Overview

audiologist explaining the anatomy of the human ear and hearing loss

Parts of the Human Ear

What we commonly call "The Ear" is only a small part of the overall organ of hearing. At first glance, we really only see the outer ear or "auricle". Though the auricle is important it only represents small portion of the hearing system, the rest being located and protected withing the skull. Anatomically, the human hearing system can be thought of in three parts: the outer ear, the middle ear, and the inner ear. These three components are connected to each other via the ear canal. All acoustic systems run through it.

The tones, sounds, and speech we hear are actually nothing but oscillations of the air. Before sound waves are turned into acoustic information with specific meaning they have to pass from the outer to the inner ear via the middle ear. On this path, the sounds reach all parts of our hearing system via the auditory nerve to finally arrive in the brain as a signal.
Diagram of the anatomy of the human ear and auditory system

How Does Hearing Work?

The Outer Ear
When looking at someone’s ear, what you generally see is the the-outer-earauricle and part of the outer ear canal extending into the head and up to the ear drum. All of this makes up the Outer Ear. This is where the sound waves arrive first and from here, much like in a funnel, they are guided inwards through the auricle.

The shape of the outer ear by design helps amplify the oscillating air (sound) like a resonator while at the same time prevent wind and other air movements from causing strong background noise.  The resulting effect improves our hearing.
The Middle Ear
The area directly behind the ear drum is called the middle ear. The ear drum itself is a thin membrane that is hit by incoming sound waves. From it, minute oscillations are conducted to three tiny ossicles (bones): the Hammer, the anvil, and the stirrup – the smallest bones in the human body.

Thanks to their unique location, they are capable of amplifying oscillations 20-fold, guaranteeing proper conduction through to the inner ear. From the middle ear, the Eustachian Tube extends to the nose and throat area. This tube ventilates the middle ear and equalizes pressure there.
The Inner Ear
the-inner-earThe inner ear begins where the Stirrup hits the next membrane – the “Oval Window”. Located in it are the organ of equilibrium and the cochlear. Approximately the size of a pea, the cochlear actually resembles a snail shell. It contains three canals filled with a liquid. Via one of these canals, the signals conducted into the liquid are directed to the tip and back via a second canal. The central canal is home to the actual organ of hearing, the organ of Corti. The bottom of the organ of hearing is covered in thousands of tiny hairs – the hair cells.

The wave movements in the liquid-filled canals change depending on frequency. The hair cells are only triggered when the amplitude is particularly great. The deeper the tones the further back in the cochlear the tiny hairs move, while high tones trigger the hair cells at the front of the cochlear. Over the years, it is common that these tiny hairs wear thin and is the main reasons for age related hearing loss.
Signal Conduction to the Brain
Even when the sound waves have arrived in the inner ear they still have no meaning. Once conducted to the auditory nerve, the sound waves are converted to electrical signals that first hit the brain stem. The signal is conducted to the areas of the brain responsible for emotional assessment. Thus meaning is attached to tones which are then connected to existing patterns in the cortex. This allows humans to understand speech, recognize the voice of a friend, and judge hazardous situations.

This means that our hearing only works if the conduction of signals from one station to the other works perfectly and only once oscillating air has been turned into a warning signal, pleasant music, or a coherent sentence.

Air Conduction vs. Bone Conduction

The stations described above show how sound waves reach the inner ear via so-called air conduction. But sound waves can also reach the inner ear via bone conduction: Oscillating air hits the outside of the skull and makes it oscillate slightly.

Conducted by the liquids in the ear, oscillations also reach the hair cells via this path. In cases where hearing loss is caused by an interruption of the oscillating air, bypassing that system through bone conduction devices like Cochlear Implants is an option. However, bone conduction is not as effective as air conduction hearing.

Did You Know?

Bone sound wave conduction is the reason that we think our voices are strange and different when we listen to a recording of ourselves. By playing our recorded voices through speakers, we hear our voices only as air conduction. When we speak, we hear our voices through both air conduction and bone conduction, which is the reason they sound different.