how the ear works

How the ear works

The ear is divided into three parts – the outer ear, the middle ear and the inner ear.

The outer ear

The outer ear is also known as the Pinna and is made of cartilage, connective tissue and skin. It is there for 2 reasons, firstly sound collection and protection of the ear canal. Moving into the ear, the external Auditory Canal is constructed in much the same way but also contains hairs and glands that produce wax. At the end of the canal is the
eardrum or Tympanic Membrane, which separates the outer ear from the middle ear. It is almost circular in shape and supported around the edge by a ligament.

The middle ear

The middle ear is beyond the eardrum and is an air filled cavity. The Eustachian Tube connects the middle ear with the nose and throat and fulfils 2 functions, pressure equalisation and drainage. Blowing your nose or swallowing causes the tube, which is normally closed, to open and lets
the air in the middle ear cavilty equalise with air pressure around you.

When the air pressure in the middle ear changes and can’t be equalised this leads to a ‘blocked up’ feeling, like that experienced on a plane. This is because the air pressure inside the ear differs from the air pressure around us, and we feel the difference until we can equalise the pressure
again. Airline staff often hand out boiled sweets, as the sucking action causes the Eustachian tube to open. This equalizes the pressure inside our ears.

The middle ear also contains the three smallest bones in the body. Collectively these are known as the Ossicles. They consist of the Malleus (or hammer), the Incus (or anvil) and the Stapes (or stirrup). These names give a broad clue as to how they work, and looking at their shapes
it is easy to see how they have been named.

At one end of the Ossicular chain the handle of the Malleus is embedded in the eardrum, with the other bones balanced against it acting as a lever. At the other end there is the Cochlea with the Stapes fixed into the oval window, one of two membranous openings in a wall of bone. The other
the round window sits a few millimetres away.

The inner ear

The Cochlea is like no other organ in the body. It does not exist as a separate component of the body, like for example a Kidney, however it is a series of hollow tubes in bone. These tubes are fluid filled and can be divided into three components: the Semicircular Canals, the Vestibule and the Cochlea.

The Semicircular Canals are concerned with our sense of balance and therefore our ability to stand upright. The Vestibule is the section which links the Semi-circular Canals with the Cochlea and is responsible for our perception of acceleration and deceleration. Lastly the shell-like Cochlea is concerned with our ability to hear.

How sound reaches the brain

The Pinna collects sound waves and passes them along the auditory canal to the Tympanic Membrane amplifying the speech frequencies by the resonant frequencies caused by the shape of the ear canal. The sound hits the eardrum causing it to vibrate, which in turn causes the Ossicles to
rock back and forth.

This rocking motion is passed into the cochlea where the inner-ear fluid is disturbed, causing thousands of small hair cells to vibrate. When these hair cells vibrate this causes an electrical impulse, which is, along with thousands of others, then conducted along the Auditory Nerve to the brain where it is filtered to remove unimportant noise and then sound to cause / meaning (comprehension) takes place.

HC FACTSHEET: How the ear works