GLOSSARY

A physiological mechanism connects the events that produce a response. Quiet inspiration illustrates how a muscle action leads to airflow.

1. Diaphragm contraction expands the thorax.
2. Lung expansion briefly lowers alveolar pressure below atmospheric pressure.
3. Air flows inward along the pressure gradient and stops when the pressures equalize at the end of inspiration.

A temporal association alone is weaker evidence than a prediction tested by controlling or measuring an intermediate step.

Further reading: OpenStax — The Process of Breathing