Anatomy & Physiology of Hearing Study Notes

Journey of sound: Outer Ear

The outer ear (pinna and EAM) gathers sound waves and directs it to the eardrum

Journey of sound: Middle Ear

The TM vibrates with the sound wave and (ossicles) make the sound vibrations stronger (“impedance matching”). These bones transmit the vibrations to the oval window that leads to the fluid-filled inner ear.

Journey of sound: Inner Ear

Sound vibrations reach the cochlea which creates waves in the cochlear fluid. Tiny hair cells in the cochlea bend which triggers the release of neurotransmitters, which activates the auditory nerve fibers.

Journey of sound: Auditory nerve and brainstem

Signals travel from the inner ear to the auditory nerve. The signals then reach the brainstem, where the sound is initially analyzed.

• sound localization and pitch recognition

Journey of sound: Primary auditory cortex

Signals continue from the brainstem to the primary auditory cortex in the brain. Sound is processed as speech, music, or environmental noise

1

Outer ear

2

Middle Ear

3

Inner ear

4

Auditory nerve & brainstem

5

Primary auditory cortex

Pinna function

Channels sound waves into the ear canal.

The outer ear includes

ear canal, pinna

The middle ear includes

malleus, incus, stapes

The inner ear includes

semicircular canals, cochlea

both the ___ and ___ muscles serve as a protective mechanism

tensor tympani, stapedius

The tensor tympani and stapedius work together to…

manage sound vibrations entering the inner ear.

The downward curve in the external auditory meatus helps protect the deeper parts of the ear from potential harm.

True

External Auditory Meatus (EAM) function

Channels sound waves towards the eardrum (tympanic membrane) and the hair and cerumen (earwax) trap particles.

The pinna and EAM are lined with

Epithelial tissue

Which part of the EAM courses down

Osseous meatus (temporal bone)

Tympanic membrane function

Vibrates with sound waves and transfers sound vibrations to the ossicles in the middle ear.

The outer and inner layer of the TM are lined with ___ and the intermediate layer is lined with ___.

epithelial tissue, connective tissue

The malleus, incus, and stapes are

Three small bones; middle ear ossicles

Malleus (largest) function

Transmits sound vibrations from the TM to the incus.

Incus (middle bridge) function

Transmits sound vibrations along the chain.

Stapes (smallest) function

Final point of sound transmission in the middle ear.

Tensor Tympani

Dampens loud sounds by pulling the malleus inward, tightening the tympanic membrane.

• more active in response to self-generated sounds

Stapedius

Pulls the stapes away from the oval window, thereby stiffening the ossicular chain and reducing movement of the stapes to protect the inner ear from loud sounds

Acoustic reflex

Protective response of the stapedius that helps minimize damage to the inner ear from sudden loud noises.

Cochlea

The inner ear’s hearing organ, where sound vibrations are converted into electrical

signals for the brain.

Organ of Corti

Inside the cochlea and lined with sensory hair cells (Stereocilia)

A

EAM

C

Tympanic membrane

D

Malleus

E

Incus

F, G, H

Lateral, posterior, superior semicircular canals

I

Vestibular nerve

J

Facial nerve

K

Vestibulochoclear (auditory) nerve)

L

Cochlea

M

Vestibule

N

Stapes

O

Auditory tube