10. Ear Anatomy and Histology (Fellow) Flashcards
What nerves innervate the tympanic membrane?
External surface: Auriculotemporal nerve and Auricular branch of the vagus.
Internal surface: Glossopharyngeal (CN IX)
What would be affected in an erosion through the medial wall of the middle ear?
The inner ear, the oval and round windows, the promontory of the labyrinthine wall, and the nerve plexus thereof (tympanic and lesser petrosal nerves).
Greater and lesser petrosal nerves carry what type of nerve fibers?
Parasympathetic (general visceral efferent) fibers.
What cranial nerve does the tympanic nerve come off of?
The glossopharyngeal (CN IX)
Which portion of the tympanic membrane is more vascular?
The superior portion.
What is a myringotomy, and where is it performed?
Myringotomy: lesion to open up the eardrum. Made in the posterior inferior quadrant to avoid vasculature.
The tympanic plexus primarily contains fibers from which cranial nerve?
Glossopharyngeal, via the tympanic branch.
What is the blood supply to the auricle of the ear?
Posterior auricular A and superficial temporal A.
What would be affected in an erosion through the posterior wall of the middle ear?
Mastoid antrum (containing mastoid air cells) and facial canal (containing facial nerve).
Where are the heads of the incus and malleus found?
In the epitympanic recess.
What would be affected in an erosion through the anterior wall of the middle ear?
Internal carotid artery, opening for the pharyngotympanic tube, and the canal for the tensor tympani.
What would be affected in an erosion through the lateral wall of the middle ear?
Tympanic membrane and external ear.
What are the respective functions of the greater and lesser petrosal nerves?
Greater petrosal: parasympathetics to the eye from facial N.
Lesser petrosal: parasympathetics to the parotid gland from glossopharyngeal N.
List the nerves that innervate the represented parts of the auricle of the ear.
TM Innervation:
(add to image: Auricular branch of Vagus and glossopharyngeal)
Superior: VII
Anterior: V
Posterior: X (arnold, cough) and C3
What would be affected in an erosion through the roof of the middle ear?
The tegmen tympani (bone) and the dura of the middle cranial fossa.
What is the bony labyrinth filled with?
What is the membranous labyrinth filled with?
Bony labyrinth: perilymph.
Membranous labyrinth: endolymph.
What nerve gives rise to the greater petrosal nerve?
Facial nerve.
What would be affected in an erosion through the floor of the middle ear?
Bulb of the internal jugular vein.
Which of these spaces contain endolymph, and which contain perilymph?
The scala vestibuli and the scala tympani are filled with perilymph. The cochlear duct is filled with endolymph.
What nerve gives rise to the lesser petrosal nerve?
The tympanic nerve - a branch of the glossopharyngeal nerve.
Note that “malleolus” is actually “malleus.” This slide has a typo.
Which is more anterior, the cochlea or the vestibular apparatus?
The cochlea.
Ear Anatomy
EAM:
PT:
distal 2/3 cartilage, proximal 1/3 bone
distal 2/3 bone, proximal 1/3 cartilage
Functions and Muscles of the Pharyngotympanic Tube
Functions: pops the ear
Levator Veli Palatini contracts longitudinally to PUSH against one wall
Tensor Veli Palatini PULLs on the other wall
Ossicle Anatomy
Malleus:
Incus:
Stapes:
head, neck, handle
body, short and long processes (short connected to posterior wall)
base vibrates on the oval window
Muscles of the Inner Ear
Tensor Tympani
Stapedius
on PT, greater wing of sphenoid, petrous part of temporal bone to handle of malleus
CN V
on pyramidal eminence on posterior wall of tympanic cavity to foramen on stapes
CN VII
BOTH limit volumn/dampen sound (reduce amplitude, prevent excessive movement)
Know What and Where Stria Vascualris is
Know the Organ of Corti
Understand depolarization and hyperpolarization of hair cells
otoliths bend hair cells
if they are bent toward the kinocillium then that is a depolarization (opens K channels)
if they are bent away from the kinocillium, that is a hyperpolarization (closes K channels)
Otoliths do this in the utricle and saccule, and gel does this in the semicircular canals
these can be targeted by certain drugs/abx and cause hearing issues
Composition, location, and origination of Perilymph
similar to CSF
drains via perilymphatic duct into SA space
from perisosteum, located between bony and membranous labyrinth (in the bony part)
Composition, location and origination of endolymph
high H, low Na
from stria vascularis
drains via endolymphatic duct into venous sinuses of dura
found in membranous labyrinth
Brief Notes on Ear Pathology
damaged TM (pressure, fluid or trauma, usually heal, may need antibiotics)
Mastoiditis (infected mastoic cells can spead into cranial fossa, tx ABX)
Otitis Media (fluid in middle ear, TM red and bulging, #1 reason for hospital visits)
Meniere’s Syndrome (vertigo and tinnitus, hearing loss, increased endolymph, tx with meds or surgery)
Viral Labyrinthitis (similar to Meniere’s but usually self limiting, resolved in 1wk)
