1. Chapter 7: The Sensory Systems
Lesson 7.2
The Ear

2. The Ear A. Anatomy of the ear B. Functions of the ear
External Ear (Outer)
Middle Ear (Tympanic Cavity)
Internal Ear (Inner)
B. Functions of the ear
1. Hearing
2. Equilibrium (balance)
C. Disorders and infections of the ear
1. Deafness
2. Tinnitus
3. External Otis
4. Otitis Media
5. Labyrinthitis

3. Anatomy of the Ear External ear Auricle (pinna)
channels sound waves in many animals
not very helpful in humans
Auditory canal (external acoustic meatus)
Short tube, one inch long, ¼ inch in diameter
Walls of the canal are lined with skin cells with Ceruminous glands = secrete cerumen (earwax)
Earwax – cleans, lubricates, and protects
Tympanic membrane (Ear drum)
Separates outer ear from middle ear
Membrane vibrates when sound waves strike it

4. Anatomy of the Ear Middle ear (Tympanic Cavity)
Small open chamber in temporal lobe of skull
Oval Window is a membrane covered opening
Ossicles (smallest bones in human body)
They connect tympanic membrane to oval window
Transmit AND amplify sound waves
Hammer = maleus
Anvil = incus
Stirrup = stapes
Eustachian tube
Connects the middle ear to the pharynx
Serves to equalize the pressure on either side of the tympanic membrane

5. Anatomy of the Ear Internal ear (inner ear)
Cochlea – Snail like structure used for hearing
Vestibulocochlear nerve – carries information to brain
Cochlear nerve (hearing information)
Vestibular nerve (balance information)
Vestibule & Semicircular canals
Used in coordination of balance.
Semicircular canals (Bony labyrinth) filled with:
Clear fluid (perilymph)
Membrane covered tubes (membranous labyrinth)
Inside tubes is thicker fluid (endolymph)

6. Anatomy of the Ear

7. Functions of the Ear
Hearing - Sound waves enter the auditory canal & cause tympanic membrane to vibrate
- This vibration stimulates the ossicles to transmit and amplify vibrations to the oval window.
- The oval window vibrations are passed to the cochlea
- Cochlea
- cochlear duct (membranous labyrinth) filled with the Organ of Corti – contains receptor hairs
- As the fluid in the cochlea vibrates, the receptor hairs are stimulated:
- short stiff hairs stimulated by high pitch sounds - long flexible hairs by low pitch sounds
- Receptor hairs transmit signals through the vestibulocochlear nerve to the brain

8. Functions of the Ear Equilibrium (balance)
Vestibule contains three semicircular canals
Tiny receptor hairs in the semicircular canals are stimulated by the moving endolymph
The receptor hairs stimulate the vestibular nerve and transmit information to the cerebellum
Information about the position of the head, orientation and motion are also sent.

9. Disorders and Infections of the Ear
Deafness – term for any loss of hearing
Many causes: damage to hair receptors, excessive earwax, scaring on the tympanic membrane, etc..
Presbycusis = age related hearing loss
In-canal hearing aid, half shell, behind the ear
Tinnitus – “ringing in the ear”
Caused by damaged hair cells (move randomly) from repeat sounds
External otitis (swimmer’s ear) = fungal infection of auditory canal
Otitis media (middle ear infection) = bacterial/viral infection
Associated with upper respiratory infections in infants (tubes to drain)
Labyrinthitis (inner ear infection) swelling disrupts semicircular canals
Causes Vertigo (dizziness), chronic = Meniere disease