3: Opioids and pain

What are nociceptors

In the skin, they detect stimuli which could be painful

this varies in perception between people and therefore they are hard to study/quantify

Where do cell bodies of sensory info come from

dorsal rot ganglia in the spine

What are the two components of pain

first/early and late

How does first/early pain transfer in the NS

Carried by myelinated a-delta neurons

spine → thalamus → somatosensory cortex

How does late pain transfer in the NS

late pain is unpleasantness or the emotional side effeccts

this is carried by thin unmyelinated c fibers for a slower transmission

thalamus → limbic structures

How do opioids effect pain, broadly?

Drugs bind to opioid receptors & bind to inhbibitory action of endogenous opioids at any stage of pain

What are the three ways opioids regulate pain

1. spinal cord by affection small inhibitory neurons

2. descending pathways in PAG (grey area of BS)

3. at higher brian sites

What are the three ways endorphins can regulate the descending pathways to inhibit spinal cord pain

1. directly inhibiting the projecting neuron

2. inhibiting excitatory interneuron

3. exciting the inhibitory opioid neuron

What do endorphins regulate?

Several descending modulatory pathways that begin in the midbrain and inhibit spinal cord pain trasnmission

the most important of these begin in the PAG (periaqueductal gray area)

What are the two descending modulatory pathways that begin in the PAG

1. terminates in medulla and includes serotinergic cells (which extend to the spine, inhibiting cell firing and decreasing pain transmission) in the raphe nuclei

2. Terminates in locus coeruleus which is full of noradrenergic cell bodies, sned axons to spine to modulate pain acitivty

How are both PAG modulatory pathways actviated?

By opioids that lead to inhibition of GABA break. The GABA break normally stops pathways from stimulating the spine