L05: Sensory Systems: Pain Flashcards
What is the definition of pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
What is pain a combination of
Sensory (discriminative) and emotional
What is nociceptors
The sensory component of pain alone
What is the stimulus for pain
Injury Heat Cold Inflammation Low ph
What does the stimuli for pain cause to the tissues
Damage
What does the pain stimuli activate
Free nerve endings
Where are the free nerve endings found
Skin
Muscle
Viscera
What does nerve endings generate when they detect a stimulus
Action potential
What is a nociceptors
The free nerve ending
What are the 2 types of nociceptors
1) High threshold mechanical nociceptors/ mechanical nociceptors
2) polymodal nociceptors
What activates mechanical nociceptors
Strong shearing force in skin
What activates polymodal nociceptors
Multiple stimulus such as sharp stimulus, heart (above 46c) chemicals released by damaged tissue
What chemicals does damaged tissue release
Potassium
Hydrogen
Prostaglandins
Bradykinin
What type of pain does the activation of mechanical nociceptors result in
Sharp pain
What type of pain does the activation of polymodal nociceptors result in
Dull burning pain
What axons/fibres are mechanical nociceptors found on
A delta fibres
What axons/fibres are polymodal nociceptors found on
C fibres
Are a delta fibres and c fibres inhibitory or excitatory fibres
Excitatory
What happens to the primary neurone when it receives a stimulus
It generates and action potential
What happens to the primary neurone when it receives the AP
It sends the AP to the second order neurone at the dorsal horn of spinal cord
Where does the second order neurone terminate
Thalamus
What type of information does both c fibres and a delta fibres carry
Noxious information
If the a delta fibre results in sharp pain what is the structure of the axon
Myelinated
If a c fibre creates a dull burning pain what is the structure of the axon
Non-myelinated
If the axon is myelinated what does it mean in terms of its propagation speed
Speed is fast / fast transmission
If an axon is un-myelinated what does it mean in terms of its propagation speed
Speed is slow/ slower transmission
What is first pain
The pain that quickly comes on and quickly off due to a delta fibres
What is second pain
Pain that gradually builds up and slowly fades away due to c fibres
What is the substantia gelatinosa
The region in the spinal cord where 2nd order neurone of cell body is for the dorsal columns
In the dorsal horn what are the layers of organisation called
Lamina
Which lamina are a delta fibres found in
Lamina 1 and 5
Which lamina are c fibre found in
Lamina 2
Which lamina are A beta fibre found in
Lamina 4
How do interneurones inhibit ascending neurones
The interneurones are inhibitory and inhibit the ascending signal to the brain
What is the gate theory of pain to non noxious input
1) Primary fibres i.e a beta that signal non noxious signal send an excitatory signal to the ascending signal
2) At the same time inhibitory neurones are sending an inhibitory signal to the ascending neurone
3) the primary fibres synapse with the inhibitory neurone so the inhibitory interneurone sends more inhibitory signal and overcomes the excitatory signal of the primary neurone
4) the gate is therefore closed for non-noxious info
What happens to the gate when there is a noxious stimulus
1) a delta or c fibres synapse with the secondary neurone and send excitatory signal which is not sufficient to open the gate on its own
2) a delta or c fibres therefore synapse with another population of inhibitory interneurones
3) these inhibitory interneurones inhibit the other inhibitor interneurones that inhibit the ascending neurone
4) the inhibitor interneurones therefore are switched off and the gate opens
5) ascending neurone sends an excitatory signal to the brain that is for noxious info
Give an example of the gate theory that comes into place in a real life scenario
1) You bang your knee (noxious info)
2) to stop the noxious info i.e pain to the brain You rub your knee
3) rubbing your knee is non-noxious info so beta fibres are activated and activate the inhibitory interneurones
4) gate is closes and you relive the pain
After overcoming the gate control what tract does the signal travel in
Spinothalamic tract
At what level of the brain do you add emotion to the pain that is perceived
Subcortical region
Where does the signal feed into the brain to localise the pain in the spinothalamic tract
Cortex
After the spinothalamic tract feeding into the brain which tract becomes activated
The descending pathways/tracts
What does the descending pathways do to the gate
Close the gate
How does descending pathway close the gate
Release 5HT, Noradrenaline, enkephalin
What is the close of the gate by the descending tract called
Intrinsic analgesia system
What is facilitated pain
The sensation of pain= afferent input duration and intensity
To experience pain what does the stimulus have to reach
a threshold
When can the threshold to cause pain decrease
After an injury
What happens after an injury when you apply a continous stimulus
You experience more pain i.e hyperalgesia
What happens when you get a pain that you previously did not get
Allodynia
What is the mechanism for getting hyperalgesia and allodynia
Sensitation of peripheral nociceptors
What is the processes involved in the sensitisation of peripheral nociceptors
1) nerve ending will have a stimulus of damaged cells
2) the stimulus causes action potential to be fired which propagates antidramic so the ap goes down the branches of the axon
3) this causes the release of substances of substance P and CGRP at the peripheral ending
3) subtance P and CGRP diffuse away from the nerve ending and interval with receptors on the blood vessel
4) as a result you get , vasodilation, plasma extravasate on and immune cell migrating and activation
5) immune cell activation causes the release of: prostaglandins, h+, bradykinin, NGF and cytokines (all referred to as inflammatory soup)
6) nerve endings that have receptors for the inflammatory soup are detected and this lowers the threefold for the AP
7) you are now sensitised
What is the process described previously for sensitisation of peripheral nociceptors called
Neurogenic inflammation
What is alloydina
Lower threshold mean more ap is fired and more noxious info is perceived from a smaller stimulus
What is hyperalgesia
A nerve ending with peripheral sensitisation has a lower threshold so when you apply a big stimulus (that also previously caused pain) causes a more pain
Where does primary hyperalgesia occur in
In the damaged tissue
Where does secondary hyperalgesia occur in
Around the site of injury
Describe the process that occurs at the dorsal horn between the primary afferent and second order neurone for normal pain (acute pain)
1) glutamate from the primary afferent is released in response to low AP firing
2) on the post synaptic membrane, AMPA (a glutamate receptor) receives glutamate
3) pain is sensed by the second neurone for signal to the brain
Which fibres/axons foes this signalling occur in
A delta
C fibre
Describe the process that occurs at the dorsal horn between the primary afferent and second order neurone in facilitated pain i.e central sensitisation
1) in facilitated pain there is lots of AP at high frequency so more glutamate is released from the primary neutrons
2) substance P is also released from the primary neurone
3) subtance P binds to NK-1 receptor on the post synaptic membrane of the second order neurone
4) glutamate binds to AMPA receptor on the post-synaptic membrane of the second order neurone
5) nk-1 and AMPA activation activates another glutamate receptor called NMDA
6) NMDA has its magnesium iron removed to glutamate can bind to it
7) NMDA causes calcium influx
8) the calcium influx triggers second messenger cascades to send a bigger signal to the brain
