Anatomy of the Ear Flashcards
3 divisions of the ear
External ear: from auricle to TM
Middle ear: from TM to stapes
Inner ear: encased in temporal bone
Contents of middle ear
Auditory ossicles (malleus, incus, stapes)
Stapedius and tensor tympani mm
Chorda tympani n. (Branch of facial)
Tympanic plexus of nn
Contents of inner ear
Vestibulocochlear organ including cochlea, vestibule, and semicircular canals
The ear has protective mechanisms from loud sounds. For example, the ______ muscle pulls the stapes posteriorly and tilts its base in the oval window, thereby tightening the ____ ligament and reducing oscillatory range. This also prevents excess movement of the stapes.
The _____ m. Pulls the malleus handle medially, tensing the TM and reducing the amplitude of its oscillations, which also protects from loud sounds
Stapedius; anular
Tensor tympani
Major structures of external ear
Helix Antihelix Tragus Antitragus Concha
Blood supply to external ear
Superiorly:
Anterior auricular arteries, which branch from superficial temporal a.
Inferiorly:
Posterior auricular a. which branches from the external carotid a. (Also gives off posterior anastomosing arcades)
Shape and length of external auditory meatus and its relation to otoscopic exam
2-3 cm in adults
Lateral third is slightly S shaped and cartilaginous
Medial two-thirds is bony so it cannot be manipulated
On otoscopic exam in adults, helix is pulled posterosuperiorly to reduce curvature of external acoustic meatus
Size of TM
1 cm in diameter
Describe orientation of TM
Concave toward external acoustic meatus with a shallow depression called the umbo
The central axis of the TM passes perpendicular through the umbo, running anterior and inferiorly as it runs laterally — thus it is oriented like a satellite dish positioned to receive signal from the ground in front of and to the side of the head
Superior to the lateral process of the malleus, the TM is thin, called the ____ ______ which lacks radial and circular fibers that are present in the remainder of the membrane — called the ____ _____
Pars flaccida
Pars tensa
The external surface of the TM is supplied by the ______ n. with some innervation by a small auricular branch of the ______ n., which may cause a ______ response when irritated
Auriculotemporal (branch of V3); vagus; cough
The internal surface of the TM is supplied by what n?
Glossopharyngeal n.
What are the 6 walls of the middle ear cavity?
Roof = tegmental wall Floor = jugular wall
Membranous lateral wall
Labyrinthine medial wall
Mastoid wall = posterior wall
Carotid wall = anterior wall
The tegmental wall (roof of middle ear) is formed from thin plate of bone called ____ ____ which separates the tympanic cavity from dura mater on floor of middle cranial fossa
Tegmen tympani
The jugular wall forms the floor of the middle ear, a layer of bone that separates the cavity from the superior bulb of the _______ v.
IJV
The membranous lateral wall of the middle ear cavity is formed by the peaked convexity of the TM. Superiorly it is formed by the lateral bony wall of the _____ ______. The handle of the malleus is attached to the TM, and its head extends into the above space.
Other structures associated with lateral wall are the _____ n. on the floor, which goes up to the tympanic plexus on the promontory and merges with it, continuing up as the _______ n. to the otic ganglion.
Also the _____ n. and the ______ canal, which are above the promontory, foot plate of stapes, and round window
Epitympanic recess
Tympanic n.; lesser superficial petrosal n.
Facial; lateral horizontal semicircular
The medial wall of the middle ear (labyrinthine wall) separates the tympanic cavity from the inner ear. It features the ______, which is formed by the initial part (basal turn) of the cochlea, as well as the oval and round windows
Promontory
The posterior wall (mastoid wall) of the middle ear cavity features an opening in the superior portion called the aditus to the mastoid antrum, connecting the tympanic cavity to the mastoid cells. This serves as a canal for the _____ n. to descend between the posterior wall and antrum, medial to the aditus.
This is also the location of the pyramidal process containing the tendon of the ______ m.
Also in this region is the ______, a branch of the facial nerve that supplies taste sensation to anterior 2/3 of tongue
Facial
Stapedius
Chorda tympani
The anterior (carotid) wall of the middle ear cavity separates it from the carotid canal. Superiorly it has the opening of the _______ and the canal for the _______ m.
Pharyngotympanic tube; tensor tympani
The ____ is the ossicle that attaches to the TM.
