Greg Detre
2/3/00
Carpenter, Neurophysiology, in CCC
dermatomes � regions projecting to each dorsal root
Pacinian corpuscle, Meissner�s corpuscle, Merkel�s discs, Ruffini endings
glabrous = hairless
free/naked endings = hairy skin, hair follicles, glabrous skin, deep fascia/visceral organs
small/unmyelinated fibres C + Ad (III + IV, II)
encapsulated endings
Ab (II)
� hair
base � Pacinian corpuscles (pressure-sensitive)
middle � Merkel�s discs
length � thin filaments link to palisade of fast-adapting endings)
free endings � warmth + pain (+ possibly mechanical stimulation too)
encapsulated endings � some for cold
others � mechanoreceptors of some kind
concentric layers of Pacinian corpuscle � complete + rapid adapter
non-directional sensitivity to local deformation - pressure
Ruffini organs � branched naked nerve endings twisted between collagen fibres that leave the capsule and anchored to nearby cells/other structures
simtulated by tension which distorts the nerve endings
adapt incompletely
similar to Golgi tendon organs (proprioception)
Merkel�s discs � close to the outside
attached by dermosomes to the bottom of the epidermis
very sensitive to deformation of the skin
incomplete adaptation
light touch receptors - contact
Meissner�s corpuscles
nerve endings associated with collagen fibres
found in the dermal folds beneath the epidermal ridges
collagen fibres are connected sideways with the epidermal cells
register sideways shearing of the shin (especially/e.g. lifting an object, in the fingertips)
density �� with age (from 50/sq mm � 10/sq mm)
because many of these receptors are completely adapting � only perceive much when the pattern of stimulation changes
feeling of touch = temporal patterns of firing of mechanoreceptors in the skin, with knowledge of the movements made
2 types of afferent fibres
small � mostly from free endings
large � mostly encapsulated endings
different modes of termination in the nervous system
different parts of the dorsal horn of the spinal cord
dorsal horn divides into 6 (c. parallel) laminae
smaller fibres enter directly from the dorsal root
� terminate� in I + II
largest fibres � III-IV
make contact with cells including short inter-neurons � II
(important in processing pain signals)
neurons in the dorsal horn = control by brain
if the descending pathways are blocked
�/span> radically alters the receptive fields of the dorsal horn cells
1. branches of the larger fibres (from encapsulated mechanoreceptors)
� turn upwards after entering the dorsal horn
form: pair of large ascending dorsal columns
� ipsilaterally up to the medulla
terminate in the dorsal column nuclei (gracile + cuneate)
gracile: inputs from sacral, lumbar and lower thoracic
cuneate: inputs from higher regions
then 2nd-order fibres � contralaterally��� realy through the internal capsule � somatosensory cortical area
(SI = areas 3, 2, 1)
lemniscal system � preserves general topographic relationship between different areas of the skin
sensory homunculus � neighbouring, but distorted shape
SII � receives somatosensory information from both sides
responds to different modalities from SI
2. smaller afferents (free endings + some encapsulated ones)
temperature, pain + light touch
� neurons in I + V, then ascend contra-laterally as spino-thalamic projection
anterior + lateral spinothalamic pathways = anterolateral system
= older than the lemniscal system
new, fast lemniscal system � precise + orderly projection directly � cortex
older, slower/diffuse projection anterolateral system � often less precise but immediately important information (often with emotional/affective quality)
one gives objective information, the other requires a response
hemisection of the spinal cord that cuts of all ascending fibres on one side below that level
loss of deep pressure + vibration on one side
loss of pain, temperature and light touch on the other
also: cutaneous fibres ascend in the posterior spinocerebellar tract
larger Ab (group II) fibres from the skin = respond to mechanical stimuli
completely adapting (e.g. Pacinian + Meissner, + some endings in hair follicles) � only respond to changes in the skin
very sensitive to vibration
�/span> sense of roughness when hand passes over textured surface
very sensitive � threshold of Pacinian = 10mm/nm??? of skin displacement (if rapidly applied)
help with grasping + when objects slip (if fingers anaesthetised, don't modify grip for slippery objects) � short latency
incomplete adaptation � signal static deformation too
Merkel�s discs + Ruffini endings
