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C h e c k o u t A B M P 's l a t e s t n e w s a n d b l o g p o s t s . Av a i l a b l e a t w w w. a b m p . c o m . 47 FUNCTIONAL ANATOMY education Respiration By Christy Cael Breathing is the result of three-dimensional shape changes in both the thoracic and abdominal cavities. The thoracic cavity is a fl exible air container capable of changing volume. By alternately increasing and reducing volume within, pressure differentials are created and air is driven in and out of the lungs. This cavity functions much like a bellows, with air rushing in when expanded and rushing out when squeezed or compressed. Directly below the thoracic cavity is the abdominal cavity. Unlike the thoracic cavity, the abdominal cavity is a fl exible fl uid container and cannot change volume. The contents of this cavity are redistributed as the thoracic cavity changes volume, much like a water balloon changes shape when you push on any side of it. The thoracic and abdominal cavities are separated by the dome-shaped diaphragm muscle. This muscle forms a horizontal seal around the bottom of the rib cage, beginning at the xiphoid process of the sternum and wrapping around to the lumbar vertebrae. Imagine opening an umbrella inside the rib cage from the bottom up. The handle of the umbrella is much like the central tendon, which pulls the fabric of the umbrella down, fl attening it during muscle contraction, increasing thoracic cavity volume, and driving inhalation. The abdominal cavity must shift, expanding side to side and front to back as the dome fl attens and the thoracic cavity expands. RESPIRATION Respiration Muscles • Inhalation: Diaphragm, external intercostals, serratus posterior superior and inferior, scalenes, pectoralis major and minor, quadratus lumborum, serratus anterior • Forced exhalation: Internal intercostals, transverse abdominis, internal and external obliques, rectus abdominis Actions • Inhalation: Rib cage expansion decreases air pressure within the thoracic cavity, air moves into the lungs • Exhalation: Rib cage compression increases air pressure within the thoracic cavity, air moves out of the lungs Inhalation Exhalation