85040
Description
Mind Map by tanitia.dooley, updated more than 1 year ago
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Created by tanitia.dooley
almost 11 years ago
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Vision
- structure of eye
- Fovea centralis- greatest visual acuity point (ability to
see detailed fine images): ~7 million cones. Normally
the point at which light is focused. Very little rods.
- Retina- pigmented retina-single layer of
cells, melanin pigment forming a 'black
matrix'-absorbs light=increased visual
acuity, decreased light scattering because
no reflection in the eye/ Sensory retina-
respond to light, 120 million ROD & 6-7
million CONES/Relay neurons-amacrine,
horizontal, bipolar cells etc
- Rod- aschromatic (black & white), slow response to light but respond to
low levels, long integration, single quanta 10^8, not in fovea, convegent
pathways-Visual field overlap allows different shades of grey
- Rod neural connections- one bipolar cell will have the input of numerous rods.
One ganglion will have the input from several rod bipolar cells=spatial
summation-signal is thus enhanced however a decreased visual acuity.
- Rod neural connections- one bipolar cell will have the input of numerous rods.
One ganglion will have the input from several rod bipolar cells=spatial
summation-signal is thus enhanced however a decreased visual acuity.
- Cones: chromatic (colour), fast response, short
integration, low sensitivity (need lots of light to percieve
colour), 10^7, dense in fovea, divergent pathways
- Cone neural connections- exhibit little or no convergence on
bipolar cells-one cone to one bipolar cells-to one ganglion
cell. Reduced sensitivity to light but increased visual acuity
- Cone neural connections- exhibit little or no convergence on
bipolar cells-one cone to one bipolar cells-to one ganglion
cell. Reduced sensitivity to light but increased visual acuity
- association neurones- ability to modify signals from
photoreceptors before reaching the brain.
- Horizontal cells-link photoreceptors and bipolar cells, amacrine cells
link bipolar cells and ganglionic cells and interplexiform cells link bipolar
cells to amacrine and horizontal to bipolar cells (negative feedback)
- Horizontal cells-link photoreceptors and bipolar cells, amacrine cells
link bipolar cells and ganglionic cells and interplexiform cells link bipolar
cells to amacrine and horizontal to bipolar cells (negative feedback)
- Rhodopsin- in rods & cone opsin in cones.
Cis form binds to opsin light converts it into
trans form which doesnt bind opsin. In dark
trans form converted back into cis form
which binds to opsin- to reestablish dark
from light need to break up rhodopsin apart
and repackage it (multistage process)-why
sometimes get after images.
- In the dark- at rest not activated- some Na
channels are open, Na entry so releasing
glutamate/glycine which binds to its receptor
on the bipolar cell=hyperpolarisation.
- In the light, Na channels close=decreased release of glutamate so no hyperpolarisation of
bipolar cells-they depolarise=APs. The no. of Na channels closing is proportional to the
amount of light. If retinal is completely released from opsin=free retinal is converted back
into vit A. When retinal is back in its origional shape it binds back to opsin
- Light and dark adaptation is simply a change in the amount of rhodopsin
that is avaliable. Bright light- excess rhodopsin is broken down so there
is not as much avaliable to initiate APs. In the dark, increased amounts
of rhodopsin avaliable so increased sensitivity to light
- Light and dark adaptation is simply a change in the amount of rhodopsin
that is avaliable. Bright light- excess rhodopsin is broken down so there
is not as much avaliable to initiate APs. In the dark, increased amounts
of rhodopsin avaliable so increased sensitivity to light
- In the light, Na channels close=decreased release of glutamate so no hyperpolarisation of
bipolar cells-they depolarise=APs. The no. of Na channels closing is proportional to the
amount of light. If retinal is completely released from opsin=free retinal is converted back
into vit A. When retinal is back in its origional shape it binds back to opsin
- In the dark- at rest not activated- some Na
channels are open, Na entry so releasing
glutamate/glycine which binds to its receptor
on the bipolar cell=hyperpolarisation.
- Rod- aschromatic (black & white), slow response to light but respond to
low levels, long integration, single quanta 10^8, not in fovea, convegent
pathways-Visual field overlap allows different shades of grey
- Fovea centralis- greatest visual acuity point (ability to
see detailed fine images): ~7 million cones. Normally
the point at which light is focused. Very little rods.
- Inverted images projected onto retina,
visual cortex corrects it (synaptic
plasticity)-why some people better
visual learners than others.
- Differences in luminance
- Each ganglion cell respond to stimulation of a
circular region of the retina (receptive field)
- On centre ganglionic cell-spot in centre of receptive field
turns on centre (G proteins linked metabotropic glutamate
receptor)-eg promotes signals. Off centre ganglionic
cell-spot in centre of receptive field turns on the surround
(glutamate-AMPA receptors)- eg if light shone on centre
can be inhibitory. There is an equal number of these ganglia
that overlap so changes in luminance are reported to the
CNS by increased no. of APs.
- On centre- G protein linked
metabotrophic glutamate receptor,
closure of cAMP gated Na
channels=hypoerpolarising the cell.
Off centre-ionotropic AMPA receptors
causing the depolarisation of cells
when glutamate binds to receptors.
- On centre- G protein linked
metabotrophic glutamate receptor,
closure of cAMP gated Na
channels=hypoerpolarising the cell.
Off centre-ionotropic AMPA receptors
causing the depolarisation of cells
when glutamate binds to receptors.
- On centre ganglionic cell-spot in centre of receptive field
turns on centre (G proteins linked metabotropic glutamate
receptor)-eg promotes signals. Off centre ganglionic
cell-spot in centre of receptive field turns on the surround
(glutamate-AMPA receptors)- eg if light shone on centre
can be inhibitory. There is an equal number of these ganglia
that overlap so changes in luminance are reported to the
CNS by increased no. of APs.
- Each ganglion cell respond to stimulation of a
circular region of the retina (receptive field)
- Neuronal pathways
- optic nerve exits the eye travels along the optic foramen and enters the
cranial vault (anterior to the pituitary). Optic nerves connect to each other,
optic chiasma. Ganglion cell axons from nasal retina cross over through
the optic chiasma projecting to the opp side of the brain
- Temporal ganglion cell axons project to the brain on their corresponding
side (they dont cross over at optic chiasma) then down optic tracts to
either -lateral geniculate nuclei (thalamus up to the cortex) or -superior
colliculi (centre for visual reflex and visual association centres)
- Temporal ganglion cell axons project to the brain on their corresponding
side (they dont cross over at optic chiasma) then down optic tracts to
either -lateral geniculate nuclei (thalamus up to the cortex) or -superior
colliculi (centre for visual reflex and visual association centres)
- optic nerve exits the eye travels along the optic foramen and enters the
cranial vault (anterior to the pituitary). Optic nerves connect to each other,
optic chiasma. Ganglion cell axons from nasal retina cross over through
the optic chiasma projecting to the opp side of the brain
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