Lecture 28: Ear Flashcards
2 functions of ear
balance and orientation
hearing
balance and orientation involves detecting
movement of body relative to outside world
hearing involves detecting
movement of outside world
3 parts of hearing and balance apparatus
inner ear
middle ear
external/outer ear
inner ear: definition/location, functions
fluid filled space within petrous portion of temporal bone
hearing and balance
middle ear: definition/location, function
air filled space within petrous and tympanic portions of temporal bone
hearing
external/outer ear: location, function
emerges from tympanic part of temporal bone and continued by additional cartilaginous pieces
hearing
waves in water vs air
waves in water don’t lose energy
waves in air lose energy from air to ear fluids
typanic ear cavity: definition, function
ear drum
air filled middle ear
bony connection to inner ear
middle ear aka
tympanic cavity
primary function of middle ear/tympanic cavity
transmit sound vibration from lateral external ear to more medial inner ear
function of tympanic membrane/eardrum
separate middle ear from external ear
3 main walls of middle ear
tympanic membrane/eardrum
ear ossicles/ossicular chain
oval window/fenestra ovalis
fenestra ovalis/oval window
on medial wall of tympanic cavity
between middle ear and inner ear
ear ossicles/ossicular chain: definition/components, location
3 little bones = malleus, incus, stapes
connect tympanic membrane to inner ear allowing for transmission of sound waves
stapes: definition/location, function
oval shaped footplate fits into oval window
causes vibrations in perilymph of inner ear
transmits vibrations from outside head to inner ear
what is the only true ossicle in non mammals
stapes
how many small bones do all mammals have in middle ear
3 = stapes, incus, malleus
incus: definition, location
intermediate bone between malleus and stapes
articulates with them via synovial joints
malleus: definition, location
body/manubrium is fixed to tympanic membrane so vibrations of membrane are passed along ossicular chain
2 muscles in middle ear associated with ossicles
tensor tympani
stapedius
“probable” actions (2) of tensor tympani and stapedius
clarify hearing
protect from excessively loud sounds
tensor tympani: OIN
O - anterior wall of middle ear
I - body of malleus
N - mandibular nerve V3
stapedius: OIN
O - posterior wall of middle ear
I - head of stapes
N - facial nerve (CN VII)
what nerve transmits sensory from mucosa lining middle ear (tympanic membrane)
glossopharyngeal
what nerve passes through middle ear cavity
glossopharyngeal
minor petrosal nerve is branch of
glossopharyngeal
1st branch of glossopharyngeal nerve
minor petrosal nerve
minor petrosal nerve: function, path/ganglion
carries parasympathetic axons from CN IX/glossopharyngeal to otic ganglion
path of facial nerve (foramina)
from internal acoustic meatus to stylomastoid foramen
through posterior wall of tympanic cavity
2 branches of facial nerve in ear
major petrosal nerve
chorda tympani
major petrosal nerve: parent nerve, function
branch of facial nerve
carries preganglionic parasympathetic axons from facial nerve to pterygopalatine ganglion
chorda tympani: parent nerve, path, functions
branch of facial nerve
carries preganglionic parasympathetic input to mandibular and sublingual ganglia
carries taste from rostral portion of tongue
crosses tympanic membrane to get to lingual nerve in infratemporal fossa, axons hitchhike to oral cavity on lingual
relationship of air pressure in middle ear cavity vs outside for most efficient functioning of tympanic membrane
must be equal
auditory/eustacean tube: function
connects middle ear cavity to nasopharynx
normal state of auditory/eustacean tube
pressed closed and must be actively opened to equalize air pressure
how auditory/eustacean tube is manipulated to maintain air pressure
tensor and levator veli palatini parallel auditory tube and open it upon contraction so pressure can equalize
otitis media: definition, how caused
infection of middle ear cavity
build up of infectious fluid in tympanic cavity
impacts sensitivity of hearing by dampening vibrations of tympanic membrane
possible lesions of nerves passing through space
what’s special about tympanic bulla in cats (+ clinical correlation)
can be palpated externally
otitis media can make area sensitive
how can stubborn otitis media infections be drained
surgically opening tympanic bulla into nasopharynx
what is the only part of the ear apparatus with directly visible aspect (and what is this aspect called)
external ear
pinna/auricle
auricle/pinna: location, functions
external ear
funnel and focus sound into external auditory canal
help with detection of sound direction
what is anatomical position of auricles/pinnas
erect and alert
rostral = concave, lightly haired surface
caudal = convex furred surface
adaptations of auricle: examples
thermoregulation = jack rabbits
communication = elephants
improved olfactory efficiency = hound dog
cerumen: definition, function
earwax
keep canal clean and free of particles that might interfere with sensitive tympanic membrane
2 components of external auditory canal
vertical canal
horizontal canal
what glands produce earwax
ceruminous glands
6 features of cartilage that supports auricle/pinna
helix
scapha
tragus
antitragus
intertragic incisor
cutaneous marginal pouch
scutiform cartilage: location/definition, function
smaller isolated cartilage associated with musculature of external ear
provide leverage for muscles
auricular muscles that provide fine control of position and attitude of auricle are considered muscle of
facial expression
is the auricle highly vascularized
yes
blood supply to auricle (2)
rostral auricular
caudal auricular
rostral auricular artery: parent artery, what supplied
superficial temporal artery
rostral concave surface of auricle
caudal auricular artery: parent artery, what supplied, how many branches
external carotid
4 large branches
rostral surface of auricle
4 branches of caudal auricular artery and where they go
medial
lateral
intermediate
deep
*caudal surface of auricle
significance of extensive blood supply to external ear (clinical correlation)
insignificant trauma can lead to vascular rupture
aural hematoma
aural hematoma: definition, intervention
blood pools in ear and separates skin from underlying cartilage
surgical intervention
sensory innervation from caudal surface of auricle (2 rami origin and 2 specific branches)
ventral rami of C2 = greater auricular nerve on lateral side
dorsal rami of C2 = greater occipital nerve on medial side
lateral vs medial sensory innervation from auricle
lateral = greater auricular nerve
medial = greater occipital nerve
2 cranial nerves: sensory innervation from rostral surface of auricle
auriculotemporal V3
vagus nerve CN X
external vs internal surface of tympanic: innervation
external = vagus + V3
internal = glossopharyngeal
auricular branch of vagus: path, what’s innervated
through petrous portion of temporal bone
external auditory canal and lateral surface of tympanic membrane
