Gate Control Theory of Pain Signals passing through the spinal chord "gate" to brain lead to experience of pain. Some neurons open and some close the (inhibitory) gate.
| Three Components to the Gate A-delta fibres |
Two fibres and one interneuron C-fibres |
|
| Slow- small | Inhibitory | Fast large fibre pressure |
| dull or chronic pain | Inter- Neuron |
"emergency" signals |
-also have descending cortical nerves to close gate 
-slow (small) fibers inhibit the inhibitory inter-neuron and activate the projection (pain) neuron, opening the gate and giving PAIN
Phantom Pain - aching, burning or sharp pain in a limb or organ that had been amputated. Why? See video from you tube of VS Ramachandran @ 3:20 (prt2)
Two possibilities:
1) Impulses that had previously closed the gate are reduced or lost
2) Once pain producing activity begins in the brain it continues without sensory input (being stimulated by neighbouring brain areas-i.e., face-hand) 
3) Other brain parts are "calling" the missing limb.
Anomalies: People born with missing limbs have never had normal sensory experiences why do they experience phantom fingers or toes?