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Descending Inhibition

2/9/2015

4 Comments

 
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So the cannibal tribe is chasing you, and you trip, fall and sprain your ankle. We know that sprained ankles are extremely painful, but if you stop to deal with your sprained ankle, the cannibals will catch you and eat you.

Your brain is going to decide that staying to nurse your sprained ankle will reduce your overall probability of survival, so it shuts the pain off. How does it do that?

1)      Your brain decides that pain is going to reduce your survival rate, so it tells the hypothalamus, “Let’s not have any pain.”

2)      The hypothalamus communicates with the Peri-Aqueductal Gray Matter (PAGM), which is the gray matter surrounding the cerebral aqueduct in the midbrain. The PAGM coordinates the body’s analgesic system. (When the PAGM is electrically stimulated, pain is shown to be eliminated or reduced).

3)      When the PAGM is activated, it sends analgesic impulses down through the brainstem, through the raphe nucleus, which synapses with a descending neuron that goes down one side of the spinal cord (dorsolateral tract) to influence analgesia at the appropriate level of the spinal cord.





























As previously described in earlier posts, a nociceptive impulse comes into the dorsal horn of the spinal cord and synapses with a second order neuron to go in the spinothalamic tract to the brain for pain to be recognised/registered.

If it is inappropriate to feel pain, analgesic impulses come down the dorsolateral tract, and at the appropriate level of the spinal cord, a neuron (analgesic neuron) will project from the dorsolateral tract into the area of the synapse between the axon of the sensory neuron and the start of the second order neuron (which would take the nociceptive impulse to the brain).



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This analgesic neuron contains chemical transmitters which fit into the pre- and post- synaptic receptor sites. When these chemical transmitters bind with the pre- and post- synaptic sites, they cause pre- and post-synaptic inhibition respectively, resulting in the whole synaptic area being turned off, inhibiting ongoing propagation of nerve impulses. Therefore, pain is not felt, as the impulse going to the brain has been blocked.

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Interesting to note: these chemical transmitters are opioids. The body produces its own opioids, endorphins, enkephalin substances.  Also interesting to note that the seed of the poppy plant has the same chemical properties as your body’s endogenous opioids. Morphine, when injected, will have the same effect of pain inhibition as these endogenous opioids.

So, when it is not appropriate for you to feel pain in order to ensure your survival , your body activates its own analgesic system, releasing its own opioids, blocking off pain. All this happens outside your awareness.

This is your amazing body.

4 Comments
Stu Hogg
3/9/2015 09:32:44 pm

Good review Sharon. Always to go over this stuff again.

Reply
Sharon Farquharson
3/9/2015 10:11:52 pm

Thanks for the feedback, Stu. Please let me know if I get anything wrong.

Reply
Postgraduate Diploma in Clinical Psychology link
28/9/2016 05:56:34 am

You have wonderful views which are evident from your writings. Keep posting such kind of blogs as they are really informative, wish you good luck for your future blogs

Reply
Sharon
28/9/2016 11:36:25 pm

Thank you for your kind words

Reply

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    Author

    Sharon is a physiotherapist focusing her treatment on TMDs and related orofacial and craniofacial pain.

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