Ear
The ear is an organ of hearing and balance, consisting of three sections: external, middle and internal. The auditory analyzer perceives sounds with a frequency from 20 Hz to 20,000 Hz, and the vestibular apparatus controls the position of the body in space.
Outer ear
The auricle is a cartilaginous funnel that collects sound waves. Its complex relief (helix, antihelix, tragus) helps determine the direction of sound vertically.
External auditory canal is an S-shaped canal 2.5 cm long, lined with skin with sulfur glands. Sulfur (cerumen) protects against infections and foreign bodies.
The eardrum is a thin membrane with a thickness of 0.1 mm and a diameter of 9–10 mm that separates the outer ear from the middle ear. It oscillates with an amplitude less than the diameter of a hydrogen atom at a threshold loudness.
Middle ear
Tympanic cavity is an air chamber in the temporal bone with a volume of about 1 cm³, containing a chain of three auditory ossicles:
- Malleus (malleus) - the handle is woven into the eardrum
- Anvil (incus) - connected with the malleus and stirrup
- Stapes (stapes) - smallest bone of the body (3 mm, 2.5 mg), rests on the oval window
This system works like a lever, increasing the pressure of the sound wave by 22 times when transmitted from the air to the liquid (perilymph of the inner ear).
The auditory (Eustachian) tube connects the tympanic cavity with the nasopharynx, equalizing the pressure (which is why swallowing helps when there is a pressure difference).
Inner ear (labyrinth)
The inner ear is located in the pyramid of the temporal bone and contains two functional sections:
Cochlea (cochlea) is a 2.5-turn spiral canal containing the organ of Corti - the actual hearing receptor. It contains about 16,000 hair cells, which convert mechanical vibrations into nerve impulses.
Hair cells are located on the basilar membrane: at the base of the cochlea it is narrow and rigid (high frequencies), at the apex it is wide and flexible (low frequencies). This is a tonotopic organization - each part of the cochlea is tuned to a certain frequency.
Vestibular apparatus consists of:
- Three semicircular canals (horizontal, anterior, posterior) - record angular accelerations (head turns)
- Vestibule (utriculus and sacculus) - linear accelerations and the position of the head relative to gravity are recorded
Hearing mechanism
Sound wave → pinna → auditory canal → tympanic membrane → malleus → incus → stapes → oval window → cochlear perilymph → basilar membrane → hair cells → auditory nerve → auditory cortex (temporal lobe).
The entire journey from ear to brain takes less than 10 milliseconds.
You can view the auditory ossicles, cochlea and semicircular canals in volume in 3D atlas Humio - zoom in on the model and study the inner ear in the smallest detail.