BIO 12D Lecture Notes - Lecture 16: Anterior Superior Iliac Spine, Thoracic Cavity, Abdominal Cavity
15 May 2020
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Document Summary
During exhalation, some respiratory muscles contract and others relax, collectively decreasing the dimensions of the thoracic cavity and forcing air out of the lungs. Are on the anterior and posterior surfaces of the thorax. Are covered by more superficial muscles that move the upper limb. Several groups of anterior thorax muscles change dimensions of thorax during respiration: scalene muscles help elevate first and second ribs during forced inspiration, thereby increasing dimensions of thoracic cavity. External intercostals extend inferomedially from superior rib to adjacent inferior rib: assist in expanding thoracic cavity by elevating ribs during inhalation, contraction increases transverse dimensions of thoracic cavity. Internal intercostals lie deep to external intercostals; muscle fibers are at right angles to external intercostals: depress ribs,but only during forced exhalation; normal exhalation takes no active muscular effort. Forms a partition between the thoracic and abdominal cavities. The most important muscle associated with breathing. The muscle fibers converge from its margins toward a fibrous central tendon.
