Flashcards in Head and Neck, Session 6 Deck (79):
Embryological origin of external ear?
auricle- prolif of cells in 1st and 2nd pharyngeal arches
external auditory meatus- 1st pharyngeal cleft
where does the EAM terminate?
at the fibrous tympanic membrane
where does the middle ear lie?
in petrous temporal bone
components of middle ear?
tympanic cavity, lying immediately medial to tympanic membrane
epitympanic recess- space superior to tympanic membrane
how does middle ear communicate with nasopharynx?
connected by Eustachian tube anteriorly
what does middle ear communicate with posteriorly?
mastoid cells in mastoid process of temporal bone
bones of middle ear?
3 auditory ossicles: malleus, incus and stapes, which conduct sound waves to inner part of ear
what are the 2 tympanic muscles stapedius (from 2nd P arch, facial nerve) and tensor tympani (1st P arch, trigeminal nerve, concerned with?
dampening large m.ments of tympanic membrane
2 parts of inner ear?
membranous and bony labyrinths- membranous lies within bony
embry origin of membranous labyrinth?
otic placodes- thickenings of ectoderm
what does bony labyrinth consist of?
cochlea- concerned with sound perception, vestibule and semicircular canals- both involved in balance, suspended in perilymph
composition of membranous labyrinth?
series of communicating sacs and ducts, and contains endolymphs
what happens at base of cochlea?
bony labyrinth communicates with subarachnoid space via cochlear aqueduct
what is the vestibule concerned with?
how do fibres of CNVIII reach inner ear?
pass through internal acoustic meatus on inner aspect of petrous temporal bone
common causes of otalgia?
external otitis and otitis media
4 temporal bone components?
squamous part- TMJ
what does the external acoustic meatus consists mainly of?
which part of the temporal bone contains the middle an d inner ears?
how can middle ear disease cause mastoiditis?
the cavity of the mastoid antrum ( a prolongation of the cavity of the middle ear), is prolonged into the mastoid process by intercommunicating air cells
what does the skin lining the external auditory meatus secrete?
cerumen- modified sebum- affords protection for delicate meatal skin
how is wax formed?
by cerumen and discarded cells of skin
to what is the apex of the eardrum (tympanic membrane) attached?
how is eustachian tube opened intermittently?
by pull of attached palate muscles when swallowing
why might a middle ear infection cause a lesion of the facial nerve?
nerve lies within the facial canal which is separated from the middle ear cavity by only a very thin bony partition
when may perforation of tympanic membrane occur?
after trauma or infection
why are people advised to take sweets to stop their ears from becoming blocked on a plane?
As during swallowing, the Eustachian tube is opened by the pull of the attached palate muscles, so this helps to keep the tube open and hence prevent blockage
how is an auricular haematoma treated?
contents of middle ear?
auditory ossicles- malleus, incus, stapes
stapedius and tensor tympani muscles
chorda tympani nerve- branch of facial nerve
tympanic plexus of nerves
innervation of stapedius?
innervation of tensor tympani?
why is tympanic membrane more easily damaged in children in otoscopy?
external acoustic meatus relatively short
auricle pulled down and back in infants to straighten meatus
how does tympanic membrane normally appear on otoscopy?
translucent and pearly gray
name given to centre of tympanic membrane?
where does acute otitis media occur?
between tympanic membrane and inner ear
most common bacterial cause of acute otitis media?
why must otitis media be treated?
if untreated, it may produce impaired hearing as result of scarring of auditory ossicles, limiting their ability to move in response to sound
why are incisions to release pus from a middle ear abscess made posteroinferiorly through tympanic membrane?
as membrane superior 1/2 much more vascular than inferior 1/2. AND incision avoids injury to chorda tympani nerve and auditory ossicles.
how are external and middle parts of ear separated?
how are middle and inner parts of ear separated?
by oval and round windows
why is skin of outer ear easily traumatised?
skin adherent to elastic cartilage, so no movement
branch of trigeminal nerve innervating skin of EAM?
auriculotemporal- branch on mandibular division
branch of vagus nerve innervating skin of EAM?
sensory nerve supply of external part of tympanic membrane?
auriculotemporal nerve- branch of mandibular division of trigeminal, and aurciular nerve- branch of vagus
sensory nerves supply of internal part of tympanic memebrane?
sensory nerve supply of auricle?
great auricular nerve from cervical plexus- C2 and C3
blood supply to auricle?
posterior auricular and superficial temporal branches of external carotid artery
where does auriculotemporal nerve provide sensory innervation to external ear?
to skin of auricle anterior to EAM
great auricular nerve does rest of auricle
composition of EAM?
outer 1/3 is elastic cartilage
inner 2/3 is tympanic plate of temporal bone
where does EAM run?
from concha to outer plate of tympanic membrane
properties of skin lining outer 1/3 of EAM?
