Gate Control Theory

Gate Control Theory implies a non-painful stimulus can block the transmission of a noxious stimulus.
Is based on the premise that the gate, located in the dorsal horn of the spinal cord, modulates the afferent nerve impulses.
The SG (substantia gelatinosa) acts as a modulating gate or a control system between the peripheral nerve fibers and central cells that permits only one type of nerve impulse (pain or no pain) to pass through.
Serving in a capacity similar to that of a “switch operator” in a railroad yard, the SG monitors the amount of activity occurring on both incoming tracts in a convergent system
Opening and closing the gate to allow the appropriate information to be passed along to the T cell.
Impulses traveling on the fast, non-pain fibers increase activity in the SG.
Impulses on the slower pain fibers exert an inhibitory influence.
When the SG is active, the gate is in its “closed” position and a non-painful stimulus is allowed to pass on to the T cell.
Example:
Bumping the head:

• The initial trauma activates the A-delta and, eventually, C fibers
• Rubbing the traumatized area stimulates the A-beta fibers, which activate the SG to close the spinal gate
• Thus inhibiting transmission of the painful stimulus