Anatomy of the Auditory System Flashcards

What are the three scalae (fluid-filled compartments) of the cochlea and what fluid fills each?

Answer: Scala vestibuli (perilymph), scala media (endolymph), scala tympani (perilymph)

The cochlea has three fluid-filled compartments: scala vestibuli (above basilar membrane) and scala tympani (below, connected at apex via helicotrema) contain perilymph (high Na+); scala media (cochlear duct) contains endolymph (high K+).

What is the pinna (auricle) and what acoustic function does it serve?

Answer: The external, cartilaginous visible part of the ear that helps collect sound, and whose asymmetric folds create direction-dependent spectral cues (HRTFs) enabling sound localization, particularly in the vertical plane

The pinna collects sound and directs it into the ear canal; its complex asymmetric folds create frequency-dependent reflections (head-related transfer functions/HRTFs) that encode sound elevation (vertical localization) cues.

What is the acoustic reflex (stapedius reflex) and what is its protective function?

Answer: A bilateral reflex contraction of the stapedius muscle triggered by loud sounds (approximately 70-80 dB above threshold), stiffening the ossicular chain to reduce low-frequency sound transmission and protect the cochlea

The stapedius reflex contracts the smallest skeletal muscle (stapedius, innervated by CN VII) in response to loud sounds, stiffening the ossicular chain, reducing transmission of low-frequency sounds by up to 15 dB to protect the cochlea from acoustic trauma.

What is the organ of Corti and where is it located?

Answer: The sensory epithelium resting on the basilar membrane in the scala media, containing inner and outer hair cells with their supporting cells, where mechanical vibration is converted into neural signals

The organ of Corti sits on the basilar membrane within scala media, housing approximately 3,500 inner hair cells and 12,000 outer hair cells arranged in rows, surrounded by supporting cells, capped by the tectorial membrane.

What are otoacoustic emissions (OAEs) and what do their presence indicate?

Answer: Low-level sounds generated by outer hair cell electromotility in the cochlea, recordable in the ear canal, indicating that OHCs are present and functioning normally

OAEs are sounds produced by active OHC electromotility in the cochlea; their presence in the ear canal (recorded with a sensitive microphone) indicates OHCs are functioning, making them a valuable screening tool for outer hair cell integrity.

What is the difference between the utricle and saccule (otolith organs) and the semicircular canals in vestibular function?

Answer: The utricle and saccule (with otolith crystals) detect linear acceleration and static head position (gravity); the three semicircular canals detect angular (rotational) acceleration in three planes

The utricle detects horizontal linear acceleration and head tilt; the saccule detects vertical linear acceleration (gravity). The three semicircular canals (horizontal, anterior, posterior) detect rotational head movements in three orthogonal planes.