ceruminous glands- secrete cerumen- offers protection, and combines with discarded skin cells to form wax- bactericidal
what may be visualised through the tympanic membrane?
how might the tympanic membrane appear in disease?
dull, red or yellow
blood vessels may be dilated
dense, white plaques due to tympanosclerosis
bulging- fluid or pus in middle ear
retracted- -ve intratympanic cavity pressure e.g. from eustachian tube obstruction
perforation- trauma or infection
how is tympanic membrane connected to inner ear?
via auditory ossicles
what is the epitympanic recess?
space superior to tympanic membrane
lining of tympanic cavity?
mucous membrane continuous with lining of Eustachian tube, mastoid cells and mastoid antrum
medial layer of tympanic membrane lined by?
respiratory epithelium- low columnar
why is equilibration of pressures between middle ear and the external environment important?
if not equalised, can result in pain in ear e.g. when on a plane, and eustachian tube dysfunction causing a -ve pressure in middle ear cavity draws TM in, reducing its ability to vibrate efficiently, and so can cause loss of hearing.
complications of glue ear?
infections can spread into middle cranial fossa via temporal bone
can spread into posterior cranial fossa via epitympanic recess and mastoid antrum
can spread into sigmoid venous sinus via mastoid air cells
problem with spread of mastoiditis and acute otitis media?
can lead to intracranial infection and death, may cause meningitis
3 layers of tympanic membrane?
outer plate- keratinised stratified squamous cells
middle- fibrous layer
inner- respiratory epithelium, part of middle ear
function of auditory ossicles?
amplify and concentrate sound energy from tympanic membrane to the oval window
what does middle ear function depend on?
how are auditory ossicles connected to inner ear?
handle of malleus attached to the tympanic membrane, and body articulates with the body of the incus, which articulates with the stapes and this osscile articulates with the Bony Labyrinth of the inner ear at the Oval Window
why might oropharyngeal infections present as earache?
referred pain as oropharynx innervated by glossopharyngeal nerve, which also innervates inner part of tympanic membrane, so pharyngitis or tonsillitis may present as otalgia
attachments of muscles assoc with auditory ossicles?
Tensor tympani Inserts into the handle of the malleus, pulls handle medially,and tenses the tympanic membrane, reducing the amplitude of its oscillations and so prevents damage to the inner ear when exposed to loud sounds as vibrations of malleus are dampened.
Stapedius pulls the stapes posteriorly and tilts its base in the oval window, tightens the anular ligament and reduces the oscillatory range, prevents excessive movement of the stapes, again offering protection from loud noise.
why might facial nerve damage cause hyperacusis?
loss of innervation to stapedius responsible for dampening movements of stapes to offer protection from loud noise, so sound painful as uninhibited movement of stapes
components of inner ear?
Vestibule-Small bony chamber, containing the Utricle and Saccule, which are sensitive to rotational acceleration and the static pull of gravity
Semi-circular Ducts and canals- communicate with the vestibule and contain receptors that respond to Rotational Acceleration in three different planes
Cochlea-Shell shaped portion of the bony labyrinth containing the Cochlear Duct
Cochlear Duct- accommodates the spiral Organ of Corti
Organ of Corti-Contains the receptors of the auditory apparatus
Perilymph separate bony and membranous labyrinths
why is otitis media more common in young children?
Eustachian tube shorter and more horizontal,making it easier for organisms to travel up it and harder for fluid to drain away from the middle ear.
Also, IS less well devloped, so URTIs more common, which can involve middle ear from nasopharynx via Eustachian tube
what is otorrhoea?
Discharge from the ear, indicates acute or chronic infection, blood / CSF discharge associated with skull fracture
2 muscles which act to open eustachain tube?
tensor veli palatine and palate levator
what does thew chorda tympani course near in middle ear?
3 major symptoms of injury to peripheral auditory system?
hearing loss- usually conductive
vertigo- when injury involves semicircular ducts
tinnitus- when injury localised in cochlear duct
what does conductive hearing loss result from?
anything in external or middle ear that interferes with sound conduction or movement of oval or round windows. People often speak with soft voice as to them, their own voices sound louder than background noise.
hearing aid or surgery can improve hearing
what does sensorineural hearing loss result from?
defects in pathway from cochlea to brain: defects of cochlea, cochlear nerve, brainstem, or cortical connections.
cochlear implants can restore hearing
In a weber's test, sound is heard loudest in L ear. Then, using Rinne's test, the 1st sound heard is loudest? What would be the problem?
Sensori-neural hearing loss of right ear
what is a cholesteatoma?
-ve middle ear pressure due to obstruction of Eustachian tube creates retraction pockets where dead skin cells accumulate, forming a necrotic mass of dead skin, and then erosion of middle ear structures and bone via lytic enzymes.