e.g. micro-electrode recording � microstimulation of a single AP in the fast-adapting fibres �/span> sensation
smaller Ad + C cutaneous afferent fibres � light touch, pain and temperature more complex patterns
warm + cold Ad fibres: fire tonically as a function of temperature
peak for���� warm fibres: 45� C
����������������� cold fibres: 30� C
incomplete adaptation � sudden warming skin �/span> transient discharge whose activity settles at a new level (same with sudden cooling)
paradoxical cold � cold receptors also respond to warming >45�C
adaptation of these receptors � perception of skin temperature
thermoreceptors: very small receptive fields
separated, not overlapping: warm/cold spots 5-15mm apart
very few fibres ascend in spinothalamic tract (c. 1000)
don't need acute spatial resolution
RF = the particular area (of skin) within which a stimulus will affect the firing of a particular fibre
one fibre � 100 hair follicles, each innervated by >1 fibres
the receptive fields are very large, with overlap
overlapping receptive fields �/span> � accuracy of localisation and less vulnerable to damage
at 2nd order level where the incoming afferent fibres are relaying � ascending 2nd-order fibres (gracile + cuneate nuclei)
excite inter-neurons too which send inhibitory connections to neighbouring 2nd-order cells
each incoming fibre stimulates its own 2nd order cell but inhibits the surrounding ones
the cells are pushing on each other�s shoulders
lateral inhibition � exaggerates changes in intensity
compensates for the blurring from the overlap of the receptive fields
or whenever there is con/divergence in the projection from one neuronal level to another
enhances edges � neural activity maximum around the border
i.e. adaptation in the spatial, not temporal, domain
e.g. hottest at the surface of hot water around your leg
� redundancy of neural signals
does not � acuity (= spatial detail)
2-point discrimination test � variation depends on the size of the receptive fields
can't tell if one point or two, but can tell when one goes
SI: large-scale sensory homunculus organisation
mosaic of columns <1mm in diameter
responses of cells at any depth within a column = particular modality and localised areas of skin
neighbouring columns: different modality, similar location
mutually inhibitory
differences between areas 1, 2, 3 � classic modalities, deep vs superficial receptors
the maps = very dynamic + flexible
bandaging a monkey�s hand �/span> different cortical map in hours
amputation/severing peripheral nerves �/span> lose cortical representation completely
SII � more complex analysis of afferent information
bi-lateral activated����� receptive fields for opposite sides of the body � mirror images
outlying���� direction-specific responses
respond to >1 stimulus modality
painful stimuli
electrical stimulation �/span> tingling �electric� sensations
lesions �/span> raised tactile thresholds
� 2-point discrimination
impairment in finer somatosensory judgements
post-parietal regions: putting things together
e.g. shape of hand-held objects = astereognosis
primary somatic sens � relatively unimpaired
pricking vs burning pain��������� Ad + C fibres
experiments on humans � peripheral nerve conduction blocked
(by anoxia or local anaesthetics)
anoxia � by inflating a cuff round the arm � affects the largest fibres first, then the C fibres
lose pressure and position sense first
then (Ad) temperature sense and pricking pain
then burning pain and itch
local anaesthetics
C fibres go first � burning pain + itch
largest A fibres last � temperature and pricking sense, then pressure
recordings from single afferents
Ad: very sensitive to mechanical deformation of the skin
large receptive fields, pain spots
C: various types
some respond to mechanical stimulation
others respond specifically to extreme cold/heat
both C + Ad fibres = free endings in the skin
2 different kinds of response/function to pain
withdrawal, e.g. when touching a hot object
rapid response + fast fibres
immobilisation � protecting the affected part from further injury through movement, e.g. back injury
long-term response; slow fibres sufficient
visceral pain = C-fibres only
also: hence warm + cold receptors, not just a single temperature receptor
stimluation of the viscera � pain
especially severe distension/constriction
yet the digestive tract � insensitive to cutting/burning/chem
often referred � body surface sharing the dorsal root
left arm <= angina pectoris
groin <= stone in ureter
itch � C fibres (blockign experiments)
