2- Anatomy and physiology of the middle ear, function and physical examination of the Eustachian tube

What are the borders of middle ear

• external and middle separated by tympanic membrane

• middle and inner ear are separated by oval window

What are the parts of the middle ear

• Eustachian tube

• tympanic cavity

• ossicles- malleus, incus, stapes

What is the function of the middle ear

• impedance matching of sound traveling in air to acoustic waves traveling in fluid

• dampen very loud sounds via stapedius reflex- acoustic reflext

Describe how the middle ear functions

• Stapedius muscle and tensor tympanis muscle of ossicles contract

• pulls stapes away from oval window + stiffens ossicular chain

• decreases transmission of vibrational energy in cochlea

• converted into electrical impulses

What is the eustachain tube

• connects middle ear to nasopharynx

• 35mm long

• normally closed and opens on swallowing due to movement of palate muscles

How does a cleft palate affect the eustachian tube

• movement is impaired

• develop accumulation of middle ear fluid → ottitis media with effusion- OME

What is the function of the eustachian tube

• Equalizes pressure differences between the tympanic cavity and the atmosphere

• Ventilate the tympanic cavity and mastoid air cells

• Drain any secretions, infection or debris from the middle ear space

What is the tympanic cavity

• air filled space located within the petrous portion of the temporal bone

• contains Ossicles- Malleus, Incus, Stapes

What are the parts of the tympanic cavity

• epitympanum

• mesotympanum

• hypotympanum

What is the epitympanum

• Above the level of tympanic membrane

• Contains most of the auditory ossicles

• Communicates with the mastoid antrum via the aditus of antrum + air cells of the mastoid process

• Separated by the middle cranial fossa superiorly by a thin bony layer; tegmen tympani

What is the mesotympanum

• At the level of the tympanic membrane

• Contains the round window, oval window, the stapes and the promontory

What is the hypotympanum

• Below the level of the tympanic membrane

• Contains tympanic cells that communicate with the mastoid air cells

• Border to the bulb of the jugular vein inferiorly

What are the walls of the typmanic cavity

• Roof- tegmental wall

• Lateral wall- membraous wall

• posterior wall- mastoid wall

• floor- jugular wall

• anterior wall- carotid wall

• medial wall- labyrinthine wall

what are the contents of the lateral wall of the tympanic cavity

Tympanic membrane, malleus, incus

what are the contents of the posterior wall of the tympanic cavity

• Chorda tympani nerve

• Pyramidal eminence for stapedius muscle

• Aditus to mastoid antrum

what are the contents of the floor of the tympanic cavity

• Tympanic branch of glossopharyngeal nerve (IX)

• Bulb of internal jugular vein

what are the contents of the anterior wall of the tympanic cavity

• Tympanic branch of internal carotid artery

• Tensor tympani muscle

• Opening of pharyngotympanic tube (Eustachian tube)

• Lesser petrosal nerve

• Chorda tympani nerve

what are the contents of the medial wall of the tympanic cavity

• Round window

• Oval window

• Cochlear promontory

• Prominence of lateral semicircular canal

• Prominence of facial canal

What are the ossicles

• Incudes the malleus, incus, stapes

• The malleus is connected to the tympanic membrane, and the stapes to the oval window

• They are put into motion by the vibration of the tympanic membrane

• Amplify soundwaves 22 times