Pain gate theory

The pain gate theory was first proposed by Ronald Melzack in 1965, and it refers to how pain signals can be regulated by the nervous system before they reach the brain.

Nociception:

Is the neural process of detecting and encoding potentially harmful stimuli, carried out by specialised sensory neuron’s called nociceptors. Perception of pain.

Dorsal Horn Role:

The dorsal horn in the spinal cord serves as a processing centre for sensory information before relaying them on towards the brain.

Role of inhibitory interneurons:

Inhibitory interneurons primarily modulate and limits the activity of neurons using GABA or glycine neurotransmitter. This maintains a balance of network function preventing overstimulation.

Substantia gelatinosa:

This is a layer of grey matter located in the dorsal horn of the spinal cord which plays a major role in modulating pain signals.

What to say in exam:

The pain gate control theory was proposed by Ronald Melzack in 1965 and it refers to how pain signals are modulated by the nervous system.

It particularly refers to how pain transmission can be regulated in the dorsal horn of the spinal cord specifically in the substantia gelatinosa.

There are 3 sensory nerve fibres involved in this process.

Firstly, we have got A (delta) fibres which are myelinated conductive fibres that transmit sharp, stinging pain normally known as first pain. Then you have got C fibres which are not myelinated and transmit dull, aching, burning pain. They are responsible for prolonged pain and are also responsible for chemical, thermal and mechanical. These small neural fibres carry nociceptive information from the periphery to the spinal cord and brain.

The gate ‘opening’:

So when an injury occurs, nociceptors are stimulated (pain receptors). A (delta) and C fibres then carry the nociceptive information into the dorsal horn of the spinal cord and synapse with the second order neurons. The second order neurons then cross to the opposite side of the spinal cord and ascend through the spinothelamic tract towards the thalamus. Then it synapses once again into third order neurons in the thalamus. Finally the third order neurons carry the information into the primary somatosensory cortex in the post central gyrus where pain is processed.

Gate ‘closing’:

A beta activity promotes inhibition. Inhibitory interneurons become more active which then causes transmission neurons to become less active. Therefore causing less nociceptive information to travel up the spinal cord and towards the brain.