It is determined
that first nociceptors (pain sensing receptors) occur
in the perioral region at 7 weeks of intrauterine life, spread in the rest
of face, the palms of the hands and feet at 11 weeks, with arms and legs at 15
weeks, all cutaneous and mucosal surfaces at 20 weeks.
Distribution of
nociceptive nerve endings in the skin of neonates was determined to be similar
in density to an adult. In addition, pain in neonates is transmitted by
unmyelinated C fibers.
These fibers
transmit impulses slowly. It starts second or seconds later than painful
stimuli and continues for minutes to increase in size. Pain transmitted by this
fiber is perceived as dispersed, continuous, dull and burning.
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