Neuroscience for Kids

TheEar

Theears contain structures for both the sense of hearing and the sense ofbalance. The eighth cranial nerve (vestibulocochlear nerve made up of theauditory and vestibular nerves) carries nerve impulses for both hearingand balance from the ear to the brain.

Hearing (Audition)
Sound waves cause the tympanic membrane(eardrum) to vibrate. The 3 bones in the ear (malleus, incus, stapes) passthese vibrations on to the cochlea. The cochlea is a snail-shaped,fluid-filled structure in the inner ear. Inside the cochlea is anotherstructure called the organ of Corti. Haircells are located on the basilar membrane of the cochlea. The cilia(the hair) of the hair cells make contact with another membrane called thetectorial membrane. When the hair cells are excited by vibration, a nerveimpulse is generated in the auditory nerve. These impulses are then sentto the brain.
(By the way...the stapes is the smallest bone in the human body. It isonly 0.25 to 0.33 cm long [0.10 to 0.13 inches] and weighs only 1.9 to4.3 milligrams.)

Loudness is measured in decibels (dB) - this is theforce of sound waves against the ear. The louder the sound, the moredecibels. Here are approximate decibel levels for some everydaysounds:
Sound Intensity
(db) -
Ticking of a Watch 20
Whisper 30
Normal Speech 50-60
Car Traffic 70
Alarm Clock 80
Lawn Mower 95
Chain Saw 110
Jackhammer 120
Jet Engine 130

Did you know?
At a temperature of 68^oF (20^oC), sound travelsat1,125 feet/sec (343 meters/sec). This is the same as traveling at 756miles/hr (1,217 km/hr). Also, as the temperature rises, the speed ofsound gets faster.

Hearing Loss
People can loseall or some of their ability to hear because of loud noises, infections,head injuries, brain damage and genetic diseases. Hearing loss is commonin older people. There are several types of hearing loss:

Conductive Hearing Loss: occurs when soundvibrations from the tympanic membrane to the inner ear are blocked. Thismay be caused by ear wax in the auditory canal, fluid buildup in themiddle ear, ear infections or abnormal bone growth.
Sensorineural Hearing Loss: occurs when thereis damage to the vestibulocochlear (auditory) nerve. This type of hearingloss may be caused by head injury, birth defects, high blood pressure orstroke.
Presbycusis: occurs because of changes in theinner ear. This is a very common type of hearing loss that happensgradually in older age.
For more on presbycusis, see:
PresbycusisInformation
Tinnitus: people with tinnitus hear a constantringing or roaring sound. The cause of this ringing cannot always be found.Some cases of tinnitus are caused by ear wax, ear infections or a reactionto antibiotics, but there are many other possible causes of this disorder.
For more on tinnitus see:

American Tinnitus Association
Fighting Phantom Noise from Time Magazine
Tinnitus Frequently AskedQuestions
Tinnitus Information &Support Center
Tinnitus Information
Tinnitus Informationfrom the Dept. of Otolaryngology at the Univ. of Washington
TinnitusInformation from Center for Sensory and Communication Disorders

Take a shorton-line, interactive quiz about the ear.

Trysome experiments that test your hearing.

There is a good animated demonstration from KidsHealth showing How the EarWorks.

The virtual tour of theear, the eye and earpage, the ear pagefrom mediscovery, the waywe hear and the ear (for medical students) provide some great information about theear and hearing disorders; there is also a very detailed tutorial on the ear. Hey! What's thepinna for?

Don't forget that yoursense of hearing can be damaged by loud noises...you can read about thisin an article from the Seattle Times called "SayWhat", from the Center for Disease Control in an article called Noise: TheInvisible Hazard, and from and article on loud music anddeafness.

The Center forDisease Control also has information about how hearing can beprotected in the work place in their page called the Hearing ConservationProgram. The BetterHearing Institute has an interesting page on hearing statistics andfacts and the Society forNeuroscience has an article about restoring hearing. The House Ear Institute, Audiology Net and the American Academy of Audiology alsohave basic information about hearing and ear health.

Try some auditoryillusions.

Hear IT! Cochlea Decibel Incus Malleus
Stapes Tympanic Membrane Vestibulocochlear Nerve

Balance (Vestibular Sense)
Balance depends on visualinformation, "feedback" from muscles and from aninner ear structure called the semicircular canal. The semicircular canalis a set of 3 fluid-filled canals that are aligned at right angles to eachother. Within parts of the semicircular canal are hair cells. When thehead is moved, the fluid in the canals moves the hair cells and anerve impulse is generated in the vestibular nerve.
Don't try this. The world record (according to theGuinness Book of Records, 1996) for balancing on one foot is 55 hr. 35min.

Did you know?

Of course you know that if you spin around in circles you willget dizzy. But do you know why? When you spin, fluid in the semicircularcanals of your ear moves around. This stimulates the hair cells. Whenyou stop spinning, the fluid still moves a bit. Since the fluid is stillactivating hair cells, your brain stills gets a message that you aremoving and you feel dizzy.

Did you know?

200,000 people in the United States are deaf; 3 million people in theUS have serious hearing problems. Gallaudet University in Washington, D.C.is an undergraduate institution for deaf and hard of hearingundergraduate students.

BACK TO: Exploring theNervous System Table ofContents

Hear IT!	Cochlea	Decibel	Incus	Malleus
Hear IT!	Stapes	Tympanic Membrane	Vestibulocochlear Nerve