The Eight Senses: Hearing

September 6, 2012
by Pharm Tao

The Eight Senses: Hearing




Physical Stimulus


The Role of the Brain


Hearing Sound waves (air pressure changes in compression and expansion through space) features:

frequency of cycles (pitch – high/low sounds from vibration rates; hertz – frequency),

intensity (amplitude, loudness, measured in decibels – vibrating are molecule density),

timbre (a complex mix of waves)

The outer ear: sound waves -> pinna (auricle) -> external auditory canal




Temporal lobes (cortical tissue for auditory processing) -> auditory nerves -> midbrain -> primary auditory cortex (for narrow frequency ranges) The human hearing range: 20 hertz – 20,000 hertz.


Temporal coding/frequency principle: the lower pitches (20-4000 Hz)

-> synchronal vibration of the basilar membrane; the sensory neurons have the action potentials with the same frequency as the sound


Place coding/place principle: the higher pitches (>5000 Hz) -> the basilar membrane in sync with sound waves, but only small groups of hair cells respond


Different frequencies of sound waves -> vibration of different basilar membrane areas


Overlap of temporal and place coding: 1000-5000 Hz (human speech range)


Conduction deafness (can still hear own voices): failure of the middle ear bones (the hammer, the anvil, and the stirrup)


Nerve deafness: with damaged cochlea, the hair cells/ auditory nerve; may be caused by loudness, heredity, and multiple sclerosis (MS).

The middle ear: eardrum (tympanic membrane) -> 3 ossicles: malleus (hammer), incus (anvil), stapes (stirrup)


The inner ear: oval window, round window, semicircular canals, vestibulocochlear, Eustachian tube, cochlea (basilar membrane, organ of Corti, hairlike receptors) -> auditory nerve -> auditory cortex


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