The ear Flashcards
the ear is divided into what 3 parts
- external
- middle
- inner
what are the functions of the ear
-hearing
-balancing/ equilibrium
what does the external ear comprise of
-auricle
-external acoustic meatus
what does the auricle do
collect sound
what does the external acoustic meatus do
conduct sound to the tympanic membrane
what is the auricle made of
elastic cartilage ( and covered by skin)
what depressions does the auricle have
-concha
-helix
-antihelix
-tragus
-antitragus
-lobule
what is the lobule of the auricle made of
fibrous tissue, fat and blood. It has no cartilage
what is the function of the outer ear
-collects sound
-localization
-resonator
-protection
-sensitive
what is the arterial supply of the auricle
-posterior auricular artery
-superficial temporal artery
whats the nerve supply of the auricle
- on the lateral surface is the great auricular nerve
-on the skin superior to the external acoustic meatus is the auriculotemporal nerve, which is a branch of the mandibular division of the trigeminal nerve
what is the lymphatic drainage of the auricle
-superficial parotid lymph nodes
-mastoid lymph nodes
-superficial cervical lymph nodes
what is the structure of the external acoustic meatus
-outer 1/3 is cartilaginous and covered by skin
-the inner 2/3 is bony and covered by thin skin which is continuous with the external layer of the tympanic membrane
-it has ceruminous and sebaceous glands in outer half which produce cerumen (ear wax)
-has a tortuous downward and forwards course
whats the nerve supply of the external acoustic meatus
-auriculotemporal branch from the trigeminal nerve
-the auricular branch from the vagus nerve
what does the tympanic membrane do
-separates the external ear and middle ear
- vibrates against malleus in the middle ear
how does the tympanic membrane appear through the otoscope
-has concavity towards the external acoustic meatus
-has a shallow cone like depression at the center called the umbo
-has a cone of light which radiates anteroinferiorly from the umbo
what are the subdivision of the tympanic membrane
-pars flaccida
-pars tensa
what are the surfaces of the tympanic membrane like
lateral surface- is concave
medial surface- is convex (at umbo)
between the fibrous and mucous layer of the tympanic membrane what is there
-handle of malleus
-chorda tympanic nerve (which crosses medially)
what are the layers of the tympanic membrane
- outer cuticular layer- composed of keratinized hairless and devoid of dermal papillae ( a thin layer of skin)
- intermediate fibrous layer- composed of outer radiating and inner circular fibers of type I & II collagen
- inner mucous layer- composed of simple columnar/squamous cells
whats the nerve supply of the tympanic membrane
-the auriculotemporal branch of the mandibular division of the trigeminal nerve which supplies the anterior half of the lateral surface
-the auricular branch(Arnolds nerve) of the vagus nerve which supplies the posterior half of the lateral surface
-the tympanic branch (Jacobson’s nerve) of the glossopharyngeal nerve which supplies the medial surface
whats the nerve supply of the tympanic membrane
-the auriculotemporal branch of the mandibular division of the trigeminal nerve which supplies the anterior half of the lateral surface
-the auricular branch(Arnolds nerve) of the vagus nerve which supplies the posterior half of the lateral surface
-the tympanic branch (Jacobson’s nerve) of the glossopharyngeal nerve which supplies the medial surface
what muscles inhibit vibration when sound is too loud
-tensor tympanic muscle which inserts on malleus (dampens vibrations of the tympanic membrane)
-stapedius muscles which inserts on stapes (dampens vibrations of the stapes)
where does the middle ear lie
in the petrous part of the temporal bone
what does the middle ear consist of
-tympanic cavity and mucous membrane
-epitympanic recess
the middle ear is connected to what
nasopharynx by the eustachian tube
mastoid air cells by the mastoid antrum
pneumatization from the nasopharynx/ retrograde infection from pharynx can cause what
-otitis media
-mastoiditis
the middle ear gets its sensory innervation from what
glossopharyngeal nerve
what auditory ossicles does the middle ear contain
malleus incus ad stapes which are joined by the synovial joints
what can affect the synovial joints of the auditory ossicles
-ankylosis
-otosclerosis
what muscles are found in the middle ear what innervates them and what do they do
stapedius muscle ( VII) and tensor tympani (V3), which dampen sounds and protect inner ear
what nerves does the middle ear contain
-the chorda tympani a branch of CN VII
-the tympanic plexus of nerves
what are the walls of the middle ear and what are their components
roof/ tegmental wall - has the tegmen tympani which is a thin plate of bone that separates the tympanic cavity from the dura in the floor of the middle cranial fossa
floor/ jugular wall - has a layer of bone that separates the cavity from the superior bulb of the internal jugular vein
