Test 2 Flashcards
sagittal
divides from right to left
midsagittal
midline plane
medial
toward the midline
lateral
away from the midline
proximal
situated close to
distal
situated away from
dextral
right
sinistral
left
transverse
divides top from bottom (horizontal plane)
superior
up
inferior
down
rostral
toward the head
caudal
toward the tail
coronal
divides front and back
anterior
front
posterior
back
dorsal
towards the back
ventral
towards the belly
outer ear
collects sound and funnels it to the tympanic membrane (eardrum)
changes the spectral (frequency) characteristics of sound which aids in sound localization
middle ear
sound wave causes eardrum to vibrate, setting the bones in the middle ear into motion
inner ear (cochlea)
turns mechanical vibrations into neural signals
sorts sounds into different frequencies
neural signals are sent from auditory nerve to the brain
what does the temporal bone surround?
ear canal, middle ear, and inner ear
what are 4 distinct portions that make up the temporal bone?
- squamous
- petrous
- mastoid
- tympanic
squamous portion
thin and fan like
lateral aspect of the bone
lies anterior and superior to the ear canal
mastoid portion
posterior portion of the bone
lies posterior to the ear canal
contains air cells
extends posteriorly from petrous portion, below and behind the squamous and petrous portion and anterior to the mastoid portion
petrous portion
pyramid shaped
projects medially from the other 3 portions
only visible in medial view from inside the skull looking out
contains sensory organs of hearing and balance and the internal auditory canal
two main components of the outer ear?
Pinna (auricle)
External Auditory Canal (EAC)
Pinna
multiple ridges and valleys change the frequency characteristics of sound which helps us localize a sound source
External Auditory Canal (EAC)
S-like tube that ends at the ear drum
Lateral 1/3 of cartilage contains:
- hairs
- sebaceous (oil) glands: lubricates the ear canal
- cerumenous (wax) glands: keeps away foreign bodies and insects
Medial 2/3 is bone derived from tympanic and squamous portions of the temporal bone
Middle ear components
tympanic membrane
3 ossicles (bones)
ligaments that suspend ossicles
muscles and tendons
eustachian tube
tympanic membrane
located at the medial end of the EAC
separates the outer and middle ear
tilts laterally at the top (about 55%)
cone-shaped with peak pointing away from the EAC and into the middle ear
What are the two distinct parts of the tympanic membrane?
Pars Tensa: inferior 2/3
- lateral outer layer: skin continuous with skin of the ear canal
- middle layer: dense fibrous tissue that adds stiffness
- medial inner layer: continuous with the mucous membrane of the middle ear
Pars Flaccida: superior 1/3
Epithelial Migration in the EAC
skin in the ear canal begins at the lateral layer of the eardrum (near the umbo)
skin then migrates from the eardrum to the ear canal
skin continues to migrate laterally, working like a conveyor belt, to move wax and debris out as the skin moves
(this is how the ear naturally cleans itself. Happens slowly, at a rate similar to fingernail growth)
tympanic membrane connected to the middle ear bones by the _________________
manubrium of malleus
umbo
tip of the manubrium
cone of light
reflection of light from the otoscope
otoscope
used to view the tympanic membrane
to view the TM, the pinna must be pulled up and back to straighten the EAC
Three parts of the middle ear
tympanic cavity: space in the temporal bone behind the TM
epitympanic recess of attic: superior to the level of the TM, contains portions of the incus and malleus
mastoid antrum: enlarged space in the mastoid part of the temporal bone, posterior to the epitympanic recess
ossicular chain
three smallest bones in the body
transmit vibrations of the TM to the oval window of the cochlea
ossicles a part of the ossicular chain
malleus
incus
stapes
malleus
attaches to TM along the maubrium
head extends into the epitympanic recess
connects to the incus
incus
transmits vibrations from the malleus to the stapes
stapes
head attaches to the incus
anterior crus, posterior crus, and footplate for a “stirrup”
footplate attaches to the oval window of the cochlea. movement of the stapes footplate in the oval window sends sound into the cochlea
sound transmission through the middle ear system order (5)
TM Malleus Incus Stapes Inner Ear
Stapedius Muscle
smallest muscle in the body (protects us from loud noises)
innervated by 7th cranial nerve (facial)
contraction pulls stapes posteriorly, stiffening the ossicular chain (acoustic reflex)
tensor tympani
4 times longer than stapedius muscle: 25 mm long
innervated by the 5th cranial nerve (trigeminal nerve)
contraction pulls the malleus in the anterior/medial direction and stiffens the ossicular chain
not part of the acoustic reflex in humans
acoustic reflex
a LOUD sound of any frequency reaching either ear causing:
- reflexive contraction of the stapedius muscle in both ears
- stiffens the ossicular chain and reduces the transmission of low frequency sounds through the middle ear system
- contracts prior to vocalization to reduce voice intensity
acoustic reflex protects the ear from ___________
loud sounds
Functional importance of acoustic reflex
- Acts as an automatic volume control to reduce high-level inputs to the inner ear
- May protect against long term noise damage
Cannot protect the ear from impulse noise (due to minimum 25-ms response time) - May improve signal-to-noise ratios for speech, by attenuating low frequency sounds without altering high frequency sounds
Eustachian tube
connects the middle ear to pharynx (throat) to equalize pressure in the middle ear.
