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BMS1052

Terms in this set (178)

photoreceptors pass their signals onto cells called
bipolar cells
receptive field for visual-
region of visual space in which light affects a cell's membrane potential
bipolar cells have an .... hard definition
antagonistic, center-surround receptive field structure
when light is shone on the receptive field of a bipolar cell

but when light is shone around the surroundings of the receptive field DUE TO ANTAGONISTIC SURROUND
turns bipolar cell off, makes it hyperpolarised

when light is shone on surroundings on receptive field.. there is DEPOLARISATION
OFF bipolar cells what channels does it use
hyperpolarised (switched off) by light in their receptive field centre
depolarised by light in their receptive field surround
preserve sign of photoreceptors
IONOTROPIC GLUTAMATE GATED CATION CHANNELS
ON bipolar cells
depolarise by light in receptive field centre
hyperpolarised by light in receptive field surround
INVERT sign of photoreceptors
metabotropic G protein coupled receptors
the way in which bipolar cells respond to glutamate released by photoreceptors differs based on
if it is an on or off bipolar cell
why is the purpose of on off antagonistic structures
helps to highlight where edges are
on and off center bipolar cells target corresponding...
on and off center ganglion cells
ganglion cells
depolarise and hyperpolarise in the same way as bipolar cells but they are SPIKING!!!
then they convey information to other parts of the brain
retinal ganglion cells project to
many places
Lateral geniculate nucleus
Pretectum
Superior colliculus
Suprachiasmatic nucleus in hypothalamus
Also, the Pulvinar, pregeniculate nucleus and accessory optic system
90% of retinal projections are to the
lgn- LATERNAL GENICULATE NUCLEUS
diffused light will give what kind of results
will give intermediate results as its not communicating anything actually important
where do retinal ganglion projections go to usually
optic nerve and then the majority go to lateral geniculate nucleus LGN which subsequently sends significant projections to the cortex- associated with conscious vision
pretectum.. does what...VIA WHAT
reflex control of pupil and lens via intrinsically photosenstivie ganglion cells

responsible for the pupillary relfex response
binocular region
where the left and right fields of view cross over
hemifield
one of two halves of a sensory visual field
signals from each visual hemifield target the ...
contalateral LGN and primary visual coertex
partial decussation
Partial crossover of each eye's optic nerve fibers in the visual pathway, so that half stay on the same side of the brain, and half cross over.
left visual cortex represents the
right visual field
site of partial decussation and what comes after it
optic chiasm is the site of partial decussation... axons after the chiasm is bundled into the optic tract
axons from the nasal retina... do they cross
yes they cross at the optic chaism.. these are the ones close to the nose on the inside
axons from temporal retina.. do they cross
no they dont cross.. these are the ones on the side
signals from each visual field target the WHICH... LGN and primary visual cortex
contralteral
nasal and temporal retina
closest to nose
closest to temple
if you had transection of left optic nerve
before decustation.. basically losing your left eye
if you had transection of left optic tract
can't process anything on the left side of each eye---the right visual field
both eyes are receiving ,processing information but only the right portion of each eye will be able to send in information to cortex
if you had transection of optic chiam

what is this called
you lose steroscopic vision, leave ability to compare images recived from 2 eyes because there is no overlap anymore

you only have left eye processing part of right visual field and right eye processing part of the left visual field
bitemportal hemianopia
serial vs parallel processing
many compuations are carried out in parallel

some processing increases in complexity and must occur serially
Brodmann's areas experiment and what did he do
mapping of regions of the cerebral cortex
he cut the brain in regions and stained it to have a look
- based on the density of cell bodies in different ways
- the patterns of myelination
there are 2 main visual streams what are they called
- parietal/dorsal/where pathway
- temporal/ventral/what pathway
- parietal/dorsal/ where pathway
all areas specialised for processing object position and motion (vision for interacting with your environment)
- temporal/ventral/ what pathway
(vision for perception)- object form and identification
retinal ganglion cells have what kind of processing

which means each circuit receives..
parallel circuits lots of them

each circuit receives inputs from the same cone photoreceptors, but the inputs are processed in different ways
parasol cells compared to midget cells
large cell bodies, large dendritic arbors and large receptive fields sensitive to rapidly changing stimuli
not colour sensitive- inputs from all cone types
M- TYPE CELLS
project to Magnocellular LGNlayer
midget cells compared to parasol cells

