Ear Structure & Function

12-13 January 2014

External EarStructures: Pinna auditory

canal ear drum

Function: Funnel

and conduct sound to middle ear

Anatomy of the Ear

Middle Ear

Structures:

Ossicles Malleus Incus Stapes Eustacian /

auditory tube

Function: Amplify and

conduct sound to inner ear

Anatomy of the Ear

Inner Ear

Structures:

Osseous labyrinth Semicircula

r canals Vestibule cochlea

Function: Receive

sound and equilibrium stimuli

Anatomy of the Ear

NOTE:Diagrams are misleading.The entire inner is bony, except for the labyrinth which is a series of cavities (spaces) within the bone.

Anatomy of the Ear

Outer (External) EarFunction:

Outer (External) EarFunction: to funnel and conduct sound to the middle ear

Pinna collect sound waves and direct to the tympanic membranes … but in humans, not very effectively.

Cerumen (ear wax) lines the external auditory canal.◦ Antibacterial◦ Also discourages bugs, mold, etc.◦ Lubricates ears◦ Helps trap / remove foreign particles

The tympanic membrane (ear drum) vibrates when sound waves hit it, transmitting the sound to the middle earA reflex tightens the ear drum in response to loud, low-pitched sounds – this reduces the sound transmitted to the ear and protectes our hearing

Disorders of the Outer EarEar Wax Blockage Ear wax can become impacted, usually from hearing

aid use or inappropriate methods of cleaning the ears Can cause temporary loss of hearing

Disorders of the Outer EarOtitis Externa (Swimmer’s Ear) Infection of external auditory ear canal, usually due to

excess moisture in the ear canal (such as from swimming), though cuts and scrapes to the ear canal can also become infected.

Picture through an otoscope. Notice that the canal is red but the ear drum is clear and not bulging.

Function:

Middle Ear

Function: to AMPLIFY the sound and conduct it to the oval window of the inner ear.

How? The tympanic membrane transmits sound to the three ossicles. The ossicles act like levers, amplifying the sound and transmitting it to the oval window, amembrane-covered opening to theinner ear.

Middle Ear

Structure Tube that connects the middle ear to the nose and throat Mostly closed, but opens when we move our jaw

Why do we have it? Equalize pressure in the middle ear Drain fluids to the throat

Eustachian Tubes

Remember: the tympanic membrane seals the middle ear from the outer ear – so the only way for air / fluids to leave the middle ear is through the eustachian tubes

This is why its helpful to yawn or chew gum on a plane ride

Otitis media (middle ear inflammation / infection) – Inflammation (often with the buildup of infected fluids)

within the middle ear Visible with an otoscope as a bulging eardrum Usually caused from a respiratory infection Babies who are allowed to drink bottles while lying down

are also very likely to get ear infections Much more common in young children, because their

Eustachian tubes are narrower and more horizontal

Disorders of the Middle Ear

myringotomy– Ear tubes are often recommended for children who

experience chronic middle ear infections or fluid build-up The tube is placed in the ear drum, but performs the

functions of a eustachian tube – ventilating and draining the middle ear.

Disorders of the Middle Ear

Hearing takes place within the cochlea of the inner ear.

Cochlea is a long, curled cavity with three layers◦ 2 layers of perilymph – a plasma-like fluid◦ In-between: a system of membranes that contain the

organ of Corti and the mechanoreceptors (hair cells) that create the nerve impulse

Hearing & the Inner Ear

Hearing & the Inner Ear

The top diagram is a cross-section of the cochlear cavity.

Take a moment to figure out …

• What fills the scala vestibuli?

• The scala tympani?

• The cochlear duct?

When the stapes beats against the oval window, it causes pressure waves within the perilymph

The movement of the perilymph disturbs the cilia (receptors) of the Organ of Corti, generating a nerve impulse

Hearing & the Inner Ear

Different frequencies (pitch) vibrate the membrane in different locations.

High pitches are heard that the front, low at the back.

When the stapes beats against the oval window, it causes pressure waves within the perilymph

The movement of the perilymph disturbs the cilia (receptors) of the Organ of Corti, generating a nerve impulse

Hearing & the Inner Ear

The round window is a membrane-covered opening just below the oval window. It bulges to keep the pressure waves from bouncing back.

Watch me!

Just for fun!

What were our objectives, and what did you learn about them?

What was our learner profile trait and how did we exemplify it?

How does what we did today address our unit question?

Closure