Term
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Definition
- lens = adjust thickness to achieve focus & change magnification, gets stiffer as they get older
- retina = image focused by lens upside down and backwards on back plate, transforms & analyzes incoming images
- choroid = covers retina with black material (itself) to decrease light diffraction
- iris = controls light level
- photoreceptors = rods (high sensitivity, low acuity) and cones (low sensitivity, high acuity)
- trade off size of receptor with sensitiity (large = more sensitive)
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Term
| Signs of Computation for Vision (3) |
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Definition
- 1)
- burst of AP marks exact moment of onset of stimulus
- continuation/steady train of AP marks intensity of stimulus (more frequent = more intense)
- turning one form of energy to another
- 2)
- flicker fusion occurs at 30 Hz
- light flashing faster than 30 Hz is seen as a continuous light because steady image more useful
- visually as action potentials riding on receptor potentials
- 3)
- contrast enhancement where AP frequency of receptors A&B stimulated toether is less than when they are stimulated separately - axon collaterals inhibit neigbor by lateral inhibition
- more relevant information in edges than there is an overall illumination level
- so at high intensity next to the edge, axon fires more & at other edge of it fires even less than normal low intensity
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Term
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Definition
- retinas have annular antagonistic center-surround with lots of convergence - enhance contrast before sending info to CNS
- more convergence in periphery than fovea
- receptive field in fovea is smaller for high resolution
- animals like frogs have retinal processing instead of cortical, "bug detectors" which allows it ot be fast and efficient but difficult to evolve a more complex system & not adaptable & processing done independently of senses
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Term
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Definition
- Ganglionic
- ganglion cells
- fat somas because they support many axons
- axons face away from amacrine cells
- opportunity for convergence & divergence
- final output stage to CNS
- Inner Plexiform
- amacrine cells - movement detection/sensitivity
- synaptic junctions between bipolar and ganglion cells
- lateral inhibition (center-surround antagonism) takes place here
- Bipolar/Inner Nuclear
- another opportunity for convergence and divergence
- integrate activity from a few (foveal) or many (extra-foveal) receptors
- Outer Plexiform
- horizontal cells
- synaptic junctions between bipolar and photoreceptors
- dense lateral inhibition here (much center-surround antagonism)
- another opportunity for convergence and divergence
- essentially set up receptive field of bipolar and ganglion cells
- Photoreceptive
- rods & cones buried in choroid plexus
- high spatial resolution
- high metabolism in photoreceptors
- evolution theory - more layers added on top of receptors
- transform light to electrical signal
- Choroid
- absorb ambient light
- collection area for waste products to be dumped
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Term
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Definition
- have outer and inner segments
- a synaptic terminal
- outer segments contain stacked disks full of photopigments
- disks eventually become detached from membrane
- phagocytosis in epithelium (metabolism)
- as many as 4 disks per hour
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Term
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Definition
- more surface area = more sensitive = less spatial resolution
- prevalent in extrafoveal/periphery
- detect presence of object
- sensitive to light intensity
- night vision
- larger receptive field
- high convergence on bipolar & ganglion
- produce rhodopsin
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Term
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Definition
- shape = less surface ara = less sensitive to light = far more spatial resolution
- in foveal region - foveate to figure out what an object is
- sensitive to colors
- day vision
- smaller receptive field
- low convergence on bipolar & ganglion
- produces cone opsin
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Term
| phototransduction at the receptor |
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Definition
- retinal takes 2 configuations = 11-cis in dark and all trans in light
- in dark, all-trans activated G-protein and that activates cGMP phosphodiesterase (second messenger breakdown)
- less cGMP = Na channels closed, hyperpolarization
- Na+ channels held open by cGMP
- in dark, rods and cones tonically depolarized
- light causes hyperpolarization
- Calcium decreases cGMP and that decrases Na and that causes hyperpolarization
- when light increases, calcium decreases, increase cGMP, increases Na = makes channels available for closing by more light (able to respond to small changes in light)
- transmitter in rods & cones is glutamate
- ultimately: when light comes on there is less glutamate released
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Term
| Receptive Fields - Ganglion, Bipolar, Horizontal, & Photoreceptors |
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Definition
- effect of neurotransmitter throughout the nervous system is determined by the response of the postsynaptic surface (dendrite, soma) not the type of transmitter
- light hyperpolarizes photoreceptor, darkness depolarizes - when depolarized, photoreceptor releases glutamate
- glutamate release is graded based on amount of light
- next in line: bipolar cells. How a bipolar cell reacts depends on if it's on-center or off-center
- on-center: less glutamate causes it to depolarize
- off-center: less glutamate causes it to hyperpolarize
- as goes the bipolar cell, so goes the ganglion cell
- horizontal cells connect the photoreceptors and create the anagonistic surround
- horizontal cell does opposite of light to other cell - targets presynaptic photoreceptor
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Term
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Definition
- receptive fields in peripheral vision = rods = nightvision
- cover 80% of retinal area
- fat soma because large input processes = converge info from many bipolar cells
- large receptive field = high sensitivity & low acuity
- show particular sensitivity to movement
- 20% of fibers in otpic tract are "M" fibers, corresponding to the magnocellular system
- fat soma also because supports thick axon = fast conducting
