Anatomy and Embryo: Ear Flashcards
auricle
collects airwaves and funnels them into external acoustic meatus
- made of elastic cartilages, lobules and depressions
blood supply to auricle?
post auricular a/v
superficial temporal a/v
innervation to auricle?
- Great auricular and lesser occipital nn (C2,3)
- auriculotemporal n (V3), facial n, vagus n.
- lymph drains to mastoid, parotid lymph nodes and to deep cervical lymph nodes
external acoustic meatus
canal traveling through tympanic portion of temporal bone to tympanic membrane
- lined by stratified squamous
- lateral 1/3 cartilaginous, medial 2/3 bony
blood supply to external acoustic meatus
post. auricular a/v
superficial temporal a/v
innervation to external acoustic meatus
auriculotemporal n (V3)
Vagus n.
all lymph drains to deep cervical nodes
otitis externa
inflammation of external ear
tympanic membrane
- converts sound waves into vibrations of middle ear ossicles.
- fibroelastic membrane, connected to malleus.
- covered externally by epidermis and internally by mucus membrane
- membrane is anterior and inferior
blood supply to tymp. membrane?
external surface: deep auricular branch of maxillary a.
internal surface: anterior tymp. branch of maxillary a.
innervation to tymp membrane?
external surface: auriculotemporal n (V3), vagus n.
internal surface: glossopharyngeal n. (endodermally derived)
how does auricle develop?
derived from cartilage of 1st/2nd pharyngeal arches
* defects often associated with most chromosomal syndromes *
how does external aud. meatus develop?
first pharyngeal cleft
- meatul plug forms, if does not degenerate by 7th month, will cause deafness and congenital hearing loss
tympanic membrane development?
external ectoderm= ectoderm of first pharyngeal cleft
middle CT= mesoderm of first pharyngeal arch
internal epithelium = endoderm of first pharyngeal arch
fn of middle ear
- contains tympanic cavity, a mucous lined space w/in petrous portion of temporal bone and auditory ossicles.
- fn = transfer of sound waves from gas to liquid medium (from external to internal ear).
- amplifies sound waves in the process via bony ossicles
- protective response to loud sounds (tensor tympani, stapedius mm.)
what forms boundaries of tympanic cavity?
roof: tegmen tympani (seperates epitympanic recess from middle cranial fossa)
floor: temporal bone (seperates from IJV)
lateral wall: tymp membrane
medial wall: promontory, oval window, round window
post wall: temporal bone
ant wall: temporal bone
what are portions of medial wall?
- promontory: mound of bone created by cochlea
- oval window(fenestrae vestibule): opens to vestibule of inner ear: contacted by stapes; transmits motion of stapes to fluid of internal ear.
- round window (fenestra cochlea): opens to scala tympani; covered with thin membrane: acts as a pressure release valve for fluids of internal ear
what does posterior wall contain?
- seperates middle ear from mastoid air cells
- aditus ad antrum = entrance to mastoid antrum
- facial canal = passage of facial n.
mastoiditis
- infections of nasopharynx can spread to auditory tube, then into middle ear.
- middle ear infections, can sometimes spread to mastoid air cells
- from mastoid air cells the infections can spread superior into the middle cranial fossa
what is contained in anterior wall
- receives opening from pharyngotympanic tube and semi-canal
- tensor tympani passes through here (works to dampen vibrations)
pharyngotympanic tube
“auditory tube”
- located in anterior wall
- mucous membrane connects middle ear and nasopharynx
- fn: balances pressure on external and internal sides of tympanic membrane
** tensor veli palatine: mm. attaches to membranous portion of auditory tube and can open the membranous tube via CN V3 (allowing for equalization of inner ear)
what are the auditory ossicles?
- malleus (contacts TM)
- incus (middle)
- stapes (contacts oval window)- vibration moves fluid within cochlear duct
- work on an amplification system, all are united by synovial joints
*** osteosclerosis = synovial joints become thick = conductive hearing loss
stapedius
= mm. of the inner ear O: post wall of tymp. cavity I: stapes fn: dampens mvmts of ossicles (contracts reflexively in response to loud noises) n: facial n - SVE
tensor tympani
O: cartilagenous part of pharyngotymp. tube
I: malleus
fn: dampens mvmt of ossicles (contracts when chewing and speaking)
n: trigeminal n (V3) SVE
paralysis of middle ear mm?
can cause hyperacusis = excessive hearing acuteness = due to loss of dampening mm.
blood supply to Tm?
- inferior tymp (ascending pharyngeal)
- ant tymp (maxillary)
- post tymp (stylomastoid)
- superior tymp (middle meningeal a.)
how does CN IX provide the ear?
glossopharyngeal n.
-supplies GVA and GVE-P to middle ear
- tympanic branch (GVA, GVE-P) enters middle ear via tympanic canaliculus; forms tympanic plexus.
- tympanic plexus provides GVA sensory and GVE-P innervation for middle ear.
- lesser petrosal n. reforms from tymp. plexus and exits midle ear via hiatus for lesser petrosal n (GVE-P)–> PS to parotid gland
how does CN VII supply ear?
supplies motor innervation to stapedius (SVE)
- enters internal acoustic meatus, courses along roof of inner ear toward middle ear
- within middle ear CN VII travels within facial canal on posterior wall
- chorda tympani is given off right before CN VII exitsmiddle ear at stylomastoid m=foramen, corda tympani passes b/w incus and malleus and exits the middle ear via petrotympanic fissure
** corda tympani: provides SVA to ant 2/3 of tongue and GVE-P to submandibular and sublingual glands
otitis media?
inflamation of middle ear; often due to spread of infection from pharynx via pharyngotympanic tube
what are three branches of facial n. in middle ear?
- greater petrosal n (GVE-P to pterygopalatine ganglion)
- n. to stapedius
- corda tympani (SVA and GVE-P to glands)
how is middle ear derived? TQ
tympanic cavity and auditory tube = first pharyngeal pouch
malleus, incus, tensor tympani: first pharyngeal arch
stapes, stapedius = second pharyngeal arch
** congenital fixation of stapes can cause deafness due to problem with 2nd arch **
membranous labyrinth
this is where sound is processed
- membranous ducts contained within bony labyrinth that are filled with endolymph
(bony labyrinth filled w/ perilymph)
- cochlear duct: processes sounds : hair cells are housed in spiral organ
Vestibulocochlear n
CN VIII
- exits brainstem at pontomedullary jn.
- passes through internal acoustic meatus to enter inner ear
- vestibular portion innervates semicircular ducts, utricle, saccule, carrying proprioceptive info
- cochlear portion innervates coochlear duct and carries info about sound
how is inner ear derived?
membranous labyrinth: develops from otic placode (ectoderm)
bony labyrinth (vestibule, semicircular canals, cochlea), from surrounding mesenchyme of otic placode
