1. Anatomy and physiology of the middle ear
Lecture 4
Anatomy and physiology of the ME

2. Anatomy and physiology of the ME

3. Illustration
Anatomy and physiology of the ME

4. Anatomy and physiology of the middle ear
Adult ME is almost oval, air filled space of roughly 2 cm3
The roof of the middle ear is a thin layer of bone, separating the middle ear cavity from the brain
Upper portion - epitympanic recess or epitympanum or attic
Communicates with mastoid antrum (cavity)
Anatomy and physiology of the ME

5. Anatomy and physiology of the ME
Below the floor of the ME is the jugular bulb
Narrowest at umbo
Behind the anterior wall is the carotid artery
The labyrinth of the inner ear lies behind the medial wall
The mastoid process beyond the posterior wall
The lateral portion of the ME is sometimes called the membranous wall because it contains the TM
Anatomy and physiology of the ME

6. ME
the middle ear is connected to the nasopharynx, area where the back of the throat and nose communicate via the Eustachian tube
The Eustachian tube (ET) and the middle ear form the middle ear cleft (space made of the up from the ME and ET
The entire middle ear cleft together with the TM is lined with mucous membrane
Anatomy and physiology of the ME

7. The mastoid Bone that surround the ear
It is honeycombed with hundreds of air cells
Each cell is lined with mucous membrane
These cells form the pneumatic mastoid of the temporal bone
ME opens up, back, and outward in an area called aditus ad antrum to communicate with the mastoid\the protuberance behind the auricle is called the mastoid process
Anatomy and physiology of the ME

8. Windows of the ME
Promontory: a section of the bony portion of the inner ear that extends to the ME, caused by the basal turn on the cochlea
Oval window: above the promontory, filled by a membrane that supports the base of the stapes
Round window: below the promontory, covered by a very thin, but tough elastic membrane
Anatomy and physiology of the ME

9. ME
The middle ear contains three tiny bones known as the ossicles: malleus, incus, and stapes. The ossicles were given their Latin names for their distinctive shapes; they are also referred to as the hammer مطرقة, anvil سندان , and stirrupركاب , respectively.
Anatomy and physiology of the ME

10. Middle ear ossicles
The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body.
They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea).
The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss.
The term "ossicle" literally means "tiny bone" and, though the term may refer to any small bone throughout the body, it typically refers to the malleus, the incus and the stapes of the middle ear.
Anatomy and physiology of the ME

11. Anatomy and physiology of the ME

12. Middle ear ossicles Malleus Manubrium, neck, head
Short anterior and lateral processes near top of manubrium
Firmly attached to TM (along manubrium, lateral process)
The head of the malleus is connected to the incus
This area of connection extends upward to the aditus ad antrum
Anatomy and physiology of the ME

13. Middle ear ossicles Incus Body, long and short processes
Long process (parallel to manubrium) bends into lenticular process
The end of the lenticular process sits squarely on the head of the stapes
Anatomy and physiology of the ME

14. Middle ear ossicles Stapes Head, neck, twocrurae, footplate
Incudo-stapedial joint
Attached to oval window – annular ligament
The posterior crus is longer and thinner than the anterior crus to aid in rocking motion
The base, footplate occupies the space in the oval window
The stapes is the smallest and lightest named bone in the human body
Anatomy and physiology of the ME

15. Middle ear ossicles The malleus and the incus are rigidly connected
Inward and outward movement of the umbo of the TM cause these bones to rotate, and transfer this force to the stapes, which result in the inward and outward motion of the oval window
Ligament connection hold each ossicle in place that their collective function in not altered by gravity, when the head changes position
Anatomy and physiology of the ME

16. Middle ear ossicles
The ossicular chain is 2 to 6 mm in length, and acts as a single unit when transmitting the sounds above 800 Hz
The action of these ossicles provide energy transformation
Anatomy and physiology of the ME

17. The Eustachian tube Also called auditory tube
The ET is lined with __________ membrane
Much of this membrane is ciliated, the top most cells contain cilia.
The movement of the cilia helps cleanse the ME by moving particles down and out of the ET
The ET enters the ME at 30° angle and passes through the nasopharynx
The tube Is kept closed due to the spring mechanism of the cartilage (adults)
Anatomy and physiology of the ME

18. The Eustachian tube
 In adult humans the Eustachian tube is approximately 35 mm (1.4 in) long
Anatomy and physiology of the ME

19. The Eustachian tube
A portion of the tube (1/3) proximal to the middle ear is made of bone; this bony part is about 12 mm in length.
 The cartilage of pharyngotympanic tube, about 24 mm in length.
Normally closed
Opens by reflex action of tensor veli palatini
Swallowing, yawning, sneezing
Innervated by trigeminal (N V)
Thought to work with action of tensor tympani
Anatomy and physiology of the ME

20. The Eustachian tube
Orifice (opening) of the ET into the nasopharynx tends to remain open until the age of 6 months
The ET in infants is shorter, wider in relation to its length and in more horizontal plane than is in adults
Anatomy and physiology of the ME

21. Functions of the ET
To equalise the pressure on both sides of the TM to minimise its mobility
Some people experience fullness when changing elevation (flying)
During ascension this fullness results when the air in the EAC becomes rarified (thin), while the ME remains at ground level pressure, the sensation of fullness occurs when the TM is pushed outward from greater pressure from within the ME
Anatomy and physiology of the ME

22. The Eustachian tube
While decent the pressure in the middle ear maybe less than the external ear so that the TM is pushed in
The solution is to yawn, swallow or open the ET to equalise the pressure
At extreme pressure changes the ET will lock shut, making pressure equalising impossible and great pain, it is likely for the TM to rupture
Anatomy and physiology of the ME