Pain pathways and central processing of pain Flashcards
where does somatosensory system receive info from
SKin Muscle Tendons Ligaments Connective tissu
What does the somatosensory system detect
Touch Brush Pressure tickle Temperature Pain
What is nociception
Neural process in which fibres (C-fibres) which detect stimuli are activated
What is pain
feeling/perception pain includes psychological component
What receptors exhibit selectivity
sensory receptors
What do mechanoreceptors detect
Touch, pressure, vibration
What do proprioreceptors detect
Position of body
What do thermoreceptors detect
Warm, cool, hot
What do nociceptors detect
Mechanical, thermal, chemical
What is the sensory system
Sensory receptors and neurones have peripheral receptive fields. are area over which you can activate the neurone
What is convergence
A single sensory neurone in the CnS can receive input from many sensory receptors
Process of transduction
Deformation of membrane
Opening of Na+ and K+ channels
Receptor potential. Local depolarisation of receptive membrane
Action potential propagated to CNS
What are receptive potentials like with stronger stimuli
What is the frequency like
Larger receptive potentials
Higher frequency
What is the intensity of the stimulus encoded by
Size of the responding receptor population and the numbers of fibres activated
What is recruitment
Increased number of responsive receptors and fibres
Which sensory fibres are a lot bigger in diameter and what does this mean
Aalpha and Abeta.
can transfer signals much quicker
How do Aalpha and Abeta fibres relay information by
Aalpha- proprioception
Abeta- mechanism
Which primary afferent fibres relay information from pain and temperature sensory receptors
Agamma
C fibres
Which primary afferent fibres have a smaller diameter and what does this mean. What other differences do they have
Much smaller diameter than Aalpha and Abeta and so transduction speed much slower.
They’re also unmyelinated which makes it slower too
What is the Tactile (touch) pathways
Central branches of touch afferent fibres ascend in the dorsal columns
synapse in the dorsal column nuclei
Cross the midline in the medulla
Ascend through the brainstem as the medial lemnisus
Thalamus: synapse on cells
Send projections to the primary somatosensory cortex, post central gyrus of parietal lobe
Where do pain tracts cross
In the spinal cord
Where do tactile tracts cross
In the medulla
Where do Abeta fibres terminate
Intermediate lamina (3-5) of dorsal horn
What do Abeta fibres release
Glutamate
Where do C fibres terminate
Superficial lamina (1-2) of the dorsal hormones
What do C fibres release
Glutamate and other peptides and transmitters
Where does spinal processing occur
Dorsal horn of spinal cord receives Ab fibres and C fibres messagees
Then processed
then out through the ventral horn
What is the spinothalamic pathway
Projection neurones project to the brain and help discriminate where the pain is
Why is it that if you’re already injured, and you accidentally hurt the injured part of your body, that it hurts more than if it was not injured
Neural responses to repeated stimulation of C fibres are not fixed and are not always proportional to the intensity of the stimulus applied
Enhanced responses for a given noxious stimulus are associated with repeated higher stimulation
(nerves are sensitised and so are easier to activate them)
What is allodynia
Condition where pain is caused by a stimulus that does not normally elicit pain (e.g. sunburn. Sunburnt skin hurts when hot/cold or when touched etc)
The graph is shifted to the left
what is hyperalgesia
abnormally increased sensitivity to pain which may be caused by damage to nociceptors or peripheral nerves and can cause hypersensitvivity to stimulus
Role of brainstem in pain processing
Through the spinoreticular tract and branches of the STT, nociceptive signals activate brainstem systems giving rise to changes in BP, respiration and orientation toward stimulus
Role of thalamus in pain processing
VPL is main somatosensory area of thalamus, but other components may be involved. Acts as the final relay before sensory signals reach the cortex
Role of cortex in pain processing
Consciousness of pain, plus limbic system for emotional response
Role of hypothalamus in pain processing
Response is mediated through hypothalamus. Neuroendocrine changes and some behaviours
What is the descending inhibitory control of pain pathway
1) Painful input from spinal cord goes to thalamus and other brainstem regions
2) from the thalamus, this goes to PAG (periaqueductal grey matter)
3) cortex and hypothalamus also feed into the PAG
4) PAG feeds into Nucleus Raphe Magus (NRM) and so does the LC (locus ceruleus) and the NRPG (nucleus reticular paragigantocellaris)
5) NRM sends messages to spinal cord (inhibitory transmitters) which inhibit excitability in spinal cord
What does the sensory system allow
Converts a natural stimulus (energy) to action potentials
Intensity and duration of the stimulus is conveyed
