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Anatomy Of The Ear

HEARING & TYPES OF HEARING LOSS

Hearing

Hearing is a very important sensory function. It helps us to become aware of our environment and to communicate with others. Although it is possible to hear with only one ear, both ears are needed for optimal function.

Sound waves travel through the air until they are captured and concentrated by the pinna (visible part of the outer ear). The pinna helps to funnel and modify the sound so that the brain can understand where the sound is coming from. Sound then travels through the outer ear canal until it reaches the tympanic membrane (ear drum). Sound waves are mechanical waves which cause the tympanic membrane to vibrate. Due to the shape and properties of the tympanic membrane, the sound waves are concentrated and transferred to the ossicles (small ear bones) of the middle ear. There are three ossicles: the malleus (hammer), incus (anvil) and stapes (stirrup). The sound waves travel through the ossicles until they reach the inner ear at the point where the stapes resides in the oval window.

The pressure of the sound waves causes vibrations in the fluid of the cochlea of the inner ear. Inside the cochlea, special hair cells in the organ of Corti converts the mechanical sound waves into electrical nerve impulses. Nerve impulses reach the brainstem via the auditory nerve in the inner ear canal. From the brainstem, it passes through several areas until it reaches the cortex of the brain where the sound is interpreted and processed.

 

 

HEARING LOSS

Hearing loss happens when a disruption occurs in one or more parts of the ear or brain that is important for hearing.

There are four types of hearing loss:  

• Conductive hearing loss – causes include birth defects, ear wax, a perforation in the tympanic membrane, fluid in the middle ear, an interruption of the ossicles or a fixed stapes. 
• Sensorineural hearing loss – occurs in the cochlea (sensory) or the auditory nerve (neural). Examples of conditions that impair the conversion of the mechanical sound waves to electrical nerve impulses and the conduction of electrical impulses via the nerve are birth defects, trauma, infections, loud noise, vestibular schwannoma (a rare type of tumour) and toxins. 
• Mixed hearing loss – a combination of conductive and sensori-neural hearing loss. 
• Central hearing loss – occurs due to damage to the brainstem and brain. Causes of central hearing loss include trauma, tumours and infections.

In most cases of hearing loss, hearing can be improved by means of medication, conventional hearing aids, surgical correction of the conduction system of sound, and implantable hearing devices.