colour sensitive?
type of cells?
project to?
p TYPE CELLS because they project to Parvocellular LGN layers

small cell bodies, dendrtiic arbors, receptive fields, senstivie to fine stimulus features
COLOUR SENSITIVE- selective cone inputs
midget cells are likely to contrubute to which perception
form perception
parasol cells are likely to contribute to which perception
motion pereception
90% of retinal projections go to
lateral geniculate nucleus LGN in the thalamus
each layer of the LGN is a
parallel represensation of the visual field and contralateral visual field
how many layers does the LGN have
6
LGN receptive field
circular and center-surround - very similar to the corresponding RGC
one line going through all6 layers of the LGN all represent the same
region of visual space, that will prefer the same orientation and have the same spatial receptive fields-- since the LGN has parallel representations
magnocellular laters of LGN
layers 1 and 2, inputs from parasol cells
parvocellular layers in LGN
layers 3-6 inputs from midget cells
contralateral layers of lgn
1, 4, 6
ipsilateral layers of LGN
2, 3, 5
inputs form the 2 eyes at the LGN is
kept seperate
where do LGN cells send their output to
primary visual cortex or V1
first cortical area
primary visual cortex what does it look like
straited/ stripy- this indicates there are areas that are denser with cell bodies
why is primary visual cortex called area 17
in the brodmann classification, it was the 17th area
M and P cells project to ....
different layers in the primary visual cortex
simple cells vs complex cells
simple cells have spatially segregated on and off region
need light in receptive field to be in very specific orientation whereas complex cells have more spatially homogenous receptive fields and position is not important
there is an over representation of what in the cortex
fovea
lots of cortex is devoted to processing this region
simple cells vs complex cells in terms of binocularity
simple cells are often monocular( respond to inputs from only one eye) while complex cells are nearly all binocular
multiple LGN cells with co-linear receptive fields will synapse onto a
single V1 simple cell
both simple and complex cells
respond best to elongated bars or edges
are orientation selective
in primary visual cortex, cells within the same cortical column...



while cells in adjacent columns
whill have similar tuning properties.. they prefer the same orientation and have similar spatial receptive field



.... prefer similar (not same) orientations
face selective neurons found where and when are they best activated
in the what pathway
found in the inferotemporal cortex - VENTRAL STREAM

best acitvated in response to a simplified iconic representation of face
motor sensitive neurons
found in the middle temporal area
they are tuned for direction

(dorsal stream)
akinetopsia
when lesions occurs in the motor sensitive neurons in the middle temporal area (dorsal stream)

impair motion perception (when things are moving)

lesions here can also impair tracking eye movements
sound is a
pressure wave, comprising successive cycles of compression and refraction of air molecules
sound frequency
number of cycles per second (Hz)
humans can hear frequneceis of
20-20000 Hz
pitch is determined by
pressure frequency
loudness is determined by
pressure intensity
first part of body that sound hits
pinna- important for sound localisation, sound filter and funnel
the outer ear funnels..
sound waves towards the tympanic membrane - ear drum- and also filters sound in a direction dependant manner
transmission sequence for air conduction
Sound waves => vibration of tympanic membrane => ossicle movement => vibration of oval window
=> movement of cochlear fluid and basilar membrane => neuronal response in hair cells within cochlea.
in bone conduction....
sound can also vibrate the bones of the skull, transferring vibrations directly to the cochlea.
beginning of the middle ear
tympanic membrane that gets vibrated
the outer ear funnels sound waves towards....
the tympatic membrane which gets viabrated (ear drum) which gets passed via the ossicles to the oval window
tympatic membrane is connected to the oval window via
a series of 3 bones called the ossicles
what seperates the middle ear and the inner ear
the oval window
fluid filled space on the other side of the oval window contain the....
inner hair cells which actually do the transduction
middle ear ensures...
efficient transfer of sound energy from air- outer ear to fluid- inner ear
3 ossicles in the middle ear
malleus, incus, stapes
ossicles act as a mechanical lever
they give an increase of 1.3 times the force of the viabrations at the tympatic membrane compared to the oval window.
there is a large 20X amplification in pressure between the 2 membranes
what surrounds the tympatic membrane
air
what surrounds the oval window
air on one side and liquid on the other side
why do you need a large amplification in pressure between the oval window and tympatic membrane
because the oval window has liquid on one side and it requires lots of pressure to move that liquid
how is the amplification of pressure between the 2 membranes acheieved
due to SA, the smaller surface area of the oval window compared to the tympatic membrane, hence if force stays constant, there will be around a 20 times amplification in pressure ahcieved by the middle ear
attentuation response

