A&P Ch 15: Ear

What do ceruminous glands produce?

Cerumen (earwax)

What is the function of the tympanic membrane?

Vibrates in response to sound waves

What is another name for the middle ear?

Tympanic cavity

What is the function of the auditory (eustachian) tube?

Equalizes pressure on both sides of the eardrum

What are the 3 divisions of the ear?

External ear, middle ear, inner ear

What are the functions of each ear division?

External & middle ear = hearing Inner ear = hearing + balance

What structures make up the external ear?

Auricle (pinna), external acoustic meatus, tympanic membrane

What are the auditory ossicles?

Malleus, incus, stapes

Function of auditory ossicles?

Transmit vibrations from the eardrum to the oval window

What is the oval window?

Connection between middle and inner ear

What is the round window?

Membrane separating inner ear fluid from the middle ear

Functions of the cochlea, vestibule, and semicircular canals?

Cochlea = hearing
Vestibule = gravity & linear acceleration
Semicircular canals = head rotation

What is the bony labyrinth?

Bone chambers that protect the membranous labyrinth

What is the membranous labyrinth?

Membranous chambers suspended inside the bony labyrinth

Difference between perilymph and endolymph?

Perilymph = low K⁺, high Na⁺
Endolymph = high K⁺, low Na⁺

What is the static labyrinth?

Maculae of utricle and saccule; detects head position, gravity, and linear acceleration

What is the dynamic labyrinth?

Crista ampullaris of semicircular canals; detects rotational head movement

What are otoliths?

Crystals in the macula that move with gravity and bend hair cells

What happens when stereocilia bend toward the kinocilium?

Hair cells depolarize

What happens when stereocilia bend away from the kinocilium?

Hair cells hyperpolarize

Which cranial nerve carries balance information?

Vestibulocochlear nerve (CN VIII)

Where does balance information go in the brain?

Vestibular nuclei → thalamus → vestibular cortex (insula)

What are the 3 chambers of the cochlea?

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

Which cochlear chambers contain perilymph?

Scala vestibuli and scala tympani

Which cochlear chamber contains endolymph?

Cochlear duct (scala media)

What is the organ of Corti?

Hearing sensory organ inside the cochlear duct

What do stereocilia do in hearing?

Bending opens mechanically gated K⁺ channels

Function of inner vs outer hair cells?

Inner hair cells = hearing
Outer hair cells = regulate basilar membrane tension

What determines loudness and pitch?

Loudness = wave amplitude
Pitch = wave frequency

Basic process of hearing?

Sound waves → tympanic membrane vibrates → ossicles vibrate → oval window vibrates → fluid movement in cochlea → basilar membrane moves → hair cells stimulated

Which part of the basilar membrane detects high vs low pitch?

High pitch = base near oval window Low pitch = apex near helicotrema

Basic CNS hearing pathway?

Cochlear nerve (CN VIII) → medulla oblongata → inferior colliculus → thalamus → auditory cortex (temporal lobe)

What is the function of the superior colliculus in hearing?

Reflex turning of head and eyes toward loud sounds