Initiation of breathing: There is spontaneous initiation of breathing in the central nervous system and the body's respiratory system performs it. Taken as a whole, this system allows the body to inhale the air containing oxygen, and to exhale the harmful carbon dioxide which is a byproduct of the metabolic reactions. Air has 21% oxygen as a constituent gas. The air is taken inside the body through the mouth and nose, following which it travels through the throat and voice box (larynx), and via the windpipe (trachea), that divides into two major air passages that lead to the right and left lungs. These two passages segregate again in the lungs into smaller branches (bronchi) which divide into even smaller ones (bronchioles or alveolar ducts). These air passages possess tiny air sacs at the terminals known as alveoli. Around 150 million alveoli are present in the human lungs and they are very thin walled. They release the oxygen into the blood, received in and exchange its carbon dioxide, and then it is exhaled out of the lungs via the same path that leads back to the nose and mouth.
An intricate area of the brain called the brain stem, (a portion of the brain connecting with the spinal cord and its nerves) triggers the automated process of breathing. This brain stem possesses the involuntary respiratory control center implying that breathing is a reflex activity and does not really happen on the will of a person. This means that we breathe without being conscious about it. Actually, breathing is a very strong reflex and it is really difficult to deliberately stop breathing for any time period. This breath actually controls each and every response of humans whether physical, mental or emotional. At the fetal stage, the breath keeps the fetus alive as the connecting cord breathes and upholds the fetus inside and makes the baby ready for the outside world (Kostikas et al., 2003). Children breathe deeply, as they fill the lower abdomen and expand the diaphragm. When there is healthy breathing, the diaphragm moves without restriction, it descends during inhalation and ascends during exhalation.