Anatomy and Physiology Ch. 3

temporal bone

internal auditory meatus

petrous portion

external auditory meatus

pinna/auricle

concha

external auditory meatus

tympanic membrane

annulus

stapes

incus

malleus

malleus

incus

stapes

what bones share a border with the temporal bone

sphenoid bone, parietal bone, occipital bone

structures of the middle ear and inner ear are contained in the _____

temporal bone

External auditory meatus (temporal bone)

bony part of the ear canal

Internal auditory meatus

opening for the auditory nerve to pass through

Petrous portion

contains the inner ear structures

Selected features of the outer ear

-pinna/auricle

-concha

-external auditory meatus

Pinna/auricle function

sound-gathering

concha fuction

collects sound and directs to the external auditory meatus

External auditory meatus (ear canal) contents

pathway and tympanic membrane

What does the external auditory meatus (er canal) contain

-cerumen glands (secrete cerumen to lubricate and trap debris)

-contains cilia to clear cerumen

What does the external auditory meatus do in relation to resonating sounds

it maximally resonates sounds that are around 3300 Hz (determined by length of tube)

sound in the external auditory meatus vs entrance of ear canal

sounds in the EAM range will be 2-4x greater than level at enterance

What is the tympanic membrane

-boundary btwn outer and middle ear

-fibrous membrane attached to bony wall of canal by the annulus

annulus

ring shaped cartilage

tympanic membrane shape

cone shaped (conical)

tympanic membrane look

somewhat translucent; can see parts of the ossicles through the membrane

Role of TM

along with the ossicles of the middle ears, the TM is important for transforming energy from sound waves (vibrating air) eventually into fluid waves in the cochlea

vibration/movement of TM

-vibrates when sound waves strike it

-vibration is transmitted to ossicles

-the stapes pushes into the fluid of the cochlea

what are the smallest bones in the body

ossicles

ossicles location

extends from medial surface of TM to oval window

malleus shape

hammer

malleus attachment

handle/manubrium attaches to TM

incus shape

anvil- long and short limbs

stapes shape

stirrup

stapes attachment

-footplate fits into the oval window of the cochlea

-held in the window by the annular ligament

ossicles transmission

transmit vibrations from the TM to inner ear

tensor tympani

stapedius

semi-circular canals

round window

oval window

cochlea

What does this triangle represent

fulcrum

cochlea

vestibular canal

cochlea duct

tympanic canal

basilar membrane

organ of corti

outer hair cells

tectorial membrane

inner hair cell

nerve fiber

basilar membrane

highest frequencies

apex

lowest frequencies

base

organ of Corti

Muscles of the middle ear

-tensor tympani

-stapedius

tensor tympany origin/ insertion

originates in bony canal/temporal tube in the from wall of the middle ear cavity and inserts into the handle of the malleus

tensor tympani contraction

pulls the handle of the malleus inward to stiffen the TM and ossicular chain

stapedius origin/ insertion

originates in a hole in the back wall of the cavity and inserts into the stapes

stapedius contraction

contraction draws stapes away from oval window and stiffens the ossicular chain

what muscles protect hearing

-tensor tympani

-stapedius

Eustachian tube location

runs from middle ear to the nasopharynx

eustachian tube purpose

provides means of pressure equalization

how does the eustachian tube equalize pressure

-swallow/ yawn contracts tensor palatini which opens the lip of the tube

-atmospheric pressure flows into middle ear space

-TM is free to vibrate due to equal air pressure on either side of it

impedance mismatch

-sound waves are vibrating air

-inner ear must be stimulated, but its filled with fluid

-sound transmission would be impeded (impedance mismatch)

TM and ossicles amplify and transform sound into

mechanical energy

Amplification can be accomplished in several ways

-TM is 20x larger than footplate of stapes and the energy is concentrated onto the small footplate

-leverage and fulcrum arrangement of ossicles

-resonating characteristic of ear canal and ossicular chain combine to amplify sounds between 1000-3500 Hz

Transmission of sound

-impedance mismatch

-TM and ossicles amplify and transform sound

-amplification is accomplished in multiple ways

-all of the above helps overcome the impedance mismatch

what are the structures of the inner ear contained in

bony labyrinth

oval window

a hole in the bony labyrinth in which the footplate of the stapes is embedded

round window

covered with a membrane that displaces to accommodate fluid waves

bony labyrinth contains 3 _____

semicircular canals at various angles

semicircular canals/ inner ear info

-filled with perilymph; they also contain an inner duct system (membranous labyrinth) filled with endolymph

-leverage from the fulcrum arrangement of ossicles

-head movements displace the endolymph, which bends hair cells (encodes movement)

vestibule

contains the utricle and saccule which contain hair cells that sense movement of head

the cochlea is ___

a coiled structure with chambers

Scala vestibuli/ vestibular canal contains ____

perilymph

Scala media (cochlea duct) contains____

endolymph

Scala tympani/ tympanic canal contains___

perilymph

the chambers of the cochlea are separated by _____

Reissner’s membrane and basilar membrane (organ of corti is situated on the basilar membrane)

basilar membrane location

stretches between bony wall and bony core

where is the organ of corti

rests on basilar membrane

what does the organ of Corti do

converts fluid waves into bioelectric energy

organ of corti hair cells info

-one row of inner hair cells

-three rows of outer hair cells

-deformed by tectorial membrane and fluid waves traveling though scala media

-convert hydraulic motion into electrical impulses that are sent to brain via auditory pathway

basilar membrane hair cells location

the entire length of the basilar membrane

hair cells in relation to frequency

where a hair cell is located along the membrane determines its frequency sensitivity

base end of BM

-narrow and stiff

-responsive to highest frequencies

-aka vestibule end

apex end BM

-wide and lax

-responsive to lowest frequencies

middle portion of BM

-intermediate width and stiffness

-responsive to mid frequencies

chochlear fluid movement

fluid in cochlea moves in phase with the footplate of stapes

vibration is transmitted along BM as a ____

traveling wave

shape of wave development over time

-build to a crest where most of its energy is spent

-quickly dissipate after crest