Central sensitization

Presented byIfrah IshaqUniversity Of The Punjab,lahore.

Definition

“An increased responsiveness of nociceptive neurons in the CNS to their normal afferent input”.

Explanation:Nerve injury leads to an increase in the general excitability of nociceptive and multi receptive spinal cord neurons (multiple synaptic input from C-fibers as well as A fibers, wide-dynamic range neurons). Process known as central sensitization.

Diagram

Typical changes of responses of individual neurons are:

Increased responses to noxious stimulation of inflamed tissue.

Lowering of threshold of nociceptive specific spinal cord neurons (they change into wide dynamic range neurons).

Increased responses to stimuli applied to non-inflamed tissue surrounding the inflamed site.

Expansion of the receptive field.

What happened during inflammation and neuropathy?

During inflammation and neuropathy a large number of spinal cord neurons express C-FOS, supporting the finding that a large population of neurons is activated.

At least at some time points metabolism in the spinal cord is enhanced during inflammation and neuropathy.

Mechanism of central sensitization

 The mechanisms of central sensitization are complex.

It may be crucial whether central sensitization is induced by increased inputs in sensitized but otherwise normal fibres (such as in inflammation),or whether structural changes such as neuronal loss contribute for neuropathic pain.

Steps involved in central sensitization

Process Taking Place Through Different Mediators

Release of neurotransmitters. Neurotransmitters activate NMDA and AMPA

receptors. That cause increase in calcium influx. Calcium act as second messenger. Activation of nitric oxide. Decreased threshold of dorsal horn neurons.

C fibers and dorsal horn of neurons

Increase of NMDA receptors.

Increase in glutamate.

Release of substance P.

Multiple signaling pathway.

Summery of central sensitization