Anatomy and Physiology of the Ear

Our ears are very complex structures built in a very particular way to enable us to hear and maintain equilibrium. The best way to begin to understand the ear is by looking at it in three sections; the outer ear, the middle ear and the inner ear.

The Outer Ear

The pinna (sometimes call the auricle) is made from cartilage, sound waves are captured by this structure and are channelled down into the ear canal (also known as the external auditory meatus) which extends inwards. The first third of the ear canal has a cartilage wall under the skin whereas the inner two thirds have a bony wall which makes it extremely sensitive to contact. In the outer third of the ear canal secretions from oil and modified sweat glands allow cerumen (earwax) to be produced. This production of earwax helps keep the ear canal moisturised and healthy. When the ear canal reaches the tympanic membrane (ear drum) it then becomes the middle ear.

The Middle Ear

The middle ear starts with the tympanic membrane which is thin layer of tissue, usually a pearly grey in colour and semi-transparent. It acts as a physical barrier between the outer ear and the middle ear and therefore protects both the middle ear and inner ear. The sound waves which have travelled down the ear canal are recieved by the tympanic membrane which vibrates, sending the vibrations to the three bones in the middle ear; the malleus, incus and stapes (together known as ossicles). These three bones are connected by ligaments which aids their ability to move with the vibrations and the sound is amplified through to the inner ear. The middle ear is a pressurised air filled space and therefore this pressure needs to be maintained which is done by the eustachian tubes. When a person swallows, the tubes open and allow new air to enter the tympanic cavity allowing a constant pressure gradient to be maintained.

The Inner Ear

The inner ear has two main parts; the cochlea which is important for hearing and the semicircular canals which are important for balance. The semicircular canals are three small tubes which are filled with fluid and has calcium crystals in the lining of the tubes. The tubes are lined up at right angles to each other and this allows the brain to know which direction the head is moving and to regulate balance.

The cochlea is a structure shaped like a snail shell which recieves sound waves sent via the ossicles and the oval window. Inside, a membrane splits it into two chambers which are filled with fluid which vibrates with sound and sets 25,000 nerve endings into motion. The nerve endings convert the vibrations into electrical impulses which travel along the auditory never to the brain. The brain then interprets the impulses it is receiving as sound.

The structure of the ear is very precise and therefore each part is necessary for us to hear. Now you can imagine how something as simple as a build up of earwax can hinder the chain of events! To learn about the causes of earwax build up, please see our blog post ‘What Causes Earwax to Build Up?’