Neurobiology vISION Flashcards
1
Q
Anatomy of the visual system
A
- Light sensitive retina occurs are back at eye
- Nerve fibres from the retina leave the eye in the optic nerve and synapse in the lateral geniculate nucleus
- Fibres then go to visual cortex
2
Q
how do we see?overview
A
Regions of the brain devoted to vision occur in occipital lobe
Our eyes transduce light into signals our brain can understand. We breakdown light into its constitue elements.
- Everythign starts in eye and goes back into primary visual cortex by LGN
- Moves forwards into brain for analysis
3
Q
A
4
Q
Cross section of human eye
A
The image is inverted and flipped over
5
Q
Eye an dhow it works briefly
A
- Iris - front portion, regulates amount of light entering eye. Forms ocloured visible part eye in front lens.
- Light enters through pupil and passes on to lens. Iris allows dilation. constriction
- Cornea - refracts light entering eye and lens which focuses on to retina. No blood vessels here and extremely sensitive to pain
- Choroid - middle layer which contains pigment which prevents blurring of vision
- Ciliary body - part eye that contects choroid to iris
- Retina - light sensitive cells here (rods and cones)
- Macula - yellow spot in retina at back eye that surrounds fovea.
- Optic disc - identifies start optic nerve
- Optic nerve -w here info leaves eye and transfers light info that has been turned into electrical stimulation
6
Q
Vision depends on light sensitive cells in the retinal at the rear of the yee
A
- Light is focussed by the cornea and lens onto the retina
- The fovea is a region where upper retinal layers are thinned
- Aqueous humour - front cavity and back cavity filled with vitrious humour
7
Q
Structure of the retina and cells
A
- Photoreceptors - made up of cones (centre retina and fovea, responsible for colour vision) and rods (outer edges of retina for peripheral vision, responsible for nioght vision)
- Outer plexiform layer - outer section (photoreceptors). Layer of neuronal synapses in retina of eye. Contains dense network synapses between dendrites of horizontal cells from inner nuclear layer, and photoreceptor cell inner segments from outer nuclear layer.
- Horizontal cell - Laterally interconnecting neurons having cell bodues in inner nuclear layer of retina of vertebrate eyes. Help intergrate and regulate input from multiple photoreceptor cells
- Bipolar cell- exists between photoreceptors and ganglion cells and transmit signals from photoreceptors or horizontal cells and pass it on to ganglion cells directly or indirectly via amacrine cells.
- Amacrine cell - interneurons in retina. Responsible for 70% of input to retinal ganglion cells (bipolar cells other 30%)
- Inner plexiform layer - area retina made up of dense reticulum of fibrils formed by intercalated dendrities of retinal ganglion cells and cells of inner nuclear layer.
- Ganglion cell - Process visual info that begins as light enterign eye and transmit it to the brain via their axons which are long fibres that make up the optic nerve.
8
Q
Photoreceptors capture light
A
- Photoreceptors have outer segment with stacks of membrane that increases their surface area greatly
- Pigment molecules collect lgiht and translate it.
- We have different types rods/ cones for wavelengths.
- Blue, green, red cones (deal with lgiht at particular wavelengths)m to see all covour need different combination
- Photon = pocket of light, energy of photo represented by wavelength.
- longer wavelengths Infra red zone, shorter less than 72o in UV range.
9
Q
The 2 kinds of photoreceptors
A
- In humans - 120m rods, 6m cones
- The rod:cone ratio variesL it is greater in nocturnal animals (more rods)
- Rods are more sensitive to light (dont discriminate between different wavelenghts) and occur in periphery
- Cones respond to different wavelengths and are found aminly in fovea
- Have inner segmet (Nucleus and organelles) and outer segment (where photoreceptiont akes place).
- Outer segment difference: rods - stack membrane bound discs which rhidosopsin pigment, Cones - photosensitive pigments in infoldings cell membrane called opsin. 3 types: each sensitive to partiuclar wavelengths.
10
Q
Anatomy of fovea
A
Where information from lens is focused
Visual acuity best at fovea
Each photoreceptor connected to single retinal ganglion cell in fovea hence high level visual acuity. Further out might be more fuzzy due to up to 50:1 ratio of photoreceptors to ganglion cells.
11
Q
Receptor potentials in photoreceptors
A
- Vertebrate photoreceptors become hyperpolarised when stimulated, unlike most receptors that become depolarised (eg, invertebrate photoreceptors)
- Light hits photoreceptor
- Photoreceptor hyperpolarises ifnormation to bipolar cell which depolarises
- Communicaiton through ganglionc ells which causes action potential
12
Q
One type rod, 3 types cones
A
COlour blindness - cones can have wrong photopigment
Haves cones dotted sorund throughout rest retina, not really blue ones tho these stay put in fovea
13
Q
Anatomy of visual system - process
A
- Ganglion cell fibres enter optic nerve and chiasm
- Fibres from nasal retina cross over (contralateral) - decussation
- Fibres from temporal retinal remain ipsilateral
- go to LGN - lateral genticulate nucleus
- Info from left visual field -> right side brsain (and vise versa)
14
Q
Pattern of optic nerve fibres
A
- Fibres representing one half of the field of view cross over to the opposite side of the brain (right visual field -> left hemisphere and vise versa)
- The fibres retain a retinopathic order in optic nerve and throughout visual system
- Optic nerve fibres enter LGN - laternal geniculate nucleus. This has multiple layers
15
Q
LGN - lateral geniculate nucleus -> cortex process
A
- Nerve fibres from LGN go to visual cortex (which is back brain, close to calcarine sulcus)
- They synapse mainly in layer IV of cortex
- The cortex is arranged in precise modular fashion - each eye contributes to both sides but remain segregated to some degree in primary cortex.
16
Q
Visual cortices image
A
Extrastriate cortex (eveyrhtign basically but V1). STraiate is basically visual cortex
17
Q
Higher visual centres
A
- From primary visual cortex there are 2 pathways:
- Dorsal pathway subserves spatial vision
- The ventral pathway subserves colour and object vision
18
Q
Disorders of Vision
A
- Visual disorders can occur anywhere in visual pathway
- Several types of abnormality of eye:
- Short and long sightedness
- Neural deficits:
- Colour blindness is caused by loss on one type cone
- Optic (retinal) neuropathy - specific to retinal blood vessel damage and regrowth.
- If you are colour blind will NOT see difference between colour rings
- 3 types colour blindness: (faulty gene on x chromsome so males)
- Trichromacy - normal colour vision usually all 3 types light cones correct
- Dichromacy - 2 types cones red and grene cones can over lap so cant distinguish.
- Protanopia - unable to perceive ‘red; light
- Deuteranopia - unable to perceive green light
- Tritanopia - unable to percive blue light
26
Q
Dmaage to visual syndrome(nbeurologiczl visual condition)
A
v1 - primary visual cortex
v4 - where colour processed/ partly processed
28
Q
Associatiove visual agnosia (nbeurologiczl visual condition)
A
- 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 cant link pictures and words
- Disruption to connections in ventral streatm of visual cortex - but no damage to those in dorsal stem (so know where they are just cant identify)
29
Q
Achromatospia (nbeurologiczl visual condition)
A
- Inability to discriminate among different hues
- Cannot see colour at all
- Dmaage to visual association cortex:
- Bilateral - affects both visual fields
- Unilateral - only affects one visual field, half world is seen in grey scale and half in colour
- Also affects memory of colour - patients cannot recall what colours objects were prior to brain injury
