Hearing

Hearing care centers

Anatomy of the Ear

anatomy-of-the-ear
1. Ear Canal
2. Eardrum
3-5. Ossicles
6. Oval window
7. Eustachian Tube (canal leading to the nose )
8. Cochlea
9. Auditory Nerve

Normal Ear Function

parts of the ear

  1. Sound is transmitted through the air as sound waves from the environment. The sound waves are gathered by the outer ear and sent down the ear canal to the eardrum.
  2. The sound waves cause the eardrum to vibrate, which sets the three tiny bones in the middle ear into motion.
  3. The motion of the three bones causes the fluid in the inner ear, or cochlea, to move.
  4. The movement of the fluid in the inner ear causes the hair cells in the cochlea to bend. The hair cells change the movement into electrical impulses.
  5. These electrical impulses are transmitted to the hearing (auditory) nerve and up to the brain, where they are interpreted as sound.

The Outer Ear

The part of the outer ear that we see is called the pinna, or auricle. The pinna, with its grooves and ridges, provides a natural volume boost for sounds in the 2000 to 3000 Hz frequency range, where we perceive many consonant sounds of speech.

The ear canal, also called the external auditory meatus, is the other important outer ear landmark. The ear canal is lined with only a few layers of skin and fine hair, and is a highly vascularized area. This means that there is an abundant flow of blood to the ear canal. Wax (cerumen) accumulates in the ear canal and serves as a protective barrier to the skin from bacteria and moisture. Ear wax is normal, unless it completely blocks the ear canal.

The Middle Ear

The eardrum, or tympanic membrane (TM), is the dividing structure between the outer and middle ear. Although it is an extremely thin membrane, the eardrum is made up of three layers to increase its strength.

The ossicles are the three tiny bones of the middle ear located directly behind the tympanic membrane. These three bones form a connected chain in the middle ear. One of the bones is embedded in the innermost layer of the tympanic membrane, and the third bone is connected to a membranous window of the inner ear. The ossicles take mechanical vibrations received at the tympanic membrane into the inner ear.

The Eustachian tube is the middle ear’s air pressure equalizing system. The middle ear is encased in bone and does not associate with outside air except through the Eustachian tube. This tubular structure is normally closed, but it can be involuntarily opened by swallowing, yawning, or chewing. It can also be intentionally opened to equalize pressure in the ears, such as when flying in an airplane. When this happens, you might hear a soft popping sound.

The Inner Ear

The inner ear is an organ located deep within the temporal bone, which is the bone of the skull on both sides of the head above the outer ear. The inner ear has two main structures: the semicircular canals and the cochlea.

  • Semicircular canals: These structures do not contribute to hearing, but assist in maintaining balance as we move.
  • Cochlea: This is the hearing organ of the inner ear, which is a fluid-filled structure that looks like a snail. The cochlea changes the mechanical vibrations from the tympanic membrane and the ossicles into a sequence of electrical impulses. Sensory cells, called hair cells, bend in the cochlea as the fluid is disrupted by the mechanical vibrations.  This bending of the hair cells causes electrical signals to be sent to the brain by way of the auditory nerve. The cochlea is arranged by frequency, much like a piano, and encodes sounds from 20Hz (low pitch) to 20,000Hz (high pitch) in humans.

Hearing loss is described by varying degrees, not percentages. Hearing loss may be mild, moderate, moderately-severe, severe or profound and vary across pitches. It is determined by a simple hearing test as the amount of volume loss you experience compared to an average of many other adult listeners with normal auditory systems. The volume, or intensity, of sounds you hear is measured in decibels (dB), 0 dB being the softest whisper and 120 dB being a jet engine. The softest sounds one can hear are called thresholds. Normal hearing thresholds for adults are considered 0 to 25 dB.

Conductive Hearing Loss

Conductive hearing loss occurs when there is a problem with the way sound is conducted to the inner ear or cochlea. The problem may lie in the outer ear (pinna or ear canal), eardrum (tympanic membrane), or the middle ear (ossicles and Eustachian tube). The inner ear remains unaffected in this type of hearing loss.

Some causes of conductive hearing loss can include outer or middle ear infections, complete earwax blockage, deterioration of the middle ear bones (ossicles), fixation of the ossicles (otosclerosis), a hole in the tympanic membrane, or absence of the outer ear or middle ear structures.

Conductive hearing losses may be temporary or permanent, depending on the source of the problem. Medical management can correct some cases of conductive hearing loss, while amplification may be a recommended treatment option in more long-standing or permanent cases.

Individuals with conductive hearing loss may report that sounds are muffled or quiet. Generally, when sounds are made louder, these individuals can hear well again.

Sensorineural Hearing Loss

ensorineural (sen-sory-nuhral) hearing loss occurs when there is a problem with the sensory receptors of the hearing system, specifically in the cochlea of the inner ear. The majority of sensorineural hearing loss occurs as a result of an abnormality or damage to the hair cells in the cochlea. This abnormality prevents sound from being transmitted to the brain normally, resulting in a hearing loss.

The hair cells may have been abnormal since birth (congenital), damaged as a result of genetics, infection, drugs, trauma or over-exposure to noise (late-onset or acquired), or damaged as a result of the aging process, a kind of hearing loss known as presbycusis (pres-be-cue-sis).

Sensorineural hearing losses are generally permanent and may stay stable or worsen over time. Routine hearing tests are needed to monitor the hearing loss. Amplification, including hearing aids or cochlear implants in the most severe cases, is a common treatment recommendation.

Individuals with sensorineural hearing loss may report muffled speech, ringing in the ears (tinnitus), difficulty hearing in background noise or that others do not speak clearly.

Mixed Hearing Loss

Mixed hearing loss occurs when a person has an existing sensorineural hearing loss in combination with a conductive hearing loss. It is, very literally, a mix of sensorineural and conductive hearing losses. This means there is a problem in the inner ear as well as in the outer or middle ear. The conductive hearing loss may be temporary or permanent, depending on the source of the problem.

Mixed hearing loss can sometimes be treated with medical management, and hearing aids are a common treatment recommendation.

Neural Hearing Loss

eural hearing loss occurs when the auditory nerve that carries impulses from the cochlea to the brain is missing or abnormal. It is difficult to determine the exact location of neural hearing loss. Some causes of neural hearing loss include genetics, acoustic tumors, in-utero exposure to certain infections, severe jaundice in infancy and low birth weight associated with premature birth.

Amplification may be recommended in some cases of neural hearing loss depending on the severity of the damage to the hearing nerve.

Individuals with neural hearing loss often have difficulty understanding speech, even when it is loud enough, as well as in background noise.

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