Clinical Anatomy of the Ear Flashcards
what are the 3 anatomical divisions of the ear?
external ear
middle ear
inner ear
what are the 2 functional divisions of the ear?
hearing (auditory system)
balance (vestibular system)
all divisions of the ear are found in what bone?
temporal
what is contained within the temporal bone?
organs of hearing and balance (special sensory)
facial (CN VII) and vestibulocochlear (CN VIII) nerves
what is the pterion?
H shaped suture between frontal, parietal, temporal and sphenoid bone
thinnest part of skull
what is the stylomastoid foramen?
foramen between the styloid process and mastoid process of temporal bone
allows passage of facial nerve from the facial canal
what cranial nerves exit the cranial cavity in each cranial fossa?
anterior = CN 1 middle = CN 2-6 posterior = CN 7-12
internal acoustic meatus is found in which cranial fossa?
posterior
what 3 structures pass through the internal acoustic meatus?
CN VII (facial) CN VIII (vastibulocohlear) labyrinth artery + vein
what does the facial nerve do?
motor to face motor to stapedius taste to anterior 2/3rds of the tongue secretomotor to salivary glands and lacrimal gland general sensation to external ear
what does CN VIII do?
balance
hearing
what is the labyrinth artery + vein?
branch of anterior inferior cerebellar artery from circle of willis
what does the external ear do?
auricle to tympanic membrane via external acoustic meatus
collects and conveys sound waves to tympanic membrane
what does the middle ear do?
tympanic membrane to oval window and eustachian tube
amplifies and conducts sound waves to the internal ear
what does the internal ear do?
oval window to internal acoustic meatus
converts special sensory information into fluid waves, then APs
then conducts APs to the brain
what is the eustachian tube?
AKA auditory tube
canal that connects the middle ear to the nasopharynx, which consists of the upper throat and the back of the nasal cavity. It controls the pressure within the middle ear, making it equal with the air pressure outside the body
describe the skeleton of the external ear?
composed of temporal bone and elastic cartilage
avascular
nutrients from the skin
describe the features of the ear canal
begins at the external acoustic meatus
composed of 1/3rd cartilage, 2/3rds bone
lined with skin
produces earwax via ceruminous glands
what are the areas of the auricle?
helix anti-helix concha tragus anti-tragus ear lobe
describe sensory innervation of the external surface of the tympanic membrane
CN X (vagus) CN V3 (mostly)
what nerves supply the external acoustic meatus (auricle?)
CN V3 = upper anterior ear
CN VII and vagus = middle of ear
spinal nerve C2,3 = rest of ear
describe lymphatic drainage of the auricle
lateral surface of superior half = parotid lymph nodes
cranial surface of superior half = mastoid nodes and deep cervical
rest of auricle = superficial cervical nodes
all eventually drain to deep cervical lymph nodes in carotid sheath
then thoracic duct or right lymphatic duct at venous angles
what does otoscopic examination consist of?
examination of external acoustic meatus and tympanic membrane
begins by straightening the EAM
adult = pull ear posterosuperiorly
child = pull ear posteroinferiorly
what nerves supply the tympanic membrane?
external = mostly CN V3 (bit of vagus) internal = CN IX
glossopharyngeal nerve provides sensory innervation to what structures?
middle ear cavity eustachian tube nasopharynx oropharynx tonsils
middle ear contains which bones, muscles and nerves?
bones - malleus - incus - stapes muscles - stapedius - tensor tympani nerves (branches from): - facial - glossopharyngeal
where are the ossicles found?
tympanic cavity
how do the auditory ossicles articulate?
via synovial joints
what are the 3 auditory ossicles?
malleus
incus
stapes
where is the tympanic recess found?
superior to the tympanic membrane (ear drum) in the tympanic cavity
what muscles are found in the tympanic cavity?
tensor tympani muscle stapedius muscle (reduces stapes movement to protect internal ear from excessive noise)
what is the eustachian tube?
