Pain and Furleys lectures

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  • Created by: Sarah
  • Created on: 30-04-17 17:15
what info does the spinothalamic tract send?
temperature, pain, pressure and touch
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what pathway doesn't have a topographic map
affective motivational pathway
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why does the affective motivational pathway have no topographic map?
neurons in the parbrachial nucleus can respond to pain from anywhere in the body
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where does the affective motivational pathway provide input to?
1) limbic system (emotional) 2) hypothalamus (homeostatic) systems
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what has a strong +ve correlation with the cingulate cortex?
pain experience/unpleasantness
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what does the intensity of pain activate? by what pathway?
somatosensory cortex by discriminative pathway
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what fibres innervate intrafusal (muscle spindle) muscles?
gamma motor neurons
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what innervates the extrafusal (outside of muscle spindle) muslces?
alpha motor neurons
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what info do 1a sensory receive?
muscle slackness
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is the spinothalamic pathway lateral or medial?
lateral
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what are the 2 routes from sensory info to the brain (somatosensory projectons)?
1)medial lenniscal tracts 2) spinothalamic tratcs
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what info does the medial lemniscal tract carry?
mechanoreceptive and proprioceptive
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where do first order neurons in the somatosensory projections carry info to and from?
from stimulus to spinal cord
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where do second order neurons in somatosensory projections carry info to and from?
from SC to thalamus
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in the medial lemniscus pathway and spinothalamic pathway what does it mean that the 2nd order neurons are commissural?
the 2nd order axons cross the midline
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what are the 2 main input components to the somatic sensory system?
1) mechanical stimuli 2) pain and temperature stimuli
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why do we need info about mechanical, temperature and pain stimuli?
to identify shape and texture of objecrs, monitor forces on body, detect harmful substances, to have a sense of ourself in the environment
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capsules in the skin are involved with what?
filtering to give specific frequencies
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what do meissner (tactile) corpusles detect?
light touch (sounds like mouse, mouse soft), texture (movement
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where are the meissner or tactile corpuscles?
deral papullae of skin esp palm, eyelid, lip, tongue
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what are the features of meissner corpuscles?
rapidly adapting, sensitive to 30-50hz
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what sensory receptors are unencapusalted nerve endings?
merkel (tactile) discs and free nerve endings
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what sensory repceptors are encapsulated nerve endings?
meissner(tactile) corpuslcels, pacinian (lamellated) corpuscles and ruffini corpuscles
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what sensory receptor detects deep pressure, stretch, tickle or vibration?
pacinian corpuscles (lamellated) STDV
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what nerve endings are rapidly adapting?
meissner corpuscles, pacinian corpuscles + hair follicles (rapidly+slowly adapting)
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what nerve endings are slowly adapting?
ruffini corpuscles, merkel(tactile) discs + hair follicles
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what frequency is pacinian corpucles sensitive to?
250-350Hz
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what is ruffini corpucles modality?
heavy touch, pressure, skin stretch and joint movements, kind of propiceptor?
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whats the location of ruffikini corpuscles?
dermis, subcutaneous tissue, joint capsules
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where are molecular receptors usually found?
on the cell surface membrane
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what is an example of cellular receptors?
merkel discs, free nerve endings
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what sensory receptor allows us to detect edge, texture and light touch?
merkel discs
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what are the 2 different classes of mechanoreceptor response?
1) phasic- fast 2) tonic- slow
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what infomation do phasic receptors give?
changes (eg intensity) of stimulus
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what info does tonic receptors give?
persistence of stimulus, continue to respond as long as the stimulus is present
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phasic mechanoreceptors?
pacinian corpusles
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tonic mechanoreceptors?
ruffini corpuscles
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what are primary afferent axon subtypes classified by?
conduction velocity (broadly reflects diameter)
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axons from the muscle are labelled by what?
I, II, IIII, IV - roman numerals (I-largest, IV-smallest)
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what is slower pain or proprioceptors?
pain receptors slower
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what are skin axons classified?
alphabet A-fastest C=slowest, A group is further broken down by greek character(alpha beta, delta is slowest!)
