Hearing & Ear

Question 1

Ear embryology

Answer 1

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

Question 2

Describe ear components
- outer middle and inner

• Describe the pathway of SOUND WAVES from auricle
• as well as the membranes at the Cochlear Duct

Answer 2

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 :)

Question 3

What nerves are found in the middle ear

Answer 3

Chorda Tympani of CN7
- anterior 2/3 taste
- Submandibular, Sublingual - secretomotor;
Tympanic branch of CN9 - goes to Parotid Gland

Question 4

Whats impedance matching and how does middle ear do this

Answer 4

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

Question 5

Sound pathway after oval window for transduction

Answer 5

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;

Question 6

Where are the higher frequency hair cells at

Answer 6

Basal of the organ of Corti

Question 7

Auditory Pathway

KIV learn the diff gyrus and brain areas;

Answer 7

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

Question 8

Tuning fork tests what are they

Answer 8

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.

Question 9

Weber test outcomes

Answer 9

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

Question 10

Rinne test outcomes

Answer 10

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

Question 11

Sensorineural problem at left ear

Answer 11

Weber

• softer side problem
• Right ear louder

Rinne
- Air louder

Question 12

Conduction problem at left ear

Answer 12

Weber

• louder side problem
• Left ear louder

Rinne
- Bone louder cos middle ear amplification gone;

Question 13

How would bilateral hearing loss present and caused by

Answer 13

Loud noise exposure;
Weber equal
Air louder

but audiometry can find out

Question 14

What can cause sensorineural loss

Answer 14

noise;
ototoxic;
labyrinthitis

• anything to cochlear

Question 15

Whats hearing aids for

Answer 15

Sensory hearing loss;