BIOL122 ear and hearing

What are the three major structural divisions of the ear?

• Outer ear

• Middle ear

• Inner ear

What structures make up the outer ear?

The Pinna and the Auditory canal.

What are the three auditory ossicles in the middle ear (in order from outer to inner)?

bones in the middle ear that transmit and amplify sound vibrations from the eardrum to the inner ear

1. Malleus (Hammer)

2. Incus (Anvil)

3. Stapes (Stirrup)

What structure connects the middle ear to the nasopharynx and helps equalise pressure?

The Eustachian tube (or auditory tube).

What are the two main fluids found inside the cochlea, and where is each located?

Perilymph: Found in the vestibular canal (scala vestibuli) and tympanic canal (scala tympani).

Endolymph: Found in the cochlear duct (scala media). Note: Endolymph is rich in K+ ions.

Where exactly does the Organ of Corti rest inside the cochlea?

It rests on the Basilar membrane.

Describe the cellular arrangement of hair cells within the Organ of Corti.

It consists of 3 rows of outer hair cells and 1 row of inner hair cells.

True or False: The 80–100 stereocilia on top of auditory hair cells are a type of true cellular cilia.

False. They are made of actin filaments and project into the tectorial membrane—they are structurally not true cilia.

How does the Basilar Membrane differentiate between high-frequency and low-frequency sounds?

High frequencies: Vibrate the base of the membrane (where collagen fibres are short and stiff)

Low frequencies: Vibrate the apex of the membrane (where collagen fibres are long and floppy).

Step-by-step, how is mechanical sound converted into an electrical signal in the inner ear?

1. Pressure waves in the endolymph cause the basilar membrane to vibrate.

2. Stereocilia bend against the rigid tectorial membrane.

3. Mechanically-gated cation channels open, causing the hair cells to depolarize.

4. Neurotransmitters are released, activating sensory neurons.

5. Signal travels to the brain via the cochlear branch of the vestibulocochlear nerve (CN VIII).

Which two muscles protect the delicate cochlea from loud environments, and how do they work?

• The tensor tympani and stapedius muscles.

• In loud environments, they stiffen to increase tension on the tympanic membrane and stapes, reducing the transmission of sound vibrations into the inner ear.

How does a cochlear implant restore hearing if a patient has congenital deafness due to dysfunctional hair cells?

• An externally worn hearing aid detects sound and transmits it to an implanted receiver/electrode array in the cochlea.

• This electrode directly stimulates the functional auditory nerve in the specific regions assigned to those sound frequencies.

What three main structures make up the vestibular apparatus responsible for equilibrium?

1. Semicircular canals (three total)

2. Utricle

3. Saccule

Match the specific semicircular canal to the dynamic rotational movement it detects:

1. Anterior

2. Lateral

3. Posterior

Anterior: Vertical movement (e.g., nodding "yes").

Lateral: Horizontal movement (e.g., shaking head "no").

Posterior: Head tilting.

What is the cupula and where is it located?

• It is a gelatinous mass located inside the ampulla (the swollen base of each semicircular canal)

• Encapsulates the stereocilia of dynamic equilibrium hair cells.

What are maculae and what specific balance information do they provide?

• Clusters of hair cells located in the utricle and saccule.

• They detect head position relative to gravity (static equilibrium)

• As well as linear acceleration and deceleration.

What unique structures sit on top of the gelatinous layer in the maculae, and how do they trigger a nerve impulse when you tilt your head?

• Otoliths (dense calcium carbonate crystals).

• When the head tilts, gravity pulls the heavy otoliths, causing the gel to shift and bend the hair cell stereocilia

• opening transduction channels to depolarize the cell.

What physiological conflict causes travel sickness or "gamer's nausea"?

• A mismatch between sensory inputs.

• e.g. when reading in a car, your eyes register a stationary environment ("still"),

• but your vestibular system feels the car's motion ("moving").

• The brain interprets this conflict as a potential threat/toxin and triggers nausea.