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where is sensory infomation organised into layers?
SC dorsal horn
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where are projections to the dorsal horn from?
cell bodies of sensory neurons in the dorsal root ganglion
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what is an example of sensory info being layered in the dorsal horn?
hair follicles, different types is represented in different layers
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how does sensory infomation remain spatially organised if it is put in layers at the dorsal horn?
it is carried into the brain by different pathway (Spinothalmaic or medial lemniscus)
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what is in different layers in the dorsal horn?
different sensory modalities eg pain vs touch
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path from sensory rec to dorsal horn layer?
sensory receptor travels along sensory afferent -> sensory cell body in DRG -> DRG projects to different layers of dorsal horn
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what pathway does the upper body follow on the medial lemnsicus tract?
lateral pathway
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where doess the lateral pathway 1st order axons synapse onto the 2nd order neurons in the MLP?
on the cuneate nuclues
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where does the medial pathway MLP synapse onto 2nd neurons?
n the gracile nucleus
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what is the name for the cuneate and gracile nucleus togetehr?
dorsal column nuclei
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where do 2nd order neurons cross the midline and ascend?
ascend in the medial lemniscus
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what does the somatopic order in the brain reflect?
that each DRG innervates a specific dermatone
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how is the topology reveresed in the medial lemniscus pathway?
2nd order axons cross the midline, switch back over in the thalmus, so lower body axons are more lateral reaching thalamus when they were medial, 3rd order neurons (thalamus to cortex) reverse topology solower body synapses on medial cortical neurons
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what is a dermatione?
the specific region of skin innervated by the dorsal root (sensory) ganglion
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why do dermatones arise?
dermis of each region of skin comes from a block- a somite
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what do somites give rise to
muscle and skeleto
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what is each drg (sensory ganglion) in the embryo associated with?
eah drg associated with specific somite that innervates tissue from that somite
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why are areas of the body not proportional to represented areas in the cortical?
have different receptive fields
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how can you find out the size of the receptive field?
assess the ability to discriminate two sharp points set at different distances
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what has each sensory neuron got?
a receptive field
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what is more of the cortex dedicated to?
receptive fields that are small like in the fingers can feel lots of different
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discrimination between two points is low where?
in large receptive fields like arms and legs
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whereis discrimination high why?
fingertips small receptive fields
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why can the information come from small receptive fields even though the num of receptors are similar?
the number of endings from different neurons per unit area is higher
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what is the number of sensory neurons innervating an area related to?
the behavioural signifance of that area eg apes use mouth to find food more innervated bigger proportion in cortex
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what fields in rodents dominat the somatosensory cortex topographic map?
whiskers
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what plane is the somatopic map preserved in?
coronal plane through postcentral gyrus
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where are different sensory modalities localised in the cortex?
along the saggital axis
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how is the cortical map shown to be plastic?
lose digits then disappereance of the area devoted to digits and increase area of neighbouring digits
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what is the area of the cortex detected to that body areea proportional to?
density of innervation in that area
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where are second order neurons located in the somatosensory pathways?
in the dorsal root nuclei
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where are the third order neurons found in the somatosensory pathways?
hthe thalamus
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where are the first order neruons in the somatosensory pathways found?
DRG
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what is a reflex?
a rapid, sterotypesd, involuntary and coordinated response to a sensory sitmulus
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what do reflexes usually involve?
muscle contraction (but can involve glandular like lactation in respone to suckling)
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features of spinal reflexes and what each suggests?
quick (few synapses) require stimulation (sensory input), involuntary+automatic only aware when they're happening (little input from higher senses), serotyped (underlying circuitry)
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what is the patellar reflex?
tap on the knee kick leg out
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go through the patellar reflex path?
tap on knee -> primary afferent carries info to SC, dorsal root of sc to direct synapse onto motor neuron, motor info out by ventral root- motor neuron stimulates extensor muscle contraction
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what kind of receptor is the golgi tendon organ?
a propioreceptor
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what does the golgi tendon organ detect?
muscle TENSION (due to muscle contraction)
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what are thegolgi tendon organ sensory afferents?
