The autonomic nervous system (ANS) regulates the functions of our internal organs (the viscera) such as the heart, stomach and intestines.
The flu is contagious a day before and five days to a week after its onset. Young children, people over 65, those with compromised immune systems, and people with a terminal illness are at risk of death from the flu.
However, the viruses that cause colds (for example, rhinoviruses) are not the same as those that cause the flu (influenza viruses). Although the typical incubation period for influenza is about one to four days, some adults can be contagious from about one day before onset of symptoms for up to two weeks. Other people who develop complications, such as pneumonia, may extend the contagious period for a week or two. For colds, most individuals become contagious about a day before cold symptoms develop and remain contagious for about five to seven days. Some children may pass the flu viruses for longer than seven days (occasionally for two weeks). Colds are considered upper respiratory infections.