CHAPTER 14.3 PAGES 456-461 Hearing and Equilibrium.

CHAPTER 14.3PAGES 456-461

Hearing

and

Equilibrium

HEARING AND EQUILIBRIUM

• the ear

• is associated with two separate functions:

• hearing

• equilibrium

• can be divided into three sections

• the outer ear

• the middle ear

• the inner ear


The Outer Ear

• comprised of the

• pinna

• the external ear flap

• collects the sound

• auditory canal

• carries sound to the eardrum.

• lined with specialized sweat glands that produce earwax.

• earwax traps foreign particles and prevents them entering the ear.


The Middle Ear

• begins at the tympanic membrane and extends toward the oval and round windows.

HEARING AND EQUILIBRIUM• the tympanic membrane is a thin layer of tissue that

receives sound vibrations, also known as the eardrum.


• the air filled chamber of the middle ear contains three small bones called ossicles, which include the:

• mallus (the hammer)

• incus (anvil)

• stapes (stirrup)

• the ossicles amplify

and carry sound in

the middle ear.


• sound vibrations that strike the eardrum and are first concentrated within the solid malleus.

• vibrations are then transmitted to the incus and finally to the stapes


• the stapes strikes the membrane covering the oval window in the inner wall of the middle ear

• the oval window is an oval shaped hole in the vestibule of the inner ear, covered by a thin layer of tissue

• sound is amplified by concentrating the sound energy from the large tympanic membrane to the smaller oval window.


• the eustachian tube

• an air-filled tube of the middle ear that equalizes pressure between the external and internal ear.

• approximately 40 mm in length and 3 mm in diameter.

• extends from the middle ear to the mouth and chambers of the nose.

• equalizing your ears on a plane by yawning or swallowing allows air to leave your middle ear through the eustachian tube.


The Inner Ear

• has three distinct structures, the:

• vestibule

• semicircular canals

• cochlea

HEARING AND EQUILIBRIUM• the vestibule

• a chamber found at the base of the semicircular canals that provides information about static equilibrium

• involved in balance

• connected to the middle ear by the oval window.

• houses two sacs

• the utricle

• the saccule

HEARING AND EQUILIBRIUM• the utricle and saccule contain granules called otoliths

that allow us to detect gravity (linear movement) and head movement.

• three semicircular canals arranged at different angles helps identify body movement

(3 canals for 3 axis of movement)

(Three semicircular canals contain fluid and allow us to detect angular acceleration such as the turning of the head)

Dynamic eq. vid: balance


• The cochlea

• a coiled structure of the inner ear that responds to various sound waves and converts them to nerve impulses.

• shaped like a spiralling snail’s shell.

• contains rows of specialized hair cells that run the length of the inner cannal.

• the hair cells respond to sound waves and convert them into nerve impulses.


Hearing

• sound like light must be converted into an electrical impulse before you can interpret it.

• you ear is so sensitive that you can hear a mosquito even though the sound energy reaching you ear is less than one quadrillionth of watt. The average light in the house uses a 60 watt bulb.

HEARING AND EQUILIBRIUM• hearing begins when sound waves push against the eardrum,

or tympanic membrane.

• the vibrations of the eardrum are passed on to the three bones of the middle ear: the malleus, the incus, and the stapes

• arranged in a lever system the three bones are held together by muscles and ligaments.


• the bones concentrate and amplify the vibrations received from the tympanic membrane (they can triple the force)

• during excessive noise a protection reflex mechanism goes into effect.

• the muscles that join the bones together contract and restrict the movement of the malleus reducing the intensity of movement.

• at the same time a second muscle contracts pulling the stapes away from the oval window.


• the oval window receives vibrations from the ossicles.

• as the oval window pushes inwards, the round window, located immediately below the oval window moves outward.

• this triggers waves of fluid within the inner ear.

• the cochlea receives the fluid waves and converts them into electrical impulses, which you interpret as sound.


• the hearing apparatus within the cochlea is known as the organ of Corti.

• it comprises a single inner row and three outer rows of specialized hair cells anchored to a basilar membrane.

• the hair cells respond to vibrations of the basilar membrane.

• vibrations in the fluid on either side of the basilar membrane cause the membrane to move.

• the hairs on the cells bend as they brush against the tectorial membrane.


• the movement of the hair cells stimulates sensory nerves in the basilar membrane

• Auditory information is the sent to the temporal lobe of the cerebrum via the auditory nerves.


• The ear conveys information about:• Volume, the amplitude of the sound wave

• Pitch, the frequency of the sound wave

• The cochlea can distinguish pitch because the basilar membrane is not uniform along its length

• Each region vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex

http://health.howstuffworks.com/adam-200010.htm

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Hearing test

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3) TREATMENTS FOR HEARING LOSS• Conductive hearing loss: caused by wax build-up, middle ear

infection, punctured eardrum• Sensorineural hearing loss: auditory nerve severed, or cochlear

hair cells damaged.

Treatments:• Hearing aid: amplifies sound

and transmit to eardrum.• Cochlear implants: converts sound (speech processor) to

electrical impulses that are sent to auditory nerve.

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TinnitusTinnitus – ringing in ear; “phantom sound”

• Malfunction of cochlea, transmitted to brain

• Temporary, after a rock concert

• Hair cells are damaged, bent, or destroyed

• Loss of hair cells as we age

• Other causes:

• TMJ, damage to inner ear by trauma, ear infection, tumors, use of ototoxic drugs (antibiotics, anticancer drugs, or antimalarial drugs) – damage to hair cells or auditory nerve or both

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CHAPTER 14.3 PAGES 456-461 Hearing and Equilibrium.

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Transcript of CHAPTER 14.3 PAGES 456-461 Hearing and Equilibrium.