Ib afferents
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what happens when the sensory (ib) afferents in the golgi tendon organ are stimulated?
activation of inhibitory interneurons which inhibit alpha motor neurons that innervate the same muscle
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what forms the golgi tendon organ?
collagen fibrils of tendon interlacing afferent terminals
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what kind of feedback is the golgi tendon reflex?
negative feedback
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what does the golgi tendon organ regulate?
muscle tension and protects muscle + tendon from damage when large forces are generated
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what does the golgi tendon organ prevent?
the muscle contracting too much
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why is the flexor reflex polysynaptic?
so the response can be sustained over time by having multiple excitatory interneurons
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what does the flexor reflex do?
withdraw limb from noxious stimuli
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what happens in the flexor reflex?
quick contraction of flexor muscle to withdraw
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what triggers the flexor reflex?
activation of nociceptive sensory receptors or nociceptors
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what is the parallel after discharge circuit?
having different amounts of synapses, the stimulus takes different times to reach the output so the signal is sustained over time
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what reciprocal inhibition happens in the flexor (withdrawal) reflex?
inhibitory interneurons are activatd to relax the extensor muscle
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why does the flexor reflex need a crossed extensor reflex?
lose balance by withdrawing a limb need to tell other side of body so is contralateral element
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what happens to the extensor muscle on the other side of the body with the leg on the ground?
contralateral motor neurons to extensor excited, extensor contracts
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what happens to the ipsilateral motor neurons in the crossed extensor reflex?
motor neurons to flexor excited, ipsilateral flexor contracts, motor neurons to extensor inhibited
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where are central pattern generators?
in the spinal cord
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what do central pattern generators do?
underlie repetitive behavior eg generate the pattern of alternating flecion and extension
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what happens to walking if SC connections to the brain are severed?
basic alteration and coordination carries on
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what organism is used to work out the cellular basis of pattern generators?
simple organisms: lamprey
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what is a critical feature of central pattern generators?
inhibition across the midlight
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to look on a molecular level of propiception which organism is used?
C elegan
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what phenomena does fit with the specificity theory?
1) phantom limb 2) modulation by other stimuli (accupunture) 3) phantom limb perceived pain 4) referral pain from viscera to skin 5) placebo effect
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what satisfys the specificity theory?
1) there are recs cellular+molecular that respond specifically to pain (Ad+ C fibres TRPV1) 2) specific pathways- spinothalamic tract 3) regions of cns that respond to pain insula and cinguate
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what nociceptors are for fast first sharp pain, can be mimicked by direct stimulation?
Ad fibres
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what are c fibres for?
slow or second more delayed longer lasting, this mimicked by stimulatin of c fibre nociceptors
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what does selectively blocking c fibres and Ad show?
specificity
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does stimulation of propiceptive and mechoceptive fibres like Aalpha and A beta elicit pain?
no they never elicit pain sensation
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why is pain such an enigma?
it is a discriminative sensation and a graded response (behavioural drive), mystifying sysptems, disappears in battle
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what is pain?
a universal human experience that is commonly generalized to psychic suffering of some kind
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what mystifying symptoms does pain present?
temporal augmentation (worse over time sunburnt), allodynia ( sensitisation to normally non-noxious stimuli), referral, persistent after sensations, emotional variability, hyperpathia (hysterical responses)
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what is specificity theory?
that pain is a distinct sensation with specific receptors, pathways and distinct pain areas in the brain
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what is convergence theory?
pain is an integrated plastic state represented y a pattern of convergent somatosensory activity within neuromatirx (distributed network)
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what is the feature of C fibres that means they respond to mechanical, thermal and chemical modalities?
polymodal
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are c fibres myelinated or unmyelinated? speed?
unmyelinated 2 m/s
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are Ad fibres myelinated? speed?
lightly myelinated 20 m/s
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what are nocicpetors classified by?
stimulus, fibre type and confuction velocity
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Ad fibres include what kind of modality?
mechano sensitive, mechanothermal-sensitive
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evidence that there nociceptors respond to apin specifically?
