Auditory System Structure and Processing (6A) - MCAT Psychological and Social Foundations

Interaural time difference (ITD). Low frequencies reach ears at slightly different times based on source location.

Systematic mapping of sound frequency across cochlea and auditory cortex. Preserves frequency information spatially throughout auditory pathway.

Base of the cochlea. The stiff, narrow base resonates with high frequencies.

Apex of the cochlea. The wide, flexible apex resonates with low frequencies.

Sensorineural: hair cells/nerve; Conductive: outer or middle ear conduction. Sensorineural affects neural transduction; conductive blocks sound transmission.

Place: location on basilar membrane; Frequency: firing rate matches sound frequency. Place uses spatial coding; frequency uses temporal coding of pitch.

Pinna → ear canal → tympanic membrane → ossicles → oval window → cochlea. Sound travels through outer, middle, then inner ear structures sequentially.

Collects and localizes sound; funnels sound into the auditory canal. The outer ear structure helps determine sound direction and amplifies certain frequencies.

Converts air pressure waves into mechanical vibrations. The eardrum vibrates in response to sound waves, initiating mechanical transduction.

Malleus, incus, stapes. These tiny bones amplify and transmit vibrations from eardrum to inner ear.

Transmits ossicle vibrations into cochlear fluid via the oval window. The footplate pushes fluid in the cochlea, converting mechanical to fluid waves.

Hair-cell sensory organ on the basilar membrane within the cochlea. Contains the actual hair cells that transduce sound into neural impulses.

Organ of Corti. Contains inner and outer hair cells that transduce sound.

Shearing between tectorial membrane and basilar membrane. Relative motion deflects hair cell bundles.

Apex of cochlea (near helicotrema). More flexible basilar membrane vibrates best at low frequencies.

Transmits stapes vibrations into cochlear fluid. The stapes footplate pushes here to create fluid waves.

Impedance matching; amplifies pressure at the oval window. Converts air vibrations to fluid vibrations efficiently.

Malleus → incus → stapes. The hammer, anvil, and stirrup transmit vibrations sequentially.

Interaural level (intensity) difference (ILD). Head shadow creates loudness differences between ears.

Interaural time difference and interaural level (intensity) difference. Brain compares arrival time and loudness differences between ears.

A1 in the temporal lobe (superior temporal gyrus). First cortical area for conscious sound processing.

Place theory; pitch depends on maximal basilar membrane displacement location. Different frequencies peak at different basilar membrane locations.

Frequency theory; auditory nerve firing rate tracks sound frequency. Neural firing synchronizes with low-frequency sound waves.

Groups of neurons alternate firing to represent higher frequencies. Overcomes single neuron firing rate limits for mid-range frequencies.

Cochlear nerve (auditory branch of cranial nerve VIII). Part of the vestibulocochlear nerve carrying auditory signals.

Deflection of stereocilia from basilar membrane vibration. Bending opens ion channels, depolarizing the hair cells.

Equalizes middle-ear pressure with atmospheric pressure. Prevents pressure buildup that would dampen eardrum movement.

Cochlea. This spiral structure converts fluid waves into neural signals.

Sensorineural hearing loss. Damage to cochlear hair cells or auditory nerve causes this type.