Final answer:
The biomechanics of breathing are part of pulmonary ventilation, involving inspiration where the diaphragm contracts for inhalation, and expiration where the diaphragm relaxes for exhalation.
Step-by-step explanation:
The biomechanics of breathing refer to the mechanical processes involved in the movement of air into and out of the lungs, primarily during what is known as pulmonary ventilation. This consists of two main steps: inspiration (inhalation) and expiration (exhalation). During inspiration, the diaphragm and external intercostal muscles contract, creating a larger thoracic cavity and reducing the pressure inside the lungs compared to the atmospheric pressure, resulting in air flowing into the lungs. Conversely, during expiration, these muscles relax, the thoracic cavity reduces in size, and the lung pressure increases, forcing air out.
When the diaphragm contracts, it moves downward, enlarging the thoracic cavity and creating a partial vacuum that allows for inhalation. This is referred to as the pump handle motion. During expiration, the diaphragm relaxes and moves upward, which reduces the volume of the thoracic cavity and increases air pressure within the lungs, thus driving the air out. Active expiration involves additional muscles such as the internal intercostal and abdominal muscles.