hearing and balance


Did you ever try to stand on one foot with your eyes closed? Try it and see what happens, but be careful! Its harder to keep your balance when you cant see. Your eyes obviously play a role in balance. But your ears play an even bigger role. The gymnast pictured below ( Figure 1.3) may not realize it, but her earsalong with her cerebellumare mostly responsible for her ability to perform on the balance beam. The parts of the ears involved in balance are the semicircular canals. Above, the semicircular canals are colored purple ( Figure 1.2). The canals contain liquid and are like the bottle of water pictured below ( Figure 1.4). When the bottle tips, the water surface moves up and down the sides of the bottle. When the body tips, the liquid in the semicircular canals moves up and down the sides of the canals. Tiny hair cells line the semicircular canals. Movement of the liquid inside the canals causes the hair cells to send nerve impulses. The nerve impulses travel to the cerebellum in the brain along the vestibular nerve. In response, the cerebellum sends commands to muscles to contract or relax so that the body stays balanced.



Hearing is the ability to sense sound. Sound travels through the air in waves, much like the waves you see in the water pictured below ( Figure 1.1). Sound waves in air cause vibrations inside the ears. The ears sense the vibrations. The human ear is pictured below ( Figure 1.2). As you read about it, trace the path of sound waves through the ear. Assume a car horn blows in the distance. Sound waves spread through the air from the horn. Some of the sound waves reach your ear. The steps below show what happens next. They explain how your ears sense the sound. 1. The sound waves travel to the ear canal (external auditory canal in the figure). This is a tube-shaped opening in the ear. Sound waves travel through the air in all directions away from a sound, like waves traveling through water away from where a pebble was dropped. Read the names of the parts of the ear in the text; then find each of the parts in the diagram. Note that the round window is distinct from the oval window. 2. At the end of the ear canal, the sound waves hit the eardrum (tympanic membrane). This is a thin membrane that vibrates like the head of a drum when sound waves hit it. 3. The vibrations pass from the eardrum to the hammer (malleus). This is the first of three tiny bones that pass vibrations through the ear. 4. The hammer passes the vibrations to the anvil (incus), the second tiny bone that passes vibrations through the ear. 5. The anvil passes the vibrations to the stirrup (stapes), the third tiny bone that passes vibrations through the ear. 6. From the stirrup, the vibrations pass to the oval window. This is another membrane like the eardrum. 7. The oval window passes the vibrations to the cochlea. The cochlea is filled with liquid that moves when the vibrations pass through, like the waves in water when you drop a pebble into a pond. Tiny hair cells line the cochlea and bend when the liquid moves. When the hair cells bend, they release neurotransmitters. 8. The neurotransmitters trigger nerve impulses that travel to the brain through the auditory nerve (cochlear No doubt youve been warned that listening to loud music or other loud sounds can damage your hearing. Its true. In fact, repeated exposure to loud sounds is the most common cause of hearing loss. The reason? Very loud sounds can kill the tiny hair cells lining the cochlea. The hair cells do not generally grow back once they are destroyed, so this type of hearing loss is permanent. You can protect your hearing by avoiding loud sounds or wearing earplugs or other ear protectors.



hearing and balance

What do listening to music and riding a bike have in common? It might surprise you to learn that both activities depend on your ears. The ears do more than just detect sound. They also sense the position of the body and help maintain balance.

instructional diagrams

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hearing is the ability to sense sound.

-->  a. true

b. false

our ears interpret the sounds that we hear.

a. true

-->  b. false

what part of the ear is involved in maintaining balance?

a) the tympanic cavity

b) the cochlear nerve

-->  c) the semicircular canals

d) all of the above

once sound waves enter the ear, vibrations pass from the eardrum to the

-->  a) hammer.

b) anvil.

c) stirrup.

d) oval window.

what part of the ear is lined with tiny hairs and filled with fluid?

a) the auditory canal

b) the eustachian tube

-->  c) the cochlea

d) the tympanic cavity

what part of the ear passes vibrations to the cochlea of the inner ear?

-->  a) the oval window

b) the round window

c) the cochlear canal

d) the stapes

how is the signal relayed to the brain to tell the body to maintain balance?

a) the signal is sent through the cochlear nerve.

-->  b) the signal is sent through the vestibular nerve.

c) the signal is sent through the eustachian tube.

d) the signal is sent through the semicircular canals.

diagram questions

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