14.1 The Neurobiology of Vision Flashcards
(43 cards)
1
Q
Label the diagram
A
2
Q
Label the diagram and the lobes
A
3
Q
Where do the nerves from the retina go?
A
- The nerves leave the eye in the optic nerve and synapse in the lateral geniculate nucleus (LGN)
- Fibres then go to the visual cortex
Transmits all light information into electical information to the brain
4
Q
Label the diagram
A
5
Q
What is the purpose of the cornea?
A
- Involved in focusing light into eye
- Transparent covering over eye: is a barrier between outside world and inner eye
- Refracts light entering the eye
- NO blood vessels
- VERY sensitive to light
6
Q
What is the purpose of the pupil?
A
- Small opening in eye by which light passes
- Size of pupil can change which can be due to light or emotion (e.g. like someone pupil dilates)
-
LOW light –> pupils dilate, more light into eye
- better to see when dark
-
HIGH light –>pupils constrict
- LESS light into eye
7
Q
What is the iris?
A
- The coloured portion of the eye
- Regulates the amount of light into the eye
8
Q
What is the purpose of the lens?
A
- Serves by focusing light to back of eye (refracts)
- Transparent structure that helps refract light onto retina
9
Q
What is the fovea?
A
- Indentation (small) at the back of the eye where there is high level detail processing of light
- Region where upper retinal layers are THINNED
10
Q
What flips the inverted image from the retina?
A
The vision cortex
11
Q
What is vision?
A
Transduction of light
12
Q
What produces tears?
A
Lacrimal gland produces tears and passes through the lacrimal ducts
13
Q
What does vision depend on?
A
Depends on light sensitive cells in the retina at the rear of the eye
14
Q
How does light reach the retina?
A
Light is focussed by the cornea and lens onto the retina
15
Q
Explain the structure of the retina (layers)
& label the diagram
A
-
Photoreceptors (allow night vision)
- Made of cones and rods
-
CONES
- More in centre of retina
- Only type in fovea of eye
-
RODS
- More in outer areas of the eye
- Used for peripheral vision
- Outer plexiform layer
-
Horizontal layer
- Form synapses with bipolar cells & photoreceptor cells
-
Bipolar cell
- Connect photoreceptors to ganglion cells
-
Amacrine cell
- Translate information
- Inner plexiform layer
-
Ganglion cell
- Gets info from retina & sends onto brain (via optic nerve)
- Their axons leave the eye
16
Q
What do photoreceptors do & how?
A
- Photoreceptors capture light
- Have outer segments with stacks of membrane that increases their surface area greatly
- Pigment molecules collect light
17
Q
What is a photon?
A
A single unit of light
18
Q
What is the wavelength of visual light and colours on the sides of the spectrum?
A
(BLUE) 380-750nm (RED)
Infra red Ultra-violet
19
Q
What are the kinds of photoreceptors?
A
- 120 million RODS (more rods in nocturnal animals)
- 6 million CONES
-
RODS
- More sensitive to light and occur in the periphery (at low light)
-
CONES
- Respond to different wavelengths
- Mainly found in the fovea (day-light, when HIGH levels of light)
20
Q
What are these and label them and what is the difference between the two?
A
The outer segments are different
21
Q
Label this fundoscopy image
A
22
Q
Label this diagram & briefly explain it
A
- At the fovea (where information from the lens is focussed) there is a 1:1 ratio of photoreceptors : ganglion cells
- At the retina there is a 50:1 ratio of photoreceptors : ganglion cells
23
Q
Explain receptor potentials in photoreceptors, bipolar cells, ganglion cells
A
-
Photoreceptors
- HYPERPOLARISING membrane potential following stimulus
-
Bipolar cells
- DEPOLARISING membrane potential
-
Ganglion cells
- Recording of action potentials then sends it to the brain
24
Q
How many types of rods & cones are there?
A
-
Cones
- Blue
- Green
- Red
-
Rods
- Blue/green
25
Explain the anatomy of the visual system after the ganglion cell fibres
1. Ganglion cell fibres enter the **optic nerve** & then the **optic chiasm**
2. Fibres from the **nasal retina** cross over (**CONTRALATERAL** - opposite side)
3. Fibres from the **temporal retina** remain (**IPSILATERAL** - same side)
**LGN** - Lateral geniculate nucleus
1. Nerve fibres from **LGN** go to the **visual cortex**
2. Synapse mainly in layer IV of cortex (**primary visual cortex** - at posterior of brain in *occipital lobe*)
26
What are the pathways from the **primary visual cortex**?
* **Dorsal pathway** --\> spatial vision e.g. WHERE something is (**FAST**)
* To *parietal cortex*
* **Ventral pathway** --\> colour and object vision e.g. WHAT (detail of what looking at) (**SLOW**)
* To *inferatemporal cortex*
27
Explain **disorders of vision**
* Is rare in females
* **More common** in *males* as on **X chromosome** (1 in 10)
* Visual disorders can occur anywhere in the visual pathway
* **Short** & **long** sightedness
* **Neural deficits**
* ***Colour blindness*** - caused by loss of one type of cone
* ***Optic (retinal) neuropathy*** - specific to the retina, blood vessel damage & regrowth
28
What is **glaucoma** & the risk factors?
