Hearing & Ear Flashcards
Ear embryology
Pinna/Auricle/External Ear
- ectoderm first branchial cleft
- from fusion of 6 hillocks;
PTT/ Euschatian Tube
- endoderm first branchial pouch
Tympanic membrane
- mesoderm first branchial arch
Ossicles
- mesoderm first and second branchial arches
- malleus first, stapes, second; long incus second
Inner ear
- ectoderm - pharyngeal pouch
Describe ear components
- outer middle and inner
- Describe the pathway of SOUND WAVES from auricle
- as well as the membranes at the Cochlear Duct
Outer: Auricle and External Ear Canal - Tympanic Membrane Middle: Malleus, Incus, Stapes; PTT tube - Oval, Round Window Inner ear: - Cochlea - Semicircular canals - Vestibule
Auricle to tympanic membrane to MIS
- malleus, incus, stapes
Stapes to OVAL Window
- round window to Scala Vestibuli, to Helicotrema to Scale Tympani to Round Window;
- from Perilymph through Ressiner’s Membrane through Endolymph through Tectorial membrane through hair cells through Basilar membrane :)
What nerves are found in the middle ear
Chorda Tympani of CN7
- anterior 2/3 taste
- Submandibular, Sublingual - secretomotor;
Tympanic branch of CN9 - goes to Parotid Gland
Whats impedance matching and how does middle ear do this
99% of sound is reflected when travelling from external air to cochlear fluid - hence sound waves are impeded / resisted
[Conduction] // compensation;
- Tympanic membrane to Oval window ratio (x20)
- ratio is 20:1 hence amplified 20x
- Lever Action of ossicles
- Malleus and Incus are the ossciles here; M to I ratio is 1.3:1 hence amplified 1.3x
- Buckling action of Tympanic membrane
overall 52x amplification
Sound pathway after oval window for transduction
Perilymph then Round window then out lmao scala vestibuli to helicotrema to scala tympani
Perilymph inside scala vestibuli
- ‘downward’ past Reissner’s membrane/ Vestibular membrane into cochlear duct, (scala media), endolymph
- Tectorial membrane to Hair cells
- 3 rows of outer Hair Cells
- amplifies sounds
- 1 row of inner Hair Cells
- signal transducer
Basilar membrane lower is the scalar tympani
Hair cells when deflected opens potassium channels
- potassium ENTERS
- Ca2+ enters, action potential in auditory nerve
Endolymph loses K+ channel hence have regeneration;
Where are the higher frequency hair cells at
Basal of the organ of Corti
Auditory Pathway
KIV learn the diff gyrus and brain areas;
Cochlea - auditory nerve - pons
- bilateral contributions past cochlear nucleus
- note lesions at BS leads mostly bilateral lesions;
BS then Auditory Cortex;
Primary auditory cortex (A1) is located on the superior temporal gyrus in the temporal lobe
Tuning fork tests what are they
Rinne test compares air conduction to bone conduction
Weber test detects unilateral sensorineural and unilateral conductive hearing loss.
They are typically performed together with the results of each combined to determine the location and nature of any hearing losses detected.
Weber test outcomes
Central - Normal Hearing
Lateralizes to one side
- can be conductive at THAT side (hears better)
- or sensorineural at contralateral side (hears worse)
- Sensory at softer side cos signal decreased
- Conductive problem at louder side cos Background noise blocked off by Middle Ear conduction
- needs Rinne test to characterize and localize
Rinne test outcomes
Normal hearing
- air should be louder than bone conduction
- bone conduction bypasses amplification of outer and middle ear; hence softer
- positive Rinne test
Bone louder - conductive problem
- Air conduction ends cos Middle ear conduction problem
- Direct bone conduction to CN 8 is louder;
Air louder - normal / sensory
– Sensory problem air still louder cos bone conduction normal, still amplifies it
Sensorineural problem at left ear
Weber
- softer side problem
- Right ear louder
Rinne
- Air louder
Conduction problem at left ear
Weber
- louder side problem
- Left ear louder
Rinne
- Bone louder cos middle ear amplification gone;
How would bilateral hearing loss present and caused by
Loud noise exposure;
Weber equal
Air louder
but audiometry can find out
What can cause sensorineural loss
noise;
ototoxic;
labyrinthitis
- anything to cochlear
Whats hearing aids for
Sensory hearing loss;