CorpusHuman Anatomy

Ear — Coronal Section

Right ear, anterior view · path of sound from auricle to brainstem

A coronal section through the right ear seen from the front, so lateral is to the left and medial to the right. The external ear (auricle and S-shaped external acoustic meatus) leads to the obliquely set tympanic membrane. Medial to it, the air-filled middle ear in the temporal bone contains the ossicular chain — malleus, incus and stapes, whose footplate sits in the oval window — with the tensor tympani and stapedius muscles, the chorda tympani, the round window below, and the auditory tube running down and medially to the nasopharynx. The fluid-filled inner ear lies deeper in the petrous temporal bone: the vestibule (utricle and saccule), three semicircular canals with their ampullae, and the coiled cochlea, drained by the vestibulocochlear nerve through the internal acoustic meatus.

Animated sound waves enter the canal and vibrate the tympanic membrane; the ossicles rock and the stapes pistons in the oval window, sending a travelling wave of perilymph along the cochlea (the round window bulges in antiphase). The inset shows one cochlear turn in cross-section: perilymph-filled scala vestibuli and scala tympani, the endolymph-filled scala media (cochlear duct) with its stria vascularis, and the spiral organ on the vibrating basilar membrane, where inner and outer hair cells are deflected against the tectorial membrane and signals pass to the spiral ganglion.

Step-by-step

  1. 1 · Auricle collects sound

    The folded elastic-cartilage auricle gathers sound waves and funnels them into the canal; its ridges filter sound by direction, giving cues for vertical localisation.

  2. 2 · External acoustic meatus

    The ≈2.5 cm S-shaped canal (lateral third cartilaginous with hairs and ceruminous glands, medial two-thirds bony) conducts sound to the eardrum and resonates at ≈3 kHz, boosting speech frequencies by ≈10–15 dB.

  3. 3 · Tympanic membrane vibrates

    Pressure waves set the thin, cone-shaped tympanic membrane vibrating. Its effective area (≈55 mm²) is about 17 times that of the stapes footplate.

  4. 4 · Ossicular chain amplifies

    The malleus (attached to the drum), incus and stapes act as a lever (≈1.3:1) and, with the area ratio, raise pressure ≈22-fold (≈25–30 dB) — matching the impedance of air to the inner-ear fluids. Stapedius and tensor tympani can stiffen the chain against loud sounds.

  5. 5 · Oval window and travelling wave

    The stapes footplate pistons in the oval window, pushing perilymph into the vestibule and scala vestibuli. A travelling wave runs along the basilar membrane, peaking near the base for high frequencies and near the apex for low ones (tonotopy).

  6. 6 · Round window releases pressure

    Because fluid is incompressible, the round-window membrane at the base of the scala tympani bulges outward each time the stapes moves in — allowing the cochlear partition to move.

  7. 7 · Hair cells transduce

    Basilar-membrane motion shears the stereocilia of hair cells in the spiral organ against the tectorial membrane, opening mechanotransduction channels: K⁺ flows in from endolymph and the cell releases glutamate. Outer hair cells amplify the motion; inner hair cells drive ≈95% of the afferent fibres.

  8. 8 · Cochlear nerve to the brainstem

    Spiral ganglion neurons fire action potentials that travel in the cochlear division of the vestibulocochlear nerve through the internal acoustic meatus to the cochlear nuclei, then on via the superior olive, lateral lemniscus, inferior colliculus and medial geniculate nucleus to the auditory cortex.

  9. Balance · Vestibular apparatus

    The utricle and saccule (otolith organs in the vestibule) sense gravity and linear acceleration; the three semicircular canals, with sensory cristae in their ampullae, sense rotation. Their signals travel in the vestibular division of CN VIII.

  10. Pressure · Auditory tube

    The auditory tube links the middle ear to the nasopharynx; it opens on swallowing and yawning (tensor veli palatini) to equalise pressure on both sides of the drum and drain mucus. Shorter and more horizontal in children, it explains their susceptibility to otitis media.

Labelled parts