Somatosensory function (pain) Flashcards
examples of pain types
nociceptive muscle superficial somatic visceral referred neuropathic.
types of muscular pain
Metabolic Overuse Tension Compression Ischaemia Tearing Viral infection Fibromyalgia Angina
what are the typical features of pain?
Aching Burning (lactic acidosis) Cramping Tightness Crushing Tenderness
why is visceral pain vague, diffused and poorly localised?
low density of sensory innervation
visceral pain
may be referred
often midline
associated with autonomic symptoms
may show visceral hyperalgesia, viscerovisceral cross-talk
types of somatic pain
Often nociceptic Related to skin Pressure Too hot/cold Inflammation Injury Infection Burns
features of somatic pain
Well-localised Sharp Stinging Aching Burning Throbbing Tightness Sensitive
where does referred pain often occur?
at sites of the body wall where innervation enters the spinal cord at the same level as the organ
pain is sharper and better localised than visceral pain
e.g in angina
what are Wind Dynamic neurones
o Receive input from A, A and C fibres.
o The most populous cell whose soma is located in the dorsal horn.
o Respond to a full range of stimuli (touch, heat and chemical) but fire more frequently to noxious stimuli.
o They fire APs in a graded fashion.
o Exhibit “wind-up”.
what is the Wind-Up phenomenon
exponentially progressive increase in firing of WDR neurons with repeated stimulation
increase in pain intensity over time when a given stimulus is delivered repeatedly above a critical rate
o Short-lasting synaptic plasticity.
o Repetitive stimulation of WDRs which induce increased evoked response and post discharge with each stimulus.
o May precipitate long-term potentiation (LTP) – i.e. long lasting increase in efficacy of synaptic transmission.
o Wind-up and LTP related to neuropathic sensitisation.
what are the two types of sensitisation?
peripheral and central
peripheral sensitisation
injury in late nerve
small area of sensitisation
central sensitisation
injury in the early nerve in spinal cord
possible large area of sensitisation if in tracts
what is neuropathic pain
pain source in the somatosensory nervous system
pain in area of neuronal dysfunction
sharp, burning, electric shcck and squeezing pain
has poor response to usual analgesic drugs
can last after an area has completely healed
allodynia
pain due to stimulus that does not usually cause pain
hyperalgesia
increased pain from a stimulus that normally causes pain
hypoalgesia
decreased pain from a stylus that normally causes pain
what is sensitisation?
increased responsiveness of nociceptive neurones to their normal input
hyperpathia
painful syndrome caused by abnormally painful reaction to a stimuli
especially a repetitive stimulus and an increased threshold
paraesthesia
abnormal sensation (spontaneous or evoked)
pins and needles
dysaesthesia
unpleasant abnormal sensation (spontaneous or evoked)
examples of neuropathic pain
complex regional pain (CRPS) syndrome
phantom limb pain
sciatica
Complex Regional Pain Syndrome
o Sensory, vasomotor, pseudomotor/oedema, motor/trophic symptoms must be present.
Characterised by neurogenic inflammation.
Displays overexpression of nociceptive nerve endings.
phantom limb pain
common among amputees
stump neuroma association
may be due to remapping of brain
treatment:
o Antidepressants – Amitriptyline, Nortriptyline, Duloxetine.
o Anticonvulsants – Gabapentin, Pregabalin.
o Opioid trial – Tramadol, Buprenorphine, Methadone, Morphine.
o Hybrid – Tapentadol.
o Topical – 5% Lidocaine, Capsaicin 0.075% cream and capsaicin 8% patches.
