The Ear Lab Flashcards
Ear functions
- sense hearing
- determine position in space
- aka balance
3 areas of the ear
- outer
- middle
- inner
Anatomical features: outer ear 3 features
- pinna
- auditory canal
- tympanic membrane
Pinna (auricle)
- subdivided: helix(upper), lobule (lower)
* composed of stratified squamous epithelium, overlying elastic cartilage
Auditory canal
•penetrates into the temporal bone
Tympanic membrane (ear drum)
- border between external and middle ear
- membrane is sensitive to sound
- vibrates as sound is funneled down the meatus
Middle ear consists of main cavity known as
Tympanic cavity
Auditory ossicles (middle ear)
- three small bones of ossicles
- magnify sound 20x
- ossicles conduct vibration to the oval windows
3 auditory ossicles
- malleus
- incus
- stapes
Malleus
•(hammer)
•handle connected to the tympanic membrane
•as membrane vibrates the malleus rocks back and forth
•amplifying sound waves
*to the incus
Incus
- (anvil)
- attached to malleus
- which is attached to stapes
Stapes
- (stirrup)
- foot plate, fits into oval window
- held in place by annular ligament
Eustachian tube (auditory tube, pharyngotympanic tube)
- opening that provides air passage from the middle ear
- opens into pharynx and equalizes air pressure
- between the outside and middle ear cavity
Inner ear: tunnels and chambers inside the temporal bone are called
•bony labyrinth
Oval window (inner ear)
- in cochlea
- allows vibrations from ossicles to move fluid back and forth
- communicates with the vestibule of the inner ear
- in turn communicates with the cochlear chamber
Cochlea (inner ear)
- hearing
- contains round and oval window
- many chambers in clusters of 3s
Vestibule (inner ear)
- consists of the utricle and saccule
- two chambers involved in interpretation of static equilibrium and acceleration
- both have regions know as maculae- cilia grouped together, with overlying gelatinous mass and calcium carbonate stones
- cilia bend indicating head change
Carbonate stones
Aka otoliths
Maculae
- cilia grouped together
- over lying gelatinous mass and calcium carbonate stones
- cilia bend indicating head change
Semicircular canals (inner ear)
- determine dynamic equilibrium
- each at 90 degrees to one another
- each filled with endolymph and is expanded at the base into an ampulla
5 structures of the cochlear structure
- oval window
- scala vestibule
- scala tympani
- scala media
- round window
Oval window (cochlear structure)
- hole in cochlea
- where the foot plate of the stapes fits
- held by annular ligament
- membranous structure to which the stapes attaches
- transmits vibrations to inner ear
Scala vestibule
- extends from the oval window to the helicotrema
- to apex of the cochlea
- filled with perilymph
Helicotrema
•a hole at the end of the helix or spiral
Scala tympani (cochlear structure)
- extends from the helicotrema
- back to the apex parallel to the scala vestibule
- into membrane of round window
- filled with perilymph
Scala media (cochlear structure)
- space between the vestibular membrane and the basilar membrane
- is the interior of the membranous labyrinth
- filled with endolymph
Round window (cochlear structure)
•membranous structure separating the scala tympani of the inner ear from the middle ear
Pathway of sound transmission
- outer ear
- middle ear
- inner ear
- cochlear nerve
Outer ear- as pathway
- sound vibrates in air
- enter auditory canal
- start vibration in tympanic membrane
Middle ear- sound pathway
•auditory bones transmit sound vibrations to oval window
Inner ear- sound pathway
- vibration of fluids begins in the canals
* stimulates the organ of corti in cochlear duct
Organ of corti
- spiral organ
* high or low pitch indicator
Cochlear nerve- pathway of sound
- stimulation of receptors of spiral organ starts transmission of sound info through cochlear nerve
- info carried to temporal lobe of the cerebrum for interpretation
Spiral organ (organ of corti) structures
-cells inside the cochlear duct, highly modified
•basilar membrane
•hair cells
•tectorial membrane
Basilar membrane (organ of corti)
•wall of membranous labyrinth bordering the scala tympani
Hair cells (organ of corti)
- hair projections
- at apical ends
- arranged in 4 long rows
- extend length of cochlear duct
- each row contains 3500-4000
- inner row: for hearing
- outer 3 rows: regulate tension of basilar membrane
- separated by gap in basilar membrane
Tectorial membrane (organ of corti)
- gelatinous shelf
- attached to spiral lamina
- tips of the longest sterocila, gate of k+ channel
Structures that detect equilibrium
- vestibule
* semicircular canals
Vestibule
- located btwn cochlea and the semicircular canals
- two sections: utricle and saccule
- filled with endolymph fluid
- has sensory organ called macula
Macula structure
- gelatin matrix
- hair cells
- otoliths
- vestibule function
Gelatin matrix (macula)
- overlying gelatinous mass
* contain calcium carbonate stones (otoliths)
Hair cells (macula)
- contain numerous microvilli called stereocilia
* and one cilium called kinocilium
Otoliths (macula)
- give weight to gelatin matrix
* composed if calcium carbonate and protein
Vestibule function (macula)
- vestibule function to maintain static equilibrium
- sense of relation if the head to the pull of gravity
- position of head in static nonmoving state
Methods of sound transmission 1
- vibrations of the perilymph in the scala vestibuli and scala tympani cause wave of movement in endolymph of the cochlear duct
- results in change of shape of the basilar membrane
Methods of transmission 2
- basilar movement causes movement of hair cells embedded in tectorial membrane
- starting depolarization and AP at threshold
Methods of transmission 3
- certain hair cells activate at one time
- activation related to pitch of the sound
- sensed as continuum along entire spiral organ
- higher pitch: near oval window end
- low pitch: detected at other end, helicotrema
Sound travels in waves and has two things
- frequency
* amplitude
Pitch
•quality of frequency and sound vibration
High pitch
- high rate of frequency
- near oval window
- starts at 20,000 hertz
Low pitch
- low frequency vibration
- sensed near the apex or helicotrema of spiral organ
- lowest having vibrations of 200 hertz
Intensity is measured in units of
- decibels
* the quality of amplitude of is the volume or intensity of sound
Semicircular canals
- above vestibule
- 3 canals at right angles of each other
- endolymph fluid fills each canal
- base of canal is ampulla
- containing a crista ampullaris sensory receptor
Crista ampullaris structure
- hair cells: sticks out of here. Contained in capula
* capula: jelly on top of hair cells
Functions of canals
- act to sense dynamic or kinetic equilibrium
- movement of head causes Fluid to move within the canals
- bends capula
- hair cells stimulated
- start AP in vestibular nerve
- brain interprets
