How The Ear Works

The human ear is a wonderfully complex and ingenious organ of the body. It allows subtle vibrations in the air to be transformed seamlessly into electrical signals that our brains can interpret as speech, music and other meaningful sounds. It can alert us to danger in our environment, bring us to tears by letting us hear beautiful music, and most importantly of all, allow us to communicate with each other. The ear can most easily be examined by looking at it in three stages, the outer ear, middle ear and inner ear. Each stage has a remarkable set of features hidden in its design and architecture, and by the end of this article you should know a little more about what makes our ears so incredible.

The outer ear

The outer ear starts with what is most visible and familiar to people, the flexible, oddly shaped looking piece of flesh on the sides of our head is called the pinna (otherwise known as the auricle). This cartilaginous structure does not, as some people think, act as a sound catching dish. Instead the folds, ridges and pits are there to shape incoming sounds and change them tonally before they enter our ear canal. This allows our brain to tell where sound is coming from to a highly accurate degree and enhances our perception of speech in crowded environments. Once sound has made its way past the pinna it travels along the ear canal, which contains hair and ear wax (also known as cerumen). Despite its bad reputation, ear wax is actually a protective substance, serving to keep the skin of the canal moist and safeguarding the delicate structures of the middle ear from infection (yes ear wax is antimicrobial and antifungal!). Its natural tendency is to migrate out of the ear canal slowly as per the outward direction of skin growth. Frequent disruption to this natural cycle by usage of cotton buds, tissues, ear plugs and other devices can cause blockages with must be resolved with microsuction.

The middle ear

The middle ear consists of some fascinating structures, most notably the ear drum (also called the tympanic membrane). The ear drum is a slightly concave, thin piece of skin that lays taught at the end of the ear canal, appearing greyish or pearly coloured through a camera or otoscope. Its job is to capture sound by vibrating in accordance to any vibrations that make their way down the ear canal, similar to the diaphragm of a microphone or skin of a drum. Connected to the ear drum are three bones: the malleus, incus, and stapes (colloquially known as the hammer, anvil and stirrup). The stapes actually looks like the stirrup of a jockey, and is the smallest bone in the human body. Not only that but attached to it is a special muscle called the stapedius, which tenses and restricts the movement of the stapes when a loud sound occurs, thus protecting the inner ear from potentially damagingly loud sounds. The malleus also has a muscle like this called the tensor tympani, which reacts slightly slower and dampens internal sounds like chewing and shouting. Together, these bones together move in tandem with the ear drum in response to vibration and send these movements through into the inner ear.

The inner ear

Similar to the retina of an eye, the inner ear (sometimes referred to as the cochlea) transforms one type of energy into another. In this case, it turns movement into electricity, and is done by special cells with tiny hairs that move and sway in response to any jostling from the middle ear bones. The cochlea is coiled like the shell of a snail, and is organised in a way that the ear can detect a wide array of frequencies (pitches), giving us the ability to hear from around 20Hz (the thud or feeling of bass from a kick drum) up to 20,000Hz (an extremely high pitched screeching sound). For the most part, our ears are far more attuned to lower frequencies than high, and humans have a natural ability to skilfully detect minor differences in pitch at the low end of the spectrum. This is in part due to the clever anatomy of the cochlea, which gives more room towards the top of the coil for capturing low sounds and more cells are dedicated to turning these types of vibrations into electricity.

Hearing loss

As we age the outer and middle ear remains largely unchanged, however the inner ear is different. Most cells in the human body (skin, muscle, blood etc) are repaired or replaced regularly once they become damaged or get too old. Our bodies are constantly renewing themselves, however this is not the case for the sensitive hair cells inside the cochlea, which once damaged cannot be replaced. When our inner ears are fully formed (towards the end of gestation), our cochleas are equipped with around 15,000 tiny hair cells which respond to sound vibration, however noise and the natural aging process will slowly reduce this number over time. Current research shows that more than 40% of people aged 50 and over have hearing loss, accounting for 1 in 6 people in the UK (projected to rise to 1 in 5 by 2035).

Hearing loss originating from the cochlea (called sensorineural hearing loss), is the most common, and thankfully easy to alleviate with hearing aids. Common symptoms include:

- Feeling you can hear speech but not clearly

- Trouble hearing people when they're facing away from you

- Difficulty hearing clearly in background noise

- Having to turn the TV up more than usual

- Asking people to repeat themselves frequently

Most often people with hearing loss can hear sounds as presently as everyone else, however the clarity is lacking, making speech appear mumbled, indistinct and unintelligible. This can be very frustrating at times, not just for the person with the hearing loss but for the family as well.

The easiest and most effective treatment for hearing loss is hearing aids, which can be programmed specifically to each individual's hearing loss, returning a natural sense of clarity and balance to the ears.

Acknowledgements

Ear anatomy image is licensed by Starkey UK.

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