tickle � represents the sensation produced by particular pattern of stimulation of the C fibres
(perhaps = the result of release of histamine from damaged tissue)
both demand a response � like all C-fibre stimuli
central pathways for pain
anterolateral system
sectioning �/span> complete peripheral analgesia (pricking + burning)
at higher levels: the two types of pain have slightly different distributions
ascending pricking pain fibres � somatosensory thalamus then � cortex (especially SII)
burning: older + more diffuse
central thalamic regions: general projections � the cortex, the ascending reticular formation, periaqueductal grey and hypothalamus
interferences with the thalamus in humans �/span> greater effect than cortex
electrical stimulation of:
ventrobasal region �/span> pricking pain
central regions �/span> intense unpleasantness
lesions of thalamus �/span> relief from chronic pain or unendurable spontaneous pain
cortex:
damage: sometimes slightly � pain
stimulation: doesn't �/span> pain sensations
relationship between type/intensity of stimulus and pain felt is very variable
depends largely on emotional state, + implications of the pain
excited/unexpected: feel little pain
apprehensive, e.g. dentist � very violent reaction to any stimulus
pain ≈ emotion triggered by certain patterns of cutaneous stimulation
difference between objective sense of the existence of noxious stimulus vs �feeling� the pain
(see frontal leucotomy for intractable pain)
pain: influenced a lot by other modes of skin stimulation
� by warmth, mechanical stimulation, rubbing, acupuncture, self-stimulation with implanted electrodes
� by specific damage to larger cutaneous afferents
�/span> � sensitivity to painful stimuli
Melzack and Wall: 1962 explanation for this antagonism between larger cutaneous afferents and smaller pain fibres
inter-neurons in the substantia gelatinosa (dorsal horn layers I + II) receive excitatory information from incoming large mechanical fibres
�/span> inhibit the neurons of the ascending anterolateral system
\ the response to a nociceptive stimulus � balance between stimulation of large/small fibres
= a gating mechanism
WDR cells (wide dynamic range) in the anterolateral system
concentric receptive field
centre: light touch + noxious
surround: inhibited by mechanical stimulation
\ large mechanical stimuli cancel out the centre, so no pain
lateral inhibition: not to � spatial overlap, but to � overlap between modalities
very small mechanical stimulus �/span> pain, without causing tissue damage
e.g. thorns + drawing pains (useful if barefoot)
pain felt at certain level of firing when heat is applied
�/span> different level of pain with same rate of firing with pressure
feeling of pain s not directly proportional to firing of �pain� fibres
descending control from brain: endorphins + enkephalins
neuropeptides (= the natural opiates) � transmitters + hormones
�/span> analgesia if injected intravenously � periaqueductal grey
excitatory pathway from periaqueductal grey � raphe nucleus in the medullary reticular formation
which � descending fibres to spinal cord, which inhibits the transmission of afferent pain impulses through an enkephalin-releasing spinal inter-neuron
thus the pain fibres projecting to the periaqueductal grey = a �ve feedback system to modify its own transmission
proprioception =
information about the positions + movements of our limbs
the forces generated by our muscles
attiude + motion relative to the earth
2 types of proprioceptors in voluntary muscles
both ≈ stretch receptors. different function because different situation in the muscle as a whole
spindles � respond to muscle length + rate of change of length
in parallel with the main contractile elements
\ their stretch � stretching of the muscle itself
Golgi tendon organs � muscle tension, force
in the muscle tendons, in series with the contractile elements and the load
\ their stretch � the tension exerted by the muscle
= found in all the striated muscles in the body
fluid-filled capsule <4mm long, ends attached to the exterior sheaths of neighbouring muscle fibres
inside: small number of intra-fusal fibres, with contractile ends, mid contains the nuclei
2 main types of intra-fusal fibres
nuclear chain fibres � thinner, nuclei lined up in a row
nuclear bag fibres � pronounced bulge in the middle, nuclei bunched together
usually 5 or 6 intra-fusal fibres/spindle
2 kinds of afferent fibres innervate the spindle:
