Karteikarten
visual system 1-5
Karten in diesem Stapel (42)
- 1source(s) of output from the retinaganglion cells
- 2two main visual pathways in the cortexventral: 'what' object feature stream- inferior temporal
Dorsal: 'where' spatial location stream- posterior parietal. - 3Role of the pupil and lensPupil 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)
- 4differences between cells of fovea and rest of retinafovea only contains cones. rest of retina contains rods and cones ( but mainly rods)
- 5what are the feed forward neurons in the retina?photoreceptors, bipolar cells and ganglion cells.
- 6What are the feedback neurons of the retina?The inhibitory interneuron; amacrine cells and horizontal cells.
- 7connections between bipolar cells, horizontal cells and photoreceptors lies in which layerouter plexiform layer
- 8The 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 - 9Differences 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 - 10what is rhodopsin made fromretinal + opsin
- 11what 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
- 12spectral sensitivity of rodsblue-green (~500nm)
- 13spectral sensitivity of conesthree different opsins each with different spectral sensitivity:
-Blue (~430nm)
-Green (~530nm)
-red (~560)
There are much less blue cones in the fovea. - 14what cells detect the graded potentials of photoreceptorsbipolar cells
- 15Types 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. - 16direct 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. - 171mm of retina corresponds to a visual angle of how many degrees?3.5
- 18why 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.
- 19which 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. - 20Receptive field organisation of ganglion cellscentre-surround organisation
- 21what is the purpose of the centre-surround organisation?Leads to a neural response that emphasizes the contrast between light and dark.
- 22Rod pathway to ganglion cellsno 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.
- 23types of GCsMost 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.
- 24Features 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 - 25features 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. - 26NonM-nonP ganglion cellsless well categorized
sensitive to different wavelengths.
-colour opponent cells - 27colour opponent cellsresponse 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. - 28neural pathway that leaves the eyeoptic nerve --> optic chiasm (combining of optic nerves from both eyes)--> optic tract
- 29what happens in the optic chiasm?left and right optic nerves join and axons originating from nasal retinas cross.
- 30Targets 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. - 31superior 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 - 32segregation 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 - 33The main input to the LGNPrimary visual cortex (~80%)- retina is not the main input.
- 34Names of the primary visual cortexstriate cortex/ V1/ Brodmann's area 17.
- 35where is the visual cortex locatedoccipital lobe of primate brain
- 36what is retinotopyWhere neighbouring cells in the retina feed to the neighbouring places on target structures.
- 37layers of striate cortex where pyramidal cells are foundIII, IVB, V and VI
- 38where are spiny stellate cells found in the striate cortex?iVC
- 39output cells of the visual cortexpyramidal cells.
- 40Inputs to visual cortex-Mangocellular - IVCa
-Parvocellulae-IVCb - 41where does kinocellular layers input in striate cortexlayers II and III
- 42In 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.