|
 
|
Many muscles are used for breathing. During deep
expiration, the abdominal muscles squeeze the abdominal contents
upward, forcing the chest cavity to become smaller. Muscles running
from the vertebrae to the ribs, and muscles running in between the
ribs flex to rotate the ribs and sternum up and out. This increases
the volume of the chest cavity during deep inspiration. However,
the principle muscle used for respiration at all times is the dome
shaped diaphragm. The diaphragm serves as a barrier between the
abdomen and thorax. When contracted it flattens and pulls itself
down, thus making more room inside the thorax. Because there is
more space available in the thorax, air rushes in to fill the space,
passing through the trachea and blowing up the lungs. When the diaphragm
is relaxed, pressure from the abdominal contents pushes the diaphragm
back up, decreasing the space available in the thorax, causing the
air to rush out, and thus deflating the lungs.
|
