CNS can control the transmission of nociceptive afferent impulses can limit perception of pain.
Gate Control Theory:
First proposed by Melzack and Wall (1965).
Basically – incoming pain can be ‘gated’ (shut off) by stimuli of other nerves – this occur because nerves can talk to one another in the substantia gelatinosa of dorsal horn.
Severity of pain is determined by a balance between excitatory and inhibitory inputs at the spinal cord – it was postulated that the large diametre myelinated afferents excite the inhibitory inter-neurons in the dorsal horn reduce the presynaptic input to dorsal horn transmission cells inhibits pain.
Gross ‘oversimplification’; does not account for behavioural aspects of chronic pain; lack of evidence for the ‘gate’
Endogenous opiate neurotransmitters that modulate pain.