9: Physiology - Pain and thermosensation Flashcards
What is pain?
Unpleasant sensory / emotional experience
Associated with tissue damage or described in terms of it
Does pain mean that tissue damage is occurring?
Not neccessarily
Which type of pain is a short-term response to prevent tissue damage?
Nociceptive pain
What is the purpose of inflammatory pain?
Stops you from touching a damaged area until healing has occurred
How long does inflammatory pain persist for?
Days - Weeks
What are some adjuvant drugs which can be used to control pain?
Antidepressants
Anticonvulsants
Local anaesthetics
Describe pain originating from the skin.
WELL LOCALISED
stabbing, pricking, burning
Pain originating from the muscle and viscera tend to be ___ localised.
poorly localised
Visceral pain tends to be ___.
Muscle pain tends to be ___.
dull
achey
Pain can be ___ to distant areas.
referred
Which receptors detect intense stimuli to cause the sensation of pain?
Nociceptors
What sort of stimulus triggers a nociceptor?
High intensity stimuli
of a THERMAL, MECHANICAL or CHEMICAL nature
Nociceptors are which order neurons?
FIrst order neurons
What are the factors influencing the conduction velocity of a neuron?
1. Myelination
2. Diameter of axon
Which type of sensory fibre transmits fast pain?
A-delta
look back at the table of conduction velocities
Which type of sensory fibre transmits slow pain?
C fibres
look back at table of conduction velocities
What does
a) fast pain
b) slow pain
feel like?
a) Stabbing, pricking, burning
b) Aching, throbbing
Which ions enter a neuron to cause a depolarisation?
Na+
Ca2+
Why does injured tissue feel hot?
One of the TRP channels responsible for noxious heat is activated
What does polymodal mean in terms of nociceptors?
Respond to more than one noxious stimulus
At which specific temperature does warmth become unpleasant heat?
43 degrees Celsius
Which two types of nerve fibre make up most nociceptors?
A-delta (‘fast’ pain fibre)
C (‘slow’ pain fibre)
Which neurotransmitters are involved in the transmission of pain signals?
Glutamate
(excitatory)
The more a synapse is activated, the more ___ it becomes.
efficient
What is released at the peripheral terminal of a nociceptor when it is activated?
Inflammatory mediators
What causes sterile neurogenic inflammation?
Release of inflammatory mediators from the PERIPHERAL terminal of activated nociceptors
Which neurotransmitter is released into the synaptic cleft when a pre-synaptic sensory fibre is activated?
Which change in membrane potential does it cause?
Glutamate
Depolarisation (excitatory post-synaptic potential)
Two ligands, AMPA and NMDA, bind to receptors to change the type of excitatory post-synaptic potential that is produced.
What does each cause?
AMPA - fast
NMDA - slow
The excitatory post-synaptic potential causes a depolarisation which overcomes threshold potential.
What happens next?
Action potential
What does repeated stimulation of a synapse cause in the long term?
Increased efficiency
giving rise to hyperalgesia and allodynia
Which intensity of stimulus is picked up by wide dynamic range cells in the lamina V?
All intensities
What does visceral pain feel like?
Dull, aching, poorly localised
What stimulus activates visceral nociceptors?
Stretching, twisting, inflammation, ischaemia
Visceral afferents from internal organs “plug in” to the spinal cord at the same spinal levels as somatic sensory fibres.
What does this lead to?
Referred pain
What are autonomic symptoms?
Symptoms caused by sympathetic activation
e.g N&V, sweating, pallor
What are the characteristics of somatic pain?
Sharp, stabbing, well-localised pain
What causes viscerosomatic pain?
Inflammation from an organ making contact with the body wall
e.g enlarged, inflamed appendix in appendicitis
What disease classically causes visceral pain followed by viscerosomatic pain?
Appendicitis
What is the jist of the Gate Control Theory?
If you can activate other sensory fibres e.g A-alpha, A-beta, you can override or ‘close the gate’ to nociceptive signals from A-delta and C
i.e distracting the brain with other stimuli can lessen the experience of pain