primary fibres � larger (group Ia) � branches to the central portions of both kinds of fibre (nuclear chain/bag) � annulospiral endings
dynamic, very pronounced adaptation
proportional to rate of change of stretch (and partly proportional to muscle length)
secondary fibres � (group II) terminate as annulosopiral/flower-spray endings, mainly on nuclear chain fibres, more peripherally than the Ia endings
group II fibres: non-adapting/static � proportional to the degree of stretch of the spindle at any moment
possible causes for adaptation is sensory receptors:
energy filtering � static information is thrown away before transduction
membrane adaptation � even steady conductance at the ending � fall off in firing frequency
in the Pacinian corpuscle: both
in the muscle spindle � mainly energy-filtering (like the concentric lamellae of the Pacinian corpuscle)
the contractile portions of the intrafusal fibres behave as much much more viscous than the central portion
spindles also receive motor innervation from Ag (g-fibres)
2 types of fusimotor fibre � static and dynamic
�/span> cause contraction of the peripheral regions of the spindle which stretches the sensory elements �/span> � firing of the afferent fibres
effect of g-stimulation (on the afferent fibres) ≈ extra stretch being applied to the muscle as a whole
= � the sensitivity of the endings to stretch
the CNS can control the sensitivity of the spindle afferents and also their adaptational properties
similar appearance to the Ruffini organs in the skin
respond to tensionin their associated tendon
innervated by group Ib afferents
seemed to have high thresholds � large forces were necessary over the whole tendon to make them fire
actually, they respond well to tensions generated by the muscle fibres they are joined to
rather than the overall tension being shared out amongst the tendinous fasiscles
respond to tension, rather than muscle length
usually reciprocal to the spindles during active movements
because extra fusal activity � tension + � length
passive movements � spindles + tendon organs = in step
both modalities use similar sensory pathways
fibres enter the dorsal roots
most synapse in a spinal nucleus = Clarke�s column
ascend homolateral posterior spinocerebellar tract � cerebellum
rostral afferents ascend � accessory cuneate nucleus of the medulla; then the cuneocerebellar tract
or the spino-olivary tract � the inferior olive which projects via climbing fibres � cerebellar cortex
apart from ascending � cerebellum, muscle proprioception fibres are involved in various reflex mechanisms within the spinal cord
especially the stretch reflex (simplest = monosynaptic excitation of a motor neuron by a Ia afferent)
some projection of muscle proprioceptors � cortex via the ventral posterior thalamus
another important source of information about limb position and movement:
mechanoreceptors in ligaments and the capsules of joints
variety of morphological types � similar to those int eh skin
Pacinian corpuscles + Golgi-like endings (large group I axons)
Ruffini endings (group II)
small nerve ifbres with unencapsulated endings
some:
complete adaptation = sensitive to rate of change
incomplete adaptation = signal limb position too
problem: most receptors� �excitatory angle� < � the entire range the joint � � sensitivity to change in position within that range
\ information about limb position is coded by frequency of firing, but also which neurons are firing
in some joints: afferent fibres fire most at extremes to warn of dislocation
other joints: the majority are mid-range
afferent information from joints follows the same pathways as corpuscles in the skin
fibres ascend in the ipsilateral posterior columnns
then relay in the cuneate + gracile nuclei
cross, then via the medial lemniscus � ventral posterior lateral thalamus, then to somatosensory cortex
or to the spinocerebellar pathways
joints contribute to proprioception (especially static)
tested: by injecting anaesthetics into the synovial fluid
or cuff blocking blood to the joint but not the muscles
hip replacement � mechanoreceptors are lost, reduced sensitivity to join position (using information from the muscles + skin)
muscle receptors help with proprioception
surgeons pull on exposed tendons �/span> conscious patients report a sense of limb movement
vibrator on muscle/tendon: stimulates the Ia stretch receptor endings preferentially because of the high rates of stretch it generates
�/span> illusion of muscle shortening, even if held stationary
muscle������������������ predominantly change of position; sense of weight
