Can You Hear Me Now?

The ear is divided into 3 sections as follows: outer ear which contains the pinna, auditory canal, and ear drum; middle ear which contains the incus, malleus, and stapes; and the inner ear which contains the oval window and cochlea. An introductory text reads, Hearing is a process in which stimuli (sound waves) are mechanically converted to vibrations that are transduced to neural messages. If one part of this complicated system is compromised, hearing loss results.

The sound waves enter through the external part of the ear labeled pinna. Text referring to the pinna label reads: 1, The pinna funnels sound waves into the auditory canal, focusing them toward the eardrum. Sound is then directed along the auditory canal to a thin cone shaped membrane labeled ear drum. Ear drum is connected to three bones. A bone attached to the ear drum with a large protruding upper part is labeled malleus, a bone with a flattened top surface bonded to malleus is labeled incus, and a small bone having a base and a head bonded to incus is labeled stapes. Text referring to the ear drum label reads: 2, vibrations of the eardrum cause malleus to push incus, which moves stapes, which presses on oval window, amplifying waves. A membrane-covered opening from the middle ear to vestibule of the inner ear is labeled oval window. Text referring to the oval window reads: 3, pressure on oval window causes fluid in cochlea to vibrate. A spiral cavity in the inner ear is labeled cochlea. Text referring to the cochlea reads: 4, Vibrating fluid in cochlea bends hair cells on basilar membrane, triggering action potentials in the auditory nerve. An enlarged version of cochlea is shown. The inner cavity of cochlea contains basilar membrane and hair cells. The sound wave enters through the oval window to cochlea and is directed toward a bundle of fibers extending from the spiral cavity to auditory cortex in the brain. Text referring to the auditory nerve reads: 5, Auditory nerve carries signals to auditory cortex in brain, where sounds are given meaning.

The chart shows absolute threshold as 0 decibels (d B). Text titled Decibels and Damage reads: The intensity of a sound stimulus is measured in decibels (d B). The absolute threshold for human hearing the softest sound a human can hear is 0 d B. Loud noises, such as the 140 d B produced by a jet engine, cause immediate damage that leads to hearing loss. Chronic exposure to moderately loud noise, such as traffic or an M P 3 player near maximum volume, can also cause damage (Carroll et al, 2017; Keith, Michaud, and Chiu, 2008). The decibels for various sounds are as follows: whispering, 20 d B; rainfall, 50 d B; normal conversation, 60 d B; hair dryer, 70 d B; and average city traffic initially shows 80 d B and then decreases to 75 d B. Continuous exposure to following sounds causes damage to ears: motorcycle (25 feet away), 90 d B; M P 3 player at maximum volume (average), 105 d B; snow mobile, initially shows 112 d B and then reduces to 105 d B. Exposure to jet engine, 140 d B makes hearing painful.