Where can nociceptors CANNOT be found?
The brain
Why is pain useful?
To avoid injury, alert a local infection, aid recovery, or indicate third pain.
What are the two types of nerve fibres which carry nociception?
- C fibers
2. A-alpha fibers
What are the characteristics of C fibres?
- long-lasting, sustained contraction
- smallest diameter, unmyelinated axons
- slow conduction velocity
- signal ongoing damage
What are the characteristics of A-alpha fibres?
- small diameter myelinated fiber
- immediate pain alert
- faster conduction velocity
- signal acute onset of painful stimulus
When do pain pathways become more sensitive?
Following an injury, or inflammation disease. injury site and the area around it become tender. this is due to sensation of sensory endings by locally released factors, and changes at CNS synapses
Why and how do damage area have local inflammatory changes?
To increase brain sensation. This happens due to mast cells in the area releasing histamine, which recruits and activates surrounding pain fibres to generate pain signals.
What is the role of natural aspirin?
An anti-clotting agent.
How can pain pathways be inhibited?
By ‘gating’ of pain impulses by non-painful stimuli of nearby nerves. this inhibits responses of ascending pain fibres.
What sensory pathway delivers pain nerve signals?
The anterolateral pathway
what is descending control?
Control which descends from the brain. pathways to the spinal cord from brain and brainstem regulate pain transmission.
What are endogenous opiates?
They are chemicals released at synapses on pain-pathways neurons. They decrease synaptic excitability, so less pain is sensed. They are released in response to acute pain or stress.
What are endocannabinoids?
They are chemical synthesised and released by neurons, but are not stored in vesicles (fat soluble). They decrease long-term sensitivity to pain and act on receptors as well as centrally. They are very slow. They are released by the postsynaptic neuron, to mediate the amount of neurotransmitter released by the presynaptic neurone.
What modulates pain transmission?
- peripheral neural pathways
- descending pathways from several brain region
- various chemical transmitters
What are some symptoms of diabetes neuropathy?
- tingling or burning in toes, feet, legs, fingers, hands, or arms
- a ‘pins and needles’ feeling
- pain or cramping
- numbness or loss of sensation
- insensitivity to heat or cold
- extreme sensitivity to even the lightest touch
- muscle weekness in hands or feet
- loss of coordination or balance that makes in harder to walk
Does muscle pain always come directly from the muscle?
No. It could be in any of the surrounding tissues, or in the muscles nerves. lack of circulation can also cause pain.
What is referred pain?
it is when feelings from the viscera are referred to the body surface. it is presumed to be due to ‘cross-talk’ of visceral and somatic sensory pathways.
What is neurogenic pain?
It is pain due to damage to a nerve. nerve compression can cause pain to be felt in the region of nerve termination.
What is phantom limb pain?
It is pain felt in a region that no longer exists (lost limbs)
What are the two causes of phantom limb pain?
- Ongoing activity in nerves that used to come from that part
- invasion of cortical representation for that part by intact body regions, so input is misinterpreted
