Introduction to the Physiology of Pain Flashcards
What is transduction?
Translation of noxious stimulus into electrical activity at the peripheral nociceptor
What is transmission?
Propagation of a pain signal as nerve impulses travel through the nervous system
What is modulation?
Modification/hindering of pain transmission in the nervous system e.g. by inhibitory neurotransmitters like endogenous opioids
What is perception?
Conscious experience of pain, causes physiological and behavioural responses
Where does pain begin?
The activation of nociceptors
What are nociceptors? How are they activated?
-Specific primary (first order) neurones that relay information to second order neurones in the CNS by chemical synaptic transmission sensory
-Innervate peripheral tissues
-Normally activated by intense noxious stimuli (mechanical, thermal or chemical)
Where are second order neurones located? What do they comprise of?
Second order neurones ascend the spinal cord in the anterolateral system (terminate in the thalamus) comprising mainly:
- The spinothalamic tract
- The spinoreticular tract
What is the spinothalamic tract (STT) involved in?
Involved in pain perception (location, intensity)
The spinoreticular tract (SRT) involved in?
Involved in autonomic responses to pain, arousal, emotional responses, fear of pain
What do third order neurones do?
Relay sensory information from the thalamus to the primary sensory cortex
What are Aδ-fibres? What do they respond to?
- Mechanical/thermal nociceptors that are thinly myelinated
- Respond to noxious/mechanical and thermal stimuli; mediate ‘first’, or fast, pain
What are C-fibres? What do they respond to?
- Unmyelinated nociceptors
- Collectively respond to all noxious stimuli (polymodal); mediate ‘second’ or slow pain
Describe the difference in character of first and second pain
- First: lancinating, stabbing, pricking
- Second: burning, throbbing, cramping, aching
Name 4 different classifications of pain + examples
- Mechanisms (nociceptive, inflammatory, pathological)
- Time course (acute, chronic, breakthrough pain)
- Severity (mild, moderate, or severe)
- Source of origin (somatic or visceral)
What is nociceptive pain?
The normal response to injury of tissues by noxious stimuli provoked by intense stimulation of nociceptors by noxious stimuli (mechanical, chemical, thermal)
Is nociceptive pain adaptive?
Yes, it functions as an early warning physiological protective system to detect and avoid noxious stimuli
What is inflammatory pain caused by?
Caused by activation of the immune system by tissue injury or infection, in response to mediators released at the site of inflammation by leukocytes, vascular endothelium and tissue resident mast cells
What does inflammatory pain cause? Why does this happen?
Heightened pain sensitivity to:
-Noxious stimuli (hyperalgesia)
-Innocuous stimuli (allodynia)
Is inflammatory pain adaptive?
Yes, it promotes repair until healing occurs
What are the two types of pathological pain?
-Neuropathic
-Dysfunctional
What is neuropathic pain caused by +examples?
Damage to neural tissue (compression neuropathies, peripheral neuropathies, central pain (following stroke or spinal injury), posthereptic neuralgia, trigeminal neuralgia, phantom limb)
How can neuropathic pain be felt?
- Burning, shooting, numbness, pins and needles
- May be less localised
What is dysfunctional pain caused by +examples?
No identifiable damage or inflammation (fibromyalgia, IBS, tension headache, temporomandibular joint disease, interstitial cystitis)
Is pathological pain adaptive? How is it treated usually?
No, it is maladaptive (not protective)
- Simple analgesics usually not very effective in pathological pain
- Sometimes treated by drugs not originally developed for pain e.g. antidepressants or antieleptics
Where does referred pain usually develop?
-Develops in one part of the body but felt in another structure away from the place of its development
- This leads to pain in an area of the skin which is distant from the internal organ where the pain originates
Where is referred pain usually felt?
Deep pain or visceral pain can be felt as referred pain; pain originating in superficial structures is not usually referred
What is referred pain caused by and what does it lead to?
Caused by convergence of nociceptive visceral and skin afferents upon the same spinothalamic level which leads to pain in an area of the skin which is distant from the internal organ where the pain originates
