How We Hear

• the outer ear
• the middle ear and
• the inner ear

The Outer Ear includes the visible parts, the pinna and the ear canal.

The Middle Ear consists of the eardrum and three tiny bones: the hammer-anvil-stirrup or, in technical terms, the malleus, incus and stapes.

The Inner Ear includes the cochlea, semi-circular canals and the hearing nerve.

As we know, sound travels in waves. Normally, these sound waves are picked up by the outer ear, conducted into the ear canal where they strike the eardrum (also called the tympanic membrane). This makes the eardrum and three bones in the middle ear to vibrate. The vibration of these three bones agitates or moves the cochlear fluid in the inner ear. This in turn makes hair cells in the cochlea bend. These hair cells convert the mechanical energy of their bending movements into tiny electrical pulses which are then sent down the auditory nerve and on to a specific region of the brain which decodes them first into sound and then into intelligible or recognizable sound.

Of course, the human body being the marvelous piece of engineering that it is, all this hearing activity happens incredibly quickly—down to the ‘decoding’ so that we can distinguish a voice from an engine roar, a male voice from a female, and even different types of voices, accents, pronunciations.

Different Types Of Hearing Loss

There are three different types of hearing loss:

1. Conductive Hearing Loss—outer/middle ear damage;
2. Sensori-neural Hearing Loss—inner ear damage, outer and middle ears all right;
3. Mixed Hearing Loss—damage to outer/middle and inner ear structures

Conductive Hearing Loss may result from obstructions or abnormalities in or damage to the outer or middle ears. Impacted wax, a perforated eardrum, fluid in the middle ear, may all cause conductive hearing loss.

Sensori-neural Hearing Loss occurs when the inner ear is damaged or obstructed, but the outer and middle ear structures are otherwise all right. Damaged or dead hair cells in the cochlea, a missing or deformed cochlea, etc, typically cause this kind of hearing loss.

Mixed Hearing Loss_is a result of damage to the outer/middle ear structures _and _also to the inner ear. This is, thus, a combination of the previous two. Examples include wax in the canal _and damaged hair cells in the cochlea; fluid in the middle ear and dead hair cells within the cochlea, etc.

Treatment and Procedures

It may be possible to treat a conductive hearing loss with surgical or medical procedures. Similarly, in cases of a mixed hearing loss, outer/middle ear damage may be amenable to treatment.

The only option for sensori-neural hearing loss, however, is appropriate amplification: hearing aids or cochlear implants.

Causes /High Risk Factors For Hearing Loss

1. Family history of hearing loss
2. Rh incompatibility
3. Hyperbilirubinemia
4. Meningitis
5. Septicemia
6. Head Trauma
7. Infectious diseases or illness during pregnancy (rubella, syphilis, etc.)
8. Alcohol/nicotine intake by the mother during pregnancy
9. Ototoxic drugs
10. Exposure to X-rays
11. Difficulty breathing at birth
12. Mechanical ventilation at birth
13. Low APGAR score, no birth cry
14. Admission into NICU
15. Premature birth and Low Birth Weight
16. Abnormalities of the Head/Neck/Face
17. Children with neuro-degenerative diseases/other syndromes known to include a Sensori-neural or Conductive hearing loss.
18. Genetic disorders
19. Consanguinity

Factors Affecting Optimal Use Of Residual Hearing

• Age at onset of deafness
• Duration of deafness
• Age at providing appropriate amplification (hearing aids/cochlear implants)
• Consistent use of functioning amplification devices
• Listening environment at home
• Educational program

Recommending Amplification Involves The Family And—

• an ENT surgeon
• an audiologist
• a teacher for the hearing-impaired, and, possibly
• a social worker/counselor and
• a psychologist

See also