Lecture 19- Pain Flashcards Preview

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Flashcards in Lecture 19- Pain Deck (41):

What is nociception?

-activation of nociceptive primary afferents


What is pain?

-conscious, affective unpleasant somaesthic percept localized to the body


What is hyperalgesia?

-increased sensitivity to noxious stimuli


Does nociception have specialised neurons?



How can you map the receptive fields of nociception neurons?

-with heat


What is the pattern of response of nociception afferents?

-do not respond till sth really happens

-high threshold

-can be chemical burn too (whereas mechanorecpetors are very sensitive)

-only starts to fire at 45 degrees then at 60 degrees very repsonsive but the non-nociceptive thermoreceptor plateus

-nociceptors= encode for temps etc that damage, opposed to other recpetors

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What are the two categories of pain?

-first (sharp pain)

-second (duller, burning pain)

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What pain do the A delta fiber convey?

-small thinly myelinated fibres, 5 microns= fast sharp pain (mechanosensors at high threshold)


What pain do C fibres convey?

thinnest nerve fibres - unmyelinated= C fiber (here myelin would slow it down if it were here due to the small size) -1 micron= sensation of diffuse, duller burning pain -the C fibres are polymodal= respond to noxius chemical and mechanical stress when very high, respond to proton concentration (acidity)


What is the most common peripheral nerve fibre?

C fibres -small and everywhere


What are the characteristics of C fibres?

-0.2-1.5 micometers -0.5-2.0 meters for second speed -temperature, pain, itch


What are the characteristics of A delta fibres?

-myelinated -1-5 micrometers diameter -5-30 M/s -pain and temperature


What are the characteristics of A beta fibres?

-6-12 micrometers diameter -35-75m/s -mechanoreceptors of skin


What are the characteristics of A alpha fibres?

-13-20 micrometers in diameter -80-120m/s -proprioceptors od skeletal muscle


Where does capsaicin bind?

-can diffuse through the membrane so it binds on the inside -VR-1 receptor


What binds to VR-1 receptor?

-capsaicin -heat and H+ (acidity)

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What is capsaicin in?

-jalapeno -red chilli -habanero


What is the nociception pathway like?

-cell body in dorsal root ganglia -small cell bodies -do their transmitting locally (segment or two) find their target cell in the superficial dorsal horn -crosses over right away -the second neuron goes to the thalamus


How is the nociception pathway different from the touch pathway?

-very different to the touch pathway wher eit was on the same side till brain stem -here it crosses over right away


What is the spinalthalamic tract?

-the nociception pathway -also called anterior lateral system (ALS)

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Where in the spine do the C fibres terminate?

-in the superficial dorsal horn(the purple)

-in the marginal zone or substantia gelatinosa

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Where in the spine do A delta fibres terminate?

can terminate in areas further away = even in the base of the dorsal horn as well as the superficial basal horn

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Is there mixing of information from nociception afferents in the spinal cord?

-yes -one cell body can get information from A delta as well as C fibre


What would happen if your spinal cord was cut in half of its width?

-feel only one side of the body

-lose nociception on one side and touch on the other

-nociception intact on one side as it crosses over locally

-the touch pathway stays on one side whereas the pain crosses over right away

-brown sicard syndrom

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What are the two main pathways of the anterolateral system?

1.Sensory-discriminative(the one to somatosensory cortex) 2.Affective-motivational (the one to insular and anterior cingulate cortex)


What is the anterolateral system pathway (detail)?

-from the spine goes to different parts of the brainstem/forebrain

-first division is to ventral posterior nucleus in the thalamus to the somatosensory S1 and S2

-second division goes to the amygdala, hypothalamus, periaquiductal grey, superior colliculus, reticular formation

-third division goes to the midline thalamic nuclei and from there to the insular cortex and anterior cingulate cortex

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What are the functions of the anterolateral system pathway?

-the one to the insularn cortex and anterior cingulate cortex is the pahtway of how it feels, motivational and connected to learning -the one to the amygdala etc. is about the emotional feelings associated with pain -the one going to the somatosensory cortex, this is how we can tell where sth hurts, can loacte it


Where is the cingulate cortex?

anterior cingulate cortex (blue)= where the last neuron from the nociceptors ends (the third goes from brain stem to here)

-lot of emotional states include this cortex (hunger, thirst)

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Where is the insular cortex?

-more cortex again after removing he upper bit of the cortex

-get lot of receptor input, from organs

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What is the nociception pathway mediating discriminative aspects of temperature like for the body(picture)?


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What is the nociception pathway mediating discriminative aspects of temperature like for the face (picture)?

trigeminal nucleus= pain and temp from the face and head

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What is the trigeminal nucleus for?

trigeminal nucleus= pain and temp from the face and head


What appears in the tissue when tissue damage?

-bradykinin= when damage in cells -ATP= leaks when cell damage -more acidic environment -histamine -prostaglandin


What activates C fibres?

-presence of bradykinin, increase in ATP, 5-HT(serotonin),prostaglandin,histamine


What is the reflex within C fibres?

-reflex= within branches of this fibre

-nerve impulse to other branches and release substance P (peptide) and CGRP=dilation of blood vessels

-red because of inflammation

-positive feedback effect= activation leads to more activation in the other terminals

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Is pain a homeostatic system?

-yes! maintaining integrity of the skin


What are phantom limbs?

-part of the body removed but they still feel like it's there -ther is not a nerve saying this is your limb= this is constructed in the brain and that can exist without the mechanoreceptors


What are the descending systems that modulate the transmission of ascending pain signals?

-originates in the somatosensory cortex

-the raphe nuclei and all that line is in the brain stem! they project to the spinal cord to the first synapse in the anterolateral system

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What happens at the first synapse of the anterolateral system when being modulated by ascending systems?

-this is how pain reduction occurs

-driven by cortical areas

-enkephalins are peptides

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What is the dorsal column pathway fro visceral pain like?

-goes from the gut etc. to the spinal cord

-then synapses in the medulla and goes to the ventral posterior nuclear complex of the thalamus

-from there goes to the insular cortex

-in the medulla crosses over in the medial lemniscus

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Is the idea of a pain pathway an oversimplification?