Hearing is for us an important sense, the disruption or total loss is extremely limiting for humans. The causes of failure of this effect are numerous, for their understanding, however, it is first necessary to briefly tell about the construction of the auditory system.
Auditory organ is called cochlea. It is a pair organ located in right and left inner ear. Cochlea notices sound signals that are transmitted from surroundings. Sound waves come through outer ear and external ear canal to the eardrum. Eardrum shakes and its vibrations are transmitted to the three little auditory ossicles located in middle ear (hammer, anvil and stirrup). Bones are interconnected and transmit vibrations directly to the inner ear to bony labyrinth containing the cochlea. In the cochlea itself, the mechanical energy is noticed by sensory cells and as neuroelectric impulses sent via nerve fibers to brain. Nerve fibers form a cranial nerve known as vestibulocochlear nerve that carries auditory information and information about body balance and position. Brain evaluates the information and interprets it as a certain noise or speech.
Scheme - anatomy of the ear and the process of sound perception
Auditory organ gradually deteriorates and is less capable of receiving audio signal. High tone perception is usually affected as the first and lower tones perception later.
Permanent excessive noise exposure
Constant exposure to noise leads to a disproportionate overload of the auditory system and can cause irreversible damage of cochlea. Therefore adequate ear protection is appropriate for people working in continuous noise.
Obstruction of the ear canal
Increased production of earwax in the ear canal can lead to a blockage that worsens the sound signal transmission to the eardrum.
Extensive inflammation of ear canal may disrupt the transmission of sound to the eardrum and infection of middle ear (otitis media) irritates sound transmission between eardrum and cochlea. Frequently recurring and inadequately treated middle ear infections may have long-lasting or even permanent negative effect on auditory sense.
Any ear injury can cause rupture of eardrum, ossicles damage, or direct damage to inner ear.
This disease affects the bony labyrinth of inner ear and of auditory ossicles. This causes transmission problem from eardrum to cochlea.
In this case, the disorder lies in the endolymph, which is the fluid filling the bony labyrinth. This damages function of cochlea and vestibular system causing hearing impairment and balance disorders (dizziness).
Tumor processes of the brain can disrupt neural transmission or brain auditory centers causing impaired perception of sound or even deafness. Typical tumor that directly affects the nerve leading auditory information (vestibulocochlear nerve) is so-called vestibular schwannoma (acoustic neuroma).
Children of alcoholics abusing alcohol during pregnancy can suffer from variety of inherited defects including deafness.
Some drugs are called ototoxic, which means they can damage the auditory nerve. Deafness is in such case a tragic side effect of treatment. Such drugs include, for example, some antibiotics and chemotherapeutics.
There are many genetic defects that cause congenital deafness. However, these are very rare from all cases of hearing impairment.
Any patient with hearing impairment of hearing loss shall be examined by a doctor, in ideal case by an otolaryngologist. The doctor can use some special tools to examine the external ear canal and outer part of eardrum. Audiometric examination may be performed to distinguish disorders resulting either by transmission disorders of sound signal to inner ear or by signal processing in sensory organ and by neural transmission to the brain. Local anatomy can be evaluated by computed tomography or magnetic resonance imaging that can diagnose tumor processes.In case of suspected neurological nature of the difficulties, it is appropriate to ensure a neurological examination.