διάφραγμα

Diáphragma comes from Greek diaphrassein (to barricade), from dia (through, across) and phrassein (to fence, to enclose). The word means a partition, a barrier, a wall that divides one space from another. The anatomical diaphragm is a dome-shaped muscle that separates the thoracic cavity (lungs and heart) from the abdominal cavity (stomach, liver, intestines). It is the wall between breathing and digestion.

The diaphragm is the primary muscle of respiration. When it contracts, it flattens and pulls downward, expanding the lungs and drawing air in. When it relaxes, it domes upward, compressing the lungs and pushing air out. Every breath you take — approximately 20,000 per day — is driven by this muscle. Hiccups are involuntary spasms of the diaphragm. The partition twitches, and air is forced past the closing vocal cords, producing the characteristic 'hic' sound.

The word was applied to other dividing devices by analogy. The camera diaphragm (an adjustable opening that controls how much light enters the lens) was named in the nineteenth century. The contraceptive diaphragm (a barrier device) was named for the same reason: it is a partition. In each case, the word names something that divides one space from another or controls what passes between them.

The Greeks believed the diaphragm was involved in feeling and thought. The word phren — mind, thought — was associated with the diaphragm, which is why 'phrenic nerve' (the nerve controlling the diaphragm), 'schizophrenia' (split mind), and 'frenzy' (from phrenitis, inflammation of the mind) all share a root. The Greeks put the mind in the muscle.