lateral/ membranous wall- has the tympanic membrane with epitympanic recess superiorly
medial wall/ labyrinthine wall - separates the tympanic cavity from the inner ear
anterior wall /carotid -separates the tympanic cavity from the carotid canal and superiorly lies above opening of eustachian tube and canal of tensor tympani
posterior wall -is connected by aditus to mastoid antrum and air cells
what is the mastoid antrum
a cavity in the mastoid process of the temporal bone
what does the aditus (opening to the mastoid antrum) do
connect the mastoid antrum to the epitympanic recess
what does the tegmen tympani do
separates the mastoid antrum from the middle cranial fossa
what does the floor of the mastoid antrum do
communicate with the mastoid air cells via several openings
what lines the mastoid antrum and air cells
mucosa
what is the mastoid antrum related to anteroinferiorly
facial nerve canal
what does the auditory tube do
connect tympanic cavity to nasopharynx and equalizes the air pressure between the middle ear and atmosphere
what is the structure of the auditory tube
the posterior third is bony and the rest is cartilaginous
what is the mucosa of the auditory tube continuous with
the tympanic cavity and nasopharynx
what is the nerve supply of the auditory the
tympanic plexus
what can open the auditory tube
contraction of the levator veli palati ,tensor veli palati, tensor tympani and salpingopharyngeus through swallowing, yawning and chewing
what are the auditory ossicles attached to
malleus- tympanic membrane
incus- connects malleus to stapes
stapes- oval window
what covers the auditory ossicles
mucous membrane lining the tympanic cavity
what is the function of the auditory ossicles
to transmit vibrations from the tympanic membrane to the oval window
what are the functions of the ligaments of the middle ear
-restrict and confine the effect of ossicles to act as a lever
-restrict movements to reduce the chance of damage to the inner ear
-prevent distortion to sound
what is the acoustic reflex
its when the stapedius and tensor tympani muscle contract in response to loud sounds, therefore reducing the transmission of sound to the inner ear
what makes up the inner ear
-cochlea
-vestibule
-semicircular canals
what is the cochlea for
hearing
what is the vestibule for
static equilibrium
what is the semicircular canal for
dynamic equilibrium
where does the internal ear lie
petrous part of temporal bone
what does the internal ear contain
the vestibulocochlea organ
what is the function of the internal ear
sound reception and balancing
what does the internal ear consist of
-bony labyrinth
-membranous labyrinth ( has sacs and ducts that contain endolymph)
what separates the bony labyrinth and the membranous labyrinth
perilymph
what is the bony labyrinth
its a fluid filled space surrounded by the otic capsule which is a dense bone
the bony labyrinth is composed of what
-bony cochlea
-bony vestibule
-bony semi-circular canals
what is the bony cochlea
its a shell shaped bony labyrinth that contains the cochlea duct
where does the spiral canal of the cochlea begin
at the vestibule and then winds around the modiolus (a bony core)
what does the modiolus contain
the cochlea nerve and blood vessels
what does the bony labyrinth communicate with
- subarachnoid space- through the cochlear aqueduct
- middle ear- through the round window closed by the secondary tympanic membrane
what is the bony vestibule
a small oval chamber that contains components of the balance system
what components of the balance system does the bony vestibule contain
-utricle
-saccule
what is the bony vestibule continuous with
- bony cochlea anteriorly
- bony semi circular canal posteriorly
- posterior cranial fossa through the aqueduct of vestibule
what is the course of the aqueduct of vestibule
it extends to the posterior surface of the petrous part of the temporal bone to open in the internal acoustic meatus
what does the aqueduct of vestibule contain
the endolymphatic ducts and blood vessels
what are the 3 canals of the bony semi-circular canal
- anterior
- posterior
- lateral
how do the 3 canals of the bony semi circular canals lie
perpendicular to each other
what do the 3 canals of the bony semi circular canals communicate with
the bony vestibule posterosuperiorly
at the end of each bony semi circular canal is what
the ampulla
what do the 3 canals of the semi circular canal contain
semi circular ducts
what does the membranous labyrinth consist of
ducts and sacs that communicate with each other other in the bony labyrinth
what does the membranous labyrinth contain
endolymph
what are the 2 divisions of the membranous labyrinth
- the membranous cochlear labyrinth
- the membranous vestibular labyrinth
what are the 3 components of the membranous vestibule labyrinth
- utricle and saccule (otolith organs)
- 3 semi-circular ducts ( superior, horizontal and posterior)
- the endolymphatic duct
the utricle and saccule communicate through what
utriculosaccular duct
what arises from the utriculosaccular duct
endolymphatic duct
what does the saccule communicate with