Its head lies in the epitympanic recess and articulates with the ______.
The neck lies against the ________
Malleus
Incus
Pars flaccida
The handle of the malleus is embedded in the TM, thus the malleus moves with the membrane. The handle serves as the insertion point for the tendon of what muscle?
Tensor tympani m
The _____ is located between the malleus and stapes, articulating with each. Its large body lies in the _____ ______ where it articulates with the malleus.
The inferior end of one of its limbs articulates with the stapes via the _____ process.
The other limb is connected by a ligament to the posterior wall of the tympanic cavity
Incus; epitympanic recess
Lenticular
The head of the stapes is directed laterally, as it articulates with the _____
The base (footplate) fits into the ____ ____ on the medial wall of the tympanic cavity
Incus
Oval window
Origin and insertion of tensor tympani m
Arises from superior surface of cartilaginous part of eustachian tube, greater wing of sphenoid, and petrous part of temporal bone
Inserts on handle of malleus
Action of tensor tympani m.
Pulls handle of malleus medially, tensing the TM and reducing amplitude of its oscillation
Innervation of tensor tympani m
Mandibular n. (V3)
Location and insertion of stapedius m
Located inside pyramidal eminence (hollow cone-shaped prominence on posterior wall of tympanic cavity)
Its tendon enters the tympanic cavity by emerging from a pinpoint foramen in the apex of the eminence and inserts on the neck of the stapes
Action of stapedius m.
Pulls stapes posteriorly and tilts its base in the oval window, thereby tightening the anular ligament and reducing the oscillatory range; also prevents excess movement of stapes
Innervation of stapedius m.
Facial n
The inner ear is innervated by the vestibulocochlear n., which enters via the internal acoustic meatus where it divides into the vestibular n. and cochlear n. What structures are supplied by the vestibular n.?
Vestibular n. enlarges to form vestibular ganglion, which then splits into superior and inferior parts to supply the utricle, saccule, and 3 semicircular ducts
The inner ear is innervated by the vestibulocochlear n., which enters via the internal acoustic meatus where it divides into the vestibular n. and cochlear n. What structures are supplied by the cochlear n.?
Supplies receptors of organ of corti (in scala media)
What artery (in general) supplies the inner ear?
Internal auditory a.
Blood supply to bony labyrinth of inner ear
Anterior tympanic branch of maxillary a.
Petrosal branch of middle meningeal a.
Stylomastoid branch of posterior auricular a.
Blood supply to membranous labyrinth of inner ear
Labyrinthine a., which is a branch of inferior cerebellar a.
[labyrinthine a. divides into 3 branches: a cochlear branch and 2 vestibular branches]
The first segment of the facial n. associated with the temporal bone surrounding the ear is the ______ segment which emerges from the meatal foramen to the internal auditory canal; it gives off the ______ n. before making its first turn.
After its first turn is the ______ segment which passes behind the ossicles.
It then makes another turn, at which point it is the _____ segment, which is what finally passes through the stylomastoid foramen
Labyrinthine; superficial petrosal n.
Tympanic
Mastoid
The bony labyrinth is the fluid filled space composed of a series of cavities contained within a dense ____ _____ of petrous temporal bone
Otic capsule
3 components/contents of bony labyrinth
Cochlea
Vestibule of bony labyrinth
Semicircular canals
The _____ is the hearing apparatus, found in the osseous labyrinth. It features the _______ window
Cochlea; round
The vestibule of the bony labyrinth contains the _____ and _____. The _____ window is on the lateral wall, occupied by the stapes.
The vestibule is continuous with the bony _____ anteriorly and the _______ posteriorly
Utricle; saccule; oval
Cochlea; semicircular canals
The semicircular canals include _______, ______, and _______.
They communicate with the ______ of the bony labyrinth; one end of each semicircular canal contains a bony ______
Anterior; posterior; lateral
Vestibule; ampulla
The membranous labyrinth contains a watery fluid called _______.
It is divided into 2 divisions: the _____ labyrinth and the _____ labyrinth
Endolymph
Vestibular; cochlear
The ____ ____ is a sensory area of the ampulla contained in each semicircular duct. It does this via sensors that record movement of ______ in the ampulla resulting frmo rotation of the head in the plane of the duct.
