Anatomy and Histology of the Ear Flashcards
What is the external ear?
Auricle to tympanic membrane
What is the middle ear?
Tympanic membrane to oval window
What is the inner ear?
Oval window to internal acoustic meatus
What arteries supply the external ear?
Posterior auricular, superficial temporal, and anterior auricular arteries
What nerves supply the external ear?
VII, lesser occipital and greater auricular (from cervical plexus), auriculotemporal (from V), X, and IX
What do ceruminous glands do?
Make wax
What glands are found in the external auditory canal?
Ceruminous and sebaceous glands
Where is the only place in the body where skin, periosteum, and bone exist directly on top of each other with no connective tissue?
Inner 1/3 of external acoustic meatus (synonymous with external auditory canal)
What is the tympanic membrane made of?
Outside layer is stratified squamous and inside layer is simple cuboidal
What is the function of the tympanic membrane? What 2 parts make up the tympanic membrane?
Moves with sound and transmits to ossicles; has flaccid and tense part
Where is the middle ear located?
In petrous portion of temporal bone
What 2 parts make up the middle ear?
Tympanic cavity proper (mesotympanum) and epitympanic recess
What are the boundaries of the middle ear (roof, floor, lateral/medial/posterior/anterior walls)?
Roof: tegmental wall
Floor: jugular wall
Lateral: membranous wall
Medial: labyrinthine wall
Posterior: mastoid wall
Anterior: carotid wall
What prominences are found in the carotid (anterior) wall?
Lateral semicircular canal, facial nerve, labyrinth wall (promontory)
What does the pharyngotympanic tube do?
Connects tympanic cavity (middle ear) with the nasopharynx (back of the throat) and equalizes pressure in middle ear
Posterolateral part is bone but the rest is cartilage
Compare the external auditory meatus to the pharyngotympanic tube?
EAM: distal 2/3 is cartilage and proximal 1/3 is bone
Pharyngotympanic Tube: distal 2/3 is bone and proximal 1/3 is cartilage
What muscles act on the pharyngotympanic tube? What do they do?
Levator Veli Palatini: contracts longitudinally which pushes against one wall
Tensory Veli Palatine: pulls on the other wall
What are the 3 auditory ossicles? What do they do?
Malleus, incus, and stapes; bridge tympanic membrane with the oval window of cochlea
What are the parts of the malleus?
Head, neck, handle
What are the parts of the incus?
Body, short/long processes
What are the parts of the stapes?
Head, limbs, and base
What is the innervation and action of the tensor tympani muscle?
Innervation: V
Action: pulls on handle to tense membrane and reduce amplitude
What is the innervation and action of the stapedius muscle?
Innervation: VII
Action: pulls stapes posteriorly tightening annular ligament attaching it to the window
What is the bony labyrinth?
Cavity within the petrous region of the temporal bone; it is lined with endosteum and is separated from the membranous labyrinth by perilymph
What is the membranous labyrinth? What is it divided into?
Made of small sacs and tubes within the bony labyrinth; forms a continuous space enclosed with epithelium; divided into cochlear duct and the utricle, saccule, and semicircular canals; contain sensory cells (hair cells)
What is the cochlear canal?
Spiral space within bone containing the cochlear duct
What is the cochlear duct?
Divides canal into 3 parallel compartments; scala media, scala tympani, scala vestibuli
What is the scala media?
Middle compartment; contains endolymph; stria vascularis is the lateral wall of scala media and is the source of endolymph
What is the scala vestibuli?
Contains perilymph moved by stapes at oval window; continuous with scala tympani
What is the scala tympani?
Connected to round window
What is the organ of Corti?
On floor of scala media resting on basilar membrane; composed of hair cells, inner/outer phalangeal cells, and pillar cells
What is the outer spiral lamina?
Inner spiraling bony shelf serving as support for tectorial membrane and spiral ganglia
How many rows of outer and inner hair cells are there?
3 rows of outer hair cells and 1 row of inner hair cells
What is the function of the external ear?
Catches sound waves and directs them to the EAM, which continues to transmit sound waves to the tympanic membrane; also serves as a spot to check temperature
What is the function of the middle ear?
Takes sound waves from external ear and turns it into a physical movement; sound waves move tympanic membrane, moves the malleus, moves the incus, moves the stapes, which pushes on the oval window
What actually leads to changes in pressure in the middle ear?
Tympanic membrane can bulge out, tensor tympani can contract or relax, and fluids can go in and out
What is the function of the inner ear?
Responsible for balance; also responsible for taking external sound waves and transforming them into usable information for the brain
What is the path of sound waves in the inner ear?
Stapes moves oval window causing fluid pressure wave formation in perilymph; wave distorts vestibular membrane causing a pressure wave within endolymph of scala media; this displaces the basilar membrane and distorts stereocilia of hair cells; pressure in perilymph is then transferred to scala tympani and exits via round window
What is the function of the cupulla?
Serves as sensor of rotational velocity
Both the saccule and utricle of the vestibule contain a macula. What makes up a macula?
Comprised of cluster of hair cells with stereocilia and overlying gelatinous material called otolithic membrane
What is an otolithic membrane?
Covered with calcium carbonate/protein crystals called otoconia
What is the function of the utricle?
Linear acceleration and head tilts in horizontal plane
What is the function of the saccule?
Linear acceleration and head tilts in vertical plane
What is the target of ototoxicity effects by antibiotics?
Hair cells
Where is the perilymphatic space?
Between bony and membranous labyrinths
Where is the endolymphatic space?
Within membranous labyrinth
Where is the corticolymphatic space?
Within organ of corti
What is damage to the tympanic membrane usually caused by? What antibiotic should you avoid in treatment?
Medial ear pressure because of fluid or barotrauma or external trauma; gentamicin
What is mastoiditis?
Infection of mastoid cells; can spread into cranial fossa via petrosquamous cranial suture; treated with antibiotics
What is otitis media?
Ear ache with possible fluid or pus in middle ear due to inflammation or infection; tympanic membrane appears red and bulged; fluid may be visible through membrane; untreated can impair hearing and scarring of auditory ossicles
What is the #1 reason for hospital visits?
Otitis media
What is Meniere’s Syndrome?
Associated with increase endolymph volume leading to abnormal signaling; cause is unclear; mild cases treated with meds, severe cases require surgical ablation; experience dizziness, vertigo, high-pitched rushing or roaring sound and fluctuating hearing loss
Where can hearing loss occur?
All portions of the ear (external, middle, internal)