Human Anatomy - Kotsan I. Ya. 2009

Respiratory muscles and types of respiration

When contracting, the Respiratory Muscles cause the chest to expand or compress, which changes the volume of both the thoracic cavity and the Lungs contained within it.

As the chest expands, the volume of the thoracic cavity and lungs increases while the air pressure inside the lungs drops; driven by atmospheric pressure, air then rushes into the lungs, producing an inhalation.

When the Muscles responsible for expanding the chest relax, and the tone of the muscles that facilitate its collapse (volume reduction) increases, an exhalation occurs.

Typically, the chest expands simultaneously in three mutually perpendicular directions: vertical, transverse, and anteroposterior.

The vertical expansion of the chest is driven by the lowering of the Diaphragm, that is, its contraction. Transverse and anteroposterior expansion occurs through the action of muscles that coordinate the movement of the Ribs outward, upward, and forward. During Respiration, the movement of each rib takes place simultaneously in two joints: the costal HEAD joint (with the exception of the last two ribs) and the costotransverse joint.

All muscles involved in the act of breathing are divided into two groups: inspiratory and expiratory muscles. Muscles that contribute to the expansion of the chest volume are referred to as inspiratory muscles, whereas those that promote the reduction of chest volume are called expiratory muscles.