Pain is transmitted to the brain by sensory nerve fibres. These nerves relay 'sensation' information (such as touch, heat, cold, sexual arousal, pressure and pain) from our bodies to our spinal cords and then on to our brains for interpretation. Sensory nerves are different from our motor nerves. Motor nerves allow our bodies to move, walk or pick up objects.
There are 3 types of sensory nerve fibres that interpret sensations in our bodies. These are:
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A - d (delta) fibres, which are medium nerve fibres that sense brief, sharp, jabbing or 'pricking' type pain. |
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C fibres, which are small nerve fibres that sense longer lasting, burning or aching sensations. |
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A - b (beta) fibres, which are large skin nerve fibres that can sense light touch, heat, cold and massage. |
When a part of our body is stretched, changed, irritated or injured, the tissues release a chemical called 'bradykinin'. This chemical attaches to the receptor endings of the sensory nerve fibres and transmit the message of 'pain' along the nerves, to the spinal cord. Here the sensory nerves meet the 'ascending fibres' or 'going up' fibres that relay the message up the spinal cord to our brains to be interpreted as a pain sensation.
Bradykinin also triggers the 'chemicals of inflammation' in our bodies such as histamine and a type of prostaglandin (different from the prostaglandin hormones used to stimulate labour contractions), which influence how intensely we perceive pain.