Flashcards
Retina and striate cortex
Cards in this deck (24)
- 1Describe the visual pathway noting the most important brain structures- nerve impulses travel from the retina to the LGN to the V1 area in the occipital lobe (1st visual cortex)-striate cortex
- the signals then split with some going throught the dorsal (parietal pathway) and some throught the ventral (temporal pathway)
- This feeds into balance vision ect. - 2why are horizontal and amacrine cells important in visual processing?Allows the lateral flow of information
w/o them only smmation would be possible to modulate signals h/e with them complicated signal processing can occur such as inhibition of certain signals - 3Explain the pathway in the vertical flow of information and why it s structure is important- retinal photoreceptors -> bipolar cells -> retinal ganglion output cells
- allows two regions for signal processing (plexiforms layers = dendritic processes) - 4Describe the position of the two types of retinal cells involved in lateral information processing and their functional role- horizontal cells - inhib cells at phtorceptor/bipolar interface (outer plexiform)
- help form receptive fields of RGC for contrast
- amacrine - inhib - bipolar/RGC interface (inner plexiform)
- form receptive fields of RGC for motion - 5Describe the two main types of RGCs' and their features- parvocellular cells
- small receptive fields (smaller than M)
- detect fine features
- colour sensitive
- magnocellular cells
- large recpetive fields - motion
-not colour sensitive but sensitive to luminance - 6Describe how parvocellular cells act as contrast detectors- looking at activeity of one p ganglion
-each p ganglion has a receptive field made up of photoreceptors
- you have on-center ganglions which receive inputs from on-center receptive field and vice versa
- if light shines on on or off centre receptive field produces high freq signal at area-specific ganglion
- if no illumination - no signal
If both illuminates avg signal
this allows measurement of contrast - 7describe how the inhibitory surround is createdmediated by horizontal cells that are connected directly to bipolar cells - these release GABA
- 8How are different responses generated in on centre and off centre ganglion?Mediated by different receptor types in on centre and off center bipolar cells
Glutamate is released upon illumination by photoreceptors
In on-centre bipolar cells = mGluRs - metabotropic - glu causes inhib
off-center bp cells = AMPR receptors
- ionotropic - glu causes excitation
Different cell responses - 9How do RGC receptive fields enhance contrast?Lateral inhibition e.g. 3 lines of information
- high firing rate from neuron B causes much higher activation of inhib interneurons for N2 and 3
- this increases the inhibition of the other neurons (n1 and N3)
- this results in a slightly decreased firing rate for neuron 2 (due to A and C inhib) but a much lower frq for N1 and 3 due to NB and C inhibition - sharpens signl - 10Explain why the hermann grid causes a optical illusion- due to lateral inhibition in retina and cortex
- there is more inhibition at the intersections of the lines and less inhibiton for the lines
- this results in the appearance of black dots at the intersections - 11What property of the retina does a scintillating grid showcase?- white dots at central retina focus, black dots in peripheral retina field
- this is because lateral inhibition is greater in the peripheral retina due to larger receptive fields - 12What i the structure of a typical amacrine cell?starburst
- central cell body and star-shaped dendritic arbour - 13what is the role of amacrine cells and how do they perform it ?motion
they do this by sending inhibitory signals to the diretional selective ganglion cells (DSGC) - it will inhibit the cell all directions of the signal apart from the one that is preferred by the DSGC
- the DSGC are also arranged around the amacrine cells in a way that corresponds to direction - top - inferior, bottom-superior, right-temporal, left-nasal - 14Give a possible explanation for idiopathic infantile nystagmus that invilves the amacrine cellsIIN - patients lose directional sensitivity to horizontal motion
- may be due to incorrect horizontal location of DSRGC relative to amacrine cells - 15\briefly describe the passage of information from the eye to the braineye -> optic nerve -> optic chiasm -> optic tract -> LGN -> optic radiation -> primary visual cortex (V1)
- Journey completed almost entirely by retinal ganglion cell axons - 16Describe what happens at the optic chiasm and what implications this has- at the OC approx 55% of RGC cross contralaterally at the optic chiasm
(the fibres from the nasal retina - section of each retina closest to nose cross)
. each cortical hemisphere sees the opposite visual field
. each hemisphere receives input from right and left eye - 17What is the function of the optic chiasm?- improves signal to noise ratio
more similar bw eyes - signal
- better hand-eye co-ordination
- brain hemisphere sees hand its controlling (90% CST decussate - increases speed of control)
- better 3D vision through retinal disparity - better binocular eyesight - 18Explain how having two eyes improves retinal disparity- horopter surface where no disparity bw eyes - image corresponds
- everything nearer - crossed disparity
- everything further - uncrossed disarity - 19Area V1 is retinotopic - what does this mean?It means the area is mapped spatially onto the primary visual cortex - each area corresponds to are of the visual field
- the fovea is cortically magnified e.g. cortical region is much larger than retinal fovea - move our eyes to optimise info from fovea to cortex - 20what are ocular dominance columns?- alternating stripes of neurons across the visual cortex that respond preferentially to the left or right eye
- similar areas for each eye are next to each other - 21How were ocular dominance columns discovered and why are they important?discovered in the 1960's in cats
- 3H proline injection into one eye - autoradiography of V1
. found that deprivation of one eye caused one set of columns to shrink
Affected by amblyopia (lazy eye - reduced vision on one eye) e.g. strabismus - 22Describe what strabismus is and name the four types of itA turn of one eye
causes input of that eye to be suppressed (prevent double vision) and reduces stereopsis - depth perception
esotropia - inwards
exotropia - outwards
hypertropia - upwards
hypotropia - downwards - 23How can amblyopia be reversed- patching better eye during development (less than 7) - decreases effect of ocular dominance
- 24What evidence is there of neural plasticity in the visual experienceAmblyopia and improvement through patching are both examples of this
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- Physiology (Physiology of excitable cells) Flashcards on Retina and striate cortex, created by Charlotte Pedley on 04/01/2019.
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- Charlotte Pedley
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