The Ear & Hearing

Question 1

State the human auditory range

Answer 1

20-20000 Hz

Question 2

Define the central auditory pathway to the brainstem and cerebral cortex

Answer 2

Cochlea –> spiral ganglion cells –> cochlear nucleus –> superior olivary complex –> inferior colliculus –> medial geniculate nucleus –> auditory cortex

Question 3

Review the pathway of sound through the external and middle ear to the cochlea, understanding the processes occurring at each stage

Answer 3

External ear - pinna –> auditory canal –> tympanic membrane
Middle ear - vibration of tympanic membrane causes ossicles to vibrate –> oval window
Sound energy –> mechanical energy

Question 4

Describe the general anatomy of the cochlea including the spiral organ and cochlea nerve

Answer 4

Oral window/round window -fluid paths-> tectorial pathway –> cochlear partition –> organ of Corti –> nerve
Vibration of basilar membrane

Question 5

Understand how mechanotransduction occurs in cochlea receptors and the different roles of inner and outer hair fells and of cochlea position in the detection of sound amplitude and frequency

Answer 5

Inner cells - one row, sense sound
Outer cells - three rows, amplify
Regulated by olivocochlear system
Frequency detected by movement along basement membrane
Bending of stereocilia opens K+ channels, depolarisation opens VG calcium channels –> triggers transmitter release and spiral ganglion
Primary sense organ –> APs -vestibulocochlear-> brain –> cochlear nucleus and auditory brainstem

Question 6

Distinguish between conductive, sensorineural and CNS related deafness

Answer 6

Conductive - blockage, ruptured ear drum, fluid accumulation, otosclerosis
Sensory - hair cell destruction (physical, noise), hair cell death (ototoxic)
Neural - spiral ganglion damage, age related hearing loss, tinnitus, auditory neuropathy, monoaural deafness
CNS - disruption to vestibulocochlear nerve as it enters brainstem or other sites along auditory pathway

Question 7

List some causes of hearing impairment

Answer 7

Loud noises - tears stereocilia
Congenital defects - inherited DFN (x-linked) A (dominant) B (recessive) 
Infections e.g. Rubella, glue ear
Ototoxic complications 
Trauma - damage to temporal bone
Age

Question 8

List methods of assessment of ears and hearing

Answer 8

Visual inspection (otoscope)
Audiograms (sensitivity vs frequency)
Otoacoustic emissions - tests amplifiers
Auditory brainstem response

Question 9

List common treatments of hearing impairment

Answer 9

Hearing aides
Cochlea implants
Hair cell regeneration
Cochlear nucleus implants

Question 10

Define the term ‘sound’ and state what properties of sound waves can be detected by the cochlea

Answer 10

Compressible wave which travels at 343 m/s in air and at over 1500 m/s in water
Cochlea detects frequency (Hertz) and volume (decibels)