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barrier between the thoracic and abdominal cavities. The oesophagus, vagus nerve, and main artery and vein to and from the lower body pass through openings in the diaphragm.
Inhalation is produced by contraction of the diaphragm, which flattens out the dome shape and moves it downwards. This increases the volume of the thoracic cavity, creating negative pressure, and consequently draws air into the lungs. Normal exhalation occurs from passive recoil of the ribcage and diaphragm, as these muscles relax and move into their original shape.
The downward pressure on the abdominal viscera from contraction of the diaphragm forces the abdominal wall to extend forward and/or the lower rib cage to expand sideways. The action of the diaphragm also stimulates and massages the abdominal viscera, assisting digestion, assimilation and excretion.
Thoracic muscles: Although the upper chest movement is relatively inconspicuous in quiet breathing, some thoracic muscles play a role. The external and parasternal intercostals (joining adjacent ribs) and the scaleni (connecting the shoulder area and spine) are activated during inspiration to hold the ribs in an expanded position that complements the force of the diaphragm.
There are eleven pairs of intercostal muscles that occupy the spaces between the twelve pairs of ribs. They are arranged in two layers, the external and internal intercostal muscles. The external intercostal muscle fibres extend in a downward and forward direction from the lower border of the rib above to the upper border of the rib below. The internal intercostal muscle fibres extend in a downward and backward direction from the lower border of the rib above to the upper border of the rib below, crossing the external intercostal muscle fibres at right angles. The first rib is fixed; therefore, when the intercostal muscles contract they pull all the other ribs towards the first rib. Due to the shape of the ribs, they move outwards when pulled upwards. In this way the thoracic cavity is enlarged anteroposteriorly and laterally. The inter
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| SR No. | 009371 |
| Book Title | Pran and Pranayam |
| Original Sutra Author | N/A |
| Author | Niranjananand Saraswati Swami |
| Publisher | Yoga Publication Trust |
| Publication Year | 2009 |
| Total Pages | 369 |
| Language | Hindi |
| Classification | Book_Devnagari |
| File Size | 11 MB |