External and middle ear Flashcards
what does the external ear consist of?
- auricle (pinna)
- external auditory meatus
why is the auricle shaped the way it is?
to collect air vibrations
what kind of cartilage is the external ear?
elastic cartilage
what muscles are in the external ear and what are they innervated by?
- extrinsic and intrinsic muscles
- facial nerve
what is the external auditory meatus?
-curved tube that leads from the auricle to the tympanic membrane
what does the external auditory meatus do?
-conduct sound waves from auricle to the tympanic membrane
what is the outer third of the external auditory meatus made of?
-elastic cartilage
what is the inner 2/3 of the external auditory meatus made of?
bone
what is the external auditory meatus lined by?
skin
the outer 1/3 of the external auditory meatus contain?
- hairs
- sebaceous glands
- ceruminous glands
- ear wax
what nerves supply the sensory innervation for lining of the external auditory meatus?
- auriculotemporal nerve
- auricular branch of the vagas nerve (mucosa)
where does the lymph drain for the external ear?
- superficial parotid
- mastoid
- superficial cervical
what color and shape is the tympanic membrane?
- pearly grey
- concave
umbo
-depression in the center of the tympanic membrane
what is the middle ear?
- tympanic cavity
- air filled cavity in the petrous portion of the temporal bone
what is the middle ear lined with and what does it contain?
- lined with mucous membrane
- contains auditory ossicles
how does the middle ear communicate with the nasopharynx in front?
-auditory tube
how does the middle ear communicate with the nasopharynx behind?
-mastoid atrium
what makes up the roof of the tympanic cavity? and what does it separate the middle ear from?
- tegman tympani (part of petrous temporal bone)
- separates the cavity from the temporal lobe and meninges
what makes up the floor of the tympanic cavity and what does it separate the cavity from?
- thin plate of bone
- separates the cavity from superior bulb of internal jugular vein
what makes up the anterior wall of the tympanic cavity and what are the two openings?
- thin plate of bone
- opening for the auditory tube
- opening for the tube of tensor tympani
what is the posterior wall of the tympanic cavity and its openings?
- opening called aditus to the mastoid atrium
- small conical projection called pyramid
why can infection spread quickly in the tympanic cavity?
- small space
- lost of important openings for infection to travel
- auditory tube can let in microbes from nasppharynx
- can spread viral or bacterial infection
- infection can erode bone into middle cranial fossa
promotory
- rounded projection caused by underlying cochlea
- on lateral wall of the inner ear (medial wall of tympanic cavity)
fenestra vestibuli
- above and behind promontory
- oval window
- on lateral wall of inner ear (medial wall of tympanic cavity)
fenestra cochleae
- below and behind promontory
- round window
- on lateral wall of the inner ear (medial wall of the tympanic cavity)
what forms the lateral wall of the tympanic cavity?
- tympanic membrane
- obliquely placed
- concave laterally
what are the three auditory ossicles?
- malleus
- incus
- stapes
malleus
- largest ossicle
- handle attaches to the medial surface fo the tympanic membrane
how do the ossicles articulate with eachother?
- malleus articulates with the incus
- incus articulates with stapes
what does the base of the stapes fit into?
-the fenestra vestibuli (oval window) on middle ear
what are the muscles associated with the ossicles?
- tensor tympani
- stapedius
origin and insertion of tensor tympani
origin: wall of the auditory tube and its oen canal
insertion: handle of the malleus
innervation of tensor tympani
-branch of V3
action of the tensor tympani
-dampen vibrations of the tympanic membrane
what is the smallest muscles in the whole body?
-stapedius
origin and insertion of stapedius
origin: pyramid on the posterior wall of the middle ear
insertion: neck of the stapes
innervation of stapedius
-branch of the facial nerve
action of the stapedius
-dampen the vibrations of the stapes
what does the auditory tube connect?
the anterior wall of the tympanic cavity to the nasopharynx
what part of the auditory tube is cartilage and what part is bony?
- posterior 1/3 is bony
- anterior 2/3 is cartilage
what does the auditory tube pass over?
-the upper border of the superior constrictor
function of the auditory tube
- equalize pressure in the middle ear with the atmospheric pressure
- usually closed, but will open to equalize pressure
where is the mastoid atrium?
-behind the middle ear in the petrous portion of the temporal bone
how does the mastoid atrium communicate with the middle ear?
aditus
what does the mastoid atrium communicate with inferiorly?
-mastoid air cells (small sinuses lined with mucosa)
what does the facial nerve enter when it reaches the bottom of the internal auditory meatus?
the facial canal
when the facial nerve reaches the medial wall of the middle ear, it expands to form…
-geniculate ganglion
what is the bend in the facial nerve called?
-genu
what foramen does the facial nerve emerge through?
-stylomastoid foramen
what muscle does the facial nerve give a branch to behind the pyramid?
-stapedius muscle
where does the chorda tympani originate>
-from facial nerve, above the stylomastoid foramen
where does the chorda tympani enter the middle ear and what does is cross?
- enters close to the border of the tympanic membrane
- crosses the handle of the malleus
what does the chorda tympani exit the middle ear through and what does it then enter?
- exits through petrotympanic fissure
- enters infratemporal fossa to join lingual nerve
what kind of fibers does the chorda tympani contain?
- taste fibers (from anterior 2/3 of tongue)
- preganglionic parasympathetic fibers headed toward the submandibular ganglion
where does the tympanic nerve originate?
-terminal branch of glossopharyngeal nerve just below the jugular foramen
what does the tympanic nerve branch to form?
-the tympanic plexus on the promontory
what does the tympanic plexus supply?
-mucosa of the middle ear
what kind of fibers does the lesser petrosal nerve contain?
-preganglionic parasympathetic fibers going to the otic ganglion
what branch does the tympanic plexus give off?
-lesser petrosal nerve
how does the lesser petrosal nerve exit the middle ear?
-through canaliculus in the roof
what foramen does the lesser petrosal nerve exit the skull through?
foramen ovale
what ganglion does the lesser petrosal nerve join?
otic ganglion
