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