Understanding Tinnitus & Sound Sensitivities
Frequently asked questions
How Do We Hear?
The human hearing mechanism can be divided into three main parts: the external ear, middle ear and inner ear called the cochlea. The cochlea is linked to the brain via the auditory nerve and the auditory Central Nervous System·
The external ear consists of the pinna, ear canal and ear drum. This section is also referred to as the outer ear and it acts as a sound funnel. The outer ear canal walls produce cerumen, or wax, which moves towards the outside for a natural extraction of the wax. Wax protects the ear, removing foreign bodies and germs from the ear canal and away from the ear drum.
The middle ear is an air-filled space containing a chain of 3 tiny bones called the ossicular chain. The 3 bones (ossicles) are called the malleus, incus and stapes. The malleus is the first bone in the chain. It is attached to the back of the ear drum on one end and to the incus on the other. The incus attaches to the stapes, which rests in the oval window of the cochlea. The middle ear is connected to the back of the nose and throat via the Eustachian tube. This tube maintains equal air pressure between the middle ear and the air around us. The eardrum and the ossicular chain are set to vibrate by the air particles in the ear canal in response to sound waves entering the ear canal.
The inner ear consists of the cochlea, a small snail-shell shaped organ set within the bone of the skull. The cochlea contains fluid and tiny hair cells which are set into a swinging motion in response to the movements from the middle ear, and stimulate thousands of nerve endings in the hearing nerve. The hearing nerve travels through the skull, carrying sound messages via the auditory CNS to the brain, which decides what the sound is. The inner ear also contains a delicate mechanism called the semi-circular canals, which contribute to our sense of balance.
Messages from the ear travel up the auditory pathways to the brain, where the interpretation of all these sound waves takes place. Along the way, other nerve pathways communicate with the auditory pathway to help us associate sounds with memories and emotions and to make involuntary judgment as to the quality and quantity of what we hear. For example, is the sound too loud, too soft, pleasant, unpleasant, is the sound liked or disliked. These non auditory pathways play a significant role in the perception of tinnitus.
Normal hearing requires sound to travel uninterrupted through the outer and middle parts of the ear to the nerve endings in the inner ear. A breakdown in the passage of the sound from the entrance to the ear canal to the inner ear is called a conductive hearing loss. When the transmission is hindered in the inner ear or the hearing nerve than this is referred to as a sensorineural hearing loss. If both middle ear and inner ear are damaged, and, the flow of sound is disturbed in both, we call this a mixed hearing loss.
Many causes are responsible for a conductive hearing loss. Wax blockage in the ear canal, a hole in the ear drum, build up of fluid, infection in the middle ear, or various problems affecting the tiny bones of the middle ear are often associated with a conductive hearing loss.
A sensorineural hearing loss can be acquired by loud noise, viral and bacterial infections, some ear diseases, some prescribed medications, head injury, blood vessel problems and the most common is the aging process. These conditions can lead to various degrees of sensorineural hearing loss.