- subcortical projections to pretectum (pupillary reflexes) and superior colliculus (visual tracking) as well as LGN and cortex
- the job of magnocellular system is to detect objects (particularly if they are moving) and bring foveal vision (parvocellular) on target for analysis
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Term
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Definition
- receptive fields in fobeal (central) vision = cones = day vision
- cover 20% of retinal area
- small soma because small input processes = converge info from few bipolar cells
- small receptive field = low sensitivity & high acuity
- 80% of fibers in the optic tract are "P" fibers, corresponding to the parvocellular system
- small soa also because supports thin axon = slow conducting
- no subcortical projections
- the job of parvocellular system is to provide detailed analysis of an object
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Term
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Definition
- retina -> LGN -> occipital lobe
- left vision = right hemisphere & vice versa, nasal parts cross through optic chiasm
- bottom halves (top of cortex) go to bottom half of visual cortex
- but visually, retina is upside-down & inside out because projected through optical lens
- fovea = posterior in visual cortex
- extrafoveal = anterior in visual cortex
- foveal representation in cortex takes up majority of area due to number of fibers it devotes to it in optic track
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Term
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Definition
- 6 layers, each layer has nearly complete retinotopic map
- 20% of fibers to LGN from retina, most from cortex, rest from RAS (in between layers, Koniocellular)
- 1, 2 = ventral, magnocellular (1 = contra, 2=ipsi)
- 3, 4, 5, 6 = dorsal, parvocellular (3, 5 = ipsi, 4,6 = contra)
- function
- relays visual info to visual cortex
- antagonistic center-surround fields = contrast
- where cortex controls/interacts with its own input
- sharpening of contrast
- modulate efficacy of synaptic transmission throughput from optic nerveto visual cortex
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Term
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Definition
- thick layer 4 = named striate cortex
- layer 4 = dark band= very dense
- massive input from LGN
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Term
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Definition
- Vernon Benjamin Mountcastle
- 3 functionally defined dimensions (also a 4th)
- ocular dominance
- orientation columns
- strategic innervation of LGN cells to stellate cells in layer 4 that then strategically converge onto the dendrites of simple cells ot form preference for linear stimulation of retina
- laminar dimension
- also blobs/pegs where double opponent color cells are located in yet another distinct columnar system within a hypercolumn
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Term
| External Auditory System's Processing Jobs |
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Definition
- amplify sound waves in an adjustable fashion
- decode the frequency of complex sounds (Fourier analysis)
- transduce sound information to AP encoded signals
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Term
| Purpose of connection to tensor tympani & stapedius |
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Definition
- ossicles connected to tensor tympani and stapedius muscles that provide adjustable gain
- used to:
- protect inner ear from harm
- increase "dynamic range" of exquisitely sensitive inner ear hair cells
- preadjust volume evel before speaking
- adjust for centripetal force produced by head rotation
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Term
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Definition
- 1) basilar membrane is tuned like a piano such that place proximal to oval window like to resonate to high frequencie & places distal resonate at low frequencies
- but this not precise for two-tone discrimination (discrimination by a single Hz)
- 2) outer hair cells sympathetically pump the membrane at different places, amplifying effect of passive resonance
- improves frequency discrimination, but still not enough
- 3) stereocilia designed like selectively tuned tuning forks, being short & stiff in high frequency & log and floppy in low frequency places
- improves frequency discrimination, but still not enough
- 4) stereocilia electrically tuned to preferntially respond to different frequencies - the depolarization/repolarization cycle is faster or slower in fast or slow stereocilia
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Term
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Definition
- cochlear nuclei
- superior olives
- inferior colliculus
- medial geniculate
- cortex
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Term
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Definition
- only area to receive monaural info
- prevalence of inhibition produced in these cells
- some enhancement center-surround antagonism in 2 tone experiment
- exaggerate difference in tones
- may enhance response to frequency change in particular direction (asymmetrical surround)
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Term
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Definition
- sources of efferents to outer hair cells to effect mechanical lateral inhibition
- need up to here for intensity discrimination
- lateral
- excited by intensity differences between ears
- localization based on head shadowing
- useful for frequencies above 1000Hz
- medial
- excited by timing differences between ears
- localization based on phase
- useful for frequencies below 1000Hz
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Term
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Definition
- receives input from both ears
- concerned w/ changes in differences between ears
- movement of sound localization
- interacts w/ superior colliculi in tracking moving sound source
- need up to here for frequency discrimination
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Term
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Definition
- main way station to cerebral cortex (feedback from cortex)
- maybe some sharpening center-surround antagonism
- selective attention ?
- polymodal responses
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Term
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Definition
- localizing complex auditory stimuli in contralateral auditory space
- organized as primary (pure auditory) and secondary (polymodal) cortex
- lateral = low
- medial = high
- orthogonally, binaural interaction columns = auditory space
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