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
what happens when the brain starts to question its map?
threat level of nervous system goes up and can cause pain or increase pain for a prolonged period of time
- Causes a ramp up phenomena of nervous system because the brain wants to know more
what is the short term effect of pain?
- Pain causes the fight or flight response to activate so ATCH is released from pituitary gland to stimulate adrenal glands producing adrenaline
- Cortisol is used to help mobilize glucose reserves
What affect does cortisol have on the immune system?
Chronic conditions including stress - 3 immune chemical seem to be very active (pro inflammatory mediates)
- Persistent inflammatory state –> decreased or prolonged healing –> smudging
what are the effects of long term pain?
-Fatigue
-Insomina
-Hypervigilance
in the ascending pathway where do 1st order neurons synapse?
Sustantia gelatinosa
what activated the 2nd order neuron in the ascending pathway?
Substance P
where does the 2nd order neuron synapse on the 3rd in the ascending pathway?
thalamus
what neuron transmitter inhibits activity at substantia gelatinosa?
GABA
in the descending pathway what is the nucleus for NE?
locus coeruleus
in the descending pathway what is the nucleus for serotonin?
Raphe Nucleus
