Lecture 19- Pain Flashcards
What is nociception?
-activation of nociceptive primary afferents
What is pain?
-conscious, affective unpleasant somaesthic percept localized to the body
What is hyperalgesia?
-increased sensitivity to noxious stimuli
Does nociception have specialised neurons?
-yes
How can you map the receptive fields of nociception neurons?
-with heat
What is the pattern of response of nociception afferents?
- do not respond till sth really happens
- high threshold
- can be chemical burn too (whereas mechanorecpetors are very sensitive)
- only starts to fire at 45 degrees then at 60 degrees very repsonsive but the non-nociceptive thermoreceptor plateus
- nociceptors= encode for temps etc that damage, opposed to other recpetors
What are the two categories of pain?
- first (sharp pain)
- second (duller, burning pain)
What pain do the A delta fiber convey?
-small thinly myelinated fibres, 5 microns= fast sharp pain (mechanosensors at high threshold)
What pain do C fibres convey?
thinnest nerve fibres - unmyelinated= C fiber (here myelin would slow it down if it were here due to the small size) -1 micron= sensation of diffuse, duller burning pain -the C fibres are polymodal= respond to noxius chemical and mechanical stress when very high, respond to proton concentration (acidity)
What is the most common peripheral nerve fibre?
C fibres -small and everywhere
What are the characteristics of C fibres?
-0.2-1.5 micometers -0.5-2.0 meters for second speed -temperature, pain, itch
What are the characteristics of A delta fibres?
-myelinated -1-5 micrometers diameter -5-30 M/s -pain and temperature
What are the characteristics of A beta fibres?
-6-12 micrometers diameter -35-75m/s -mechanoreceptors of skin
What are the characteristics of A alpha fibres?
-13-20 micrometers in diameter -80-120m/s -proprioceptors od skeletal muscle
Where does capsaicin bind?
-can diffuse through the membrane so it binds on the inside -VR-1 receptor
What binds to VR-1 receptor?
-capsaicin -heat and H+ (acidity)