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

Anatomy and physiology of the ME

Illustration Anatomy and physiology of the ME

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

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

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

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

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

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

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

Anatomy and physiology of the ME

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

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

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

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

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

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

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

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

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

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

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