Visual System Overview Flashcards
What is the general structure of the retina?
3 layers of neurones, 2 layers of synapses
Inner plexiform layer (Ganglion cells synapse to amacrine and bipolar cells)
Outer plexiform layer (Bipolar and horizontal cells synapse to photoreceptors)
What are the stimulatory neurones in the retina?
Photoreceptors, bipolar cells, Ganglion cells
What are the inhibitory neurones in the retina?
Horizontal cells and amacrine cells
What is the lateral geniculate nucleus responsible for?
preprocessing of visual information
What area of the brain is responsible for preprocessing of visual information?
Lateral geniculate nucleus
What is the ventral stream responsible for?
object feature recognition
What part of the brain is responsible for object recognition?
inferior temporal - ventral steam
What is the dorsal stream responsible for?
Spatial location
What area of the brain is responsible for spatial location ?
Posterior parietal - dorsal stream
What are the main differences between rods and cones?
Rods - Active in dim light, Full outer segment
Cones - Active in bright light, Disks shed from tips distaly
How are photoreceptors activated?
Normally release glutamate
Cyclic GMP activates non selective ion channels on membrane of photoreceptors
Light converts Cyclic GMP into GMP
Channels close
Membrane hyperpolarises
Less glutamate released
ON bipolar cells
depolarise when light intensity increases
OFF bipolar cells
hyperpolarise when light intensity increases
What is the mechanism of ON cell activation?
- mGluR instead of AMPAR receptors
- Go G protein
- removal of cGMP not required for ion channel closure
What are the candidates for reason for different mechanism in ON cells?
TRMP1 - expressed in ON cells and not OFF cells
Nyctalopin - required for light and glutamate responses in ON cells
Define receptive field
Area in retina that activates a visual neurone when illuminated
What is a centre surround receptive field?
Illumination of centre and surround leads to opposite responses (centre depolarises, surround hyperpolarises)
How does centre surround visual field work?
Multiple photoreceptors converge onto one bipolar cell
Some activate directly (centre)
Some converge via horizontal cells (Surround)
Horizontal cells are inhibitory
Stops hyperpolarising photoreceptors
Leads to depolarisation of bipolar cells
In ganglion cells inhibition comes from amacrine cells
Function of pupil
regulates amount of light that falls on retina
Function of lens
focuses image on fovea
Fovea
part of retina highest visual acuity - contains only cones
