarizing</li></ul>

Question 24

Amacrine Cells: Function, Action, Importance

Answer 24

<ul> <li>Lateral inhibition of the retinal through pathway</li> <li>Axonless</li> <li>Release inhibitory NTs (GABA and glycine)</li> <li>Important for modulating the synapse between bipolar and ganglion cells <ul> <li>Input: Bipolar</li> <li>Output: Bipolar and Ganglion</li> </ul> </li></ul>

Question 25

Types of Ganglion Cells? (2)

Answer 25

M and P cells

Question 26

M Cells? (4): Size, Number, Receptive Field, Function

Answer 26

<ul> <li>Large</li> <li>10% of ganglion cells</li> <li>Large receptive field</li> <li>Motion detection, flicker and analysis of gross features</li></ul>

Question 27

P Cells? (4): Size, Number, Function

Answer 27

<ul> <li>Small</li> <li>80-90% of ganglion cells</li> <li>Visual acuity and colour vision</li> <li>P ganglion cells respond best when a specific wavelength of light is shone on their receptive field</li></ul>

Question 28

Output Targets? (2) of Ganglion Cells

Answer 28

“Many brain regions but majority to LGN<br></br><ul> <li>Axons of ganglion cells form the optic nerve, and project to the lateral geniculate nucleus (LGN) in the thalamus</li> <li>LGN neurons project through the optic radiations to the visual cortex in the occipital lobe</li><li><img></img><br></br></li></ul>”

Question 29

Optic Chiasm (2)

Answer 29

“<ul> <li>Fibres from left and right optic nerve form Optic chiasm <ul> <li><strong>Nasal</strong> fibres of the optic nerve (from the nasal side of the retina) <strong>cross</strong> at the optic chiasm</li> <li><strong>Tempora</strong>l fibres of the optic nerve (from the temporal side of the retina) <strong>don’t</strong> <strong>cross</strong> at the optic chiasm</li> </ul> </li> <li>Lies at base of the brain (anterior to the pituitary)</li></ul><div><div><img></img><img></img></div> <div>Left hemisphere: Right visual hemifield (both eyes)</div></div>”

Question 30

LGN:Cells and Layers (3)

Answer 30

“<ul> <li>M cells (layers 1 – 2), which receive input from M ganglion cells (1 Layer for each eye)</li> <li>P cells (layers 3 – 6), which receive input from P ganglion cells (2 Layers for each eye)</li> <li>Hence, left and right LGN receive inputs from both eyes (segregated information)</li></ul><div><img></img><br></br></div>”

Question 31

Optic Radiation (3): What is it, location, path

Answer 31

“<ul> <li> <div>White matter tract where LGN neurons (M/P) axons project through</div> </li> <li> <div>Temporal and parietal lobes</div> </li> <li> <div>Synapse in V1</div> <div><br></br></div> <div>Optic Radiation = White thick structure</div> </li><li><div><img></img><br></br></div></li></ul>”

Question 32

Alternative name and location (1) V1

Answer 32

<ul> <li>Area 17 located in the occipital lobe, surrounding the calcarine fissure</li></ul>

Question 33

Representation of visual field (1)V1

Answer 33

Information from each visual hemifield projects to the contralateral visual cortex

Question 34

“Or<span>g</span>anisation? (3) of V1”

Answer 34

“Retinotopic organization: Neighbouring cells within the retina project to neighbouring cells in the LGN and thus cortex<br></br><ul> <li>Posterior-most (outer) part of the V1 encodes central vision</li> <li>Anterior-most part of the V1 encodes peripheral vision (inner)<br></br><br></br><img></img><br></br></li></ul>”

Question 35

Layers? (2)V1

Answer 35

<ul> <li>6 layers of the visual cortex, but input from the LGN projects to layer 4C <ul> <li>M type GC/LGN cells input to layer 4Cα</li> <li>P type GC/LGN cells input to layer 4Cβ</li> </ul> </li> <li>Inputs are segregated into ocular dominance columns, where inputs from each part of the eye are adjacent and interspersed</li></ul>

Question 36

Functions? (2)V1

Answer 36

“Orientation selectivity: Neurons respond best to bars moving in particular orientation<br></br>Orientation columns: Between layers of the cortex, neurons in a particular location will respond the same way to bars of light, and neurons in a different location will respond differently<br></br><br></br><img></img><img></img><br></br>”

Question 37

Mixing of information from each eye (1)V1

Answer 37

“Mixing of information from each eyes occurs in layers IVB and Layer III (Inputs to 4Cα M and 4Cβ P are segregated)<br></br><br></br><img></img><br></br>”

Question 38

Defects: Retina/Optic Nerve; Chaism; Far back

Answer 38

<ul> <li>Retina/Optic Nerve <ul> <li>Lose ability to see in one eye</li> </ul> </li> <li>Chiasm <ul> <li>Lose left hemifield in left eyes and right hemifield in right eyes</li> </ul> </li> <li>Far Back <ul> <li>Lose vision in same hemifield on both sides</li> </ul> </li></ul>

Question 39

Area MTLocation (1)

Answer 39

Middle temporal lobe

Question 40

Function (1)Area MT

Answer 40

Processing object motion.

Question 41

Inputs (2) to MT

Answer 41

<ul> <li>Receives retinotopic information from V2 and V3</li> <li>Receives input from cells in layer 4B of V1 (i.e. M type cells)</li></ul>

Question 42

Area V4Inputs (1)

Answer 42

Receives input from the blob and interblob regions of the V1 (via. V2)

Question 43

Area V4Receptive Fields (1)

Answer 43

Large receptive fields that are both orientation and colour selective

Question 44

Function (1)Area V4

Answer 44

Perception of shape and colour

Question 45

Area ITInput (1)

Answer 45

Output of V4

Question 46

Area ITFunctions (2)

Answer 46

“<ul> <li>Neurons respond to abstract shapes and colours</li> <li>Important for visual memory, perception, and faces</li></ul><div><img></img><br></br></div>”

Question 47

What is the optic disc

Answer 47

Blind spot (No rods and cons)