joints�������������������� predominantly static position
skin����������������������� predominantly load (and perhaps position sense)
efference copy������ predominantly load
see book
horse radish peroxidase (HPP)
retrograde trasnmission � identify the origin of efferents)
Golgi silver stain
stains whole neurons at random
procion yellow
most of a single neuron to make the micro-electrode cell
labelled amino acids (e.g. tritiated leucine)
orthograde: identify where the soma projects to
related technique for tracing axonal pathways
to study the degeneration resulting from injury to a nerve fibre
2 kinds of degeneration:
orthograde/Wallerian degeneration � distal to the cut
retrograde � in the direction of the cell body
Nanta stain identifies certain of the orthograde degeneration products
retrograde degeneration �/span> various characteristic change in the cell body
transneural � when the degeneration change extends beyond the synapse to affect the next neuron along
problem with degeneration studies � can't tell whether the neuron originates in the damaged area, or is just connected to a fibre which passes through
select cells associated with a particular protein
usually a peptide transmitter
using immunohistochemical stains = labelled antibodies which enable the identification of a group of cells within a nucleus which share common function
recording
stimulation
lesions
imaging
local metabolic rates � deoxyglucose � apparent when the brain is subsequently sectioned
Lashley � cast doubt on simple-minded views of localisation
the effect on rats in a maze depended on the quantity of cortex removed, not where from
plasticity � the ability of one area of the brain to take over the function of another
scotopic � mesopic � photopic
illuminance = light falling
luminance = emitted
albedo = diffusion
visual range = 1015
luminance/illumination �/span> black/white paper in sunlight
20% range at any one time though � eye responds to albedo
adaptation � 40 mins, 2 stages
focal distance = function of:
radius of curvature
ratios of the refracture indices of the 2 media
cornea, front + back of lens
lens: change shape, alter focal length = accommodation
nutrients from the aqueous humour
radial suspensory ligaments � contracted by the fibres of the ciliary muscle (parasympathetic innervation)
range of accommodation � near and far points
age �/span> � elasticity of the lens, presbyopia
myopic vs hypermetropic������� spherical correction of the lens
astigmatism � non-uniformity in the radius of the corne
chromatic aberration, spherical aberration
retina inside out � nerves exit through blindspot optical disc
fovea centralis inside the macula lutea(???)
cones only � 2-3mm across
much neural processing in the retina � otherwise very thick optic nerve, �/span> immobility of the eye, larger blind spot
optic nerve fibres � 2 synapses from the retinal receptors
considerable convergence: ganglion + amacrine � spiked discharges
receptors, bipolar and horizontal cells: passive
outer segment: grossly modified cilium, photopigment, surface invaginations
inner segment: including nucleus, mitochondria, synapse terminal
photopigment � chromosphore (retina)
protein/oligosaccharide complex (opsin)
rods:
light���� �/span> isomerism of the retinal
����������� �/span> series of changes in the configuration of the rhodopsin
�������������� �/span> dissociation of the opsin from the retinal
pigment = bleached
can be regenerated by enzymes in the receptors and the pigment epithelium behind
this slow regeneration = the long-time-course of recovery of red sensitivity during dark adaptation
retinal reflection densitometry
cones can function at higher levels because regenerate quicker + bleach less, though the mechanism is similar to rods
see pg 45
bleaching and G-protein �/span> phosphodiesterase (PDE)
cGMP � GMP which reduces Na permeability (by � cGMP)
hyperpolarises the receptor
single rod can respond to single photon
cones are less sensitive, especially because � convergence + pooling
the time-course of the hyperpolarisation = very short
as usually with indirect transduction with a lengthy cascade
large stimuli �/span> plateau � closure of all Na channels
S-shaped saturation curve
photoreceptors respond to light (+ve stimulus) with �ve response
(hyperpolarisation + consequent � in neurotransmitter release at the synaptic ending)
in the natural world, dark = the stimulus � fly, predator, shadow etc
photoreceptors tonically release glutamate
rod bipolars depolarise in response to light
fovea � acuity preserved over sensitivity
