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[L. in, in, + spirare, to breathe]
Inhalation; drawing air into the lungs; the opposite of expiration. The average rate is 12 to 18 respirations per minute in a normal adult at rest.
SEE: diaphragm for illus.; SEE: respiration
Inspiration may be costal or abdominal, the latter being deeper. The muscles involved in forceful inspiration are the external intercostals, diaphragm, levatores costarum, pectoralis minor, scaleni, serratus posterior, superior sternocleidomastoid, and sometimes the platysma.