What is the Difference Between Central and Peripheral Sensitization

The main difference between central and peripheral sensitization is that central sensitization is the increased responsiveness of nociceptors in the central nervous system, whereas peripheral sensitization is the increased responsiveness of nociceptors in the afferent nerve stimulus.   

Central and peripheral sensitization are two pain signals detected by the nervous system. Pain is a stimulus sensed by nociceptive neurons.                 

Key Areas Covered

1. What is Central Sensitization
– Definition, Features, Importance
2. What is Peripheral Sensitization
– Definition, Features, Importance
3. Similarities Between Central and Peripheral Sensitization
– Outline of Common Features
4. Difference Between Central and Peripheral Sensitization
– Comparison of Key Differences

Key Terms 

Central Sensitization, Peripheral Sensitization

What is Central Sensitization

Central sensitization is the amplification of the sensory input by the central nervous system. It is the increased responsiveness of nociceptors in the central nervous system. It occurs in either normal or sub-threshold afferent input. Central sensitization results in hypersensitivity to stimuli. It also causes responsiveness to non-noxious stimuli and increases pain response outside the area of injury. The effect of the central sensitization process is the recruitment of additional subthreshold synaptic inputs to nociception resulting in a greater field of receptivity and the increased output of nociception. Also, the effect persists beyond the initial noxious input. This results in pain hypersensitivity.

Figure 1: Central Sensitization

Furthermore, the CNS undergoes functional, chemical, and structural changes, making it more sensitive to pain in central sensitization. It increases membrane excitability and synaptic efficacy. By that, it brings subthreshold synaptic inputs to nociceptive neurons. Also, central sensitization is responsible for spatial, temporal, and threshold changes in pain sensibility.

What is Peripheral Sensitization

Peripheral sensitization is the increased sensitivity to an afferent nerve stimulus after an injury. It produces a flare response due to nociceptors’ increased production of neuropeptides. This process is called primary hyperalgesia or primary allodynia before the injury. However, peripheral sensitization can occur in response to inflammation. Chemical mediators of inflammation, including histamine, bradykinin, acids, and serotonin, stimulate the nervous system by bringing the membrane potential closer to the depolarization potential. It causes peripheral sensitization. Also, this results in the upregulation of the sodium-specific nociceptive channels through a protein enzyme cascade.

Figure 2: Potential Mechanism(s) for Nociceptor Sensitization in severe COVID-19

Moreover, the upregulation of nociceptive channels makes the neurons more sensitive to the chemical mediators of inflammation. It causes ion influx and generates the action potential that regards the pain. 

Similarities Between Central and Peripheral Sensitization

• Central and peripheral sensitization are two processes of sensitization of pain.
• They occur in physical damage at a peripheral site.
• Nociceptors are the neurons responsible for sensing pain. 

Difference Between Central and Peripheral Sensitization

Definition

Central sensitization is a state in which the central nervous system amplifies sensory input across many organ systems. In contrast, peripheral sensitization refers to a reduction in the threshold and/or an increase in the magnitude of responsiveness at the peripheral ends of sensory nerve fibers. 

Type of Nervous System

Central sensitization occurs in the central nervous system, while peripheral sensitization occurs in the peripheral nervous system.

Occurrence

Central sensitization occurs in neuroplastic changes, while peripheral sensitization occurs in inflammatory responses, leading to exaggeration and extension of pain response. 

Examples

Phantom limb pain is an example of central sensitization, while osteoarthritis, back pain, and chronic joint injuries cause peripheral sensitization.

Conclusion

In brief, central and peripheral sensitization are two types of pain sensitization processes. Central sensitization occurs in the central nervous system in response to neuroplastic changes. Phantom limb pain is an example of central sensitization. In comparison, peripheral sensitization occurs in the peripheral nervous system in response to inflammatory responses such as osteoarthritis, back pain, and chronic joint injuries. Therefore, the main difference between central and peripheral sensitization is the type of nervous system involved in sensitization. 

References:

1. Central sensitisation. Physiopedia. (n.d.). 
2. Peripheral sensitization. Physiopedia. (n.d.-b). 

Image Courtesy:

1. “Widespread Pain Index Areas” By Jmarchn – Own work (CC-BY SA 3.0) via Commons Wikimedia
2. “Potenziali meccanismi per la sensibilizzazione ai nocicettori nel COVID-19 grave” By Amelia J – Own Work (CC-BY SA 4.0) via Commons Wikimedia