Hearing is one of the major senses and like vision is important for distant warning and communication. It can be used to alert, to communicate pleasure and fear. It is a conscious appreciation of vibration perceived as sound. In order to do this, the appropriate signal must reach the higher parts of the brain.
Hearing impairment - A reduction in the ability to perceive sound; may range from slight inability to complete deafness HI- it is a distinction between deaf and hard of hearing. Deaf means not being able to hear sound or above certain intensity (sound) level. Hard of hearing means being able to hear
Hearing sensitivity is measured in a decibel which means the units of relative loudness of sounds.
Zero decibels (0 db)- average person with normal hearing can detect the faintest sound. Each succeeding number of decibels that a person cannot detect indicates a certain degree of hearing impairment.
Congenitally deaf (born deaf)
Adventitiously deaf (acquire deafness at some time after birth)
Other two terms used:
prelingual deafness (deafness occurs at birth or early in life before speech and language develop)
Postlingual deafness (occurs after the development of speech and language)
Some professional classify according to hearing threshold levels.
Mild (26 – 40 dB)
Moderate (41 – 55 dB)
Moderate – severe (56 -70 dB)
Severe (71 – 90 dB)
Profound (91 dB and above)
Over 5% of the world’s population – 360 million people – has disabling hearing loss (328 million adults and 32 million children). Disabling hearing loss refers to hearing loss greater than 40dB in the better hearing ear in adults and a hearing loss greater than 30dB in the better hearing ear in children. The majority of these people live in low- and middle-income countries. Approximately one-third of people over 65 years of age are affected by disabling hearing loss. The prevalence in this age group is greatest in South Asia, Asia Pacific and sub-Saharan Africa.
ANATOMY AND PHYSIOLOGY OF THE EAR
What is the ear?
Anatomy of the ear
The ear is the organ of hearing. The parts of the ear include:
* external or outer ear, consisting of:
* pinna or auricle - the outside part of the ear.
* external auditory canal or tube - the tube that connects the outer ear to the inside or middle ear. * tympanic membrane - also called the 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
* eustachian tube - a canal that links the middle ear with the throat area. The eustachian tube helps to equalize the pressure between the outer ear and the middle ear. Having the same pressure allows 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 (contains the nerves for hearing)
* vestibule (contains receptors for balance)
* semicircular canals (contain receptors for balance) How do we hear?
Hearing starts with the outer ear. When a sound is made outside the outer ear, the sound waves, or vibrations, travel down the external auditory canal and strike the eardrum (tympanic membrane). The eardrum vibrates. The vibrations are then passed to three tiny bones in the middle ear called the ossicles. The ossicles amplify the sound and send the sound waves to the inner ear and into the fluid-filled hearing organ (cochlea).
Once the sound waves reach the inner ear, they are converted into electrical impulses which the auditory nerve sends to the brain. The brain then translates these electrical impulses as sound.
MEASUREMENT OF HEARING ABILITY
Hearing loss may be categorized by...
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