What are the steps of inspiration and expiration? How is breathing controlled? (pages \(191-92,194-95)\)

Breathing is an essential process in the human body that involves the movement of air in and out of the lungs. This exchange of air is necessary for the continuous supply of oxygen and removal of carbon dioxide. Breathing consists of two main phases: inspiration (inhaling) and expiration (exhaling). During inspiration, oxygen-rich air is drawn into the lungs, and during expiration, carbon dioxide-laden air is expelled from the lungs.

Inspiration, or inhalation, is the process of drawing air into the lungs. During inspiration, the diaphragm (a dome-shaped muscle located at the base of the lungs) contracts, flattening and moving downward, while the external intercostal muscles between the ribs contract, causing the rib cage to expand. This expansion increases the volume within the thoracic cavity, thus decreasing the pressure in the lungs. As a result, air flows into the lungs through the respiratory tract (nose, mouth, trachea, and bronchi) due to the pressure difference between the atmosphere and the lungs.

Expiration, or exhalation, is the process of expelling air from the lungs. During expiration, the diaphragm and the external intercostal muscles relax, allowing the diaphragm to return to its dome-shaped position and the rib cage to contract. This contraction decreases the volume in the thoracic cavity and increases the pressure within the lungs. The increased pressure causes the air inside the lungs to flow out through the respiratory tract.

The process of breathing is controlled and regulated by the respiratory control center located in the medulla oblongata, a part of the brainstem. The respiratory control center receives and processes sensory information from the body through chemoreceptors, which are sensitive to changes in blood pH, oxygen, and carbon dioxide concentrations. When blood carbon dioxide levels rise, the chemoreceptors signal the respiratory control center, which in turn increases the rate and depth of breathing to remove excess carbon dioxide and maintain appropriate levels of oxygen and carbon dioxide in the body. The respiratory control center can also receive inputs from higher brain areas and other factors such as emotions, speech, exercise, and diseases that influence the rate and depth of respiration. In summary, breathing is a vital process that consists of inspiration and expiration, controlled by the respiratory control center in the medulla oblongata. By understanding the mechanisms of respiration, we can appreciate the complex coordination between the respiratory system, muscular system, and nervous system to maintain appropriate levels of oxygen and carbon dioxide in the body.