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Sound

Sound is defined as vibrations that travel through the air or another medium as an audible mechanical wave. It is produced from a vibrating body. The vibrating body causes the medium (water, air, etc.) around it to vibrate thus producing sound.

The Loudness of sound is measured in decibels (dB) and the pitch or the frequency is measured is measured in hertz (Hz)

Humans can detect sounds in a frequency range from about 20 Hz to 20 kHz. (Human infants can actually hear frequencies slightly higher than 20 kHz but lose some high-frequency sensitivity as they mature; the upper limit in average adults is often closer to 15–17 kHz.)

Ear & Its Anatomy

The ear is the organ of hearing and balance. The parts of the ear include:

• External or outer ear, consisting of:

○     Pinna or auricle. This is the outside part of the ear.

○     External auditory canal or tube. This is the tube that connects the outer ear to the inside or middle ear.

• Tympanic membrane (eardrum). The tympanic membrane divides the external ear from the middle ear.
• Middle ear (tympanic cavity), consisting of:

○     Ossicles. Three small bones that are connected and transmit the sound waves to the inner ear. The bones are called:

■     Malleus

■     Incus

■     Stapes

○     Eustachian tube. A canal that links the middle ear with the back of the nose. The eustachian tube helps to equalize the pressure in the middle ear. Equalized pressure is needed for the proper transfer of sound waves. The eustachian tube is lined with mucous, just like the inside of the nose and throat.

• Inner ear, consisting of:

○     Cochlea. This contains the nerves for hearing.

○     Vestibule. This contains receptors for balance.

○     Semicircular canals. This contains receptors for balance.

How do you hear?

Hearing depends on a series of complex steps that change sound waves in the air into electrical signals. Our auditory nerve then carries these signals to the brain.

1. Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
2. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.
3. The bones in the middle ear amplify, or increase, the sound vibrations and send them to the cochlea, a snail-shaped structure filled with fluid, in the inner ear. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.
4. Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the basilar membrane—ride the wave. Hair cells near the wide end of the snail-shaped cochlea detect higher-pitched sounds, such as an infant crying. Those closer to the center detect lower-pitched sounds, such as a large dog barking.
5. As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open. When that happens, chemicals rush into the cells, creating an electrical signal.
6. The auditory nerve carries this electrical signal to the brain, which turns it into a sound that we recognize and understand.

The symptoms of hearing loss depend on the type of hearing loss you have—and the severity. A person with mild hearing loss in both ears, for example, experiences sound differently than a person with a profound hearing loss in just one ear.

General symptoms of hearing loss

For adults with any kind of hearing loss, these are all indicators that you may not be hearing as well as you used to. You may experience all or just a few of these scenarios:

• Friends or family say you turn the television or radio up too loud.
• You struggle to understand speech, especially in noisy environments.
• You have difficulty hearing people on the phone.
• A feeling that you can hear, but not understand.
• You are not sure where sound is coming from, known as localization.
• You often ask people to repeat themselves.
• You’re dependent on a spouse or a loved one to help you hear.
• You find yourself avoiding social situations.
• You feel exhaustion after attending social events, known as listening fatigue.
• You notice tinnitus, or ringing in the ears.
• Paradoxically, some sounds seem too loud, known as “recruitment”

There are several types of hearing loss, which can be categorized based on their causes and the parts of the auditory system that are affected. Here are the main types of hearing loss:

1. Conductive Hearing Loss: This type of hearing loss occurs when there is a problem with the outer or middle ear, which hampers the transmission of sound waves to the inner ear. It can be caused by conditions like earwax buildup, fluid in the middle ear, ear infections, a perforated eardrum, or abnormalities in the ear structure.
2. Sensorineural Hearing Loss: Sensorineural hearing loss results from damage to the inner ear (cochlea) or the auditory nerve pathway to the brain. It is the most common type of hearing loss and can be caused by aging (presbycusis), noise exposure, genetics, certain medications, head trauma, or illnesses like meningitis or Meniere’s disease.
3. Mixed Hearing Loss: Mixed hearing loss is a combination of conductive and sensorineural hearing loss. It means there is a problem in both the outer/middle ear and the inner ear or auditory nerve.
4. Neural Hearing Loss: Neural hearing loss, also known as auditory neuropathy, occurs when the cochlea is functioning correctly, but the auditory nerve has a problem transmitting signals to the brain. This type of hearing loss can be present at birth or acquired due to factors like premature birth, genetic disorders, or certain medical conditions.
5. Central Hearing Loss: Central hearing loss is caused by a problem in the central nervous system, particularly in the brain’s auditory pathways. It can result from tumors, strokes, brain injuries, or neurological disorders.
6. Functional Hearing Loss: Functional hearing loss refers to hearing difficulties without any organic or structural abnormalities in the auditory system. It is typically related to psychological or emotional factors rather than physical causes.

It’s important to note that hearing loss can range from mild to profound, depending on the severity of the impairment. If you suspect hearing loss, it’s advisable to consult an audiologist or an ear, nose, and throat (ENT) specialist for a proper evaluation and diagnosis.

• Damage to the inner ear. Aging and exposure to loud noise may cause wear and tear on the hairs or nerve cells in the cochlea that send sound signals to the brain. When these hairs or nerve cells are damaged or missing, electrical signals aren’t transmitted as efficiently, and hearing loss occurs.

Higher pitched tones may become muffled to you. It may become difficult for you to pick out words against background noise.

• Gradual buildup of earwax. Earwax can block the ear canal and prevent conduction of sound waves. Earwax removal can help restore your hearing.
• Ear infection and abnormal bone growths or tumors. In the outer or middle ear, any of these can cause hearing loss.
• Ruptured eardrum (tympanic membrane perforation). Loud blasts of noise, sudden changes in pressure, poking your eardrum with an object and infection can cause your eardrum to rupture and affect your hearing.

Risk factors

Factors that may damage or lead to loss of the hairs and nerve cells in your inner ear include:

• Aging. Degeneration of inner ear structures occurs over time.
• Loud noise. Exposure to loud sounds can damage the cells of your inner ear. Damage can occur with long-term exposure to loud noises, or from a short blast of noise, such as from a gunshot.
• Heredity. Your genetic makeup may make you more susceptible to ear damage from sound or deterioration from aging.
• Occupational noises. Jobs where loud noise is a regular part of the working environment, such as farming, construction or factory work, can lead to damage inside your ear.
• Recreational noises. Exposure to explosive noises, such as from firearms and jet engines, can cause immediate, permanent hearing loss. Other recreational activities with dangerously high noise levels include snowmobiling, motorcycling, carpentry or listening to loud music.
• Some medications. Drugs such as the antibiotic gentamicin, sildenafil (Viagra) and certain chemotherapy drugs, can damage the inner ear. Temporary effects on your hearing — ringing in the ear (tinnitus) or hearing loss — can occur if you take very high doses of aspirin, other pain relievers, antimalarial drugs or loop diuretics.
• Some illnesses. Diseases or illnesses that result in high fever, such as meningitis, may damage the cochlea.

Those who have difficulty hearing can experience distorted and incomplete communication that seriously impacts their professional and personal lives putting an individual at risk for isolation and withdrawal. Studies have linked untreated hearing loss effects to:

• Avoidance or withdrawal from social situations
• Reduced alertness and increased risk to personal safety
• Impaired memory and ability to learn new tasks.
• Irritability, negativism and anger
• Fatigue, tension, stress and depression
• Social rejection and loneliness
• Reduced job performance and earning power.
• Diminished psychological and overall health.

Many important studies have been conducted to understand hearing loss and its relation to other serious health issues such as dementia, diabetes, heart disease, depression, and fall rates in older adults. When hearing loss is present at the same time as one of these health concerns, the term comorbidities is often used as it describes the presence of two or more chronic diseases or disorders affecting a person. Researchers have taken more interest in comorbidities including hearing loss as individuals who live with untreated hearing loss tend to face higher risk for other physical and cognitive issues.