what happens if there are loud sounds?
mechanism that prevents damange to inner ear by preventing loud sounds from actually causing large viabrations of the oval window

if there are loud sounds, there will be contraction of 2 middle ear muscles and this reduces the movement of the ossicles and thus reduces the viabration at the oval window.
the inner ear-
a coiled, fluid filled structure. now it is fluid that is carrying the viabrations
the staples in the oval window viabrate...
the fluid filled section
the viabration in the fluid filled cavity goes by what directon
down the top part and then comes back via the bottom part
if the spapes is viabrating the oval window, the round window..
willl be bulging backwards and forwardss to compensate to allow the liquid somewhere to actually move.
movement of the basilar membrane
intermediae membrane that moves around in response to the sound viabrations,... acting like a physical filter.

viabrates in response to specific frequencies
low frequencies will cause the basilar membrane to...
the parts near the apex will viabrate the most
high frequencies will cause the basilar membrane to..
close to the base of the cohlea will viabrate the most
why is the base of the basilar membrane more sensitive to higher frequencies
because the base is naorrower and stiffer than the apex
natural sounds we hear are compelx.. hence in the basilar membrane
we are likely to get multiple part of the basilar membrane moving simultanously- complex viabrations
oval window gets pushed in and out by the
stirrup
do we lose high frequencies or low frequencies as we grow older
more likely to lose high frequencies
What are the 3 fluid compartments in the ear called (the top one and the return one)
where are they linked
and what fluid do they contain
pressure wave is carried through the scala vesitbuli and then back down scala tympani they are linked at the apex of the cochlea via the basilar membrane and they are filled by perilymph
scala vestibuli and scala tympani are....
continuous with one another
perilymph
extraculluar fluid that is contained in the scala vestibuli and the scala tympani that is high in sodium ions and low in potassium ions.... close to normal extracellular fluid
endolymph
extracellular fluid contained in the scala media that have an unusually high potassium contentration
scala media WHAT DOES IT CONTAIN
3rd fluid filled cavity in cochlea
filled with endolymph, has the inner hair cells
what is the endolympth doing
bathign the hair cells (auditory receptor cells that do the transduction)
endocochlear potential
what does this mean about the potential difference with auditory receptor cells
endolympth has a very high positive potential +80 mv relative to the perilymph..

hence, the voltage potential difference with auditory receptor hair cells and the endolympyh can be as high as 120-140mV
inner hair cells are sitting underneath the
tectorial membrane although they are not actually attached
movement of the basilar membane changes the membrane potential in
movement of the basilar membrane physically moves the inner hair cells .. which sit ontop of the basilar membrane.. causes memrabe potential in hair cells to change
tectorial membrane is physically connected to .....
longest hairs of outer hair cells, but is not connected to inner hair cells
hair cells are spiking or non spiking..
spiral ganglion cells?
non spiking

spiral ganglion cells whcih the hair cells tranduce onto is spiking
stereocillium of the inner hair cells structure
come together at the top and arranged in height order with the smallest on the left
how does sound tranduction between the inner hair cells and the endolymph work
tips of the sterocillia are mechanically coupled...they are protein tip links between the channels and the adjacent sterocillia

when sound viabrations cause the stereocillia to deflect, the protein tip links open, all the channels open
how does sound tranduction between the inner hair cells and the endolymph work

what ion is flowing WHAT IS INTERESTING HERE
potassium, due to the potential difference between endolymph and the intracellular fluod

