at the same time provided a detailed description of the physiological mechanisms
through which psychological factors could influence an individual’s experience of pain.
In a nutshell, gate-control theory proposes that a neural gate in the spinal cord can
modulate incoming pain signals and that a number of factors influence the opening
and closing of the gate. Broadly speaking, these are
1 the amount of activity in pain fibres;
2 the amount of activity in other peripheral fibres; and
3 messages that descend from the brain (or central nervous system).
When the neural gate receives information from each of these sources it decides
whether to open or close the gate. When the gate is open, pain is experienced.
The theory postulates that the gating mechanism is located in the substantia
gelatinosa (i.e. the grey matter that extends along the length of the spinal cord) of the
dorsal horns in the spinal cord. When we are exposed to a painful stimulus the gating
mechanism receives signals from pain fibres (A-delta and C-fibres) located at the site
of the injury, other peripheral fibres (A-beta fibres), which transmit information about
harmless stimuli and the brain (or central nervous system) to open the gate. The pain
fibres then release a neurotransmitter called substance P that passes through the gating
mechanism (substantia gelatinosa) and stimulates transmission cells that in turn transmit
impulses to specific locations in the brain (e.g. thalamus, limbic system, hypothalamus).
28 BIOLOGICAL BASES OF HEALTH AND ILLNESS
FIGURE 2.5Anxiety and worry can open the gate leading
to the experience of greater pain.