So many people were having a problem with the descending pain pathway. So I'm going to make this little vignette and go through it so you can listen to it at your own convenience. So when you look at slide 42, you can see on the spinal cord the primary first order aerant neuron that comes into the dorsal horn and it intervates with that second order spino misenyphalic neuron.
Remember this is the spino misus misenyphalic tract which is going to ascend and either terminate in the locus ceruius the blue spot or the perryqual ductal gray. that when that painful stimulus comes in, right, you're going to excite that glutamate neuron that's within that spinal misinphalic tract. And initially what happens in the locus ceruius is that there is an excitation of a noradinurgic neuron that descends back down into the dorsal horn of the spinal cord and releases norepinephrine in the sp in the dorsal horn.
So it is activating alpha 2 both postsaptically and presinaptically to attenuate that pain response. Well, then let's look at what happens to the other fibers that extend to the perryqueductal gray. Glutamate is going to excite the enke interneuron that is going to then release the brakes if you will.
It's going to inhibit the GABA neuron which is normally keeping the system quiet. So the glutamate excites the enke neuron. and kelin is released onto a GABA neuron which is normally firing.
And now that GABA neuron no longer fires and so what happens now? A glutamate connection from the perryqueductal gray to the rafiamagnus is allowed to happen. So glutamate gets released into the rafiamagnus onto another enkeon.
This then causes the release of enein on another GABA inter neuron and reduces the amount of GABA that is flowing if you will in the Rafy magnus. What does this do? Well, now there is a serotonin neuron from the medulla, the rafi magnus in the medulla and it is excited now because its inhibition has been released.
And what happens? Well, serotonin is released into the dorsal horn and it causes other inter neurons containing enke to release more ene. Now that is a summary of the descending pain pathway.