AKA auditory tube or pharyngotympanic tube
connects anterior wall of the middle ear cavity to the nasopharynx
what is the significance of the eustachian tube?
infection can spread through the tube (e.g from pharynx/tonsils to the ear) causing pain and hearing loss
common sensory nerve supply (CN IX) so tonsillitis or pharyngitis can mimic earache (referred pain)
sensory supply to laryngopharynx?
CN X
what type of innervation does the facial nerve supply?
special sensory
sensory
motor
parasympathetic
where does the facial nerve connect to the CNS?
brainstem at pontomedullary junction
where does the facial nerve travel within the brain?
directly into internal acoustic meatus in the posterior cranial fossa
where does the facial nerve enter the skull from the ear?
internal acoustic meatus through the stylomastoid in the temporal bone
what are the 2 branches of the facial nerve in the middle ear cavity?
chorda tympani - supplies anterior 2/3rds of tongue and submandibular and sublingual glands
facial nerve - enters middle ear in internal acoustic meatus, travels through petrous temporal bone in facial canal which connects to the stylomastoid foramen, where the facial nerve enters the skull
what are the 4 muscles of facial expression?
frontalis
orbicularis oculi
elevators of lips
orbicularis oris
how can the muscles of facial expression be tested?
ask patient to:
- frown (orbicularis)
- close eyes tightly (orbicularis oculi)
- smile (elevators of lips)
- maintain puffed out cheeks (orbicularis oris)
what is the buccal fat pad?
pad of fat in the cheeks
lost in illness, age and malnutrition
where is the inner ear found and what forms it’s boundaries?
contained within petrous part of temporal bone
extends from oval window to internal acoustic meatus
what nerve supplies the inner ear and what are it’s branches?
CN VIII
- cochlear branch (hearing)
- vestibular branch (balance)
what is the otic capsule?
dense area of bone within the temporal bone (in area of middle ear)
what is contained within the otic capsule?
contains bony labyrinth of spaces which is filled with perilymph fluid
what is contained within the perilymph in the otic capsule?
membranous labyrinth
communicating sacs and ducts
contains endolymph suspended within
what bony labyrinths exist inside the otic capsule?
cochlea (spiral consisting of 2.5 turns)
semi-circular canals (X3)
what is the cochlear duct?
long balloon like structure within the cochlea filled with endolymph
- APs conducted to the brainstem here via the cochlear nerve
what are the semi-circular ducts?
inter-linked balloon-like structures within the semi-circular canals filled with endolymph
- APs conduced to the brainstem here via the vestibular nerve
what are maculae?
regions where clusters of hair cells are found
hair cells are stimulated by movement of endolymph and detect angular movement change
what are the utricle and saccule and what do they do?
regions of the semi-circular ducts (vestibular apparatus)
utricle = detects horizontal movement
saccule = detects vertical movement
what are the 7 steps in sound transmission?
- sound waves make tympanic membrane vibrate
- vibrations transmitted through ossicles
- base of stapes vibrates in oval window
- vibration of stapes creates pressure waves in perilymph
- hair cells in the cochlea are moved, APs stimulated and conveyed to brain via cochlear nerve
- pressure waves descend and become vibrations again
- pressure waves are dampened at the round window
what is the organ of corti and where is it found?
sensory organ of the ear containing receptor cells which detect auditory stimuli
found on the basilar membrane of the cochlear duct
what are the 2 windows of the cochlear duct?
oval window
round window
what is the cochlear duct and where is it found?
divides the cochlear canal into 2 parts
- scala vestibuli
- scala tympani
suspended by the spiral ligament
describe the path of the vestibulocochlear nerve
vestibular nerve axons come from the semi-circular ducts (including utricle and saccule)
cochlear nerve axons come from the cochlear
both axons travel together through the internal acoustic meatus and connect with the brainstem at the pontomedullary junction
