The Lungs
Before any sound can be produced at all, there has to be a source of energy. In speech, the energy takes the form of stream of air, which has in normal circumstances been set in motion by the lungs. The lungs are found in cavity in the chest (or thorax) known as the thoracic cavity. This cavity is bounded at the black by the spinal column, at the front by the ribs and breastbone (or sternum), and at the bottom by the dome-shaped muscle known as diaphragm, which separates the lungs from the lower cavities of the abdomen. The structure surrounding the thoracic cavity is referred to as the thoracic cage. The act of respiration takes place through the action of the thoracic cage, which enables the lungs to act as a kind of bellows, allowing air to flow inwards and outwards.
In order to speak, we must first inhale. Signals from the nerve centre in the brain stem (where respiration is controlled) cause the muscles of the thoracic cage to contract: in particular, and the diaphragm to move downwards. The result is to expand the chest, and thus the lungs, temporarily causing the air pressure in the lungs to be reduced. Air immediately flows into the lungs, in order to equalize the pressure with that of the atmosphere outside the body. We then exhale. We contract the chest, and thus the lungs, by lowering the ribs and raising the diaphragm, forcing the air out. But we never exhale all the air. Only about a quarter of the air in the lungs is used while we are engaged in normal conversation – though the amount increases to some extent if our speech becomes loud of effortful, as in shouting, acting, public speaking, or producing a ‘stage whisper’.
The Lungs Before any sound can be produced at all, there has to be a source of energy. In speech, the energy takes the form of stream of air, which has in normal circumstances been set in motion by the lungs. The lungs are found in cavity in the chest (or thorax) known as the thoracic cavity. This cavity is bounded at the black by the spinal column, at the front by the ribs and breastbone (or sternum), and at the bottom by the dome-shaped muscle known as diaphragm, which separates the lungs from the lower cavities of the abdomen. The structure surrounding the thoracic cavity is referred to as the thoracic cage. The act of respiration takes place through the action of the thoracic cage, which enables the lungs to act as a kind of bellows, allowing air to flow inwards and outwards. In order to speak, we must first inhale. Signals from the nerve centre in the brain stem (where respiration is controlled) cause the muscles of the thoracic cage to contract: in particular, and the diaphragm to move downwards. The result is to expand the chest, and thus the lungs, temporarily causing the air pressure in the lungs to be reduced. Air immediately flows into the lungs, in order to equalize the pressure with that of the atmosphere outside the body. We then exhale. We contract the chest, and thus the lungs, by lowering the ribs and raising the diaphragm, forcing the air out. But we never exhale all the air. Only about a quarter of the air in the lungs is used while we are engaged in normal conversation – though the amount increases to some extent if our speech becomes loud of effortful, as in shouting, acting, public speaking, or producing a ‘stage whisper’.
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