ions are moving down their potential gradient not their concentration gradient
deflection to the right of the mechanically gated channels and sterocillia...
to the right means towards the longest stereocillium.. opens mechanically gated channels, allowing K+ influx which depolarises the neuron (hair cells)... opens voltage gated calcium channels.. neuro transmitter (likely glutamate) release onto a spiral ganglion neuron which will generate an action potential.
delection of the bundle to the left, towards the shortest stereocillum causes
closing of the mechanically gated potassium channels
different frequencies preferentially vibrate...........
different regions of the basilar membrane
what happens after glutamate release form hair cells
onto the neurites of spiral ganglion cells.. will caryy AP away.
spiral ganglion cells are tuned for
neurons are frequency selective. can predict the tone of pitch that they will preferentially respond to by their position on the cochlea
louder sounds will generate large aps in the
spiral ganglion cells
if you only have the spike rate of one spiral ganglion cell, can you predict the frequency ?
no because it can also be impacted by the intensity (loudness of the sound)
outer hair cells: inner hair cells
ration is about 3:1
many outer hair cells can synapse onto a...

whereas how many spiral ganglion cells innervate a single inner hair cell
many outer hair cells spiral onto a single spiral ganglion cell
10 spiral ganglion cells innervate each inner hair cell
role of outer hair cells
they are connected to the tectorial membrane- act as amplfiiers, increasing the sensitivity of the inner hair cells
spiral ganglion cells project to the
cortex via the cochlear nucleus, inferior colliculus and thalamic medial geniculate nucleus.
due to the tonotopic organisation, adjacent hair cells have
adjacent characteristic frequecies
in all visual and somatosensory systems, pathways synapse in the ...
thalamus before reaching the cortex
auditory systems are mostly organised
tonotopingally.. spatially arranged specific to sounds of different frequencies and different intensities.
ITD sound localisation
interaural time delay
distinguishing sounds based on when they reach the ears
ILD sound localisation
interaural level differences
distinugises sounds using circuitry that can measure intensity of sound waves in both ears.. noises from front will have the same intensity in both ears
phase locking
where you have aps occuring at specific phases of the viabrations of sound wave
...... Action potentials occur at the same point (phase) in each cycle for a given frequency
can phase locking still be valid if it doesnt occur every cycle
yes, as long as it stilll occurs in the same spot when it does occur
example of when phase locking occurs NOT on every cycle
given that neurons have a refractory period of at least
-1ms, a single neuron cant fire 1000 action potentials per second- no way to get a single neuron ap at a phase locked on any cycle for a sound frequency that is higher than like 300 hZ (the majority of the case)
with very high frequencies of sound (5kHz+), phase locking is...
hence can ITD be used
impossible.
interaural time delay.. depend on phase locking whic breaks down above 5kHz+
hence ITD cant be used
coincidence detector neurons..
when will they depolarise
how many detector neurons
receive inputs from both the left and right cochlear nerve but receives inputs after different types of delays... will only delpolarise and cause a potential downstream if the left and right signals synpase at the same time

can have multiple decector neurons
delay lines use
they use difference axonal conduction delays to match temporal offset
delay lines in ipsilateral ear
delay lines are all the same length
in mammals, the delay lines are only found on the
contralateral (opposite) ear
proprioception
gives you indication of your position of limbs
how can we quantitely test touch perception
two point dicrimination threshold- how far apart do two points have to be in order to reliably judge them as two rather than one
highest sensitivty to touch where
- tip of index finger, lip
mechanoreceptors
peripheral touch receptors
how many types of touch receptors?
4
mechanically gated cation channels
Membrane tension, or stretch, can open ion channels.
--meaning Na+ can enter the cell, depolarising the membrane.

