Pain pathway

 

Mechanism of the pain pathway

 

Nociceptors are sensory receptors present in the skin, viscera, muscles, joints and

meninges which are all sensitive to noxious stimuli (stimuli that may be damaging to

tissues). These free nerve endings are part of the primary afferent fibres that

transmit impulses along the peripheral nerve to the dorsal horn in the spinal cord.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sensory neurones subsequently synapse with the ascending spinothalmic tract to

project to the thalamus and cortex. Activation of the different types of primary

afferent fibres will transmit particular information about the sensory stimulus. The

primary afferent fibres include;

 

 Aβ fibres are myelinated and have a low threshold for stimulation for non

noxious stimuli such as touch. It is therefore not involved in the transmission

of pain.

 Aδ fibres are slightly myelinated and activated by thermal or mechanical stimulus

 to produce sensation of sharp pain.

 C fibres are unmyelinated and so produce the slowest transmission of impulse to the spinal cord. Chemical, thermal or mechanical stimulus triggers these fibres to produce dull burning pain. 

 

 Interneurones are present in the dorsal horn of the spinal cord to modulate pain perception by the release of GABA and enkephalins to decrease activity in the dorsal horn nuclei located in the spinal cord.

Therefore, analgesics can intervene on the pain pathway to provide pain relief for patients.