Breathing Mechanism by Enhanced By Science

During resting inspiration the diaphragm and external intercostal muscles contract. The diaphragm is the main inspiratory muscle. It separates the chest cavity from the abdominal cavity and at rest is curved, with its convexity oriented towards the chest cavity. By contraction, the diaphragm flattens and lowers by approx. 1.5 to 2 cm during resting inspiration and 7-8 cm in forced inspiration. By lowering, the diaphragm increases the longitudinal diameter of the thoracic cavity, but also the transverse diameter at its base. The volume increase resulted by contracting this muscle allow a quantity of air to be introduced into the lungs, quantity known as current volume = tidal volume (VT). Complete paralysis of this muscle makes breathing impossible. The contraction of the external intercostal muscles, cause the ribs to horizontalize and rotate, while projecting the sternum anteriorly. As a result the anterior-posterior and transverse diameters of the thoracic cavity increase.

Besides the diaphragm and external intercostal muscles, the accessory muscles also contract: the scalene muscles, the pectoralis muscles, the serratus muscles, the sternocleidomastoid muscles, the trapezius muscles.

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