Our Ears are divided into 3 parts
The Outer Ear
The outer ear consists of the pinna, the ear canal and the eardrum. The eardrum or tympanic membrane separates the outer from the middle.
The Middle Ear
The middle ear consists of an air filled cavity containing a chain of three little bones. These bones are called the malleus, incus and stapes, and transmit sound vibrations from the eardrum to the inner ear, connecting with the inner ear at the oval window.
A small tube called the eustachian tube connects the air-filled middle ear cavity with the back of the throat. It’s role is to equalise the air pressure in the middle ear to that of outside the ear.
The Inner Ear
The inner ear consists of the cochlea which is filled and contains hair cells that respond to sound waves. These hair cells connect to nerve endings which in turn to connect to the auditory nerve. From here the audiotory nerve the links into the higher cortical pathways of the brain.
The organ of balance also resides in the inner ear. It is for this reason that certain conditions affecting hearing, can also affect your balance.
How We Hear
Sound waves travel along the ear canal and cause the eardrum to vibrate, in the same way as a normal drum. The movement of the eardrum causes the little bones in the middle ear to vibrate, and these cause the oval window (the entrance to the cochlear) to vibrate also .
This enables sound to be transmitted to the cochlea in the inner ear, which in turn sets the cochlea fluid in motion.
The tiny hair cells in the cochlea respond by creating electrical signals. These are carried along the auditory nerve to the brain, where they are processed and interpreted as sound.
High pitched sounds are detected by the hair cells at the basal end of the cochlea, and low pitched sounds towards the apical end of the cochlea
Types of Hearing Loss
Sensorineural (Nerve Deafness) Hearing Loss
Sensorineural hearing loss occurs when the hair cells in the cochlea are damaged, resulting in a diminished sound signal being sent to the brain. Sensorineural hearing loss is usually permanent and
does not normally respond to medical or surgical treatment. As well as noticing a reduction in the volume of sound, people with sensorineural hearing loss may also have a distortion in sound clarity. Recruitment (increased sensitivity to loud sound) can also be present.
Age and noise exposure are the tow most common causes of Sensori Neural Hearing loss.
Management for sensori neural hearing loss is typically by prescription and fitting of Hearing Aids, with an accompanying rehabilitation program.
Conductive Hearing Loss
Conductive hearing loss occurs when there is disruption of the mechanical sound transmission in the outer or middle ear. It is usually a temporary condition and can often be corrected or improved with medical or surgical treatment. People with conductive hearing loss notice a reduction in the volume of sound. Hearing aids may be considered if medical or surgical treatment is ineffective.
Ear infections and Glue ear are the most common cause of Conductive hearing loss.