The Ear

Three major areas of the ear and function

1) External (outer) ear - hearing only

2) Middle ear (tympanic cavity) - hearing only

3) Internal (inner) ear - hearing and equilibrium

Receptors for hearing and balance respond to seperate

stimuli

Receptors for hearing and balance are activated

independently

Auricle (Pinna) is composed of what two things?

What is its function

1) Helix (rim).

2) Lobule (earlobe).

Function: Funnels sound waves into auditory canal.

External Acoustic Meatus (auditory canal) -

Structure and function

Structure:Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands

Function: Transmits sound waves to eardrum

Tympanic membrane (eardrum) is the boundary between?

Boundary between external and middle ears

Tympanic membrane (eardrum) - two functions:

1) Connective tissue membrane that vibrates in response to sound

2) Transfers sound energy to bones of middle ear

Middle Ear (Tympanic Cavity) - Structure, and Flanked laterally/Flanked medially

Structure: A small, air-filled, mucosa-lined cavity in temporal bone

Flanked Laterally: by eardrum

Flanked Medially: By bony wall containing oval and round windows

Middle Ear: Epitympanic recess

Superior portion of the middle ear

Middle Ear: Mastoid Antrum

Canal for communication with mastoid air cells

Middle Ear: Pharyngotympanic (auditory) tube -

Name the two functions

1) Connects middle ear to nasopharynx

2) Equalizes pressure in middle ear cavity with external air pressure

Otitis Media -

1) What is it?

2) Who does it affect mostly?

3) What can it cause?

4) How is it treated?

1) Middle ear inflammation

2) Especially in children and people with shorter, more horizontal pharyngotympanic tubes

3) Most frequent cause of hearing loss in children

4) Antibiotics or myringotomy to relieve pressure if severe

Ear Ossicles - Define

Three small bones in tympanic cavity:

1) Malleus

2) Incus

3) Stapes

Ear Ossicles - Suspended by what? and joined by what?

Suspended by: ligaments

Joined by: synovial Joints

2 Ear Ossicle Functions:

1) Transmit vibratory motion of eardrum to oval window

2) Tensor tympani and Stapedius muscles contract reflexively in response to loud sounds to prevent damage to hearing receptors

Two Major Divisions of the Internal Ear:

1) Bony Labyrinth

2) Membranous Labyrinth

Internal Ear: Bony Labyrith

1) What type of channels?

2) Name the three regions

3) What is it filled with?

1) Tortuous channels in temporal bone

2) Three regions: vestibule, semicircular canals, and cochlea

Filled with perilymph - similar to CSF

Internal Ear: Membranous Labyrinth

1) Structure

2) What is it filled with?

1) Series of membranous sacs and ducts

Filled with potassium-rich endolymph

Vestibule

1) Structure

2) Contains

1) Central egg-shaped cavity of bony labyrinth

2) Contains two membranous sacs

Vestibule: Membraneous Sacs

1) Name the two types of sacs and what they are continuous with

2) Functions

1) Saccule - is continuous with cochlear duct, and Utricle - is continuous with semicircular canals

2) Functions: House equilibrium receptor regions (maculae) and respond to gravity and changes in position of head

Semicircular Canals

1) How many?

2) What lines the canals?

3) What do they communicate with?

1) Three canals (anterior, lateral, and posterior) that each define ⅔ circle

2) Membranous semicircular ducts line each canal

3) communicate with utricle

Semicircular Canal: Ampulla

1) Define

2) What does the ampulla respond to?

1) Ampulla of each canal houses equilibrium receptor region called the crista ampullaris

2) Receptors respond to angular (rotational) movements of the head

The Cochlea:

1) Size

2) Extension

3) Coils around what?

4) Contains what? Which ends?

1) Size of split pea

2) Extends from vestibule

3) Coils around bony pillar (modiolus)

4) Contains cochlear duct, which houses spiral organ (organ of Corti) and ends at cochlear apex

Cochlea:Three Chambers

1) Scala vestibuli—abuts oval window, contains perilymph

2) Scala media (cochlear duct)—contains endolymph

3) Scala tympani—terminates at round window; contains perilymph

Scalae tympani and vestibuli are continuous with each other at

helicotrema (apex)

Cochlea:

1) Roof

2) External Wall - function

3) Floor - composed of

1) Roof: vestibular membrane

2) External wall: is stria vascularis - secretes endolymph

3) Floor composed of:

Bony spiral lamina

Basilar membrane, which supports spiral organ

The cochlear branch of nerve VIII runs from spiral organ to the

brain

Sound

pressure disturbance.