Anatomy of Pain
Pain vs Nociception
- Nociception = the PNS and CNS’ information about the
internal or external environment, by nociceptor
activation
- Nociceptors are sensory neuron that responds to
damaging or potentially damaging stimuli by sending
“possible threat” signals to the spinal cord and the brain
- Primary afferent nociceptors are the receptors that sit in
the skin or in internal organ structures
o give primary/important information about what
is going on in their internal and external
environment.
- This information is then conveyed up the spinal cord →
brainstem → thalamus → cerebral cortex where it is
determined as pain.
- These pathways receive nociceptor information all the
time. But a specific threshold has to be reached for it to be relayed as pain.
- Pain is a product of higher brain centre processing
- Pain can also be perceived in the absence of nociception and vice versa
Types of Noxious Stimuli
- Nociceptive pain can fall into 3 different types:
o Mechanical can be manifested as:
▪ Pressure
▪ Swelling
▪ Abscess
▪ Incision
▪ Tumour Growth
o Chemical can be manifested as:
▪ Excitatory Neurotransmitter
▪ Toxic Substance
▪ Ischaemia
▪ Infection
o Thermal can be manifested as:
▪ Burning
▪ Scalding
- Mechanical pain can be detected both internally and externally
- Toxic substances – internal, e.g. can be lactic acid and even blood to certain cells, and
external, e.g. carcinogens
- Ischaemia (restriction in blood supply to tissues) is a chemically noxious stimulus.
- Infection is a chemically noxious stimulus especially pathogens and microbes.
- Burning can be from both hot and cold sources.
, Pain
- Not all pain is equal – can be both good and bad
- Pain is defined as an unpleasant, sensory or emotional experience that is associated with
actual or potential tissue damaging stimuli.
Nociceptive Pain
- Nociceptive or acute pain is the result of exposure to a brief noxious stimulus e.g. a pin prick.
- The response to these types of pain is an adaptive sensation where the primary function is
to protect the body from injury.
- Also has homeostatic function
o E.g. when asleep some of the tossing and turning is so that you don’t cut off the
nerve supply for too long – this is detected when the sensory info isn’t coming back
to the brain
Prolonged pain
- Pain over a long period of time
- Results after injury to body
- Its aim is to prevent further injury.
- It does this by developing an area of hypersensitivity.
o Therefore, it reduces the activation threshold of the nociceptors in that area.
- This gives you peripheral sensitization (reduced threshold).
- The prolonged pain resides once healing is complete.
- Sunburn is good example of prolonged pain.
Chronic/Neuropathic Pain
- Present for more than 2-3 months
- Disease or damage to the CNS, PNS and NS dysfunction
- Pain persists in absence of initial injury
Classification of Pain
o Somatic
o Visceral
o Superficial
o Cancer
o Psychogenic
o Referred
- Somatic pain is very similar to the nociceptive pain and overlaps with acute or nociceptive
pain.
o To do with cuts or deeper cuts.
- Visceral pain is caused by activation of the nociceptors that are located in the viscera
themselves. These nociceptors are highly sensitive to distention (stretching), ischaemia and
inflammation from infection.
o But the visceral nociceptors are insensitive to cuts and also burning.
- Superficial pain falls under a branch of somatic pain. But felt more in the superficial tissues
such as skin. Whereas some other types of somatic pain is also MSK pain.
Pain vs Nociception
- Nociception = the PNS and CNS’ information about the
internal or external environment, by nociceptor
activation
- Nociceptors are sensory neuron that responds to
damaging or potentially damaging stimuli by sending
“possible threat” signals to the spinal cord and the brain
- Primary afferent nociceptors are the receptors that sit in
the skin or in internal organ structures
o give primary/important information about what
is going on in their internal and external
environment.
- This information is then conveyed up the spinal cord →
brainstem → thalamus → cerebral cortex where it is
determined as pain.
- These pathways receive nociceptor information all the
time. But a specific threshold has to be reached for it to be relayed as pain.
- Pain is a product of higher brain centre processing
- Pain can also be perceived in the absence of nociception and vice versa
Types of Noxious Stimuli
- Nociceptive pain can fall into 3 different types:
o Mechanical can be manifested as:
▪ Pressure
▪ Swelling
▪ Abscess
▪ Incision
▪ Tumour Growth
o Chemical can be manifested as:
▪ Excitatory Neurotransmitter
▪ Toxic Substance
▪ Ischaemia
▪ Infection
o Thermal can be manifested as:
▪ Burning
▪ Scalding
- Mechanical pain can be detected both internally and externally
- Toxic substances – internal, e.g. can be lactic acid and even blood to certain cells, and
external, e.g. carcinogens
- Ischaemia (restriction in blood supply to tissues) is a chemically noxious stimulus.
- Infection is a chemically noxious stimulus especially pathogens and microbes.
- Burning can be from both hot and cold sources.
, Pain
- Not all pain is equal – can be both good and bad
- Pain is defined as an unpleasant, sensory or emotional experience that is associated with
actual or potential tissue damaging stimuli.
Nociceptive Pain
- Nociceptive or acute pain is the result of exposure to a brief noxious stimulus e.g. a pin prick.
- The response to these types of pain is an adaptive sensation where the primary function is
to protect the body from injury.
- Also has homeostatic function
o E.g. when asleep some of the tossing and turning is so that you don’t cut off the
nerve supply for too long – this is detected when the sensory info isn’t coming back
to the brain
Prolonged pain
- Pain over a long period of time
- Results after injury to body
- Its aim is to prevent further injury.
- It does this by developing an area of hypersensitivity.
o Therefore, it reduces the activation threshold of the nociceptors in that area.
- This gives you peripheral sensitization (reduced threshold).
- The prolonged pain resides once healing is complete.
- Sunburn is good example of prolonged pain.
Chronic/Neuropathic Pain
- Present for more than 2-3 months
- Disease or damage to the CNS, PNS and NS dysfunction
- Pain persists in absence of initial injury
Classification of Pain
o Somatic
o Visceral
o Superficial
o Cancer
o Psychogenic
o Referred
- Somatic pain is very similar to the nociceptive pain and overlaps with acute or nociceptive
pain.
o To do with cuts or deeper cuts.
- Visceral pain is caused by activation of the nociceptors that are located in the viscera
themselves. These nociceptors are highly sensitive to distention (stretching), ischaemia and
inflammation from infection.
o But the visceral nociceptors are insensitive to cuts and also burning.
- Superficial pain falls under a branch of somatic pain. But felt more in the superficial tissues
such as skin. Whereas some other types of somatic pain is also MSK pain.
