Pain and Thermosensation Flashcards
What is pain?
An unpleasant sensory or emotional experience, associated with actual tissue damage or described in terms of such damage
Pain is not a single entity and may be classified in 3 forms. What are these 3 forms?
- Nociceptive
- Inflammatory
- Pathological
Describe nociceptive pain.
This is acute pain e.g a pin prick or visceral distension
Describe inflammatory pain.
This is prolonged pain e.g sunburn or an inflamed wound
Describe pathological pain.
This is neurogenic pain e.g IBS, fibromyalgia, arthritis, diabetes, cancer, AIDs
What is chronic pain?
When pain arises spontaneously without any underlying pathology
Describe the characteristics of pain that are associated with the skin.
- well localised
- pricking
- stabbing
- burning
Describe the characteristics of pain that are associated with muscle.
- poorly localised
- aching
- soreness/tenderness
- cramping, stabbing, burning
Describe the characteristics of pain that are associated with viscera.
- poorly localised
- dullness
- vagueness
- fullness
Where is visceral pain often referred to?
A somatic structure
What are nociceptors?
Specific peripheral primary sensory afferent neurones, normally activated preferentially by intense stimuli (ie. thermal, mechanical, chemical) that are noxious, or damaging
First order neurones that relay information to second order neurones in the CNS by chemical synaptic transmission….this described what?
Nociceptors
Where are the cell bodies of nociceptors located?
In the dorsal root ganglion and trigeminal ganglia
What happens in response to a noxious stimuli?
DEPOLARISATION - which elicits an AP to propagate to the CNS
What are the different types of noxious stimuli?
- Chemical
- Mechanical
- Thermal
What do nociceptors comprise?
Aδ- and C-fibres
- not all Aδ- and C-fibres are nociceptors)
In nociceptors, where does transduction begin?
In free nerve endings
What type of nociceptors are Aδ fibres?
Mechanical / Thermal
Describe the myelination of Aδ fibres?
Thinly myelinated
What is the conduction velocity of Aδ fibres?
Conduction velocity of 6 – 30 ms-1
What do Aδ fibres respond to?
Noxious mechanical or thermal stimuli
What do Aδ fibres mediate?
‘First’ or fast pain
Describe the myelination of C fibres.
Unmyelinated
What is the conduction velocity of C fibres?
Conduction velocity of 0.5 – 2.0 ms-1
What do C fibres respond to?
ALL noxious stimuli
What term describes the function of C fibres?
Polymodal
What do C fibres mediate?
‘Second’ or slow pain
Outline the series of events that occur in response to a thermal noxious stimuli.
- Thermal stimuli
- Heat/cold sensitive receptors
- Na+/Ca2+ influx
- Depolarisation (membrane graded)
- Voltage activated Na+ channel activation
- AP’s to the CNS
What does noxious stimuli in the long term result in?
Increases spinal excitability contributing to hyperalgesia and allodynia
- the synapse becomes more efficient the more it is used
How to afferent C fibres transmit info to the CNS?
Via release of glutamate and peptides within the DORSAl horn