1911385
Description
Flashcards by emmabrudenell, updated more than 1 year ago
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Created by emmabrudenell
about 9 years ago
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| Question | Answer |
| 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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