Pain gate theory

In physiotherapy pain gate pathway and pain control theory is important for the explanation behind the physiologic pain control.

1. Pain Gate Mechanism Dr. Rekha Marbate [Assistant Professor]

2. Introduction Analgesic effect of interferential therapy – explained by inhibition type-C nociceptive fibers. Pain gate theory- developed by Melzack and Wall

3. the maximum frequency of transmission in C nerve fibers is 15 Hz and in Aδ fibers is 40 Hz. The application of frequencies higher than this could block transmission along these fibers altogether

4. Short duration pulses at a frequency of 100 Hz may stimulate large diameter nerve fibers which will have an effect on the pain gate in the posterior horn, and inhibit transmission of small diameter noci-ceptive traffic .

5. In order to selectively activate the descending pain suppression system, a frequency of 15 Hz is required. The stimulation of small diameter fibers produced will eventually cause the release of endogenous opiates ( enkephalin and β endorphin) at a spinal level.

6. Pain Pathway afferent fibers are of two types A Delta fibers: Fast conducting large diameter myelinated fibers , which conducts with a velocity of 5–30 m/s. C-fibers: Slow conducting small diameter nonmyelinated fibers , which conducts with a velocity of 2–5 m/s .

7. Neurons involved in pain conduction • • • Primary : from the ‘nociceptors’) to the dorsal horn of the spinal cord. Secondary: from the dorsal horn to the thalamus. Tertiary: from thalamus to cortex and awareness. Tertiary Neuron S e c ondary Neuron P r i m ar y Neuron N oc i c e pt o r s

8. Continued.. primary afferent fibers transmit impulses from the sensory receptors to the dorsal horn of the spinal cord. Second order afferent fiber carry sensory impulses from the dorsal horn of the spinal cord to the brain. First order neurons include A-alpha, A-beta, A-delta and C-fibers. A-alpha and A-beta fibers are characterized by having large diameter afferents and A-delta and C-fibers are characterized by having small diameter afferents . The second order afferents are nociceptive specific

9. A nociceptive neuron transmits pain signals . Its cell body lies in the dorsal root ganglion . A-delta and C-fibers transmits the sensation of pain . Fast pain is transmitted over the larger, faster-conducting A-delta afferent neurons and originates from receptors located in the skin . Slow pain is transmitted by the C afferent neurons and originates from both superficial (skin) and deeper (ligaments and muscle) tissue .

10. Most nociceptive second-order neurons ascend to higher centers along one of three tracts: (1) Lateral spinothalamic tract , (2) Spinoreticular tract, and ( 3) Spinoencephalic tract , with the remainder ascending along the spinocervical tract or as projections to the cuneate and gracile nuclei of the medulla. Approximately 90% of the wide dynamic range second-order afferents terminate in the thalamus.

11. Mechanism of pain gate control

12. Factors which influence opening and closing the gate are: The amount of activity in the pain fibers. The amount of activity in other peripheral fibers Messages that descend from the brain .

13. Gate may be closed by: Physical Pain - Analgesic Remedies Emotional Pain - Being in a ‘good’ mood Behavioral Factors - Concentrating on things other than the injury Relaxation and Contentment – Mental factors: - work, T.V., book, Activity - Taking exercise, counter-stimulation- heat, massage, acupuncture

14. Gate is opened by Physical Factors - Bodily injury Emotional Factors - Anxiety & Depression Behavioral Factors - Attending to the injury and concentrating on the pain Lack of Activity – Mental Factors –

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