Hearing: How does it work?

The ears are sensitive organs and are delicate. Sounds in the environment produce tiny changes in air pressure. The ears sense certain changes and transfer the information for processing to the brain. Also, they are essential to keeping balance.

The sense of hearing that a person has is extremely flexible. This can detect exceptionally quiet sounds, determine whether a noise is originating from far or closer, and isolate a specific sound within dense background noise.

In the US, 1 in 8 people aged 12 and older experience hearing loss in both ears.

We discuss the anatomy of the ear in this article, explain how hearing functions and examine common causes of hearing loss.

How does hearing work?

A lady listening to music
Each section of the ear has a distinct purpose.

The ear has three main sections: the ear outer, middle, and inner. Each segment at hearing serves a distinct function.

Outer ear

The visible part of the outer ear is also known as the pinna. The primary task is to obtain as much sound as possible from the surrounding environment.

After that, external sounds join a narrow channel called the ear canal.

Middle ear

Through the help of a thin membrane called eardrum, or tympanic membrane, the middle ear amplifies the incoming sound.

The eardrum divides the outer ear from the middle ear and allows the inner ear to receive sound waves.

The echo is intensified by three tiny bones, called ossicles. The ossicle names are:

  • The malleus, or hammer: This connects to the eardrum.
  • The incus, or anvil: This connects to the malleus.
  • The stapes, or stirrup: This is the smallest bone in the body and links to the incus.

The eardrum vibrates when sound waves enter it. This vibration pushes the ossicles and further transmits sound into the ear.

The Eustachian tubes meanwhile are small, mucus-lined passages that help maintain healthy middle ear pressure. Stable pressure allows proper transmission of the sound waves.

These tubes connect the middle ear to the rear of the throat. By forcing air into the Eustachian tubes, a person can “pop” their ears.

Inner ear

The sounds join the cochlea until the ossicles intensify the sound waves.

The cochlea is a small curled tube full of liquid that sits inside the ear. This has an internal membrane, which is called the basilar membrane, lined in hair cells. Shock allows the fluid to rise and fall, going up and down the hair cells as they “ride on the wave.”

Growing hair cell has stereocilia along its top — tiny hair-like projections —. The stereocilia bumps into the structures above them as the hair cells move up and down. The bumping causes them to bend and this activates ion channels, providing a signal to the brain that the ear is transmitting.

Higher and lower sound pitches trigger hairs in different parts of the cochlea. The brain receives knowledge about pitch from the activated hair location.

Such information is sent by the cochlea alongside the auditory, or cochlear, nerve. The signal reaches the medulla, a part of the stem of the brain. The brain stem is the closest part of the brain to the back of the neck.

The auditory nerve passes information from the brain into the cochlea as well. These nerve fibers help block irritating sounds, allowing us to concentrate on only one sound among others.

Pitch and intensity

People refer to the frequency of pitch, and quantify it in hertz. The higher the sound-pitch, the higher the hertz.

Intensity is another term for loudness, which is expressed by people in decibels ( db).

The human ear normally detects 20–20,000-hertz sounds. Some people will hear sounds as low as 12 hertz or as high as 28,000 hertz in ideal lab conditions though.

Hearing abilities differ considerably from person to person. With age it tends to decline, especially hearing higher frequencies.

Most of the daily sounds are from 250–6,000 hertz. The ears are however most attuned to 2,000–5,000 hertz sounds.

As for intensity: People can hear 0–140 db sounds. A whisper is around 25–30 db, and usually 45–60 db for conversation. One chainsaw is roughly 120 db.

The sound of a jet that takes off 25 meters away is about 150 db and can break the eardrums.

The ears and balance

Even the ears are important to maintaining balance. The inner ear comprises the vestibular system, a part of the body primarily responsible for spatial orientation and movement control as it relates to balance.

Three thin, fluid-filled loops sit just above the cochlea, called semicircular canals. One detects movement up and down, the second detects movement side by side and the third detects tilting.

The fluid shifts in the semicircular canals when a person moves his or her head. These channels also contain thousands of tiny, sensitive hairs which bend over them as the fluid flows. This bending relays knowledge about the type of motion to the brain.

If a person spins and stops all of a sudden, the fluid continues to travel for some time, pressing against the hair. The hairs keep sending signals to the brain so the brain thinks the person is still spinning. This is dizziness.

The semicircular canals are connected by a vestibule and the cochlea. It comprises two sacs, called the utricle and the saccule, which transmit information to the brain about how the head moves in relation to gravity and acceleration.

For example, the saccule lets a person say whether they are going up or down in an elevator and, more importantly, whether they lie down or stand up.

Hearing loss

Hearing loss may be caused by various health problems, lifestyle factors and injuries.

There are two forms which are common. If sound can not pass into the outer and middle ear, conductive hearing loss occurs.

Fluid in the middle ear, an ear infection, a tumor, ossicle damage and an earwax buildup may cause conductive hearing loss for each. This form is often treatable.

While, the most common cause of permanent hearing loss leads to damage to the inner ear: sensorineural hearing loss. Causes include aging, genetic disorders, and hearing-toxic medications, or ototoxic medications.

Some people have damage to the inner ear alongside sound conduction problems. That results in what physicians call “mixed hearing loss.”

A doctor can also refer to hearing loss as bilateral that affects both ears or single-sided, one ear.

There are some potential reasons for loss of hearing:

  • Loud noises in the short term: Exposure to one extremely loud noise, from an explosion, for example, can reduce the ability to hear.
  • Loud noises in the long term: Exposure to loud noises over a long period can gradually reduce hearing. This may occur, for instance, in people who regularly use heavy machinery without ear protection.
  • Injury: Some injuries, such as traumatic brain injuries, can cause hearing loss. An injury may puncture the eardrum or otherwise damage the middle ear.
  • Smoking: A 2019 study linked smoking tobacco with an increased risk of sensorineural hearing loss.
  • Otosclerosis: This condition affects the small bones of the middle ear, preventing the ossicles from moving.
  • Ménière’s disease: This causes dizziness, sensorineural hearing loss, and tinnitus, or ringing in the ears.
  • Acoustic neuroma: An acoustic neuroma is a type of tumor that can cause tinnitus and a feeling of a blockage in the ear.
  • Cholesteatoma: This is a rare, atypical buildup of skin cells deep within the ear. Without treatment, it can damage the inner ear.
  • Presbycusis: This refers to natural hearing loss due to aging, and it is the most common cause of sensorineural hearing loss. Sounds may become more muffled and conversations harder to follow.

What is earwax?

The ear canal conceals earwax, or cerumen. It helps prevent drying out of the skin, and keeps the ear canal clean.

Earwax also provides some protection against bacteria , fungi, insects and wind. The antibacterial properties can stem from its mild acidity and lysozyme presence — an enzyme that breaks down the walls of bacterial cells.

Dead skin is the main constituent of earwax. It also contains hair and gland secretions inside the ear canal. Certain earwax constituents contain fatty acids, alcohols, and cholesterol.

Summary

The ears are a delicate and complex component of the sensory system. To help the person hear and understand his physical location, they send signals to the brain.

The ears convey information so easily that many people give no attention to the intricate nature of listening. Nevertheless, repeated or unexpected exposure to loud noise, aging and cigarette smoking may cause hearing loss for each.

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