ANATOMY AND PHYSIOLOGY OF THE MIDDLE EAR Flashcards
What are the three regions of the middle ear?
Epitympanum (above the tympanic membrane), Mesotympanum (middle), Hypotympanum (below).
What type of epithelium lines the tympanic cavity?
Respiratory ciliated epithelium containing goblet cells.
Why can upper respiratory tract infections (URTI) affect the middle ear?
The mucosa of the middle ear is continuous with the mucosa of the eustachian tube, nasopharynx, and oropharynx.
What is the most common causative agent of otitis media, sinusitis, and URTI?
Streptococcus pneumoniae.
What is the main function of the middle ear?
Impedance matching and sound pressure transformation.
How do sound waves transform as they travel through the ear?
Sound waves > Vibrations > Pressure > Electrical signals.
What is the function of the eustachian tube?
Equalizes static differences in air pressure between the middle ear and the external auditory canal.
What are the two muscles in the middle ear, and what is their main function?
Tensor tympani and stapedius; both dampen sound vibrations to protect the inner ear.
What is the innervation of the stapedius muscle?
Facial nerve (CN VII).
What is the innervation of the tensor tympani muscle?
Mandibular division of the trigeminal nerve (CN V3).
What is Prussak’s space, and why is it clinically significant?
It is a compartment around the malleus and incus where cholesteatomas can form in chronic otitis media.
What is the roof of the tympanic cavity called, and what does it separate?
Tegmen tympani; it separates the brain from the middle ear.
What is the clinical significance of the tegmen tympani in chronic otitis media?
It can lead to complications like meningitis if the infection spreads to the brain.
What are the ossicles of the middle ear?
Malleus, Incus, and Stapes.
What is the central connection of the malleus to the tympanic membrane?
The umbo, located at the tip of the malleus handle.
What is the significance of the stapes’ footplate?
It covers the oval window and transmits vibrations to the inner ear.
What is the blood supply to the malleus and incus?
Anterior tympanic artery, with branches to the malleal and incudal arteries.
Why is the long process of the incus prone to aseptic necrosis?
It is supplied by a single nutrient vessel, making it susceptible to damage during infections.
How is the stapes supplied with blood?
Inferior tympanic artery, superior tympanic artery, and their collateral branches.
What are the main borders of the mesotympanum?
Anterior: Eustachian tube; Posterior: Facial nerve; Medial: Promontory; Inferior: Stapes and round window.
What is the hypotympanum, and what does it contain?
The region below the tympanic cavity that contains tympanic cells communicating with mastoid air cells and borders the internal jugular vein bulb.
What are the six walls of the tympanic cavity?
Anterior: Tubal opening and carotid wall; Inferior: Internal jugular vein; Posterior: Mastoid antrum; Superior: Tegmen tympani; Medial: Oval and round windows, Promontory; Lateral: Tympanic membrane.
What is the eustachian tube’s structure in children versus adults?
Children: 17-18 mm, 10 degrees from horizontal; Adults: 35-37 mm, 45 degrees from horizontal.
Why is otitis media more common in children?
The eustachian tube in children is shorter, more horizontal, and allows easier spread of nasal infections to the middle ear.
What are the two muscles associated with the eustachian tube, and what are their functions?
Tensor veli palatini (opens the tube during swallowing/yawning) and levator veli palatini (closes the tube by elevating the soft palate).
Why does the eustachian tube open during yawning or chewing?
The tensor veli palatini muscle retracts to enlarge the tubal lumen.
What is the shape of the eustachian tube when open?
An inverted ‘J’ shape.
What is the significance of the promontory in the tympanic cavity?
It overlies the basal turn of the cochlea and marks the medial wall of the middle ear.
How does the middle ear protect itself from loud noises?
Tensor tympani and stapedius muscles dampen vibrations to reduce pressure on the inner ear.
What causes cholesteatomas in the middle ear?
Keratinous material accumulation, often associated with chronic otitis media, that can erode bone.
What is the difference in composition between the eustachian tube and external auditory canal?
Eustachian tube: 1/3 bony, 2/3 cartilaginous; External auditory canal: 1/3 cartilaginous, 2/3 bony.
What complication can arise from a poorly functioning eustachian tube?
Middle ear infections, ear pain, and decreased hearing due to improper pressure equalization.
