visual system 1-5

Frage	Antworten
source(s) of output from the retina	ganglion cells
two main visual pathways in the cortex	ventral: 'what' object feature stream- inferior temporal Dorsal: 'where' spatial location stream- posterior parietal.
Role of the pupil and lens	Pupil regulates the amount of light that falls on the retina. lens focuses image onto the fovea (the part of the retina with the highest visual acuity)
differences between cells of fovea and rest of retina	fovea only contains cones. rest of retina contains rods and cones ( but mainly rods)
what are the feed forward neurons in the retina?	photoreceptors, bipolar cells and ganglion cells.
What are the feedback neurons of the retina?	The inhibitory interneuron; amacrine cells and horizontal cells.
connections between bipolar cells, horizontal cells and photoreceptors lies in which layer	outer plexiform layer
The three major classes of retinal ganglion cells (only output of the retina)	-ON cells- on spike when light is on. -OFF cells- only spike when light is off. -ON/OFF cells- shorter spikes, but spikes when light is on and off
Differences between rods and cones	-Rods- more disks and higher photopigment concentration=more sensitive to light= scotopic vision -Cones- phototopic vision, three types of photopigment in cones
what is rhodopsin made from	retinal + opsin
what are rods not used in day light vision?	in bright light, additional light causes no more hyperpolarisation, thus daylight vision depends entirely on cones, whose photopigments require more energy to become bleached
spectral sensitivity of rods	blue-green (~500nm)
spectral sensitivity of cones	three different opsins each with different spectral sensitivity: -Blue (~430nm) -Green (~530nm) -red (~560) There are much less blue cones in the fovea.
what cells detect the graded potentials of photoreceptors	bipolar cells
Types of bipolar cells and receptor they express	-OFF bipolar cells- ionotropic glu receptor (excitatory)- mediate classical depolarizing EPSP from influx of Na. -ON bipolar cells- metabotropic glu receptor (inhibitory)- GPCRs respond to glu by hyperpolarizing- as amount of cGMP on postsynaptic side falls, closing Na channels.
direct and indirect inputs to bipolar cells	-Direct- from 1 (fovea) to 1000's of direct synaptic input from photoreceptors- receptive field centre -Indirect- connected to a ring of photoreceptors via horizontal cells- receptive field surround.
1mm of retina corresponds to a visual angle of how many degrees?	3.5
why are bipolar cells said to have a center-surround receptive field?	The response of the membrane potential in the surround to light is the opposite to the response of the receptive field center to light.
which types of ganglion and bipolar cells connect in which layers of the IPL?	-Upper part: axons and dendrites of OFF cells. -Lower part: axons and dendrites of ON cells.
Receptive field organisation of ganglion cells	centre-surround organisation
what is the purpose of the centre-surround organisation?	Leads to a neural response that emphasizes the contrast between light and dark.
Rod pathway to ganglion cells	no direct rod pathway to ganglion cells, rod cells activate a special class of amacrine cell. All form gap junctions with ON cone bipolar cells and inhibitory (glycinergic) synapse with OFF ganglion cells. Cones do have direct pathway via bipolar cells.
types of GCs	Most GCs have a centre-surround receptive field with either a ON of OFF centre. they can be further catergorized into Parvolcellular (Midget) cells or Magnocellular (parasol) cells.
Features of Parvocellular (midget cells) ganglion cells	-80% -Small dendritic tree -Small receptive field -transmit info about high resolution detail- form/colour -Slow conduction velocity and sustained discharge as long as stimulus is still on -Low sensitivity to low contrast stimuli
features of magnocellular (parasol cells) ganglion cells	-10% -Large dendritic tree -Large receptive field. -Transmit info about motion -High conduction velocity and transient burst of APs. -High sensitivity to low contrast stimuli.
NonM-nonP ganglion cells	less well categorized sensitive to different wavelengths. -colour opponent cells
colour opponent cells	response to one wave length in receptive field is cancelled by another wavelength in receptive surround. two types of oppenency are found; red vs green and blue vs yellow. white light activates centre and surround equally so response is cancelled.
neural pathway that leaves the eye	optic nerve --> optic chiasm (combining of optic nerves from both eyes)--> optic tract
what happens in the optic chiasm?	left and right optic nerves join and axons originating from nasal retinas cross.
Targets of the optic tract	-Small number to hypothalamus: involves in sleep and wakefulness with daily light/dark cycle. -~10% to midbrain: pretectum for control of pupil size and certain eye movements. Superior colliculus (optic tectum). -Most to LGN which gives rise to axons that project to primary visual cortex.
superior colliculus	-Integrates info from different sensory modalities -Main function is regulation of saccadic movements. -object localisation; orientating reflex, smooth pursuit, prediction of movement, saccadic movement
segregation in the LGN	-right nasal retina and left temporal retina = right LGN. -Right eye; layers 2,3,5 -Left eye; layers 1,4,6 -Layers 1,2 contain mangocellular GCs -Layers 3-6 contain parvocellular GCs. -Kinocellular layers lie between these layers and contain nonM-nonP cells
The main input to the LGN	Primary visual cortex (~80%)- retina is not the main input.
Names of the primary visual cortex	striate cortex/ V1/ Brodmann's area 17.
where is the visual cortex located	occipital lobe of primate brain
what is retinotopy	Where neighbouring cells in the retina feed to the neighbouring places on target structures.
layers of striate cortex where pyramidal cells are found	III, IVB, V and VI
where are spiny stellate cells found in the striate cortex?	iVC
output cells of the visual cortex	pyramidal cells.
Inputs to visual cortex	-Mangocellular - IVCa -Parvocellulae-IVCb
where does kinocellular layers input in striate cortex	layers II and III
In which layers of the visual cortex is there mixing of left and right eyes?	layers II and III but magno and parvocellular processing streams a still segregated.

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