tilts downward at a 45 degree angle
**almost horizontal in infants and young children.
functions of the outer and middle ears
head shadow effect
pinna effect
gain due to ear canal resource
head-related transfer function
gain due to middle ear characteristics
azimuth
location of sound source in the horizontal plane
elevation
location of sound in the vertical plane
head shadow effect
the head impedes the transmission of high frequency sounds (>1500 Hz) to the “far” ear
occurs because high frequency sounds have wavelengths that are smaller, so they cannot bend around the head
Pinna effects
diffraction and reflection of sound waves by the pinna modify the transmission of high frequency sounds
due to the irregular shape, ridges, and depressions of the pinna
affects sounds with frequencies >4,000 Hz.
how the sound is changed depends on the location of sound source relative to the ear
pinna effects permit some sound localization when binaural cues are not available.
what is the resonant frequency of the ear canal?
3000-4000 Hz
head related transfer function
shows changes in sound level due to the presence of the head, pinna, and ear canal as a function of frequency
(provides a way to measure the effects of head, pinna, and ear canal of sound)
binaural cues
used for sound localization when two ears are present
intramural level differences (ILD)
SPL at near ear > SPL at far ear
due to head shadow effect
exists for high frequencies (>1500 Hz)
interaural time difference (ITD)
sound arrives sooner at the near ear than at the far ear
exists for all frequencies
listeners rely on…
ITD at low frequencies (<1500 Hz)
ILDs at high frequencies (>1500 HZ)
Head shadow effect
reduces sound levels (at the far ear) for frequencies .1500 Hz
Ear Canal Resonance
increases sound levels for frequencies between 2000-5000 Hz, with a peak gain of 15 dB at 3000-4000 Hz
Pinna effects
alters the amount of gain for frequencies >4000 Hz
middle ear transformer
air and water have different impedances
if sound vibrations traveled directly from air to water, there would be a 30 dB loss in intensity
the middle ear compensates for this loss of energy by increasing sound pressure (+33 dB)
3 mechanisms for impedance matching
- area ratio mechanism
- ossicular lever mechanism
- curved membrane mechanism
the gain created by these middle ear mechanisms helps to compensate for the 30 dB loss of energy due to the impedance mismatch between air and cochlear fluids
area ratio of eardrum stapes
area of TM = 56.7 mm²
area of oval window = 3.2 mm²
P = F/A: Force applied to TM is delivered to the oval window, which has a smaller area
pressure increases proportionally
ratio = 17.7 to 1
the amount of pressure increase: 20 log (17.7/1) = 25 dB gain
curved membrane buckling mechanism
the TM curves between its outer edge and its attachment to the manubrium
there is a greater displacement in the unattached regions of the TM than at the manubrium
ossicular lever action
the manubrium of the malleus is 1.3 times longer than the long process of the incus
force x displacement must remain constant
smaller displacement at the incus is accompanied by the increase in force