Crista ampullaris; endolymph
Hair cells of the crista ampullaris, like those of the maculae, stimulate primary sensory neurons, whose cell bodies are in the _____ _____
Vestibular ganglia
_____ = areas of specialized epithelium in the utricle and saccule
Maculae
The maculae of the ______ is in the floor of this structure, oriented parallel with the base of the cranium
The maculae of the ______ is vertically placed on the medial wall of this structure
Utricle
Saccule
Describe innervation of hair cells in the maculae of the utricle and saccule
Innervated by fibers of vestibular division of vestibulocochlear n.
Primary sensory neurons are in vestibular ganglia, which are in the internal acoustic meatus
The semicircular ducts open into the _____ through 5 openings, reflective of the way the surrounding semicircular canals open into the vestibule
Utricle
The utricle communicates with the saccule through the utriculosaccular duct, from which the ____ duct arises.
Endolymphatic
The ______ n. innervates the superior and horizontal semicircular canals, as well as the superior portion of the vestibule (utricle)
Superior vestibular n.
The _____is continuous with the cochlear duct through a uniting duct
Saccule
The _____ n. innervates the posterior semicircular canal as well as the posterior portion of the vestibule (saccule)
Inferior vestibular n.
Waves of hydraulic pressure created in ______ of the vestibule by vibrations of the base of the stapes ascend to the apex of the cochlea by way of the scala _______.
Pressure waves then pass through the helicotrema and descend back to the basal turn of the cochlea by the scala _______. Here, the pressure waves again become vibrations, this time of the secondary tympanic membrane in the _____ window, and energy is dissipated in the tympanic cavity.
Perilymph; vestibuli
Tympani; round
Primary receptor of auditory stimuli
Spiral organ of corti
The spiral organ of corti is situated on the basilar membrane in _____ _____. It is overlaid by a gelatinous _____ ______, which its hair cells are embedded in
Scala media; tectorial membrane
The top portions (aka closer to center of spiral) of organ of corti detect ______ frequency sounds
The base (aka nearer to oval window) detects ____ frequency sounds
Low
High
Trauma to the cartilaginous auricle may lead to what condition
Auricular hematoma
Describe auricular hematoma and potential complications
Localized collection of blood between perichondrium and auricular cartilage, causing distortion of contours of auricle
As the hematoma enlarges, it compromises blood supply to the cartilage. If untreated, fibrosis develops in overlying skin forming a deformed auricle (cauliflower ear)
How might a lesion of the facial n. affect perception of auditory stimuli?
Lesion of facial nerve may lead to paralysis of stapedius m., meaning that its movement will be uninhibited when vibratory stimuli occur
This leads to excessive acuteness of hearing — intolerance of noise
What changes occur with eustachian tube with age?
Increases in length and S-shape straightens out slightly, leading to a better angle for drainage
Tx options for chronic middle ear infection
Myringotomy — incision to release pus from middle ear abscess
May be followed by insertion of tympanostomy or pressure equilization tubes in the incision to enable drainage of effusion and ventilation of pressure
Why are myringotomy incisions made posteroinferiorly through the TM?
Because superior half of TM is more vascular than inferior half; this also avoids injury to chorda tympani and auditory ossicles
Cause of meniere syndrome
Excess endolymph production or blockage of endolymphatic duct
Symptoms and characteristic signs of meniere syndrome
Recurrent tinnitus Hearing loss Vertigo Pressure sensation in ear Distortion of sound Sensitivity to noise
Characteristic sign = ballooning of cochlear duct, utricle, and saccule caused by increase in endolymphatic volume
Nerve supply to external ear
Facial n. —> majority of helix
Vagus n. and glossopharyngeal n. —> concha
Auriculotmeporal n. (branch of CN V) —> anterosuperior helix
Lymphatic drainage from external ear occurs anteriorly to ______ nodes, posteriorly to _____ nodes, and inferiorly to _____ nodes
Interparotid; posterior auricular; deep digastric
[teachmeanatomy says lymphatic drainage from outer ear is to preauricular, posterior auricular, and superficial temporal nodes…]
Sensory innervation to lateral (outer) surface of TM vs. medial (inner) surface of TM
Outer surface innervated by CN V3, VII, and X
Inner surface innervated by CN IX
Embryologic origin of epitympanic structures vs. mesotympanic structures
Epitympanic structures arise from first branchial arch (malleus, incus)
Mesotympanic structures arise from second branchial arch (stapes)