heat responses- nociceptor only becomes excited at 45 degrees thermoreceptor is already saturated response before pain, afferents activity who correlate with pain (nociceptors)
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what are nociceptors?
afferents with free nerve endings
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what is the modality of free nerve endings?
pain, hot, cold
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where are free nerve endings dound?
epithelia and CT
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what are specific molecular receptors with nocicpetive nerve endings activated by?
heat and ho chilis
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what is the vanilloid which is the active component in chillis?
capsaicin
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what receptor is activated in nocicpetive Ad and C fibres at 45 degrees?
capsaicin receptor (TRPV1)
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what else activates capsaicin rec TRV1?
capsaicin, vanoillid in chillis
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what odes capsaicin mimic?
endogenous vanilloids relasd by the body when the tissues are stressed
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what is activated in Ad fibres at even higher thresholds of 52 degrees?
relatd receptors, other TRPs = transient receptor potential proteins
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so how are the moecular receptors thought to work?
respond to capsaicin in chillis, capsacicin rec is activated at 45 degrees (high heat), thought to detect release of chemicals released from stressed tissues
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why are molecular recs like capsaicin and transient receptor potential proteins called heat detection machines
they respond directy to heat
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what is another name for the spinothalamic system?
anterolateral system
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what pathway does the discriminative pathway involve??
the spinothalamic tract
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what are the 2 components of central pain pathways?
1) sensory discriminative 2) affective motivational
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what is the sensory discriminative pathway for?
signals location, intensity, type of stimulus
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why is it called the sensory discriminative pathway?
enables you to discriminate wheres it from? how bad does it hurt? what type of stimulus hot etc
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what does the affective motivational pathway give?
signals unpleasantness and enables ANS- fight or flight
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what do spinothalamic projections preserve?
topography
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measurement of activity in the somatosensory cortex indicates what?
1) region does respond to painful stimuli, rsponse correlates to intensity of pain 2) this is spatially mapped
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what is the insula and cinguate cortex part of?
the limbic system (emotional responses)
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when comparing mris between painful stimuli and non painful mechanical stimuli what did this show?
painful sitmuli activate the same part of the somatosensory cortex as the non-mechanical stimulation
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what was the difference in mri with painful (c fibre) or non painful mechanical stimulaiton?
painful stimuli activates other regions too-cingulate cortex and insula
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what is the cingulate cortex and insula part of which pathway?
affective motivational
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does the affective motivational pathway share any paths with the spinothalmaic (anterolateral) system?
yes shares some paths
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what pathway to do with pain shows little or no topographic mapping?
affective motivational pathway
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why does the affective motivational pathway show no topography?
neurons in the parabrachial nucleus can respond to pain anywhere on the body
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where does the affective motivational pathway input to?
limbic system (emotional) and hypothalmic (homeostatic) systesm [for flight or fight]
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what is there a strng correlaion with activity in the parabrachial nucleus?
correlation of painful experience, how unpleasant it is
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what pathway gets info about intesnity of pain to the somatosensory cortex?
sensory discriminative pathway
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what is hyperalgesia?
increased response to a painful stimulus, damage is already there becomes hypersensitive
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what is allodynia
sensitisation to normally non noxious stimuli eg sunburn touching skin wuldnt usually hurt
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why do you get hyperalgesia?
nociceptor threshold LOWERED
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what enzyme do painkillers (analgesics) ibuproben and aspirin work on?
cyclooxygenase
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what does the enzyme cylooxygenase do?
prostaglandin synthesis
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what do prostaglandins do to the ap?
lower the threshold for the action potential
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what happens in peripheral tissue inflammatory response?
release soup of inflammatory substances which affect nerve function, recruit mast cells and neutrophils, increase local blood flow
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what is released in the inflammatory response which directly affects the nociceptive molecular receptors eg TRPV1?
bradykinin
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what can central sensitisation be caused by?
local release of substances like prostaglandins from nociceptive dorsal horn neurons
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what is central sensitisaiton?
something becoming painful when it wasn't that painful before but occurs from cns
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what releases prostanglandins in the dorsal horn
nociceptive dorsal horn neurons
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what is the consequences of prostaglandins in the dorsal horn?
