Intro to Pain: Neurophysiology & Neuroscience of pain Flashcards
`What is pain?
Unpleasant sensory & emotional experience associated with actual or potential tissue damage, or described in terms of such damage
Describe the pain created by C-Fiber
-longer lasting & slower pain
- unmyelinated
Describe the pain created by A Delta Fiber
- Initial pain
- thinly myelinated
Describe C & A delta fibers
-Nociceptive
-Free nerve endings that convey pain, temperature, & crude touch
Describe A beta fibers
- Non Nociceptive
- Touch, pressure & vibration
what are the three ways nervous system can be stimulated?
- Mechanically
- Thermally
- Chemically
Describe pain processing mechanisms (ascending pathway) that would happen in response to injury to R medial knee up until the 1st order neuron synapse on the substantia gelatinosa
- Injury
- Release of cytokines (PG)
- PGs stimulate (+) C fibers & A- Delta fibers
- C fibers & A Delta fibers (1st order neuron) carry the nociceptive information to the ipsilateral dorsal horn of the spinal cord
- At same time, info from surrounding levels are also sensing in info that needs to be regulated
- 1st order neuron synapse on substantia gelatinosa
Describe the pain processing mechanism (ascending pathway) that would dhappen after the 1st order neuron synapse on substantia gelatinosa
- Activates Substance P which then activates 2nd order neurons which project to spinothalamic tract
- 2nd order neuron ascends through spinal cord & brain stem & projects to thalamus
- In thalamus, 2nd order neuron will synapse on 3rd order neuron
- 3rd order neuron projects to the primary somatosensory cortex on the left side of the brain
- Perception of pain is produced
- Seek appropriate medical care
What happens within the dorsal horn?
-nociceptive information is sent to dorsal horn
-Neurons synapse on interneuron
-Interneurons determine what actually gets sent to the brain
Describe the gate control theory
-A beta fibers are activated with light touch
-Send action potential into posterior grey horn & give off collateral neurons which synapse on interneurons
-Interneurons release GABA
-GABA inhibits activity at substantia gelatinosa
Describe the descending analgesic pathway
- Activation of A delta & C fibers produces stimulation of hypothalamus, thalamus, cortex & amygdala
- Causes a projection to the Periaqueductal grey matter & stimulation (+) of the locus coerulues (NE) & stimulation of raphe nucleus (serotonin)
- Send projections down to substantia gelatinosa of the dorsal horn
- Release NE & serotonin to interneurons in dorsal hour
- Interneurons’s release enkephalins, endorphins & dynorphins
- Inhibits substantia gelatinosa resulting in decreased pain
what occurs with persistent nociception via C fibers?
-Permanent neuroplastic change
-Interneuron may die due to high levels of amino acids
Why is it a problem if interneurons begins to die?
-Decreased ability to modulate nociception & pain experience
-Now everything that gets projected to brain including light touch which may now be painful
What is allodynia?
pain in the presence of a non-threatening stimulus due to the lack of interneuron stimulation
what central changes occur with/ are caused by pain?
- Homunculus become blurry
- Enlarged map
- Difficulty with L vs R discrimination