Ear Flashcards
Describe middle ear
Tympanic cavity
Small hour-glass shaped cavity embedded in petrous temporal bone
Has ossicles
Describe the internal/inner ear
Series of interconnected fluid-filled (endolymph) ducts, tubes, sacs (membranous labyrinth) suspended within fluid-filled (perilymph) bony canals and cavities (osseous labyrinth)
Match air transmission, bone conduction, and fluid conduction to the parts of the ear
Air transmission: external auditory meatus
Bone conduction: ossicles of middle ear
Fluid conduction: inner ear
Describe the parts of the auricle/pinna
Helix: outer free margin
Lobule
Tragus and antitragus: protect external auditory meatus
Concha: central depression
What innervates the pinna?
GSA sensory fibers from auriculotemporal (V3), lesser occipital (C2-3), great auricular (C2-3)
What innervates the skin of the concha?
VII, IX, X
What is the blood supply to the auricle?
Superficial temporal and posterior auricular arteries
Describe auricular hematoma
Trauma to pinna may cause hemorrhaging in subcutaneous tissue
If hematoma is not evacuated and bandaged, subsequent scar tissue may grossly deform the auricle (cauliflower ear)
What does the skin lining the outer 1/3 of the external auditory meatus contain? Clinical relevance?
Sebaceous and seruminous glands, which secrete cerumen (ear wax)
Accumulation of cerumen may be firmly adherent to epithelia of EAM and/or tympanic membrane
Causal removal of a mass of ear wax may avulse the tympanic membrane and ossicle
When infected, the furuncle is very painful due to close adhereance of skin to underlying periosteum
What innervates the outer epidermis or skin of the tympanic membrane?
GSA fibers from trigeminal and vagus nerves
Describe the pars tensa
Middle fibrous layer of the most of the tympanic membrane
Attached to fibrocartilaginous ring which rests in tympanic sulcus and manubrium of malleus
Describe the pars flaccida
Part in the antero-superior quadrant of the tympanic membrane that does not have the fibrous layer
What innervates the inner mucous membrane of the tympanic membrane?
GVA fibers of glossopharyngeal nerve via tympanic plexus
What is the central concavity of the tympanic membrane?
Umbo
What do the borders of the pars flaccida form? What courses through them?
Anterior and posterior mallear folds
Chora tympani n
What middle ear structures are in the superio-posterior area of the tympanic membrane?
Long process of incus
Stapes
Fenestra vestibuli
What middle ear structures are in the superio-anterior area of the tympanic membrane?
Auditory tube
What middle ear structures are in the inferio-posterior area of the tympanic membrane?
Fenestra cochleae
What middle ear structures are in the inferio-anterior area of the tympanic membrane?
Carotid canal
Describe otitis media
Inflammation of middle ear cavity that is relatively common in infants and children
May result in accumulation of fluid & mucous and decrease in hearing
More common in infants because auditory tubes are oriented horizontally which impedes drainage from tympanic cavity
Tubes are downward in adults
Describe fractures of the petrous temporal bone
Severe head trauma may cause basilar skull fractures such as transverse or longitudinal fractures of temporal bone
Otorrhea, otorrhagia, vestibular disturbances, deafness, or Bell’s palsy may result
Often associated with brain trauma and considerable mortality/morbidity
What structures are near the medial wall of the middle ear cavity?
Semicanal for facial nerve Fenestra vestibuli Stapes Stapedius Pyramid Prominence Tympanic plexus Tensor tympani Fenestra chocleae Auditory tube
What structures are near the lateral wall of the middle ear cavity?
Epitympanic recess Malleus Incus Tympani membrane Chorda tympani Auditory tube Tensor tympani m Facial n
Describe the course of the facial nerve in the ear
Facial nerve is NOT in middle ear
After leaving brainstem, facial nerve travels laterally in internal auditory meatus before entering facial canal
Within the canal, geniculate ganglion is located just above and medial to promontory of middle ear cavity
At the level of the ganglion, the nerve turns sharply and posteriorly as it forms external genu
After about 1.0 cm, the nerve courses downward, sends a branch to stapedius muscle, and exits stylomastoid foramen
Where is the cochlea in relation to the facial nerve?
Cochlea is anterior
What does the external ear include?
Auricle (pinna)
External auditory meatus
What forms the roof of the tympanic cavity?
Tegmen tympani
What forms the floor of the tympanic cavity?
Superior bulb of the internal jugular vein
Describe the articulations of the malleus and relationship to chorda tympani n
Manubrium of malleus is attached to fibrous layer of tympanic membrane
The head articulates with incus in epitympanic space
Chorda tympani n crosses the neck of the malleus
Describe the articulations of the incus
Incus is wedged between malleus and stapes
Body articulates with malleus at incudo-mallear joint
Its long crus articulates with head of stapes
Describe the articulations of the stapes
Head articulates with long crus of incus
Anterior and posterior crura connect head to footplate
Footplate articulates with fenestra vestibuli
Describe otosclerosis
Ossification or scarring of small ossicular joints that prevents transmission of sound from tympanic membrane to fenestra vestibuli
May result in significant hearing impairment
Typically, tests for bone conduction are normal, but nerve conduction is reduced
Describe location of tensor tympani muscle
Located in semicanal above auditory tube, from which it arises
Its tendon loops laterally around processus cochleariformis and inserts on handle of malleus
What innervates tensor tympani muscle?
Branch of mandibular nerve (V)
What is the function of the tensor tympani muslce?
Tightens tympanic membrane and attenuates its vibrations
Describe location of stapedius muscle
Located in pyramid on posterior wall of middle ear cavity
Its tendon exits a minute opening at apex of pyramid and inserts on neck of stapes
What innervates the stapedius muscle?
Facial nerve
What is the action of the stapedius muscle?
Pulls stapes out of fenestra vestibuli
This is a protective mechanism to prevent excessive movement of stapes due to loud sound
What is the blood supply to the middle ear cavity?
Stylomastoid branch of posterior auricular artery
Anterior tympanic artery
What are the functions of the inner ear?
Cochlear receptors for hearing
Receptors in semicircular ducts: detect angular acceleration
Receptors in sacculus and utricle: detect linear acceleration
What does the cochlear division of VIII nerve innervate?
Organ of Corti (spiral organ)
Conveys auditory information
What does the vestibular division of VIII nerve innervate?
Maculae utricle, saccule, and cristae ampullaris of semicircular ducts
Conveys static and dynamic position-sense information for equilibrium
What is the blood supply to the inner ear? Clinical relevance?
Labyrinthine artery, which a branch of the anterior inferior cerebellar artery
Arteriosclerosis of this artery may result in vertigo, nausea, and other inner ear abnormalities
What does the cochlear (VIIIc) nerve pass through?
Bony core of cochlea called modiolus
