Inner Ear + Hearing Flashcards
What is the function of the inner ear
Convert mechanical signs to electrical which can be detected by brain
Maintain balance by detecting position and movement
What is the inner ear made up of and what fluid
Bony labyrinth - endolymph
Membranous labyrinth - perilymph
What is in the bony labyrinth
Cochlea
Vestibule
Semi-circular canals
What is in membranous labyrinth
Duct of cochlea
Semi-circular duct
Utricle and saccule
What nerves to inner ear
Vestibulocochlear nerve
- Vestibular for balance
- Cochlear for hearing
Facial nerve passes but doesn’t innervate
What is the cochlea
Organ of hearing
Consists of three adjacent tubes separate by membranes
Stapes (final ossicular bone) moves back and forth against window creating pressure wave in cochlea which travel up and down tubes
What are tubes called
Scala vestibule- travels up
Basilar membrane
Scala tympani - travels down
What is the organ of corti and how is it involved in hearing
Structure containing tiny hair cells on basilar membrane
If wave with certain frequency reaches that resonant point, membrane releases burst of energy
Moves the hair cels
Send electrical impulse to cochlear nerve
What hearing problems do problems with outer or middle ear cause
Prevents conduction so conductive hearing loss
What do problems with cochlea or cochlear nerve cause
Sensory neural loss
What is bone conduction
Sound goes right through bone directly to inner ear
i.e. if you put tuning fork directly on mastoid bone
Measures purely inner ear function
What is air conduction
Normal pathway of sound through the ear
- Through canal, hits ear drum which vibrates causing ossicular bones to vibrate which connect to cochlea
What are tuning fork tests
Weber’s
Rinne’s
What does Weber test
Lateralisation
Put tuning fork in middle of head
If localise to side of deafness = conductive hearing loss
If localise to other side = sensorineural
What does Rinne’s test
Compares loudness of air compared to bone conduction
AC > BC = positive (what you want)
If BC > AC = conductive loss as doesn’t have to travel through outer and middle ear where as if outer and middle ear not working then air conduction can’t happen
If AC > BC if deaf ear then sensorineural
What should you check first if hearing loss
Look for wax
What is 1st line investigation of hearing difficulty and how do you interpret
Audiometry
Test different sound levels and freq
Test for air conduction and bone conduction
Plot the lowest volume patient can ear
If bone conduction normal and air abnormal
- Problem is in outer ear
If bone conduction abnormal then even if sensorineural fine won’t work as won’t conduct
If gap between air and bone conduction
- Conductive hearing loss
If both lines at same level
- Sensorineural loss
What types of audiometry
Pure tone - determines faintest tone a person can hear Visual reinforcement Play audiometry Can also test air or bone conduction Sensorineural = both imapired Conductive = only conduction
