Wk 25 - Pain 2 Flashcards
Define pseudo-unipolar
Single axon extending from cell body that forms 2 extensions: dendrites + axon
Outline the different types of sensory receptors
- Chemoreceptors: sense chem
- Mechanoreceptors: sense touch, pressure + distortion
- Photoreceptors: sense light
- Thermoreceptors: sense temo
- Nociceptors: respond to variety of stim + sense tissue damage
What is a nociceptor?
- Excitatory neurons
- Release glutamate as primary NT
What are the different types of nociceptors?
- Thermal: activated by noxious heat/cold
- Mechanical: respond to intense pressure + incisions
- Chemical: spices
- Polymodal: respond to thermal, mechanical + chemical
- Silent: active when tissue inflamed
What is the ascending pathway?
Neural projections which sensory info travels periphery to brain
What does the ascending pain pathway include?
- Dorsal column: 1st order neurons = Aa/Ag fibers
- Spinothalamic tract: lateral (Ag + C fibers) + anterior (Ab)
- Spinocerebellar tracts
Outline the pain pathway
- 1st order neurons: signals from periphery to spinal cord/medulla
- 2nd order neurons: signals from spinal cord/medulla to thalamus
- 3rd order neurons: signals from thalamus to primary sensory cortex
What happens in 1st order neurons?
Sensory stimulus signaled via:
- Fast conducting Aa/Ab fibers
- Slow conducting C + Ag fibers
Outline the descending pain pathway
- PAG receives projections: cingulate, insular, prefrontal cortex, hypothalamus + amygdala
- PAG sends projections: RVM + DLPT
What is the descending pain pathway?
Modulates pain sensation (enhance or inhibits)
What does the descending pain pathway include?
- Anterior cingulate + insular cortex
- PAG
- Nuclei in amygdala + PVG of hypothalamus
- DLPT (5-HT neurons)+ RVM (NA neurons)
Which NT are involved in the descending pain pathway?
- Opioidergic
- Noradrenergic
- Serotonergic
- Cholinergic
- GABA-ergic
- Endocannabinoids
Outline the mechanism of what happens when the spinal cord receives input from the RVM
- 5 HT release
- Hyperpolarization: ascending fiber + dorsal horn projection w/ 5-HT1 receptor
- Depolarisation: spinal GABAergic interneurons w/ 5-HT2A + 5-HT3 receptors
Outline the mechanism of what happens when the spinal cord receives input from the DLPT
- NA release
- Hyperpolarization: projection neurons when interacting w/ a-2A receptors
- Hyperpolarization: primary afferent fibers w/ a-2B/C receptor
- Depolarisation: dorsal horn inhibitory interneurons via a-1A receptor
Give examples of what different neurochemicals do to the pain ascending pathway
- Glutamate + substance P = stim pain ascending pathway
- GABA, enkephalin + endorphin = block pain signal
