Pain Flashcards
Define pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.
What are the purposes of pain?
- Prevents further tissue damage.
- Initiated escape/ withdrawal/ protective reflexes and behaviours
- Promotes avoidance behaviour
- Immobilisation of damaged tissue to aid in recovery process
Does the brain feel pain?
The brain does not contain nociceptors and therefore cannot experience pain.
How does a headache occur?
Pain receptors are in the Meninges which cause the headache sensation. When the meninges become inflamed, or you experience pain in this are, this is what causes the headache.
Why don’t you have pain receptors in the brain?
Nociceptors are present to help avoidance behaviour. There is no real scenario where avoidance of using the brain would be helpful because in any scenarios such as infection or trauma to the brain, this is likely to be fatal and so there is no need to have nociceptors in the brain.
What are nociceptors?
Receptors preferentially sensitive to noxious stimulus or to a stimulus which would become noxious if prolonged.
What is meant by the term noxious?
Harmful, poisonous or very unpleasant to normal tissues.
What are the types of noxious stimulus?
Chemical
Thermal
Mechanical
What type of nociceptors are sensitive to noxious chemical stimuli and where are these found?
Sensitive to polymodal nociceptors found on C-fibres.
What type of nociceptors are sensitive to noxious thermal stimuli and whereare these found?
- Sensitive to polymodal nociceptors found on C-fibres.
- Chemothermal nociceptors which are found in A-delta neurones.
What type of nociceptors are sensitive to noxious mechanical stimuli and where are these found?
- Sensitive to polymodal nociceptors found on C-fibres.
- Chemothermal nociceptors which are found in A-delta neurones.
- Mechanoreceptor found in A-delta neurones.
What is nociceptive pain?
A warning device which is activated to impending damage to an organism.
What activates nociceptive pain?
Noxious stimulus acting on specialised high-threshold sensory apparatus (nociceptors) found in the skin, muscle and viscera.
What are nociceptors in terms of their structure?
Free sensory nerve endings that respond to a variety of noxious stimuli that cause or have the potential to cause tissue damage.
What effect do non-noxious stimulus have and what receptors do they activate?
They activate low threshold afferent receptors which eventually leads to the processing of innocuous signals to the CNS.
What is meant by the term innocuous?
Non-harmful
What effect do noxious stimulus have and what receptors do they activate?
High intensity stimulus activate low threshold afferent receptors and the high threshold nociceptors. This is then processed in the CNS to produce a physiological pain.
What causes rate of conduction alone nerve axons to vary?
- Diameter of the nerve axon
- Myelin sheath or not
How does myelin sheath affect the conduction rate along nerve axons?
Myelin sheath increases rate of conduction as the action potentials can jump by saltatory condition between gaps in the myelin sheath called Nodes of ranvier.
Describe the classifications of nerve fibres.
Classified as A, B or C.
A fibres are large and myelinated.
C fibres are small and unmyelinates.
Describe fast pain; how this is stimulated, what receptors are triggered , what is the function of this and what fibres are used.
Stimulation of high threshold thermo/mechanical nociceptors triggers fast pain which is usually conducted by A-delta fibres. This has a protective function such as withdrawing from a harmful situation.
Describe slow pain; how this is stimulated, what receptors are triggered , what is the function of this and what fibres are used.
Slow pain is responsible for the delayed pain sensation that occurs after tissue injury. This is caused by activation of high threshold polymodal pain receptors which activate slow conduction via un-myelinated C-fibres.
The purpose of this is to encourage healing by eliciting behaviour to protect the damaged area.