Thorax Lab 1 Module 2

SECTRA TABLE WORK: Page 4 of 5

Expiration:

Passive (quiet) expiration occurs when the muscles of inspiration relax, allowing the thoracic cavity to recoil naturally and air to exit the lungs.

However, during forced expiration, additional muscles are activated to forcibly expel air from the lungs:

Tap on image to enlarge

	Add the abdominal muscles, including the internal and external obliques and the rectus abdominus muscles. These muscles increase intra-abdominal pressure, which in turn forces the diaphragm superiorly, reducing thoracic volume.
	Add the subsets of the internal and external intercostal muscles involved in expiration. These fibers help decrease the anterior-posterior and transverse diameters of the thoracic cavity. These movements are especially important when coughing.

As these muscles contract, the neck and back muscles relax and decrease the cross sectional area of the thorax. Leaning forward also reduces the height of the thoracic cavity, a posture often seen during sneezing or labored expiration.