The Ear and Hearing Flashcards
What is sound?
An oscillation of pressure through a compressible medium such as gas or liquid.
What determines the pitch of a sound?
Frequency (Hz).
What determines the volume of a sound?
Intensity (amplitude of pressure change).
What is the human range of hearing?
20 Hz to 20,000 Hz.
What are the main parts of the outer ear?
Pinna (auricle), external auditory meatus, tympanum.
What is the function of the pinna?
Funnels sound, helps in vertical sound localisation, and filters human speech frequencies.
What is the external auditory meatus lined with?
Hair, sebaceous glands, ceruminous glands.
How much does the ear canal amplify human speech?
By 10–15 dB.
What is the tympanic membrane?
A collagenous membrane that vibrates in response to sound waves.
What are the ossicles of the middle ear?
Malleus, incus, stapes.
What is the function of ossicles?
Act as a lever system, amplifying sound pressure by 20x.
Which two muscles dampen middle ear sound?
Tensor tympani (CNV3) and stapedius (CNVII).
What is the acoustic/attenuation reflex?
Muscle contraction in response to loud sounds or vocalisation.
What is the function of the Eustachian tube?
Equalises pressure between middle ear and nasopharynx.
Which nerve runs through the facial canal and crosses the middle ear?
Chorda tympani (taste to anterior 2/3 of tongue).
What nerve innervates the stapedius?
Nerve to stapedius (branch of CNVII).
What nerve innervates the tensor tympani?
Mandibular branch of trigeminal nerve (CNV3).
What are the two main functions of the inner ear?
Balance (vestibular system) and hearing (cochlea).
What converts mechanical energy into neural signals?
Inner ear fluid movement → hair cell activation → CN VIII.
What are the two types of labyrinths?
Bony labyrinth (perilymph-filled), membranous labyrinth (endolymph-filled).
What are the three scalae of the cochlea?
Scala vestibuli, scala media (cochlear duct), scala tympani.
What structure contains the Organ of Corti?
Cochlear duct (scala media).
What is the function of the Organ of Corti?
Converts mechanical vibration into action potentials.
Where is high-frequency sound detected in the cochlea?
Base of cochlea.
Where is low-frequency sound detected in the cochlea?
Apex (helicotrema).
What do outer hair cells do?
Amplify mechanical input to inner hair cells.
What do inner hair cells do?
Send sensory input to the brain via cochlear nerve.
What causes hearing loss from noise?
Irreversible damage to hair cells.
What is the order of the auditory pathway?
Organ of Corti
Cochlear nerve
Cochlear nuclei (cross over)
Superior olivary complex
Lateral lemniscus
Inferior colliculus
Medial geniculate nucleus
Auditory cortex
Where is the auditory cortex located?
Superior temporal gyrus (Brodmann areas 41 & 42).
How are time differences detected?
Medial superior olivary nucleus (MSO).
How are intensity differences detected?
Lateral superior olivary nucleus (LSO).
How is vertical sound localisation achieved?
Shape of the pinna and body structures like head and shoulders.
How does bone conduction differ from air conduction?
Bone conduction bypasses outer and middle ear and transmits vibration directly to inner ear.
Why does your own voice sound deeper to you?
Bone conducts lower frequencies better.
What is conductive hearing loss?
Problem in conducting sound through outer/middle ear.
What is sensorineural hearing loss?
Damage to cochlea, CN VIII, or auditory cortex.
What does the Rinne test compare?
Air conduction (AC) vs bone conduction (BC).
What is a normal Rinne test result?
AC > BC.
What indicates conductive hearing loss in Rinne test?
BC > AC.
What result is seen in sensorineural hearing loss?
AC > BC, but both are reduced.
What is the Weber test used for?
Lateralisation of hearing to determine type of unilateral hearing loss.
In sensorineural loss, where is the sound heard louder?
Normal ear.
In conductive loss, where is the sound heard louder?
Affected ear.
What is the function of the ossicles?
Amplify and transfer sound from eardrum to inner ear.
What part of the cochlea detects high-pitched sounds?
The base.
What part of the cochlea detects low-pitched sounds?
The apex.
What structure detects head position and movement?
Vestibular system.
What type of fluid fills the cochlear duct?
Endolymph.
What membrane contains the sensory cells for hearing?
Basilar membrane with the Organ of Corti.
What structure lies at the base of the cochlear spiral and contains vascular and neural tissue?
The modiolus.
What are the fluid-filled compartments of the cochlea and what do they contain?
Scala vestibuli – perilymph
Scala media – endolymph
Scala tympani – perilymph
What separates the scala vestibuli from the scala media?
Reissner’s (vestibular) membrane.
What separates the scala tympani from the scala media?
Basilar membrane.
What part of the ear contains the Organ of Corti?
Cochlear duct (scala media).
What triggers depolarisation of inner hair cells?
Shearing force causes hair cell stereocilia to deflect and open mechanically gated ion channels, allowing K⁺ influx from endolymph.
Why does endolymph allow depolarisation with K⁺?
It has high K⁺ concentration, which enters the negatively charged hair cells when stereocilia bend.
What is tonotopy?
Spatial arrangement where sound frequency is represented along the basilar membrane and preserved in auditory pathways up to the cortex.
What property of the basilar membrane allows tonotopy?
It varies in stiffness and width along its length.
Why can’t the attenuation reflex protect against gunshots or explosions?
Reflex latency is 50–100 ms, which is too slow for sudden loud sounds.
What hearing loss might occur with a CNVIII lesion?
Sensorineural hearing loss.
What is presbycusis?
Age-related hearing loss, typically sensorineural, affecting high frequencies first.
What is Ménière’s disease?
A disorder of the inner ear with vertigo, hearing loss, and tinnitus, associated with endolymphatic hydrops (increased pressure).
What is otosclerosis?
Abnormal bone growth in middle ear, commonly at stapes footplate, leading to conductive hearing loss.
What is the result of the Rinne test in conductive hearing loss?
Bone conduction (BC) > air conduction (AC).
What is the result of the Weber test in unilateral sensorineural hearing loss?
Sound lateralises to the normal ear.
Why does the Weber test lateralise to the affected ear in conductive hearing loss?
There’s less ambient noise masking bone conduction in that ear.
What frequency tuning forks are typically used for Rinne and Weber tests?
Rinne – 512 Hz
Weber – 256 Hz (lower frequency for bone conduction detection)
What are the utricle and saccule responsible for sensing?
Linear acceleration and head position relative to gravity.
What structures detect rotational (angular) acceleration?
Semicircular canals (anterior, posterior, lateral).
How is dizziness from vestibular dysfunction described?
Often as vertigo – a spinning or moving sensation.
What makes the mammalian middle ear unique?
Presence of three ossicles – malleus, incus, and stapes.
What ossicle do reptiles and birds have?
Only the stapes (columella in birds).
What is the evolutionary origin of the malleus and incus?
Derived from jaw bones in early vertebrates.
Mnemonic for ossicles in order of sound transmission?
MIS – Malleus → Incus → Stapes.
Mnemonic for cochlear fluid compartments?
“VMT”
Vestibuli (top)
Media (middle)
Tympani (bottom)