opposite in periphery
bi-polars � antagonistic centre-surround receptive fields
2 types: flat vs invaginating
some respond only transiently to change in illumination
due to feedback inhibition from the amacrines (lateral + self-inhibition)
distinct morphologies of amacrine cells; peptides + functions
W: wide-field ganglion cells � sustained responses to steady light level overa� wide field, very slow conducting
�/span> tonic responses to constant illumination, e.g. tonic pupil light reflex
hormonal responses to time of day/year
Y: large, fast conductance � respond well to movement + changes in light intensity
X: smaller, slower, ustained responses, simple linear summation when different parts of the receptive field simultaneously illuminated
these differences: dendritic trees, bipolar (sustained) vs amcrine (transient)
code specifically for colour, movement in particular direction etc.
fast adaptation: image projected on cornea disappears quickly from view
pupillary light reflex � puny in coparison with the massive range
field adaptation � increment threshold, Weber-Fechner relationship, receptor noise �/span> dark light, automatic gain control (Ca in the receptors inhibit GMP regeneration �/span> transient responses in brighter light)
bleaching adaptation �/span> change log I, equivalent background, +ve after-image
contrast = the Weber fraction
acuity = measure of the fidelity of transmission of fine details
quality of the optics + density of retinal receptors + neural processing
pointspread function � excitation is spread over a finite error
� in contrast + spatial detail
gratings � spatial frequency + contrast
Snellen chart in opticians
pupil size � diffraction
glare � contrast
nasal decussation at the chiasmus
different tasks:
boundaries/edge detection � recognition
movement detectors � proprioception
whole-field tonic units � time of day, pupil control
recognition � geniculate/cortex, localise � superior colliculus, visual proprioception � pretectum, pons + brainstem
also � control of accommodation, pupils, hormones
require different kinds of processing
6 levels���� 2, 3, 5 = ipsilateral
����������������� 1, 4, 6 = contralateral
magno � larger, � SC + sub-cortex mainly���������� Y
parvo � smaller, � cortex, slower����������������������� X
LGN similar organisation to retinal ganglion cells
wavelength sensitive antagonistic surrounds�������� Y/B, R/G
response to light change sby activity in the rest of the brain
�gating� � common to other thalamic relays
the various layers are strictly in register, insofar as:
same area of retina � single radial column
though: distortion � centre � representation
optic radiation � occipital lobe
area 17 � primary visual cortex = striate cortex (stripe of Gemari(???) = due to massive inflow of afferent fibres)
18 � prestriate������ 19 � medial
OR 17 = V1, 18 = V2-4, 19 = V5
connections between = both direction + via the pulvinar
4 � cells with similar receptive field properties to retinal ganglion + LGN
layers 6+ ?� - pyramid cells output to other layers, cortex etc.
other layers � inter-neurons of different kinds, including stellate cells
many � mapped with single spots of light
central strip flanked by antagonistic = simple cells
respond best to a line of particular position + orientation = line detectors
prefer moving/flashed stimuli, non-diffuse light
complex cell � respond to a bar/edge of specific orientation, anywhere within their field of view
complex cells do not have inhibitory areas, so cannot be mapped with spots of light
more effective � moving stimuli
show responses of opposite sign if move in oppostie direction = recognition without localisation�� ����� binocoular
end-stopped (hypercomplex) cells � specific for orientation + length
responses to colour � less evident in area 17
colour-opponent resopnses = simple/concentric type
gathered in blobs
orientation-specific responses = grouped in columns perpendicular to the cortical surface
the cells in a column share preferred orientation
this orientation changes systematically across the cortex surface
dominance bands across columnns � L/R/L/R
hypercolumn � 1�mm patch checkerboard � both eyes, all orientations + 2 blobs
IVc simple cells = one eye only
complex cells on each side = binocular
some have receptive fields identically situated relative to the foveas of each eye
others have pairs which don't exactly correspond � retinal disparity = source of information re depth (distance from plane of fixation)
feature extractors � �grandmother� cells?