* When there is damage in the **connection** between the eye & the brain (usually in the optic nerve)
* Up to **50%** of people with disease _don't_ know they have it
* Causes **thinning** of the nerve fibre layer in the retina and gradually results in *_loss of vision_* and **_un_**treated glaucoma eventually leads to *_blindness_*
* Risk factors:
* Family history of *glaucoma*
* Increasing age
* Prolonged steroid use
29
What is **AMD** & the risk factors?
* **AMD** - age related macular degeneration
* **Commonest** cause of blindness in western world
* **Peripheral** vision remains _unaltered_ (causes blurry vision, wavy/distorted lines or a central blind spot
* Risk factors:
* Increase age
* Female
* Smoking
30
Explain *diabetic retinopathy*
Deterioration of the tight junctions of blood vessel wall causing **blockage**, **excudates** (plasma leakage), **haemorrhages**, **micro aneurysms**
31
Explain **retinal vein occlusion** & predisposing factors
* **Blockage** of a retinal vein. Predisposing factors are:
* *Increasing age*
* *Systemic hypertension*
* *Raised Intra ocular pressure and long sighted spectacle corrections*
* There is some visual loss depending on the severity of the occlusion but some recovery after 6 months
32
Explain **presbyopia**
* Means 'old eye' (can be particularly due to eye muscles)
* Ages of 40-45 showing *difficulties* with reading. Other symptoms include holding reading material further from the eyes and blurry distance vision immediately after reading
* Due to the lens becoming ***_inelastic_*** *making focusing on near objects difficult*. Rectified by the use of bifocals, varifocals, separate reading spectacles or contact lenses
33
Explain **cataracts** & how it can be treated
* Any **opacity** of the lens. May present as gradual *_blurring*_ of the vision, seeing _*double_* in one eye or increased sensitivity to glare
* Cataracts are more common with *_increasing_* *_age_*. Excessive unprotected exposure to UV light, smoking, poor nutrition and prolonged steroid use also contribute
* Cataracts can be **removed surgically** by replacing the *_lens*_ with a clear _*plastic lens implant_*
34
Explain **Balint's syndrome**
* Bilateral damage to parieto-occipital region
* Region between parietal and occipital regions
* Involved in spatial perception
* Dorsal stream only is affected
* Includes:
* ***_Optic ataxia_***
* Difficulty reaching for objects under visual guidance
* ***_Ocular apraxia_***
* Difficulty in visual scanning
* ***_Simultanagnosia_***
* Difficulty perceiving more than one object at a time
35
What is **optic ataxia**?
Difficulty reaching for objects under visual guidance
36
What is **ocular apraxia**?
Difficulty in visual scanning
37
What is **simultanagnosia**?
Difficulty perceiving more than one object at a time
38
Explain what happens when there is **damage** to **V1**
* _No conscious awareness_ of being able to see
* Known as ***_Blindsight_***
* ***__***Information goes *straight for processing* so information retained but without awareness
* Patients report a ‘gut feeling’ but insist they cannot see
39
Explain what happens when there is **damage** to **V4**
* _No_ colour perception OR memory of colour
* ***_Achromatopsia_***
40
Explain what happens when there is **damage** to **V5**
* *_Cannot process motion_* so objects moving become invisible
* ***_Akinetopsia_***
41
Explain what happens when there is **widespread damage** to **all** but **V4**
* Severely impaired visual processing but colour information retained
* ***_Chromatopsia_***
* Caused by *_carbon monoxide_* poisoning
42
What is **visual agnosia** & types?
*_Cannot_* perceive visual stimuli accurately
* ***_Apperceptive_*** visual agnosia
* Cannot perceive *_objects_*
* ***_Prosopagnosia_***
* Failure to recognise *_faces_*
* Damage to *fusiform* face area
* Region of extrastriate cortex dedicated to face and complex object recognition
* ***_Associative visual agnosia_***
* Inability to identify objects perceived visually
* Form can be matched with similar objects or drawn from memory
* Can still describe what objects are when named
* Just can’t link pictures and words
* Disruption to connections in ventral stream of the visual cortex
* But no damage to those in the dorsal stream
43
What is **achromatopsia** & explain it
* _Inability_ to discriminate among different hues (a colour/shade)
* Cannot see colour at all
* Damage to visual association cortex
* **Bilateral**
* Affects both visual fields
* _NO_ memory of colour
* **Unilateral**
* Only affects one visual field
* Half the world is seen in grey-scale
* Half the world is seen in colour
* Also affects memory of colour
* Patients cannot recall what colours objects were prior to brain injury
