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veins
arteries
pleura
heart
vein
trachea
Structure of the Lungs
aorta
85
BSY
aorta
alveoli
Respiratory muscles
The expansion of the chest during inspiration occurs as a result of muscular activity, partly voluntary and partly involuntary. The main muscles of respiration in normal, quiet breathing are the intercostals and the diaphragm. During difficult or deep breathing they are assisted by the muscles of the neck, shoulders and abdomen.
The diaphragm and abdominal muscles act like bellows at the base of the thorax, pulling and pushing air into and out of the lungs. Muscular effort is required for both exhalation as well as inhalation. However, only diaphragmatic action is sufficient in resting states and most normal activities. When the abdominal, neck and shoulder muscles are also brought into action, exhalation becomes an active process and the extra force causes rapid exhalation.
Diaphragm: The diaphragm is dome-shaped and consists of a sheet of muscles and tendons attached to the lower ribs, bulging upwards into the thoracic cavity. It forms the dividing
