Hearing is one of the five senses. It is a complex process of picking up sound and attaching meaning to it. The ability to hear is critical to understanding the world around us.
The human ear is a fully developed part of our bodies at birth and responds to sounds that are very faint as well as sounds that are very loud. Even before birth, infants respond to sound.
The ear can be divided into three parts leading up to the brain – the outer ear, middle ear and the inner ear.
The outer ear consists of the ear canal and eardrum. Sound travels down the ear canal, striking the eardrum and causing it to move or vibrate.
The middle ear is a space behind the eardrum that contains three small bones called ossicles. This chain of tiny bones is connected to the eardrum at one end and to an opening to the inner ear at the other end. Vibrations from the eardrum cause the ossicles to vibrate which, in turn, creates movement of the fluid in the inner ear.
Movement of the fluid in the inner ear, or cochlea, causes changes in tiny structures called hair cells. This movement of the hair cells sends electric signals from the inner ear up the auditory nerve (also known as the hearing nerve) to the brain.
The brain then interprets these electrical signals as sound.
Hearing loss causes and types
Approximately 95 percent of hearing loss in the adult population is sensorineural in nature. In this type of hearing loss, the problem is due to damage to or degeneration of the inner ear (sensory) or auditory nerve (neural). The most common causes of sensorineural hearing loss are noise exposure, age, and hereditary predisposition. Sensorineural hearing loss cannot be medically or surgically corrected.
Approximately five percent of hearing loss in the adult population is conductive in nature. In this type of hearing loss, the problem is due to mechanical or structural damage to the outer and/or middle ear, resulting in reduced sound transmission to the inner ear. Common causes are impacted wax, perforated eardrum, middle ear infection, otosclerosis (stiffening of the middle ear bones), cholesteatoma, and congenital anomalies. In most other cases, medical intervention can result in partial or complete restoration of hearing.
Mixed hearing loss is a combination of sensorineural and conductive hearing loss.