The structure of the human ear

Anatomy of The Ear

The outer ear is a small part of the overall hearing organ. At first glance, we only see the part of the ear that protrudes from the head, called the auricle. The more significant portion of the ear is protected inside the skull. The human hearing system consists of three components: the outer ear, the middle ear, and the inner ear. They are connected via the ear canal, and all acoustic systems run through them.

The tones, sounds and speech we hear are nothing more than oscillations (a movement back and forth in a regular rhythm) of the air. Before sound waves are turned into acoustic information that we can recognise and understand, they are delivered from the outer to the inner ear via the middle ear and pass through all parts of our hearing system via the auditory nerve before finally arriving in the brain as a signal.

How exactly does the ear work?

The outer ear

Together, the auricle (the area in front of the eardrum) and the outer ear canal form the only part of the ear that we can see. The outer ear is shaped so that oscillating air that arrives is amplified and structured to prevent wind and other air movements from causing intense background noise. The outer ear is where sound waves first arrive, and from here, they are funnelled inwards through the auricle to the middle ear. 

The middle ear
The Middle EarThe area behind the eardrum is called the middle ear. The eardrum itself is a thin membrane stretched like a drum that is hit by sound waves that are transported to three tiny little ossicles (tiny bones) named after their shape: the malleus (hammer), incus (anvil) and stapes (stirrup). These ossicles are the smallest bones in the human body and can amplify sound up to twenty times because of their location. The tiny stapes bone attaches to the oval window that connects the end of the middle ear to the beginning of the inner ear. The Eustachian tube (a narrow passage leading from the pharynx to the middle ear cavity) is responsible for ventilating and equalising pressure between the air outside and air within the middle ear.
The inner ear
The Inner Ear

Within the inner ear is the cochlear, which is approximately the size of a pea and resembles a snail shell. The cochlear contains three canals filled with 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 Organ of Corti (the actual organ of hearing), which is covered in thousands of tiny hairs.

Within the inner ear is the vestibular organ (responsible for your balance) and the cochlear, a snail-shaped organ approximately the size of a pea. The cochlear contains three canals filled with fluid that moves in response to the oval window's vibrations. It also includes a tiny structure called the organ of Corti (the actual organ of hearing) covered in thousands of tiny hairs (hair cells). Wave movements in the canals change depending on the frequency and are only triggered when the amplitude is particularly significant. Deeper tones move the hairs cells located further back in the cochlear, while higher tones trigger hair cells at the beginning of the cochlear. As you get older, these tiny hairs wear, which is one of the main reasons for age-related deafness.

Signal conduction to the brain

When sound waves arrive in the inner ear, they still do not have meaning. Sound waves that arrive at the auditory nerve are converted into electrical signals that then hit the brain stem. These signals are transported to the brain areas responsible for emotional assessment and assigned meaning connected to existing tones and patterns in the cortex. Transporting these signals allows us to understand speech, recognise the voice of a friend and judge situations. 

Our hearing only works if we can transport signals from one station to another, and only once oscillating air has been turned into a sound or tone that we can understand.

Air conduction versus bone conduction

The Auditory Pathways

The processes above show how sound waves reach the inner ear via air conduction. Although not as effective, sound waves can also contact the inner ear via bone conduction. The 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. 

Did you know?

If you find your voice strange in video recordings, you're not alone! Bone sound wave conduction is responsible for this. When we hear our voices in video recordings, the sound waves are only conducted via the air. The bone conduction portion that we usually get at the same time during talking is missing!