Our ears are one of the smallest, yet most impressive organs on the human body. Their ability to allow us to remain conscious in the environment that we live in enables us to thrive in an uncertain world. Not only do our ears keep us alert, but they also enable us to remain balanced. If we didn't have ears, we would not be able to stand erect or even walk without falling over!
How does the ear work?
- The ear enables us to hear sound
Your ear is made up of three sections, the outer ear, the middle ear and the inner ear. All three sections are important for hearing.
The outer ear - Sound waves coming from our immediate environment are directed into the ear canal via the outer ear and cause the tympanic membrane or eardrum connecting the outer ear to the middle ear to vibrate. The outer ear is also responsible for the production of ear wax. This waxy substance may seem like a nuisance to some; however it plays a very important role in keeping the ear canal clean, thereby preventing you from getting any nasty ear canal infections. Ear wax also acts as an insect repellent, helping to prevent any bugs from flying into the ear canal.
The middle ear – The middle ear is a hollow space located in the temporal bone and contains an opening to the Eustachian tube. This tube connects the middle ear to the nasopharynx. Vibrations are passed on from the tympanic membrane (located in the outer ear) and amplified by three tiny bones found in the middle ear called ossicles (the malleus, incus and stapes). These three bones are responsible for transferring the vibrations from the ear drum to the cochlea.
Fact time: Did you know the stapes are the smallest bone in the human body and can also be called the stirrup, as it resembles a stirrup found on a horse riding saddle. Ever wondered why your ears pop when flying in an airplane? This is because the increased altitude you are flying at affects the pressure in your ears and is where your Eustachian tube plays an important part! It acts as a pressure valve, equalizing the pressure between your middle ear and the atmosphere around you every time you swallow. So whenever you hear sound whilst flying, always remember to swallow.
The inner ear – The inner ear consists of three semi-circular canals, the cochlea, the saccule and utricle. The inside of the cochlea is not hollow. It contains a liquid/gel substance. The transfer of vibrations from a hollow, air filled cavity in the middle ear to the gelatinous substance found in the inner ear is important for the amplification of sound waves.
Attached to the basilar membrane of the cochlea are tiny hair-like cells. These hair cells are very sensitive to any movement or vibration coming from the middle ear. When the malleus, incus and stapes in the middle ear vibrate, the delicate hairs found in the cochlea start to move back and forth along a roof lining called the tectorial membrane.
When this happens, nerve impulses are sent via the auditory nerve to the brain enabling us to hear. But how are we able to hear different volumes? A loud external noise causes the tympanic membrane and ossicles to vibrate more. This results in an increased movement of the hair-like cells found in the cochlea. Signals are then sent via the auditory nerve to the brain giving us the message that this is a loud sound.
Fact time: Did you know loudness is measured in a unit called decibels (dB). Decibels measure the force of the sound wave reaching the ear.
Humans can hear sound with frequencies between 20 Hz and 20 kHz whereas bats can hear frequencies of up to 130 kHz.
- The ear enables us to remain balanced
Within the inner ear is an organ known as the vestibular apparatus. This organ is composed of three canals positioned at right angles to each other as well as another structure called the utricle. It is these three semi-circular canals that enable you to remain upright, as well as giving us our coordination, whilst the utricle and saccule are responsible for our sense of gravity.
Within the three canals are delicate hairs swimming in a fluid substance. These hair-like structures are responsible for maintaining your sense of balance.
As your head moves or turns the fluid in the semi-circular canals moves over the hair like structures, displacing them. These hair-like structures contain nerve endings which allow a message to be relayed every time the hair-like cells are displaced by the fluid substance that surrounds them. The impulse is then sent to the central nervous system, which relays messages or impulses back down to our muscles, causing them to contract and relax in certain ways to ensure you don't fall over!
The semicircular canals monitor the rotation of one's head, whilst the utricle and saccule monitor the position of our head in relation to gravity.
Within the utricle and saccule is a structure known as the macula. Within this macula is delicate nerve endings connected to a gel like structure composed of calcium carbonate. As you experience gravity, for example when riding on a merry go round, the calcium carbonate particles move around in the gel like structure. The information on the movement of the calcium carbonate particle is then relayed to the brain, so that our bodies may monitor our heads position in relation to gravity and make provision for our bodies to remain in a suitable position.
Our visual system, proprioceptors (muscle receptors) and hearing, all help in maintaining your balance: