Ear Flashcards
Auricle
. Primarily formed the auricular cartilage
. Lobule is lower part of auricle
. Non-cartilaginous and contains fatty eraolar tissue
External auditory meatus (EAM)
. Canal extending from external opening to tympanic membrane
. Cartilage forms walls of lat. 1/3rd
. Bone forms walls of med. 2/3rd
. Skin w/ hair, sebaceous glands and modified sweat glands that produce cerumen (ear wax) line the cartilaginous portion of EAM
General sensory innervation to auricle and EAM
. Auriculotemporal n. To ant. Sup. Portion of auricle, EAM, and external surface of tympanic membrane
. Vagus n. To area around meatus, inf. Portion of EAM and the external surface of tympanic membrane
. Facial n. To area around meatus
. Lesser occipital n. (C2/3) to post. Sup. Auricle
. Great auricular n. (C2-3) to post. Inf. And lat. surface of auricle
Tympanic cavity
. Located w/in petrous temporal bone
.houses auditory ossicles
. Lined w/ mucosa that is continuous w/ pharyngotympanic tube, mastoid air cells, and mastoid antrum
Tympanic cavity boundaries
. Roof: tegmen tympani formed by petrous portion of temporal bone
. Floor: thin layer bone. Internal jugular v. Arises opposite
. Lat. wall: opening from EAM closed by tympanic membrane
. Med. wall: formed by bony labyrinth of inner ear, facial canal
. Ant. Wall: opening to pharyngotympanic tube
. Post. Wall: aditus, facial canal
Tympanic cavity ant. Wall features
. Opening to pharyngotympanic tube
. Post. Lat. 1/3 of tube is bony, remainder is cartilaginous
. Tensor tympani m.: sup. Portion of only tube directly beneath the tegmen tympani, attaches to handle of malleus
. Opening of cartilaginous portion of tube in inf. Portion of bony tube
. Pharyngotympanic tube connects middle ear to nasopharynx
. Normally tube is closed but opens to allow passage and mucus into/out of tympanic cavity
Posterior wall features
. Aditus: sup. Opening leading to post. Open area (mastoid antrum) that leads to mastoid air cells w/in mastoid process
. Prominence of facial canal: vertical portion of this canal courses w/in post. Wall and contains descending portion of facial n.
. Pyramidal eminence: small, bony projection that encloses stapedius m.
Mastoiditis
. Infection of mastoid air cells
. Difficult to treat and have potential to spread intracranial
. Primary treatment is IV antibiotics followed by oral antibiotics
. Can require surgical drainage
lateral wall features
. Tympanic membrane set in temporal bone at inner part of EAM, external surface concave
. Handle of malleus attaches to internal surface of membrane and appears as projection of membrane in external view
. Umbo: peak of depressed central area inf. To handle of malleus
Cochlear promontory
. Rounded prominence on med. wall of cavity formed by outward projection of cochlea
Tympanic plexus
. Branch of CN IX that courses over promontory
. After CN IX exits jugular foramen, the tympanic n. Splits off and enters tympanic cavity via tympanic canaliculus
. Tympanic n. Composed of general sensory fibers and preganglionic parasympathetic fibers branches and combines w/ postganglionic sympathetic fibers from internal carotid a. Plexus to form tympanic plexus
Post. To promontory on the med. wall of tympanic cavity are__-
. Oval window: more sup. Opening, connects to vestibule of inner ear, footplate of stapes covers oral window , oval window membrane transmits vibrations from stapes to perilymph of vestibule
. Round window: more inf. Opening, connects to cochlea, round window membrane dissipates change in cochlear pressure
. Prominence of facial canal: houses the facial n. As it courses post. W/in med. wall of tympanic cavity, bone covering the nerve may be absent in this area, exposing the facial n. To mucosa of tympanic cavity
Auditory ossicles
. Malleus, incus, and stapes
. Ossicles connect to one another by synovial joints and span tympanic cavity btw tympanic membrane and the oval window
Malleus
. Head, neck, and handle
. Head lies in epitympanic recess and articulates w/ incus
. Neck lies against tympanic membrane and handle is embedded in tympanic membrane
. Tendon of tensor tympani m. Inserts into handle
. Chorda tympani n. Crosses btw neck of malleus and long crus of incus
Incus
. Body, long crus, and short crus
. Body articulates w/ head of malleus in epitympanic recess
. Long crus articulates w/ head of stapes
. Short crus attaches via ligament to post. Wall of tympanic cavity
Stapes
. Head, neck, and 2 limbs that attach to footplate
. Head of stapes articulates w/ long crus of incus
. Footplate fits into oval window
Tensor tympani m.
. Courses from bony pharyngotympanic tube
. Attaches to handle of malleus
. Contraction pulls the tympanic membrane med., tensing it, and dampening effect of sound waves
. Innervated by n. To tensor tympani (CN V3)
Stapedius OIAN
. O pyramidal eminence
. I: tendon to neck of stape
. A: pulls footplate away from oval window and dampens sound energy
N: motor from CN VII
Hyperacusis
. Caused by axial n. Paralysis
. Moderate to extreme sensitivity to loud noises due to loss of stapedius function
Course of facial n. Through temporal bone
. Enters internal acoustic meatus and bends post. At geniculum of facial n. Where geniculate ganglion is
. Courses post. W/in med. wall of tympanic cavity got short distance then descends w/in pot. Wall of tympanic cavity
. Gives off 4 branches in facial canal
. Facial n. Proper exits facial canal at sylomastoid foramen
Branches of facial n. Branches off in facial canal
. Greater petrosal n.: branch at geniculate ganglion but don’t synapse, then exit tegmen tympani and course along floor of cranial cavity
. N. To stapedius
. Chorda tympani: courses ant. Btw malleus and incus and exits middle ear cavity via petrotympanic fissure
. Auricular branches
Bony labyrinth of of inner ear
. Cochlea, vestibule, and semicircular canals housing membraneous labyrinth
. Cochlea coils 2.5 times, round window opens into it
. Vestibule lies btw cochlea and semicircular canals and is in communication w/ both, oval window in wall of this
. 3 semicircular canals (ant., post., lat.) are set and right angles to each other
. Lat. canals of opposite sides are horizontal in orientation
. Ant. Canal of 1 side lies in same plane as post. Canal of opposite side
. Perilymph btw wall of bony labyrinth and outer wall of membranous labyrinth
Membranous labyrinth
. Inside bony labyrinth
. Cochlear duct, utricle and saccule, and 3 semicircular ducts w/ ampullae
. Semicircular ducts open into utricle
. Utricle and saccule communicate via utricosaccular duct
. Saccular continous w/ cochlear duct
. Parts of labyrinth lie btw 2 perilymph-filled chambers
. Contains endolymph that produces fluid waves in response to fluid waves produced in perilymph
Components to hearing
. Mechanical translation of sound waves into sonar waves
. Translation of sonar waves into sensorineural impulses
How vibrations get to membrane of oval window?
. Sound waves pass through EAM to vibrate tympanic membrane
. Vibrations pass from tympanic membrane to malleus, incus, and the stapes
. Footplate of stapes vibrates on oval window membrane
How do vibrations go from oval window membrane to round window membrane
. Vibrations from oval window create sonar waves in perilymph of vestibule
. Sonar waves pass along one perilymph-filled channel to ascend to the apex of the cochlea
. Vibrations then descend via other channel and are dissipated back to tympanic cavity at membrane of round window
How do sonar waves go from perilymph to sound
. Perilymph-filled chambers produce sonar waves in endolymph of cochlear duct
. Stimulate hair cells of cochlear division of CN VIII
. Hair cells generate nerve impulses that are sent to the brain and are perceived as sound
. Different regions of cochlear duct perceive different pitches
Conductive hearing loss
. Damage to or loss of any structure that assists in creating movement at oval or round windows or disrupts sound transmission in outer or middle ear
. May be temporary issue
. Congenital conductive hearing loss may be due to absence or malformation of external or middle ear structures, surgical correction may be possible or hearing may be improved by amplification w/ conventional or bone conduction hearing aid
Sensorineural hearing loss
. Lesion or damage to any portion of nervous system that is involved w/ conduction and interpretation of n. Impulses from vestibulocochlear n.
. Loss of components w/in cochlea causes sensorineural deafness that is frequency-specific (can’t heat specific pitches)
. Loss of hair cells will result in almost complete instability to detect specific frequencies regardless of how loud they are
. Can only be corrected w/ cochlear implant
Translational motion
. Linear acceleration and tilting of head in x, y, or z direction
. Maculae: specialized areas of sensory epithelium located w/in utricle and saccule, consists of hair cell receptors and assoc. supporting cells
. Gelatinous membrane overlies haircell bundles w/ otolithic membrane embedded in otoconia above it
. Otoconia make otolithic membrane heavier than surrounding fluids so when head tilts gravity causes the membrane to shift relative to maculae that stimulates hair cell receptors
Rotational acceleration
. Rotation about thee axes (roll, pitch, yaw)
. Ampullae: dilations at one end of each semicircular duct
. W/in ampullae are hair cell receptors embedded w/ gelatinous substrate
. Angular acceleration of endolymph in semicircular ducts distorts the gelatinous mass which stimulates hair cell receptors
. Semicircular canals 90 degree angles to one another in all 3 directions
. Canals of both ears act in concert to coordinate equilibrium
Benign paroxysmal positional vertigo
.common cause of vertigo in people over 50
. Patients experience mild to intense dizziness following specific head positioning changes
. Otoconia becomes dislodged and settle in semicircular canals resulting in sensitivty to specific positional changes
. Epilepsy maneuver helps