can be linking proteins involved or also physically gated G protein couples receptors.. they are typically involved in pain recepion
is the somatosensoery neuron, spiking?
yes
mechanically gated with linked proteins
movement of one part of the neuron relative to another will cause depolarisaiton due to the linking proteins, opens non specific cation channels INTRACELLULAR AND EXTRACELLULAR
mechanically gates cation channels with g protein
they are g protein coupled receptors
slow to activate, long lasting
likely to be involved in encoding pain
the cell bodies of sensory afferents are in the

sensory afferents are what kind of polar neurons
dorsal root ganglion

unipolar neurons
each sensory axon is associated with only a ......, which
single TYPE of mechanoreceptor
superficial receptors have what size receptive fields
they have smaller receptive fields so they can contribute more to fine position discrimination
merkel cell name and location
skin type
SA 1- superifical- tip of epidermal sweat ridges
hairy + glabrous
meissner corpuscle cell name and location
skin type
RA 1- superficial
glabrous skin
Merkel discs
SA1, encode the shape and size of objects touching the hand
they have small RF and slow adaptation
Ruffini ending cell name and location
skin type
SA 2-deep tissue- dermis
hairy+glabrous
Pacinian corpuscles cell name and location
skin type
RA2- deep tissue: dermis
hairy +glabrous
RA1
meissner's corpuscles
Pacinian corpuscles
RA2 receptors (rapidly adapting)
concentric, fluid filled layers of lamalae of connecting tissue (like an onion) around axon temrina
most sensitive mechanoreceptor
what happens when u apply sustained pressure to RA2 receptor
different lamalae layers can shift relative to each other, they absorb the pressure, hence ony initial part of sustained touch is signalled by Pacinian corposcules
in the absense of laminae, this rapid adaption does not occur
how high frequency do RA2
30-500 Hz VERY HIGH- directly accounts for human perceptual threholds
all mechanoreceptos are found in HAIRY skin apart from

what does this indicate?
meissner corpuscle- indication they have a role in fine touch
mechanoreceptors that start with M are
superficial
which mechanoreceptors encode the shape and size of objects touching the hand
merkel discs SA1
reading braille

what does it require
what is the best mechanoreceptor for this?
requires high acuity and small receptive fields

Slowly adapting Merkel disks provide the most useful information about the Braille stimulus due to their small RF and slow adaptation.
the cell bodies of sensory afferents are in the
dorsal root ganglion (not in the spinal cord)
sensory afferents are...
uni polar neurons
spike initiation zone is near the specialised accessory structure
cell body is outside the spinal cord in the dorsal root ganglion
down at low frequcies,
at high frquencies,---- human perception touch
human perception follows the meissnam corp

at high frequencies, following the sensitivity of RA2- PACINIAN CORP
do mechanoreceptors differ in receptive field size
yes
superficial receptors typically associated with

neurons?
multiple superficial receptors are associated with a single neuron and axon

they have small receptive fields
deep receptors are typically associated with
a single axon and neuron
corpuscles of touch..why? which means
adapt very quickly due to their shape which means their firing rate drops in response to sustained stimuli
do mechanoreceptors differ in adaption rate
yes
human threshold compared to neural threshold
Lowest amplitude of a vibration that can be reliably detected...
Lowest stimulus intensity that reliably evokes 1 AP per cycle
smaller stimuli Merkel cells...
Smaller stimuli IS PREFERRED- activates a smaller number of receptors more strongly
density is inversely proportional to RF size... hence the highest densities of mechanoreceptors belong to
Meissners corp and Merkel cells
what is PRIMARY about the primary sensory area 4 things
-receives the denses inputs from VP nucleus in thalamus
- neurons are responsive to only a single sense- here only for somatosensory stimulu
- lesions to primary areas will affect basic perception of sensory touch
- electrical stimulation evokes touch sensation
neuros spatio- temporal receptive field
the way the neuron responds over time depends on where the skin is touched
central zone for neuro spatio-temporal field
follows the same trend of rate in different spaces being stimulated
do sensory neurons typically have simple spatio-temporal receptive fields
no they are normally quite complex, habe areas where spiking is increased and have areas where spiking is decreased
why is surround inhibition useful
lets you know about edges in space
why is replacement inhibition usefel
lets you know about edges in time- when did you start and stop touching something
adjacent regions in the somatosensory cortex correpond to
adjacent regons in the skin
plasticity
the neural represenation map can change according to things that happen in the real world such as over representation or under representation of fingers...
e.g if a finger is cut off, you can get overexplansion of the other fingers and reorganisation
areas with a higher densitiy of sensory receptors are associated with more
cortical surface area
discrimintation performance is higher for skin regions with
Smaller receptive fields
Higher receptor density
Larger regions of cortex devoted to processing
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