3.2-3.3 Vision Flashcards
Eyeball Anatomy: Outer Layer (2)
<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>
Eyeball Anatomy: Inner Layer (5/6th) (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>
Factors limiting visual acuity (2)
Neural factors: How neurons are connected<br></br>Optical factors: How much can light hit neurons (3)<br></br>
Optical factors: How much can light hit neurons (3)
1.Pupil Size<div>2. Clarity of Optical Media</div><div>3. Refractive errors (Leads to blurring)<br></br><br></br></div>
Optical Factor:Pupil Size (1)
<ul> <li>Pupil Size (1) <ul> <li>Smaller = More Clear</li> </ul> </li></ul>
Optical Factors: Clarity of Optical Media (2)
<ul> <li>Clarity of Optical Media (2) <ul> <li>Cataracts (Len opacity)</li> <li>Corneal Opacity</li> </ul> </li></ul>
Optical Factors: Refractive errors (Leads to blurring) (4)
<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>
Basic Properties of Rods: Vision, Types, Colour, Number, Fovea
<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>
Basic Properties of Cones: Vision, Types, Colour, Number, Fovea
<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>
Why can photoreceptors respond to light (2)
<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>
PhototransductionStep 1 (2): Change in Structure
“<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>”
Phototransduction Step 2 (2): Depolarisation
“<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>”
PhototransductionStep 3 (2): Dark vs Light
“<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>”
<br></br>TLDR Summary of Phototrasnduction (4)
“<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>”
Retina: General neuralstructure and function (2)
“<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>”
Retina: Pathways and Interactions
”"”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>”
Bipolar Cells: Function, Types
<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>
Define Receptive Field? (1)
<ul> <li>Area of the retina when stimulated, causes a change in ganglion cell membrane potential</li></ul>
Types? (4) Ganglion cells. What is the shape of the receptive field?
<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>
Function? (1) Ganglion Cells
<ul> <li>Output of retina neurons</li></ul>
Action? (1) Ganglion Cells
In response to light, they release glutamate and fire APs (Only cell in the retina that does it)
“<img></img>What is the red and green”
Red: Horizontal Cells (Input and Output: Both photoreceptors)<div><br></br></div><div>Green: Amacrine Cells (Input: Bipolar & Output: Bipolar and Ganglion)</div>
Horizontal Cells: Function, Action, Response
<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>
Amacrine Cells: Function, Action, Importance
<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>
Types of Ganglion Cells? (2)
M and P cells
M Cells? (4): Size, Number, Receptive Field, Function
<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>
P Cells? (4): Size, Number, Function
<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>
Output Targets? (2) of Ganglion Cells
“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>”
Optic Chiasm (2)
“<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>”
LGN:Cells and Layers (3)
“<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>”
Optic Radiation (3): What is it, location, path
“<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>”
Alternative name and location (1) V1
<ul> <li>Area 17 located in the occipital lobe, surrounding the calcarine fissure</li></ul>
Representation of visual field (1)V1
Information from each visual hemifield projects to the contralateral visual cortex
“Or<span>g</span>anisation? (3) of V1”
“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>”
Layers? (2)V1
<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>
Functions? (2)V1
“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>”
Mixing of information from each eye (1)V1
“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>”
Defects: Retina/Optic Nerve; Chaism; Far back
<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>
Area MTLocation (1)
Middle temporal lobe
Function (1)Area MT
Processing object motion.
Inputs (2) to MT
<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>
Area V4Inputs (1)
Receives input from the blob and interblob regions of the V1 (via. V2)
Area V4Receptive Fields (1)
Large receptive fields that are both orientation and colour selective
Function (1)Area V4
Perception of shape and colour
Area ITInput (1)
Output of V4
Area ITFunctions (2)
“<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>”
What is the optic disc
Blind spot (No rods and cons)
