Week 3 - Neurobiology of pain Flashcards
What is the purpose of pain?
To promote avoidance behaviour
Prevents further tissue damage
Initiates withdrawal behaviours/reflexes
Immobilisation of damaged tissue to aid in recovery process
Do we feel pain in the brain?
No.
We feel pain when the signals reach our brain.
Also, the brain does not contain nociceptors, so can’t experience pain.
What is the meninges?
3 membrane layers around the brain that DO contain nociceptors, so that’s why we can sometimes feel pain in our head.
What is pain caused by?
It is caused by the transmission of impulses from the site of tissue damage along pain nerve fibres towards the central nervous system.
What is a noxious stimulus?
A stimulus in the environment that can cause damage to normal tissues.
E.G. fire
What are the types of noxious stimuli?
Chemical
Thermal
Mechanical
What are nociceptors?
They are receptors that are sensitive to noxious stimuli or a stimulus which would become noxious if prolonged.
Is there just one type of pain receptor?
No.
There are many types of receptors that are sensitive to different types of pain.
What is the sensory processing pathway from a low intensity (non-noxious) stimuli?
Low-intensity non noxious stimulus > low threshold afferent > processing in CNS > innocuous sensation
What is the sensory processing pathway from a high intensity noxious stimuli?
High intensity noxious stimuli > nociceptor > high afferent threshold > processing in CNS > painful sensation
How is information transmitted from the nociceptor?
Nociceptor activated > Info enters into spinal cord > reflexes activated > info travels to thalamus directly via spinothalamic tract and indirectly via spinoreticular tract producing a stress response.
The limbic system produces an emotional response.
Info is also sent to somatosensory cortex to localise pain.
What can increase rate of conduction in the axon?
Larger nerve diameter
Myelination of the nerve fibre
What is saltatory conduction?
This is where the action potential jumps between the nodes of ranvier.
What are the different types of nerve fibres?
A Fibre - large and myelinated.
B fibre
C fibre - small and unmyelinated.
What is fast (first) pain?
- You can get it when there is a stimulation of HIGH THRESHOLD thermo/mechano nociceptors which results in fast pain.
- transmitted by fast conducting A-delta fibres.
- Result in protective function - removal/withdrawal from harm.
What is slow (second) pain?
- It is the activation of high threshold polymodal pain receptors which activate slow conducting unmyelinated C-fibres.
- It is responsible for delayed pain sensation that occurs after tissue injury.
- encourages healing by eliciting behaviour to protect the damaged area.
What are the other types/sources of pain?>
Cutaneous pain
Somatic pain
Viscera pain
What is cutaneous pain?
Injury to skin/superficial tissues
Nocicetors at below skin at high concentrations allow for well defined LOCALISED pain sensation.
What is somatic pain?
Injury to ligaments, tendons, bones, blood vessels, nerves.
Low concentration of nociceptors produces dull, poorly localised pain.
Longer pain duration than cutaneous pain.
What is visceral pain>?
Pain in bodies organs or internal cavities.
VERY LOW concentration of nociceptors, so pain is very difficult to localise - may refer to area unrelated to injury site.
What is Ruch’s hypothesis?
It states that visceral and somatic pain receptors come together on the same spinal cord pain-transmitting neurons.
For example, it’s why when you have a heart attack, you feel pain in your left arm.
what is tension type headache
pain radiating from neck, back, eyes, rest
of body
Unknown precise pathophysiology – may
involve muscle tension, anxiety, depression
what is thunderclap headache
Sudden onset and very severe
headache
may be a sign of a severe underlying issue
what is a Cluster headache
Attacks occur in cyclical patterns or clusters, potentially over a period of weeks to months with remission
periods.
Despite being very
painful, not life threatening
what are Hypnic Headaches
Occur in the elderly, particularly at night and last for up to one hour
what are Cold Stimulus Headaches
Ingestion of cold food/drink results in rapid onset short duration headache which subsides spontaneously
what complex sensations can pain v=be a response to
behavioural dimensions
emotional dimensions
sensory dimensions
what is pain based on
the interaction of peripheral pain receptors, central processing and modifying factors
how can pain be quantified
validated questionnaires: hospital anxiety & depression (HAD), pain locus of control (PLC), brief pain inventory (BPI), McGill pain questionnaire (MPQ)
physical evidence: pallor, sweating, high BP, tachycardia, nausea, vomiting, fainting, dizziness, Anxiety, fear etc
what is the time course of pain response
seconds- fast/slow pain sensations, inflammation develops
minutes/hours- Inflammation, hyperalgesia, allodynia
hours/weeks/months- Hyperalgesia/allodynia disappear, tissue repair occurs
if persists for months/years= chronic issue
What is hyperalgesia?
An increased response to a stimulus which is normally painful.
What is allodynia/
It is when you feel pain in tissue from a stimulus which is normally innocuous (non-noxious)
What are the 4 classifications of pain/
Neuropathic
Nociceptive
Mixed origin
Psychogenic
What is neuropathic pain/
It is pain for no reason.
The pain becomes the pathology usually via damage to the CNS/PNS
what are pain mediators and what do they do
they sensitise us to pain
they are released from when tissues are damaged, inflammation provoking the chemical stimulation of nerves
what chemical stimulations are included in pain mediations
bradykinin, prostaglandins, seratonin and histamines
