Flashcards in Pain Deck (70)
What is pain?
Pain is the feeling or perception of irritating, sore, stinging, aching, throbbing, miserable, or unbearable sensations arising from a part of the body.
What is the sensory process for pain?
Nociception is the sensory process that provides the signals that trigger pain.
What is Congenital Analgesia?
The inability to feel pain from birth
Where are nociceptors found?
Nociceptors are found in the periphery as simple free nerve endings.
Where do peripheral nerve fibers terminate?
Peripheral nerve fibre branches & terminates as naked, unmyelinated endings in dermis.
What is the process of pain and hyperalgesia?
Tissue damage and inflammation triggers release of substances e.g prostaglandins, bradykinin and histamine that can sensitize peripheral nociceptors and induce hyperalgesia.
What is hyperalgesia?
Abnormally heightened sensitivity to pain.
What are the types of nociceptors?
Transduction of nociceptive stimuli occurs in the free nerve endings of unmyelinated ‘C’ fibres and thinly myelinated ‘Ad’ fibres.
What are the different modalities that nociceptors respond to?
Mechanical: respond to strong pressure.
Thermal: respond to burning heat / extreme cold.
Chemical: respond to histamine or other chemicals
Most nociceptors are polymodal and respond to what?
Mechanical, thermal & chemical stimuli.
What is the use of microneurography?
To see the distribution of nociceptors on the skin
What is the process of microneurography for comparison of thermoreceptor and nociceptor?
Thermal stimuli applied to receptive field of cutaneous thermoreceptor and nociceptor
B. Record afferent firing in response to incremental temperatures
C. Graph plotting afferent firing frequency versus temperature
What type of fibres do thermal and mechanical nociceptors have?
Aδ fibres (myelianted)
What type of fibres do polymodal nociceptors have?
C fibres ( unmeyelinated)
What is the general prinicpile of large diameter fibres?
Large diameter, rapidly conducting afferents (I/II) associated with low threshold mechanoreceptors.
What is the general prinicpile of small diameter fibres?
Small diameter, slow conducting afferents (III/IV) associated with nociceptors and thermoreceptors.
What is the characteristic of 1st pain?
Fast A-delta fibres
Sharp or prickling
Mechanical or thermal nociceptors
What is the characteristic of 2nd pain?
Dull ache, burning
How are the role of each sensory afferent in pain perception investigated?
It is possible to selectively anaesthetise C fibres and A delta fibres to dissect out the role of each sensory afferent in pain perception
What is the role of perception of nociception that is small and myelianted and one that is unmyelianted?
Small and myelinated --> sharp pain
Unmyelianted --> burnign pain
What is the route of nociceptive fibres?
Nociceptive fibres have their cell bodies within the dorsal root ganglion.
Afferent terminals enter the dorsal horn and travel up/down a short distance within the Zone of Lissauer.
Afferent terminals synapse onto neurones within the superficial laminae of the dorsal horn.
Principle areas innervated by nociceptor afferents are lamina I and lamina II (substantia gelatinosa).
How is nociceptive input from viscera and skin detected?
Nociceptive afferents from internal organs e.g. viscera and the skin enter spinal cord through common routes and target overlapping populations of spinal neurons
This ‘cross-talk’ accounts for referred pain whereby visceral pain is perceived as having a cutaneous source by the sufferer.
What is the referred pain of angina?
Pain is localised by the patient to the upper chest wall and the left arm
Where is referred pain for appendicitis at early stages ?
Pain is referred to the abdominal wall around the navel.
Pain afferent release what excitatory neurotransmitter?
What is the important neuropeptide in pain afferents?
What type of pathway is the ascending pain pathway?
What are the 3 components of the ascending pain pathway?
Lateral (neo-) spinothalamic tract.
Anterior spinothalamic tract to the reticular formation and
periaqueductal grey matter
What is dissociated sensory loss?
A unilateral spinal lesion will produce sensory loss of touch, pressure, vibration and proprioception below the lesion on the same side.
Diminished sensation of pain below the lesion will be observed on the opposite side.