Physiology of Pain Flashcards
What is pain?
An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage
What are the three forms of pain and are they adaptive or maladaptive
Nociceptive pain - adaptive
Inflammatory pain - adaptive
Pathological pain - maladaptive
What is nociceptive pain
Acute pain that occurs immediately at the time of inury
What is the purpose in nociceptive pain
Helps us limit damage to the body and avoid further damage
What is inflammatory pain
More persistent pain that generally subsides after healing
What is pathological pain?
Pain that persists after injury that has been resolved or arises out of the blue with no precipitating injury. It has outlived its biological purpose
What type of pain is the most difficult to treat
Pathalogical pain
What are nociceptors?
Specific peripheral primary sensory afferent neurones normally activated preferntially by intense stimuli (thermal, chemical or mechanical) that are harmful
What do nociceptors do?
They are first order neurones that relay information to second order neurones in the CNS by chemical synaptic transmission
Describe how noceiceptors work when exposed to an intense stimuli
The free nerve ending in the peripheral location senses the harmful stimuli and depolarisation occurs due to this. If the depolarisation is large enough, it triggers an action potential which then goes along the axon to the soma which then triggers the release of transmitter substances in the central terminal
Nociceptive pain is high threshold. What does this mean?
It is provoked only by intense stimuli that activate nociceptors
What does Nocicpetive pain overide
Most other ongoing activities of the nervous system
Inflammatory pain is both adaptive and protective. True or False
True
What causes inflammatory pain
Activation of the immune system in injury or infection
What does pain hypersensitivity cause
Heightened sensitivity to noxious stimuli and allodynia (innocuous stimuli now elicit pain)
How does inflammatory pain help the body to heal
It discourages physical contact and discourages movement
What is required to alleviate suffering
Reduction in ongoing inflammation (rheumatoid arthritis)
How do nerve cells in inflammatory pain become more sensitive
Due to the increase of inflammatory cells such as macrophages, mast cells, neutrophils and granulocytes in the affected area
How does pathological pain arise?
It results from abnormal nervous system function - may be neuropathic or dysfunctional
How do we describe what pathological pain is
Maladaptive with no protective function
WWhat happens in the absence of pain?
Gross damage to the body
Patients with congenital insensitivity to pain (CIP) may have what types of injuries?
Anything: lip and tongue injury bruises and cuts multiple scars bone fractures joint deformity premature mortality due to multiple injuries/ infections
What do nocicpetors innervate
Peripheral tissues
WHat are the 2 different types of nociceptor fibres
A delta and C fibres
What are A delta fibres
Mechanical/ thermal nociceptors that are THINLY myelinated. They mediate first pain
They respond to noxious mechanical and thermal stimuli
What are C fibres
Nociceptors that are unmyelinated
They respond to all noxious stimuli
Mediate second pain
Gibe examples of the sensation of first pain
Lancinating
Stabbing
Pricking sensations
Give examples of the sensation of second pain
Burning
Throbbing
Cramping
Aching sensations
How do chemical stimuli activate the peripheral terminal
H+ activates acid sensing ion channels, ATP activates P2X and P2Y receptor, bradykinin activates B2 receptors
How do thermal stimuli activate the peripheral terminal
members of the transient receptor potential (TRP) family particulalry TRPV1 activated by noxious heat. TRPV1 is greatly sensitised in inflammation to become active at body temperature
What does a stimulus do to ion channels in a nerve terminal and what does this do
Opens the ion channels to elicit a depolarising receptor potential
Describe the amplitude of the generator potential
It is grades and proportional to stimulus intensity
What does the local current flow trigger?
All or none action potentials at a frequency proportional to the amplitude of the receptor potential
I.e. the greater the depolarisation or the receptor potential, the greater the action potential frequency
Where are the nociceptor neurones most sensitive
At the lower end of the stimulous strength
What is the unusual property of peptidergic polymodla nociceptors
They have both afferent and efferent functions
What are the afferent functions
Transmit nociceptive information to the CNS via release of glutamate and peptides within the dorsal horn
What are the efferent function
They release pro-inflammatory mediators (e.g. calcitonin gene related peptide, substance P) frmo peripheral terminals - contributes to neurogenic inflammation
What does the noxious stimulation in the long term do?
Increases spinal excitability contributing to hyperalgesia and allodynia
Why are C fibres described as being peptigerdic
They utilise peptides as their neurotransmitter at the central termius
