Hearing: middle ear, cochlea and auditory pathway !
- Mechanism
- Exam priority: medium
The ear turns sound waves into nerve signals: the middle ear boosts them, the cochlea sorts them by pitch.
Updated 2026-11-01
Also called: Cochlea, Rinne and Weber
See it in 3D: Eardrum · Malleus · Incus · Stapes · Cochlea · Auditory cortex · Vestibulocochlear nerve (VIII)
What it is
Sound vibrates the eardrum; the ossicles transfer that energy to the oval window, compensating for the loss that would occur passing from air to fluid. Inside the cochlea a travelling wave peaks at a different place on the basilar membrane for each frequency. Inner hair cells send the signal; outer hair cells amplify it. The pathway is bilateral from the brainstem upward.
How it works, step by step
- Sound waves vibrate the tympanic membrane.
- Malleus, incus and stapes transmit the motion; the stapes footplate pushes the oval window.
- Pressure waves travel through perilymph and set up a travelling wave on the basilar membrane, peaking at the site tuned to that frequency.
- Basilar membrane motion shears hair cell stereocilia against the tectorial membrane; K⁺ from endolymph enters and depolarizes the hair cells.
- Inner hair cells release glutamate onto cochlear nerve fibres; outer hair cells contract and lengthen, amplifying weak sounds.
- Cochlear nuclei → superior olivary complex (compares the two ears to locate sound) → lateral lemniscus → inferior colliculus.
- Medial geniculate body → primary auditory cortex in the transverse temporal gyrus; each ear projects to both sides.
Useful numbers
| Parameter | Value | Note |
|---|---|---|
| Human hearing range | ≈20–20 000 Hz | upper limit falls with age |
| Most important speech frequencies | ≈500–4000 Hz | |
| Normal conversation | ≈60 dB | |
| Prolonged exposure that risks damage | above ≈85 dB | hours per day |
| Endocochlear potential | ≈+80 mV |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Clinical notes
- Presbycusis: age-related loss of high frequencies first, from basal hair cell loss; understanding speech in noise suffers.
- Noise-induced loss shows a dip around 4 kHz on the audiogram.
- Acute otitis media causes conductive loss from fluid behind the eardrum.
- Stapedius paralysis (facial nerve, as in Bell palsy) makes sounds uncomfortably loud (hyperacusis).
- Unilateral sensorineural loss with tinnitus warrants evaluation for vestibular schwannoma.
Test yourself
Think of the answer, then tap the question to see it.
Why is the middle ear needed to hear well?
Most sound energy would reflect when passing from air to cochlear fluid. The large eardrum focused onto the small oval window and the ossicle lever raise pressure about 20-fold (impedance matching).
Which part of the cochlea is damaged first in presbycusis and noise exposure, and what does the patient notice?
The base, which codes high frequencies. Consonants and speech in noisy places become hard to understand.
Weber lateralizes to the left ear and Rinne shows bone conduction better than air on the left. What type of loss?
Left conductive hearing loss (for example, middle ear fluid or wax).
Why does a unilateral stroke in the auditory cortex not cause deafness in one ear?
From the cochlear nuclei upward, pathways cross at several levels, so each ear is represented in both hemispheres.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- The vestibular system, tone and posture
- Sensory receptors, coding and neuronal circuits
- The cerebral cortex and language
Related conditions
- Presbycusis (age-related hearing loss)
- Acute otitis media
- Vestibular schwannoma (acoustic neuroma)
- Ménière disease
- Bell palsy
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 14.1 Sensory Perception (OpenStax (Rice University), 2022); Physiology, Ear (StatPearls (NCBI Bookshelf), 2024); Inner Ear Anatomy and Cochlear Physiology (StatPearls (NCBI Bookshelf), 2024); Presbycusis (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 53). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.