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Anat & Phys W3.1
Middle Ear Structure
| Question | Answer |
|---|---|
| Where is the ME space (cavity)? | An air filled space within the temporal bone. |
| What is another name for the ME space (cavity) ? | Tympanum |
| What are the dimensions of the ME space? | ~2-4mm on horizontal plane ~13mm on vertical plane ~2 cubic centimeters volume |
| What are the two main portions of the tympanum? | Attic (top portion) and Proper space |
| What is the superior wall (ceiling) of the ME called? Describe it. | Tegmen tympani Roof of the ME space and the floor of the brain area. Continues posteriorly to the roof of the tympanic atrium. Indirect communication between the ME cavity and the mastoid air cells (sometimes the air pockets can get infected). |
| What is the inferior wall (floor) of the ME called? Describe it. | Tympanic plate (of the temporal bone). Jugular fossa/jugular bulge on the floor of the ME space due to the jugular vein beneath. |
| Describe the anterior wall of the ME space. | - Thin plate of the bone with 2 perforations (1 - eustachian tube exits from the anterior wall into the nasopharyngeal cavity; 2 - Oriface for the tensor tympani muscle) - Carotid bulge, which is sometimes called the "carotid wall" |
| What are the two muscles in the ME? | Tensor tympani and Stapedius |
| What is the posterior wall of the ME space called? Describe it. | A.k.a. - mastoid wall; Formed by the temporal bone; CN VII travels from the medial wall and courses down the posterior wall. |
| What are the major features of the medial wall? | Promontory forms the innermost wall formed by the basal turn of the cochlea. Oval window and round window are here. |
| Describe the lateral wall of the ME space. | Tympanic membrane. Lateral portion of attic is formed by section of squamous portion of the temporal bone. |
| What is the inward displacement of the TM? What are the dimensions of the TM? | Inward displacement of 2mm at the umbo (Concave). ~8-9mm in diameter along horizontal axis ~9-10mm in diameter along vertical axis ~.1mm thick Area is ~55mm squared |
| What are the layers of the TM? | 1) Outer layer - epidermal lining of EAM 2) Middle layer - fibrous (collagen) material (radial and circular fibers). Low density at pars flaccida and High density outside of pars flaccida. 3) Inner layer - Continuation of mucosal lining of ME cavity. |
| Pars flaccida | More opaque and prone to perforations. |
| Pars tensa | Clearer. Should be able to see the cone of light (indicative of a healthy TM and ME space (no fluid). |
| How is the TM at birth? Adulthood? | TM reaches full size in-utero and at birth the TM is very thin and compliant. At birth, TM is laying down at 140 degree angle at upper wall (pretty much on the ground) and adult TM is oriented about 40 degree angle at lower wall. |
| How long is the malleus? | 9mm |
| How long are the long and short processes of the incus? | 7mm for the long process and 5mm for the short process |
| Where does the stapes rest? | Base fits into tenestra vestibuli (oval window) |
| What attaches to the TM? | Manubrium of malleus attaches to the pars tensa. |
| What does the anterior ligament attach to? | Attaches to the anterior process/head and neck region of the malleus. |
| What does the posterior ligament attach to? | Connects to the short process of the incus. |
| What does the superior ligament attach to? | Descend from tegmen to superior surface of malleus/incus. Supports from above. |
| What does the annular ligament attach to? | Holds the stapes in place. Tighter fit in posterior area than in anterior area. |
| What is the primary purpose of the eustachian tube? | Equalize pressure b/w ME and outside environment. |
| How longh is the eustachian tube? Where does it lie in terms of cartilidge and boney portions? | ~36mm long. 1/3 boney portion and 2/3 cartilaginous |
| What are the two muscles within the eustachian tube? What nerves innervates them? | Tensor veli palatini (CN V - trigeminal) Levator palatini (CN X - vagus) |
| Torus tubaris | Bulge of tissue surrounding the oriface of the eustachian tube. One of the spots that can be infected and close off the ET when swollen. |
| What is the orienatation of the eustachian tube in a child? | Shorter and wider. Increased mass of lymphoid tissue. Fairly horizontal. Orienation makes it easier for pathogens to migrate from the nasophayrnx to migrate to the ME. |
| What is the orienatation of the eustachian tube in an adult? | Longer and narrower. Slopes downward at ~45 degree angle. |
| What are the types of Otitus Media? | 1) Acute OM 2) OM w/out effusion 3) OM w/ effusion (Serous) 4) Chronic OM |
| Cholesteatoma | Destructive and expanding growth of keratinizing squamous epithelum. |
| Atelectasic TM | Condition where the pressure difference in the ME space is so negative that the TM is essentially draped over the ossicles as if it was covering them with seran wrap. |
| Otosclerosis | Abnormal bone growth in ME. Typically fixating the stapes to the oval window. |
Created by:
duda713
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