BIOL 1162 – The Ear: Hearing and Balance

A comprehensive set of question-and-answer flashcards covering the anatomy of the ear, the physiology of hearing, auditory pathways, equilibrium mechanisms, and related clinical concepts.

What are the three main regions of the ear?

External ear, middle ear, and internal (inner) ear.

Which visible structure forms most of the external ear?

The auricle (pinna).

What glands in the auditory canal secrete earwax (cerumen)?

Ceruminous glands, a type of apocrine sweat gland.

Which membrane separates the external ear from the middle ear?

The tympanic membrane (eardrum).

How does the eardrum transmit sound energy to the middle ear?

It vibrates with incoming sound waves and moves the auditory ossicles.

Name the three auditory ossicles in order from lateral to medial.

Malleus (hammer), incus (anvil), stapes (stirrup).

Which two tiny muscles protect the ear by limiting ossicle vibration?

Tensor tympani (acts on malleus) and stapedius (acts on stapes).

What tube connects the middle ear to the nasopharynx and equalizes pressure?

The pharyngotympanic (auditory or Eustachian) tube.

What are the two membrane-covered openings on the medial wall of the middle ear?

The oval window (superior) and the round window (inferior).

What is another name for the internal ear?

The labyrinth.

Into which two major parts is the labyrinth divided?

The bony labyrinth and the membranous labyrinth.

Which fluid fills the bony labyrinth?

Perilymph.

Which fluid fills the membranous labyrinth?

Endolymph.

Which ion is abundant in perilymph but scarce in endolymph?

Sodium (Na⁺).

Which ion is abundant in endolymph but scarce in perilymph?

Potassium (K⁺).

Name the three regions of the bony labyrinth.

Vestibule, semicircular canals, and cochlea.

Which two membranous sacs are found in the vestibule, and what do they detect?

The utricle and saccule; they detect linear acceleration and gravity.

What sensory receptor is located in the ampulla of each semicircular canal and what does it detect?

The crista ampullaris; it detects rotational (angular) acceleration.

What is the name of the receptor organ of hearing?

The spiral organ (organ of Corti).

In which membrane are the stereocilia of outer hair cells embedded?

The tectorial membrane.

Which membrane forms the flexible floor that supports the spiral organ and vibrates with sound?

The basilar membrane.

Which three fluid-filled chambers make up each turn of the cochlea?

Scala vestibuli, scala media (cochlear duct), and scala tympani.

Which cochlear chambers contain perilymph?

Scala vestibuli and scala tympani.

Which cochlear chamber contains endolymph?

Scala media (cochlear duct).

Through which window do vibrations from the stapes enter the cochlea?

The oval window.

Which window acts as a pressure-relief opening for cochlear fluid movement?

The round window.

How are pitch (frequency) and cochlear location related?

High frequencies activate hair cells at the cochlear base near the oval window; low frequencies activate hair cells toward the apex.

In what units is sound frequency measured?

Hertz (Hz).

What frequency range is audible to the average human ear?

Approximately 20 Hz to 20,000 Hz.

How is loudness encoded by cochlear hair cells?

Greater basilar-membrane displacement releases more neurotransmitter, producing more frequent action potentials.

Which cranial nerve carries auditory impulses to the brain?

The vestibulocochlear nerve (CN VIII), cochlear branch.

Which thalamic nucleus relays auditory information to the cortex?

The medial geniculate nucleus.

Where is the primary auditory cortex located?

In the temporal lobe.

What structures compose the vestibular apparatus?

The semicircular canals and the vestibule (utricle and saccule).

What are otoliths and what is their role?

Calcium carbonate crystals embedded in the otolithic membrane; they add weight, helping detect linear acceleration.

What happens when macular hair cells bend toward the kinocilium?

They depolarize and increase their rate of nerve impulses.

Define vestibular nystagmus.

Involuntary oscillating eye movements that occur during and immediately after rotation.

What causes motion sickness?

A mismatch between visual input and vestibular (inner-ear) signals.

What is tinnitus and give one possible cause.

Perception of ringing or clicking in the ears; causes include cochlear-nerve degeneration, middle/inner ear inflammation, or aspirin (salicylic acid) side effects.

How do hair cells in the crista ampullaris respond to rotation?

Endolymph inertia bends the cupula, causing depolarization in one direction and hyperpolarization in the opposite direction.

Why can’t constant-velocity rotation be sensed after a few seconds?

The endolymph catches up with canal rotation, eliminating cupula displacement and sensory input.

What is the function of the auditory (Eustachian) tube during swallowing or yawning?

It opens briefly to equalize air pressure in the middle-ear cavity.

Which auditory ossicle is attached directly to the tympanic membrane?

The malleus.

Which ossicle’s footplate fits into the oval window?

The stapes.

What is the name of the bony axis around which the cochlea coils?

The modiolus.

What type of neurons make up the spiral ganglion?

Bipolar sensory neurons.

What neurotransmitter is most likely released by depolarized hair cells?

Glutamate.

How does stereocilia deflection lead to hair-cell depolarization?

Lateral deflection opens mechanically gated K⁺ channels, allowing K⁺ influx from endolymph.

Why does the basilar membrane become more flexible toward the apex?

Its decreasing stiffness enables resonance with lower-frequency sound waves.

Where along the basilar membrane are high-frequency sounds detected?

Near the base, close to the oval window.