Industrial Screening Audiometry Ltd

How Ears Work

The human ear can be broken up into 4 main sections: the external ear, the middle ear, the inner ear and the hearing processing centers of the brain.

All four parts work together to conduct sounds from outside the head to the brain.

Each part of the hearing system and how they work will be explained in easy to understand terms, except the hearing mechanisms of the brain (central processing centers) because of its extreme complexity.

External Ear

The external ear has 2 parts: the Pinna which is the outside portion of the ear that is visible on the side of the head and the Ear Canal which extends from the pinna to the tympanic membrane (ear drum). The pinna is mostly skin and cartilage with some muscular attachments (this is what allows us to "wiggle" our ears). The twists and folds of the pinna enhance high frequency sounds and also help us to determine where sounds are coming from.

Sounds coming from the front and sides become enhanced as they are directed into the ear canal while sounds from behind us are reduced. This helps us to hear what we are looking at while reducing some of the distracting background noise.

The ear canal is a small, twisting, tunnel-like tube that connects the pinna to the ear drum. It is about 2.5cm in length and has a diameter about the size of a pea.

The outer two-thirds of the ear canal is surrounded by cartilage and contains glands the produce ear wax, while the inner third is surrounded by bone.

Ear wax has many uses in the ear canal including maintaining a consistent level of humidity, preventing dust and other objects from going deeper, and also helps prevent bugs from going into the ear canal.

Middle Ear

Ear wax has many uses in the ear canal including maintaining a consistent level of humidity, preventing dust and other objects from going deeper, and also helps prevent bugs from going into the ear canal.

Sounds travel down the ear canal and strike the ear drum causing it to vibrate. These vibrations are then transferred to the chain of small bones in the middle ear.

The middle ear bones are the smallest bones in the human body and are very delicate. Muscles and ligaments hold this fragile chain of bones in place and allow them to vibrate back and forth with sounds.

The first bone in the chain is the Malleus (hammer), the second is called the Incus (anvil), and the last bone is the Stapes (stirrup). The sound vibrations cause the stapes to move back and forth. This motion is thus transferred to the inner ear.

There is a small tube that connects the middle ear space to the throat called the Eustachian Tube. This tube allows fresh air to fill the middle ear periodically. Changes in outside air pressure (flying, diving) may cause the tympanic membrane to bend.

The Eustachian tube should then open and allow the air pressure in the middle ear space to equalize with the air pressure outside.

The tympanic membrane can then unbend and "pop" back to its original position. This produces the "popping" sensation that most people experience when traveling in the mountains or flying on an airplane.

Inner Ear

The inner ear contains two main parts: the Vestibular or balance part and the Cochlea or hearing part.

These 2 parts are interconnected and play an important role in our senses. The purpose of the Vestibular portion of the inner ear is to help us maintain our sense of balance.

The cochlea or hearing portion of the inner ear is shaped like a spiral sea-shell or snail. Its purpose is to take the vibrations of the middle ear bones and transform them into nerve impulses that will then go to the brain.

It accomplishes this by allowing the middle ear bone called the stapes to vibrate back and forth through a small opening in the cochlea.

This opening is connected to fluid filled canals. The vibration of the stapes causes pressure waves in the cells. The frequency (pitch) and intensity (volume) of the sound determine which hair cells are bent.

When the hair cells bend, they release a nerve impulse to the brain. These nerve impulses are perceived by us as sounds.

The inner ear is very delicate and can easily become damaged. There are many causes of hearing loss, and today, exposure to loud noise is one of the most common causes of hearing loss.

In older people, presbycusis (hearing loss due to the ageing process) often occurs due to degenerative changes in the inner ear, the nerve pathway to the brain, and in the brain itself.