Somatosensation II Flashcards
What are the two aspects of pain?
Sensory and affective
What is sensory pain?
Location, intensity, duration and quality
What is affective pain?
Unpleasantness (painfulness) or effects on arousal, mood and behaviour
What are nociceptors?
Neurons specialised for detection of painful stimuli
How does the skin differentiate between nociceptive and non-nociceptive stimuli?
Thermoreceptors respond above normal skin temp at a level rate, whereas nociceptors gradually increase beyond the thermoreceptor level
What is the difference between A delta and C fibres?
A delta fibres conduct quicker
What is the TRPV1 receptor involved in?
The transduction of noxious heat
How do the TRPV1 receptors work?
Noxious heat opens the channel, which allows calcium and sodium ions to depolarise it
How is nociceptive pain maintained after injury?
Inflammatory soup of cytokines, prostaglandins and small signalling molecules keep the depolarisation going
What is hyperalgesia?
Increased pain sensitivity
What is allodynia?
Painful response to normally non-painful stimuli
What does substance P cause?
Stimulation of mast cells and vasodilation
Where are dorsal horn interneurons located?
Superficial and deep layers of the dorsal horn
Where do the dorsal neurones get their synaptic input from?
C and A delta fibres
What does multimodal mean?
Receive convergent nociceptive and non-nociceptive inputs
What causes referred pain?
Dorsal horn interneurons receiving convergent inputs from visceral afferents
Where do dorsal horn interneurons cross and ascend?
Anterolateral white matter
Where does the STT project to (and via?)
Primary somatosensory cortex
Do the STT and DCML axons converge?
No because the pathways are parallel
What is the primary somatosensory cortex necessary for?
Localisation of pain
What does stimulation of the S1 give rise to?
Referred tactile sensations (not painful)
What are the two systems involved in central pain processing?
Lateral and medial systems
Where do the two central pain processing systems diverge
The level of the thalamus
Which system is the lateral system in parallel with?
DCML
Which type of pain is the lateral system involved in?
Sensory- discriminative
Which part of the cortex does the lateral system arise from?
Primary and secondary somatosensory
Where does the lateral system project via?
Specific somatosensory thalamic nuclei
Where does the medial system arise from?
Anterior cingulate and insular cortex
Which type of pain is the medial system involved in?
Affective- motivational
Where does the medial system project to?
Different cortical areas via non-specific midline thalamic nuclei
How do we know endogenous opioids are produced in the body?
Opium receptors in the body
What is periaquiductal grey?
Major pain sensory cortex and the site of neurons that contain endogenous opioids
Where is the main source of enkephalins?
Periaquiductal grey
What are enkephalins mainly associated with?
Particular Neuro-modulatory transmitter substances
What do enkephalins integrate with?
Opiate containing nuclei that project back down the dorsal horn of the spinal cord
How do enkephalins produce an analgesiac effect?
Act on raphe nuclei which project into the spinal cord to release enkephalins that presynaptically inhibit incoming C fibres
What are the types of pain treatment used as neurophysiological response to tissue damage?
NSAIDs and opiate drugs
What drugs (/class of drugs) is used to treat chronic pain?
Antidepressants at a lower dose and without a diagnosis of clinical depression
What is the definition of chronic pain?
Pain for >3 months with a high prevalence
What may chronic pain be due to?
Nerve damage from prior injury - neuropathic pain
How do you treat intractable pain as a last resort?
Anterior cingulotomy
What is an anterior cingulotomy?
Targeted lesion to disconnect anterior cingulate cortex on both sides
