Anatomy and Physiology of the Ear

Anatomy

The study of the structure of organisms and the relation of their parts

* Outer ear
* Middle ear
* Inner ear

What are the 3 parts of the ear?

Anterior

Towards the front

Posterior

Towards the back

Superior

Above

Inferior

Below

Central

* More near the center
* Nervous system / inner hear

Peripheral

* Outer edges
* More near the surface

Frontal

Separates us front to back

Coronal

What is another name for frontal?

Transverse

* Separates us from top to bottom
* Cuts us horizontally

Axial

What is another name for transverse?

Longitudinal

* This separates us from left to right
* Perpendicular to frontal / coronal plane

Sagittarius

What is another name for longitudinal?

Site of lesion

Where is the problem?

Etiology

What caused the problem?

Temporal bone

Most of the auditory pathway is within what bone?

* Central auditory nervous system
* External ear

What 2 things are not housed in the temporal bone?

* Pinna
* Ear canal

What 2 things does the outer ear involve?

Auricle

What is another name for pinna?

* Collect and resonate sound
* Assist in sound localization
* Function as a protective mechanism for the middle ear

The outer ear (auricle / pinna and ear canal) serves to do what 3 things?

The ear vibrates or oscillates at a specific range of frequencies better

What does resonate mean?

Pinna

The visible portion of the ear that consists of skin-covered cartilage

Helix

What is the top red dot?

Triangular fossa

Antihelix

Concha Cavum

Antitragus

External auditory meatus

Tragus

Lobule

External auditory meatus (EAM)

A narrow channel leading from an opening in the side of the head

23-29 mm

How long is the external auditory meatus in millimeters?

2\.5-3 cm

How long is the EAM in cm?

Skin-covered cartilage

The outer 1/3 of the canal is composed of what?

Skin-covered bone

The inner 2/3 of the EAM is what?

Elliptical

What type of shape is the external auditory meatus in?

Cerumen

A waxy oil produced from sebum in the EAM

Direct sounds to the TM

The main purpose of the EAM is to do what?

Resonator

The EAM serves as a what?

High frequencies

Does the EAM vibrate at high or low frequencies?

* Protects ear from foreign objects and creatures
* Lubricates canal
* Has anti-microbial properties
* Helps neutralize and fight against infections

What are the 4 purposes of cerumen?

* Tympanic membrane
* Malleus
* Incus
* Stapes

What are the 4 things that is included in the middle ear?

Tympanic membrane

* This is a membrane that is made up of several layers of skin that is embedded into the body portion of the canal
* It is fairly taut and concave

3

How many layers does the tympanic membrane have?

* Outer (cuticular)
* Intermediate (fibrous)
* Inner (mucous)

What are the 3 layers of the TM called (with their other names as well)?

Outer (cuticular)

* This TM layer is a continuation of the epithelial lining of the EAM
* It has the same skin as on the EAM

Intermediate (fibrous)

* This TM layer contains 2 layers
* It provides tautness of the eardrum
* It helps the membrane vibrate to produce the sound

Superficial

This layer of the Intermediate (fibrous) layer has fibers that radiate to the periphery (like a sunburst)

Deep

This layer of the intermediate (fibrous) layer of the TM has circular fibers that mostly run around the periphery (around the outer portion of the ear drum)

Inner (mucous)

This layer of the TM is continuous with the mucosa of the middle ear

Cuticular

What is another name for the outer layer of the TM?

Fibrous

What is another name for the intermediate layer of the TM?

Mucous

What is another name for the inner layer of the TM?

* Pars flaccida
* Pars tense

What are the two main parts of the TM?

Pars flaccida

* This is smaller and more compliant
* Located superiorly
* It moves easier and is more flaccid

Pars tensa

* This part of the TM is larger and stiffer
* Located inferiorly
* Contains all the layers of the ear drum

Pars tensa

What part of the TM contains all three layers of the ear drum?

Cone of light

This is a reflection of the otoscope when the eardrum is structured the way it is supposed to be structured

Eustachian tube

This is a tube that connects from your middle ear with the ear-filled space to the back of your throat that allows drainage to occur

Ossicular chain

This is a series of 3 small bones / ossicles that are attached to the tympanic membrane

* Malleus
* Incus
* Stapes

What are the 3 bones of the ossicular chain?

Malleus

This bone in the ossicular chain has a long process called the manubrium that connects to the TM

Manubrium

What is the long process called that attaches to the TM?

Head

What part of the malleus attaches to the body of the incus?

Incus

Short process (crus)

This process of the incus attaches to a recess in the wall of the tympanic cavity

Long process

This process of the incus attaches to the stapes

Stapes

This is the third and final bone of the ossicular chain that consists of the head, two crura, and a footplate

Footplate

This is part of the stapes that is fitted into the oval window and is held in place by the annular ligament

Annular ligament

What ligament hold the footplate of the stapes in place?

Two crura

This is what attaches to the footplate of the stapes

Oval window

Where does the footplate of the stapes fit into?

* Stapedius
* Tensor tympani

What are the 2 muscles of the middle ear?

Reflexively and bilaterally

How do the muscles of the middle ear contract? (Occurs in 2 ways)

Amplifier

This is what the middle ear does to help us correct the “impedance mismatch” between air and the fluid of the inner ear

Transducer

What does the middle work as?

Fluid

Sound travels through what in the inner ear?

Air

Sound travels through what in the outer ear?

Area ratio

This is where energy that is caught by the larger tympanic membrane is concentrated onto the smaller oval window membrane

Malleus-incus lever

This is where the ossicle bones form a system of levers which are linked together and driven by the eardrum to form a lever motion

Cochlea

This is the part of the inner ear that is responsible for hearing

Vestibular system

This is the part of the inner ear that is responsible for balance

Semicircular canals

The vestibular system includes what?

Petrous portion

The inner ear is in what portion of the temporal bone?

Cochlea

A fluid filled space within the temporal bone that is responsible for hearing

• Scala vestibuli

• Scala media

• Scala tympani

What are the 3 chambers that are housed in the cochlea?

Reissner’s membrane

This is the membrane that separates the scala vestibuli from the scala media (C in the picture)

Basilar membrane

• This membrane separates the scala media and the scala tympani

• This is what moves to create the traveling wave

• A in the picture

Perilymph

The scala vestibuli and scala tympani is filled with what kind of fluid?

Endolymph

The scala media contains what kind of fluid?

Perlymph

What is endolymph created by?

Oval window

• This is attached to the stapes (center most ossicle) footplate

• It is the “entrance” to the scala vestibuli

Round window

• This is covered by a membrane

• It is more of an opening in the cochlea

• This membrane allows pressure waves to be released

• It is the “exit” from the scala tympani

Helicotrema

The apex of the cochlea that connects the scala vestibuli and scala tympani is called what?

Organ of corti

This is housed within the scala media and is the sensory for hearing

Basilar membrane

What does the organ of corti sit on?

Sensory cells of hearing

What is contained in the organ of corti?

Inner hair cells

• There are about 3500 of these hair cells

• These hair cells are flask shaped

• They are lined up in a single row

• The stereocilia of this type of hair cell is not attached to the tectorial membrane

• Each individual hair cell produces a lot of clarity on auditory information

Flask-shaped

What type of shape are inner hair cells?