Physiology and pathology of pain Flashcards
what is pain
an unpleasant sensory and emotional experience which we primarily associate with tissue damage or describe in terms of such damage or both
NOT A STIMULUS
final product of complex-information processing network
what is the brief pathway of pain
Step 1. Periphery
- Detection
- Transmission to spinal cord (first order neurons)
Step 2. Spinal cord
- Processing
- Transmission to brain (Thalamus) (second order neurons)
Step 3. Brain
- Perception, learning, response
Step 4. Modulation
- Descending tracts
what is nociception
the detection of tissue damage by specialised transducers connected to A-delta and C fibres
what are the structure and function of nociceptors
free nerve endings of A-delta and C fibres
respond to thermal, chemical and mechanical noxious stimuli
where are the primary afferent/1st order neurons for pain found and where do they synapse
cell body in dorsal root ganglion
synapse at spinal cord
what are the 4 sensory primary afferents and what are their characteristics
Aa + AB
- myelinated
- large diameter
- proprioception, light touch
Adelta
- lightly myelinated
- medium diameter
- heat, pain - fast
C
- unmyelinated
- small diameter
- innocuous temp, pain - slow
what is the different between A-delta and C pain primary afferents
A-delta
- fast pain
- the immediate sharp pain
C
- slow pain
- later dull pain
e. g. someone pinches you
- immediate sharp pain - A-delta
- as the sharp pain fades and transforms into a dull pain - C fibres
what neurons receive input from first order synapses and where are they found
Nociceptive specific - input from A-delta and C
Low Threshold Mechanoceptive - input from Aa
Wide Dynamic Range - Ab and interneurons
found in the spinal dorsal horn
what is the major ascending tract for nociception
lateral spinothalamic tract
where does the lateral spinothalamic tract go to
thalamus - acts as a second relay station
ventroposterior thalamic nuclei
medial thalamus
where does the thalamus connect to
cortex
limbic system
brainstem
where does pain perception occur
somatosensory cortex
where is the affective and emotional component of pain as well as the descending control of pain located
brainstem centres
what is the descending pathway for pain
brain - dorsal horn
through peri aqueductal grey matter
noradrenergic system
what does the descending pathway usually do to the pain signal
decreases it
what is hyperalgesia
the increased perception of pain or the perception of non-noxious stimuli as noxious
caused by an exaggerated response to normal and supernormal stimuli
happens when there is tissue injury or inflammation
what is the difference between primary and secondary hyperalgesia
primary - hyperalgesia occurring at the site of injury
secondary - hyperalgesia occurring in the surrounding uninjured tissue
what is allodynia
decreased threshold for response to pain
i.e. light touch perceived as painful
how does spontaneous pain occur
spontaneous activity of the nerve fibres - mainly during nerve injury
what is the gate control theory of pain
Adelta/C fibres excite projection neurons
= pain
Ab fibres excite inhibitory interneurons
inhibitory interneurones inhibit the projection neurons
= decreased perception of pain
what is central sensitisation and what are the components
the response of second order neurons in the CNS
acts at the level of the spinal cord
- wind up
- classical
- long term potentiation
what occurs in wind up sensitisation
involves only activated synapses
progressively increases response of neurons - to make the area more sensitive
only over the course of the stimulus - terminates with the stimulus
what occurs in classical sensitisation
the opening up of new synapses (silent nociceptors) if intensity strong enough
allows for secondary hyperalgesia (surrounding area) and can outlast initial stimuli duration
once activated can be maintained by low intensity stimuli
what occurs during long term potentiation
involves mainly activated synapses
occurs primarily for very intense stimuli
strengthening of synapses
