15a. Inner Ear, Hearing and Vestibular Function Flashcards
What is the name of the eardrum?
Tympanic membrane
What is connected to the tympanic membrane?
Malleus
Name the auditory ossicles
Malleus
Incus
Stapes
What is the stapes connected to?
Oval window
What does the eustachian tube connect the middle ear to?
Nasopharynx
What are the functions of the eustachian tube?
Equalise pressure
Drain fluid from the middle ear into the throat
What is impedance?
Resistance to movement
How is impedance combatted in the ear?
Energy from the large surface area of the tympanic membrane is concentrated onto the oval window
Lever action of the ossicles amplifies vibration
What comprises the vestibular apparatus?
Utricle
Saccule
3 semi-circular canals
What information is received by the vestibular apparatus?
Balance
Co-ordination
Head positions
What lobe does information from the vestibular apparatus go to?
Temporal
What is mechanotransduction?
Sound waves are converted to nerve impulses by the displacement of fluid
What does pushing in of the oval window cause?
Movement of fluid in the scala vestibuli
What fluid is found in the scala vestibuli?
Perilymph
What cochlear labyrinth is connected to the round window?
Scala tympani
What fluid is found in the scala media/ cochlear duct?
Endolymph
What is contained in the scala media?
Organ of Corti
What separates the scala vestibuli from the scala media?
Reissner’s membrane
Which membrane separates the scala media from the scala tympani?
Basilar membrane
What is the composition of perilymph?
Similar to CSF
High Na+
Low K+
What is the composition of endolymph?
Low Na+
High K+
What is found in the lateral wall of the cochlea?
Stria vascularis
What makes up the stria vascularis?
Capillaries and marginal cells
What is the function of marginal cells?
Maintain the resting potential of endolymph by maintaining high K+
What membrane lies above the hair cells of the Organ of Corti?
Tectorial membrane
What happens when hair cells in the Organ of Corti are bent against the tectorial membrane?
Cilia bend
Influx of K+
Depolarisation causes opening of voltage gated Ca++ channels
Glutamate is released
What does amplitude of a sound wave correspond to?
Volume
What is the normal hearing threshold?
0-90dB
What volume causes pain?
130dB
What does frequency of a sound wave correspond to?
Pitch
How are different frequencies differentiated from by the Organ of Corti?
Location of the hair cells along basilar membrane of the scala media
Low: Close to helicotrema
High: Close to base
What is the normal audible frequency threshold?
20-20,000 Hz
What is the frequency of speech?
100-3400 Hz
What hearing test is used to test frequency?
Pure tone audiometry
What is an audiogram?
Plot of thresholds for amplitude and frequency
What is sensorineural deafness?
Degeneration of hair cells in the Organ of Corti and/or cochlear nerve fibres
What are the causes of sensorineural deafness?
Loud sound
Vascular lesion
Ototoxicity
What can cause ototoxicity?
Aminoglycosidases: antibiotics and loop diuretics
What is conductive deafness?
Impaired sound transmission in external or middle ear
What are the causes of conductive deafness?
Wax
Foreign body
Perforated tympanic membrane
Infection
What test is used to differentiate between sensorineural and conductive deafness?
Weber and Rinne
What does the Weber test detect?
Unilateral loss
Patient must know which ear is affected
What result is positive for conductive hearing loss in the Weber test?
Patient hears tuning fork louder in the affected ear
What result is positive for sensorineural hearing loss in the Weber test?
Tuning fork is louder in healthy ear
What is the Rinne test used to evaluate?
Air and bone conduction
How is the Rinne test conducted?
Tuning fork is placed on the mastoid process until the patient can no longer hear it
Quickly place near auditory canal
Compare times it took to hear
What is a normal/positive Rinne result?
Air conduction> bone conduction
What is a negative Rinne/ conductive loss result?
BC> AC
Due to blockage of air entering ear
What is the result for sensorineural hearing loss in the Rinne test?
AC> BC but decreased duration of hearing AC