Anatomy and Physiology of the ear

Anatomy and Physiology of the Ear

 

 The ear consists of 3 parts

 

The outer ear consists of the ear canal which extends to the eardrum. It directs sound vibrations to the ear drum and sets it into vibrations.

The middle earBehind the eardrum lies the middle ear. It is an air-filled space situated between the ear drum and inner ear. It has a chain of the body’s three smallest bones – the Hammer (Malleus), the Anvil (incus) and the Stirrup (stapes). The ear drum vibrations are conducted to the internal ear by this small chain of bones.

For the ear drum to vibrate freely, there has to be air on both sides of the drum. Nature has made a clever provision for air on the inner aspect of the ear drum to come from the back of the nose through a tube (Eustachian tube) which is responsible for maintaining air in the middle ear and the inner aspect of the ear drum. Unfortunately, for this reason, all diseases of the nose have an effect on ventilation of the middle ear. Common colds, sinus infections, nasal tumours, adenoids can all affect the function of the Eustachian tube and cause a middle ear type of deafness (conductive deafness).

The internal ear – Deeper inside is situated the inner ear with the organs of hearing and balance, which are filled with fluid and surrounded by fluid.

The hearing portion is a coiled tube shaped like a snail shell (cochlea). From the tiny hair cells of the inner ear, the sound waves are converted into electrical impulses, which are transmitted to the brain’s hearing centre by the nerve of hearing.

The balance portion has three semi circular canals and the vestibule.

The semicircular canal systems of the two sides convey information of angular acceleration of the head to the brain in the three planes of space – horizontal, vertical and oblique.

The vestibule consists of the Utricle and Saccule which inform the brain of head position head in space in the yaw and pitch planes.

These impulses are transmitted by the nerve of balance as electrical impulses to be conveyed to the brain stem nucleii and finally to the cerebellum and other brain centres.