Gate theory

Gate-control theory of pain

the basic tenet of this theory is that nociceptive signals can be suppressed by the activity of inhibitory interneurons that function as gates to decrease transmission by the second order neurons in the spinothalamic tract
the inhibitory interneurons are thought to be tonically active - therefore, under normal conditions (no external stimuli), neither the C or Aβ fibres are active, the second order neuron is inhibited by the interneuron and no nociceptive signals are sent to the thalamus
activation of the C fibre causes excitation of the second order neuron as well as inhibition of the inhibitory interneuron, therefore nociceptive information is passed on to the thalamus
simultaneous activation of the Aβ fibre reactivates the inhibitory neuron, decreasing the flow of nociceptive signals
- a simple example would be that rubbing your elbow decreases the pain associated with a bumped elbow - rubbing the skin activates large-diameter, myelinated afferents (Aβ) associated with mechanoreceptors, subsequently activating interneurons activity
- trans-cutaneous electrical nerve stimulation (TENS) is a treatment for pain that also activates this suppression mechanism by delivering a small current to the skin overlying a nerve
the CNS also has the ability to block pain at the spinal cord level - brainstem neurons that release endorphins are part of an endogenous analgesia system that decrease pain perception