Because of the chemical nature of impulse and the axon-dendrite structure. Because of the chemical nature of impulse and the axon-dendrite structure. http://www.biologymad.com/nervoussystem/nerveimpulses.htm (Best technical explanation and excellent graphics and animations)
Newborns may sneeze, and this is typically attributed to the irritation of their nasal passages. The most common irritants, explains Dr. Iannelli, are smoke (and simply smoking outside is not enough), animal dander from pets in the house, dust mites, and mold.
A sneeze is a reflexive action usually produced by your body in response to an irritant in the nasal mucosa. However, all reflexes have thresholds. Similar to the knee jerk when the doctor hits it with a little rubber hammer, we sneeze when dust or other irritants stimulate specific areas of nasal tissue. When those areas inside your nasal cavity and sinuses are stimulated, a signal is then sent to your brain.