cochlea through the ductus reuniens
the utricle and saccule contain receptors where and for what
they have receptors in the macula which respond to linear acceleration and static pull of gravity
where do the 3 semi-circular ducts open into
the utricle through 5 openings
the semi-circular ducts contain receptors for what and where
they have hair cell receptors in the ampullary crest that respond to rotational acceleration in 3 different planes
the semi-circular ducts stimulate what
sensory neurons whose cell bodies are in the vestibular ganglion
what controls equilibrium
the vestibular apparatus i.e. the saccule and utricle of the vestibule and the 3 semi circular canals
what is static equilibrium
a state of balance relative to the force of gravity
what is dynamic equilibrium
its the maintenance of balance during sudden movements
what controls static equilibrium
sensory hair cells within the macula of the utricle and saccule
in static equilibrium what happens when head position is changed
the otolith membrane that has dense calcium carbonate crystals (otoliths) will respond to gravity. this movement will open transduction channels in the hair cells, producing local potentials which summate to form a nerve AP
what is in the ampulla of the semicircular canals
the crista ampullaris which contains hair cells and supporting cells
what covers the crista ampullaris
a gelatinous mass called the cupula
the neurological connection between eyes and semi circular canals is for what
tracking
what is the course of the endolymphatic duct
it transverses the vestibular aqueduct and emerges in the posterior cranial fossa
where does the endolymphatic duct open into
the endolymphatic sac that is under the dura mater
the endolymphatic duct is a reservoir for what
endolymph formed by blood capillaries
.the membranous cochlear labyrinth is composed of what 3 chambers
- the cochlear duct/ scala media
- scala vestibuli
- scala tympani
what does the cochlear duct contain
endolymph
where does the scala vestibuli begin
oval window
where does scala tympani end
round window
what does scala vestibuli and scala tympani contain
perilymph
where does the scala vestibuli and scala tympani meet
helicotrema
where is the cochlear duct suspended between
the spiral ligament on the external wall of the cochlear canal and the osseous spiral lamina of the modiolus
what are the boundaries of the cochlear duct
roof- formed by the vestibular membrane
floor- formed by the basilar membrane + outer edge of osseus spiral lamina
in the cochlear labyrinth whats the receptor of auditory stimuli
the spiral organ of corti
what covers the spiral organ of corti
gelatinous tectorial membrane
what does the spiral organ of corti contain
hair cells (tips of which are embedded in the tectorial membrane) and their supporting cells
movement of hair cells in contact with the tectorial membrane do what
they transduce mechanical vibrations into electrical signals which generate nerve impulses along the cochlear branch of CN VIII
cell bodies of sensory neurons are located where
in the spiral ganglia
whats the pathway for nerve impulses from the inner ear
the nerves follow the CN VIII en route to the medulla, pons, midbrain and thalamus then to the primary auditory cortex in the temporal lobe
what do slight differences in the timing of nerve impulses arriving from the the 2 ears at the superior olivary nuclei in the pons do
it allows us to locate the source of a sound
what do outer hair cells of the organ of corti do
they amplify mechanical input to the the inner hair cells
what do inner hair cells in the organ of corti do
they send information to the brain
what is a summary of how we hear
-sound waves are channeled into the ear canal by the pinna
-the sound waves hit the tympanic membrane and cause it to vibrate
-this changes the sound waves into mechanical energy
-the malleus which is attached to the tympanic membrane starts the ossicles into motion
-the stapes then moves in and out of the oval window of the cochlea and creates a fluid motion/ hydraulic energy
-the fluid movement causes membranes in the organ of corti to shear against the hair cells, which creates an electrical signal that is sent up the cochlear nerve to the brain and the brain interprets it as sound
otoscopic examination is for what
the external acoustic meatus
the external acoustic meatus can be examined for what conditions
otitis externa- which is inflammation of the auricle and external acoustic meatus
perforation of the tympanic membrane- due to otitis media
otitis media- which is when a bulging red tympanic membrane indicates pus in middle ear + blockage of the auditory tube
mastoiditis- which is an infection of the mastoid antrum
earache- which is a symptom of the otitis externa of media
what are middle ear disorders
acute otitis media
otosclerosis
disarticulation
mastoiditis
tympanosclerosis
OME
TM perforation
TM retraction
cholesteatoma
middle ear disorders can be found in people with what
-down syndrome
-treacher collins syndrome
-BOR syndrome