1) hyperalgesia as lowered ap threshold 2) allodynia- neurons becomes sensitive to non nocipceptive input gives allodynia
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what causes hyperpathia?
fibre/axonal loss (in pns or cns) results in raising detection threshold
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what does hyperpathia do the threshold?
increases the dection threshold
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why do you get explosive pain in hyperpathia?
the detection threshold is raised, need greater stimulation to exceed, when it does exceed and you feel it its has greater excititability
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what else other than prostaglandins causes central sensitisation?
when central pathways themselves are damaged
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what diseases damage the central pathways?
diabetes, shingles, ms, after strole
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what does phantom limbs tell us?
central representation of pain is not passive- persists without peripheral input, central maps are preformed as kids born without limbs get phantom limbs
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what does phantom limbs tell us about the pain we experience?
it is a central representation of what we expect pain to be
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what suggests that pain may be represented centrally?
blocking pain pathways does not block the pain for phantom limbs
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what is pain referral?
where pain in the viscera is perceived as coming from particular locations of the skin according to what organs affected
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what is reffered pain useful for?
clincal diagnosis of organ dysfunctiom
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what do they understand about referred pain?
thought to reflect convergence of visceral afferents onto similar pathways as cutaneous (skin afferents) in the CNS
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what is the placebo effect?
suggestion pain will be relieved results in pain relief mind obver matter think it will help so it does
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what indicates that mechanisms exist to overcome severe pain
war veterans not feeling pain, people walking on fire, placebo effect
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stimulation of what activates brainstem nuclei that modulate the activity of dorsal horn neurons?
periaqueductal grey
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what do brainstem nuclei modulate?
the activity of dorsal horn neurons
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what can inhibit nociceptive fibres in the dorsal horn?
enkephalin
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what releases enkephalin
enkephalin releasing interneurons
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what inputs activate nkpehalin releasing interneurons that inhibit nociceptive fibres?
descending inputs
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what is enkephalin? what are the other ones of this family?
endogenous opioid peprides, DEE dynorphins, enkephalin and endorphins
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whats an example of modulation occuring locally?
rubbing site f injury relieves pain
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how does rubbing the site of injury relieve pain?
lcoal inhibition by Ab mechanoreceptors of nocicpetive C fibres inputs in the spinal cord
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what do Ab mechanoreceptors do to modualte pain locally?
c fibre and Ab fibre go into SC together, Ab inhibits c fibre by inhibitory local circuit neuron
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who proposed the gate or sensory interaction theory?
melzack and wall
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what does the sensory interaction or gate theory suggest?
pain perception is result of convergent sensory information
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what seems to be important in whether pain is perceived?
gate circuits (inhibitory local circuit neurons)
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what is pain meant to do?
warn and motivate us!
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where is the somatopic map preserved?
coronal plane through the postcentral gyrus
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what is localised along the saggital axis?
sensory modalities
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what re all movements initated by skeletal muscles iniated by?
lower motor neurons
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what can central pattern generators do?
generate complex behaviours without input from the brain
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who found using dogs that eletrical stimulation of the primary motor cortex elicits contraction of contralateralbody muscles?
fritsch and hitzig
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what are upper motor neurons?
neurons in the brain that control motor funciton
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is the motor cortex somatically mapped?
yes
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what cortical layers are the betz/pyramidal cells in?
layer 5
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where are the main inputs to the cortical layers?
to stellate cells in layer 4
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which layers are the main outputs?
3, 5 and 6
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how much of the cortex is a 6 layered structure?
90%
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descibe layers of cortex?
molecular layer, ext granular layer, ext pyramidal layer, int granular layer, int pyramidal layer, fusiform layer
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where are acons tothe corticospinal tract derived from?
large yramidal or betz cells in layer 5
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who correlated the site of stimulation with the location of muscle contraction to make a topographic map?
sherrington penfield
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what does proportions of the topographic map of the motor cortex reflect?
reflects the density of innervation (and beh significance)
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