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Discuss the Biology of Human Hearing and Deafness

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Discuss the biology of human hearing and deafness

The ear is a complex sensory organ, part of the auditory system responsible for sound detection and maintaining body balance. Residing on opposite sides of the head, the ear is able to aid in localizing sound waves from different sources. The pinna is part of the outer ear that is visible to the human eye, symmetrically positioned to receive sound waves which are later converted to electrochemical impulses perceived by the temporal lobe of the brain.

The mammalian ear comprises of the major parts that include; the outer, middle and inner ear. The external part of the ear collects sound vibrations from the medium of air which is then amplified by the middle ear and finally to the inner ear through a liquid medium.

The pinna (auricle), concha(ear canal), ear drum (external auditory meatus) are the three vital organs that make up the framework of the outer ear. The auricle is a thin yellow cartilage with a lateral surface that is attached to the skull by muscles and ligaments. It detects sound waves directing them into the ear canal. The concha is a portion very vital for hearing covered by skin that have glands lying underneath the outer portion to produce cerumen (commonly known as ear wax) which filters and supplies nutrients to the ear working inconjuction with superficial hairs that aid in blocking harmful substances from gliding through the canal. The concha acts as a resonator channeling waves into the entrance of the eardrum (tympanic membrane) (ingram). Sound pressure waves moves inwards focusing on the ear drum which in turn vibrates amplifying frequencies ranging between 3khz to 12khz . This amplification makes man sensitive to frequencies bound in this range.(Dale Purves, 2001)

The middle ear contains a hollow-air filled space with 3 bones suspended by ligaments. The ossicles couple sound energy from the ear drum to the oval window of the cochlea. The 3 bones, are arranged such that the malleus (hammer) causes movement to the incus(anvil) which then causes movement in the stapes (stirrup) . These ossicles aid in amplifying sound waves up to six times higher.

The eardrum vibrations cause the stapes footplate to push on the oval window causing the fluid contained in the cochlea to move. The cochlea is part of the inner ear dedicated to hearing; converting sound pressure patterns from the outer ear into electrochemical impulses. The inner ear comprises of 3 semi- circular canals and a vestibule that help in maintaining body balance. The ampulla helps in dynamic balance while the utricullus and sacullus help in static balance (Anson and Donaldson,1992)

In summary, the hearing mechanism includes transduction of sound to nerve impulses perceived by the temporal region of the brain. However there are various shortcomings in the auditory system that may lead to defective hearing or worst yet, deafness. Hearing impairment concept is broad and comprises many disorders. They are classified into conductive and sensory hearing loss.

Conductive hearing loss is commonly caused by obstruction of the ear canal by ear wax and pressure build up in the middle and inner ear therefore the sound waves are not able to reach the cochlea. External ear canal malformation, malfunctioning of bones in the middle ear, infections leading to scar tissues, are some of the defects that may result in hearing loss at different degrees and disrupt the auditory system.

Sensorineural hearing loss results majorly due to disruptions in the inner ear specifically the cochlea. The nerve transmitting impulses to the brain are interrupted causing a deterioration in sound detection. Damage to hair cells in the cochlea due to old age causes a slow hearing impairment. This is common in adults over the age of 70 as the cells begin to degenerate.



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