Pain Flashcards
What is specificity theory?
Pain is a distinct sensation
- Detected and transmitted by specific pathways to distinct “pain areas”
What is convergence theory?
Pain is an integrated plastic state
- Represented by a pattern of convergent somatosensory activity within the distributed network
What is a nociceptor?
An afferent with a free nerve ending
How are nociceptors classified?
According to activating stimulus, fibre type and conduction velocity
- Light myelinated A delta fibres
- Unmyelinated C fibres
What are the 2 categories of pain?
Fast
Slow
Describe fast pain
- Sharp and immediate
- Can be mimicked by direct stimulation of A delat fibre nociceptors
Describe slow pain
Delayed, diffused and long lasting
- Can be mimicked by stimulation of C fibre nociceptors
Does stimulation of A delta or A beta fibres elicit pain?
No never
- distinct set of A delta and C fibres (nociceptors) specifically associated with pain detection
At what temperature is the capsaicin receptor activated?
45*C
What are the 2 components of central pain pathways?
Sensory discriminative
Affective-motivational
Describe the sensory discriminate pathway
- Signals location, intensity and type of stimulus
Describe the affective motivational
- Signals ‘unpleasantness’ and enables autonomic
What tract is involved in the discriminative pathway?
The spinothalamic tract
What is the affective-motivational response to pain?
- Shares pathways with the anterolateral system
- Neurons in parabrachial nucleus can respond to painful stimuli from anywhere on the bodies surface
- Strong correlation of pain with cingulate cortex
What is hyperalgesia?
Increased response to a painful stimulus
- Hypersensitivity
What is Allodynia?
Painful response to a normally innocuous stimulus
What are the peripheral effects of the inflammatory response?
- Tissue damage releases a ‘soup’ of inflammatory substances, can affect nerve function, recruit mast cells and neutrophils and increase local blood flow
Function of bradykinin?
Directly affects the function of nociceptive molecular receptors
- Such as TRPV1
Describe central sensitisation
Sensitisation can result from the activity dependent local release of substance
- Prostaglandins from nociceptive dorsal horn neurons
- Lowers thresholds for ap , gives rise to hyperalgesia
- Results in allodynia
Describe hyperpathia
- Variant of hyperalgesia and allodynia
- Fibre/axonal loss/damage results in raising detection threshold
- Explosive pain
Describe phantom limb pain
Experienced after amputation
- Central representation of the body is not passive
- Central maps may be partly preformed
- Pain may be a result of what we expect it to be
Describe referred pain
- Pain due to damage in the viscera perceived as coming from specific locations in the skin according to the organ affected
Describe the central modulation of pain
Mechanisms exist, voluntary or involuntary, to overcome severe pain
What is the physiological basis of pain modulation?
Stimulation of periaqueductal grey activates brainstem nuclei
- Modulates activity of dorsal horn neurons
- Descending inputs activate enkephalin which releases interneurons to inhibit nociceptive fibres
How does pain relief happen locally?
Local inhibition by mechanoreceptors (A delta) of nociceptive (C fibre) inputs in the spinal cord
What did Melzack and Wall propose?
Pain perception is the result of integration of convergent sensory information
