Pain Gate Theory/ Electrotherapy

Pain gate theory

Pain in detected by nociceptors: A delta and C fibres

|                                                                     |                                                                     |
|A delta fibres – sharp pain                                         |C fibres – throbbing dull ache                                       |
|Large in diameter, myelinated                                       |Small in diameter, unmyelinated, slow                               |
|Conduction velocity 6-30 m/sec                                       |More than Aδ x 2                                                     |
|Mechanical & thermal stimuli                                         |1% speed of Aδ                                                       |
|“transitory” pain                                                   |Conduction velocity 0.5-1.7 m/sec                                   |
|salutatory conduction                                               |polymodal - Chemical, thermal & mechanical stim.                     |
|                                                                     |2o pain                                                             |

Melzack & wall, 1965

With grade one and grade two we are stimulating the A-beta fibres which travel through the dorsal root ganglia into the dorsal horn of the spinal cord at the level of lamina 2 in the substantia   gelatinosa, with the purpose of closing down the pain gate ahead of any nociceptive signals by the A-delta and C fibres that travel up the afferent pathways in the spinothalamic and spinoreticular pathways.

A-beta fibres
    ■ The largest peripheral nerve fibre
    ■ Large diameter
    ■ Myelinated
    ■ Respond to low stimuli (and are therefore ‘low threshold’) such as light touch, pressure and proprioception.
    ■ Impulses transmitted 30-100m/sec to the CNS
    ■ Normally relate non-noxious ‘mechanical’

Polysynaptic inter neurones...