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Anat and Phys W5
Gross Anatomy of the Labyrinth
| Question | Answer |
|---|---|
| What is the bony labyrinth? | A complex cave in solid bone. The bone surrounding the immediate walls of the otic capsule is the hardest bone in the body. Fracturing the temporal bone does not guarantee the cochlea is broken. |
| What is the membranous labyrinth? | Delicate membranes lining the bony labyrinth. Closely related to neural tissue; soft tissue that lines the cavity. |
| What are the three parts of the bony labyrinth? Describe each. | 1) Vestibule - "Central Room" into which the other compartments open 2) Semicircular Canals - 3 canals (Anterior, Posterior, & Horizontal) 3)Cochlea - snail's shell |
| What are the openings to the vestibule? | 1) Oval window (at basal turn) 2) Round window (at basal turn) 3) Six ends of the three semicircular canals (Sup. and Post. canals have common crus and merge) 4) Cochlear duct 5) Cochlear canaliculus (houses perilymphatic duct) 6) Vestibular aquaduct |
| Where is the oval window located in relation to the round window? | Superior |
| What does the cochlear canaliculus contain? Talk about it. | Contains perilymph. It is connected via a narrow channel containing fibrous tissue to the spinal fluid compartment. It is one possible route by which an ear infection can cause meningitis. |
| What are the vestibular aqueducts? | Narrow, bony canals that travel from the inner ear to the endolymphatic duct. |
| What does a dysfunction of the endolymphatic duct do? Describe the disorder. | Implicated in cochlear hydrops. Cochlear hydrops results in pressure, roaring tinnitus, and low frequency HL that appears to be sensorineural. |
| Describe Enlarged Vestibular Aqueduct dysfunction. What happens with EVA in children. | Considered enlarged if bigger than 1.5mm in size and the duct and sac grow too large. Most children with EVA will develop some type of HL. 5-15% of kids with SNHL. SNHL tends to be progressive. Does not seem EVA causes HL, but provides clues to HL. |
| What is the current belief for the purpose of the endolymphatic sac and duct? | To ensure ion balance in the inner ear. |
| What syndrome can be a symptom of EVA? Describe it. | Pendred syndrome. Can cause childhood HL. Progressive SNHL, affects thyroid, may have balance issues, liver, and kidney problems. |
| What is the most well-known cause of EVA and HL. | Mutations to SLC26A4 (PDS gene) on chromosome 7. |
| How can you diagnose EVA? | MRI or CT scan. |
| What is the treatment for EVA? | No known proven treatment associated to treat or slow progression. No evidence for steroids for sudden SNHL related to EVA. Surgery and/or draining liquid out of endolymphatic sac or duct is ineffective and destroys residual hearing. |
| Describe the cochlear aqueduct. | Allows for transfer of cerebral spinal fluid. Narrow, bony canal that surrounds the perilymphatic duct. Runs a downward oblique course between the cochlea and the subarachnoid space. |
| Describe the perilymphatic aqueduct. | Surrounded by cochlear aqueduct. The perilymphatic duct connects the scala tympani and the subarachnoid space. |
| Describe the cochlear aqueduct being patent or closed. | Canal is patent early in life, but may close later in life. It is estimated that 50% of adults will have a patent cochlear aqueduct at 50 years of age. |
| What is the modiolus? | Bony central core of the cochlea. Contains VIIIth nerve cells. Continuous with the internal auditory meatus. |
| What is the osseous spiral lamina? | Bony shelf spiraling around the modioulus. Narrower at the apex than the base of the cochlea. SL is composed of two thin plates b/w which the AN fibers pass. |
| What attaches to the spiral lamina? | Upper shelf of SL serves as the attachment point for the tectoral membrane. Lower shelf serves as attachment point for the basilar membrane. |
| Habenula perforata | Small holes in the lateral most aspect of osseous spiral lamina. Allows for AN fibers from hair cells to pass through to form the modioulus and eventually an AN trunk. SL is wider at the base than apex, helps form start of anatomical divisions of cochlea. |
| Dimensions of the cochlea. | Coiled helix; 2.5-3 turns; 1 cm wide; 35 mm from base to apex |
| Helicotrema | Point at apex in cochlea where upper and lower cavities can communicate with each other (fluid interaction - as the both recieve perilymph from cochlear aqueduct) |
| The three fluid filled chambers of the cochlea. | 1) Scala vestibuli 2) Scala tympani 3) Scala media |
| Fluids that fill the three chambers in the cochlea. | 1) Perilymph - scala vestibuli and scala tympani 2) Endolymph - Scala media 3) Corilymph - Believed to in BM and TM area |
| Reissner's membrane | Thin membrane (several cells thick); permeable but is responsible for separating endolymph and perilymph; separates SV and SM |
| Two layers of Reissner's membrane | 1) Epithelial 2) Mesoepithelial |
| Physiologically, how is the basilar membrane different from the Reissner's membrane? | BM is thicker and more fibrous. |
| Attachment point of BM. | Runs from spiral lamina to spiral ligament;location of organ of corti. |
| Dimensions of BM. | 25-35mm in length in adults; 0.04mm at base and 0.36mm at apex. |
| Two sections of the BM. | 1) Acurate zone - partly enclosed in osseous spiral lamina, thus vibrates very little 2) Pectinate - moves more freely |
| Tonotopic organization of the BM. | Base is narrower and stiffer, which means high frequency is dominant. Apex is wider and stiffer, which means low frequency dominant. |
| Range of human hearing. | 20 - 20,000 Hz |
| Movement of Reissner's membrane. | Does not move much and the movement is not frequency specific. |
| What is the cochlear aqueduct similar to (in an analogy)? | Cochlear aqueduct is like a "gateway" for the cochlear cannalicus bringing in perilymph. |
| Where is endolymph generated? | Stria vasularis |
| What is the purpose of the endolymphatic duct and the endolymphatic sac? | Used to maintain equilibrium. |
| Composition of perilymph. | High in Sodium and lowe in Potassium. Similar in composition of extracellular fluid (fluid outside of cells) and CSF. |
| Composition of endolymph. | High in potasium and low in sodium. Similar to intracellular fluid (fluid inside of cells). |
| Compressability of the cochlear fluids. | The fluids are imcompressible. Compressive movement at oval window due to stapes movement results in equal movement at round window. |
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duda713
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