Hearing

Main

Hearing is one of the five basic senses that allows us to perceive sound from our environment. It is a complex process involving the ears and the auditory nervous system working together to convert sound waves into electrical signals that the brain can interpret. The auditory cortex in the brain is responsible for processing and interpreting these signals as sound.

Phases of hearing:

1. Sound waves enter the outer ear and travel through the ear canal to the eardrum.

2. The eardrum vibrates, transmitting the vibrations to the ossicles in the middle ear.

3. The ossicles amplify and transmit the vibrations to the cochlea in the inner ear.

4. The vibrations create waves in the fluid of the cochlea, stimulating sensory hair cells.

5. The hair cells convert the mechanical vibrations into electrical signals.

6. The auditory nerve carries the electrical signals to the auditory cortex in the brain.

7. The brain processes and interprets the signals as sound.

Terms

• Cochlea: A spiral-shaped structure in the inner ear, about the size of a pea, lined with sensory hair cells that convert sound vibrations into nerve signals.

• Ossicles: Three tiny bones (malleus, incus, and stapes) in the middle ear, with the stapes being just 3mm long, that transmit sound vibrations from the eardrum to the inner ear.

• Auditory cortex: The region of the cerebral cortex responsible for processing auditory information.

• Inner ear: The innermost part of the ear, containing the cochlea and vestibular system, responsible for hearing and balance.

• Sensory hair cell: Specialized cells in the cochlea that convert mechanical vibrations into electrical signals.

• Auditory nerve: The nerve that carries electrical signals from the hair cells in the cochlea to the brain.

Analogy

Hearing can be compared to a microphone system. The outer ear acts like a funnel, directing sound waves to the eardrum, similar to how a microphone picks up sound. The ossicles in the middle ear function like the diaphragm of a microphone, converting sound waves into mechanical vibrations. The cochlea in the inner ear is like the microphone's transducer, transforming these vibrations into electrical signals. Finally, the auditory nerve is like the microphone cable, carrying the signals to the brain for interpretation, just as a cable carries the electrical audio signal to a speaker.

Misconception

A common misconception is that we hear solely with our ears. While the external ear is important for funneling sound, the actual perception of sound occurs much deeper, in the cochlea of the inner ear and the auditory cortex of the brain. Many people also believe that hearing loss is only a problem for the elderly, but it can affect people of all ages, especially those exposed to loud noises without proper protection.

History

1. 1500s: Anatomists Vesalius and Falloppio describe the structure of the ear.

2. 1800s: Hermann von Helmholtz proposes the "place theory" of hearing, suggesting that different frequencies stimulate specific regions of the cochlea.

3. 1900s: Georg von Békésy discovers traveling waves in the cochlea, leading to a better understanding of frequency coding.

4. 1970s: Researchers begin to unravel the organization and function of the auditory cortex using electrophysiological recordings and lesion studies in animals.

5. 2000s-present:

   • Advances in neuroimaging techniques provide new insights into the processing of complex sounds and speech in the human auditory cortex.

   • Molecular biology and genetics research shed light on the development and regeneration of sensory hair cells.

   • Cochlear implants and other assistive devices continue to improve, offering better hearing outcomes for individuals with hearing loss.

How to use it

1. To clean your ears safely, use a soft, damp cloth to wipe the outer ear. Avoid inserting objects like cotton swabs into the ear canal, as this can push earwax deeper and potentially damage the eardrum.

2. Protect your hearing by wearing earplugs or noise-cancelling headphones in loud environments, keeping the volume of personal audio devices moderate, and getting your hearing checked regularly.

3. Limit exposure to loud noises, both in terms of volume and duration. Keep the volume of personal audio devices at a moderate level, and take regular breaks from listening.

Facts

• The human ear can typically hear frequencies between 20 Hz and 20,000 Hz.

• The eardrum is a thin, cone-shaped membrane about 10mm in diameter that vibrates in response to sound waves.

• The cochlea is about the size of a pea but contains over 16,000 sensory hair cells.

• Exposure to sounds above 85 dB for extended periods can cause permanent hearing loss.

• When you speak, your voice sounds different to you compared to a recording because you hear it through both air and bone conduction. Bone conduction transmits lower frequencies more efficiently, making your voice sound deeper and richer to yourself.