2 streams:
complex localisation � posterior parietal areas (movement(???))
complex recognition � inferotemporal regions (� specificity + colour)
monkey temporal lobe cells � faces, hands � sheep sex hierarchy
lesions �/span> subtle effects, e.g. difficulty in recognising/appreciating the significance of visual objects
localisation � direction + distance (= more difficult)
distance
superior colliculus (= tectum in lower animals)
2 layers
upper: receives visual information from the retina, LGN + visual cortex
lower: motor, projecting � brainstem + upper spinal cord re eye + head movements
no orientation specificity; large, overlapping, circular RFs
interested in where, not what
responsive to targets movign in particular directions, especially away from fovea
orderly arrangement on the surface of the colliculus
= map of visual space
electrical stimulation �/span> eye/head movement of right size/direction
function = bring objects of interest � fovea
though primate lesions don't seem to affect this
saccades = movements to look at visual stimulus � fast, steplike + visual tracking (oculomotor system: smooth pursuit)
<= prepontine reticular formation
held in check by inhibitory pause cells in the brainstem, = tonically active except during saccades inhibited by the superior colliculus
the superior colliculus itself is tonically inhibited until find + recognise something interesting to look at, by the substantia nigra <- basal ganglia <- posterior parietal cortex
distance
relies on high level cues � monocular and binocular
monocular
accommodation
movement parallax
interposition/overlap
size of known objects
linear perspective
texture gradient
shadows
aerial perspective
binocular
corresponding points
disparate images � cortical cells have binocular input
relative distance + stereopsis
disparity detectors
�Panum�s(???) fusional area�
vision � sensing the movement of the head in space
relies on knowledge of any eye movement (from the efference copy)
assume that the larger area = stationary
visual movement detectors (pons + pretectal mule? � VPS)
large receptive fields, respond to detailed pattern moving unison
rate of firing � velocity
� vestibular nuclei + cerebellum
adaptation under prolonged stimulus �/span> waterfall illusion
sense of visual motion � balance of the 2 opposite direction cells
fascia???
comlete/incomplete (re adaptation of skin receptors)???
horn???
corpuscle???
which receptor = vibration???
the fast-completely adapting pressure ones like Meissner (+ Pacinian???)
definitely Pacinian
fire tonically???
feedback/forward, post/pre-synaptic, different levels/modalities ???
astereognosis /<schwa><ssm>stErI<schwa>g"n<schwa>UsIs, <schwa><ssm>stI<schwa>r-; eI-/ n.E20. [f. A-10 + STEREOGNOSIS.] Med. Inability to identify the nature, size, and shape of objects by touch, as a symptom of disorder of the central or peripheral nervous system.
where/what is the dorsal root???
histamine???
why would we have evolved the lateral inhibition to � overlap between modalities???
is it because they�d presumably be signalling the same thing??? but if so, why allow the mechanical stimulation to override the pain??? perhaps because the mechanical stimulus tells us more
what is mech stimulation???
just pressure or deformation, right???
so there may be physiological grounds for dissociating the objective sensation of pain from the �feeling� of it
which bit of the brain is it that causes you to cease to value/�feel� pain in a real way, even though you know it�s there???
position of golgi tendon organs vs spindles???
intrafusal???
annulospiral endings???
passive movements???
slow???
sectioned???
cut???
why has recording been unsuccessful for motor???
tetradotoxin, onabain
emmetropic(???) = normal/perfect vision
cilium???
hair???
is glutamate usually excitatory???
blobs???
types of eye movements???