1. ANATOMY THE EAR
Dr. J.K. GERALD, (MD, MSc.)

2. Main Components of the Ear
Divided into 3 main parts:
Outer Ear
-Pinna, ext. auditory canal
Middle Ear / tympanic cavity
-TM, auditory ascicles, ET
Inner Ear / labyrinth
-Oval window, SM, vestibule, cochlea

4. Structures of the Outer Ear
Pinna (Auricle)
Gathers sound waves
Aids in localization
Amplifies sound waves

5. External Auditory Canal:
Approx. 1 inch (2.5cm) long
“S” shaped
Outer 1/3 surrounded by cartilage; inner 2/3 by mastoid bone
Allows air to warm before reaching TM
Isolates TM from physical damage
Cerumen glands moisten/soften skin
Presence of some cerumen is normal

6. MIDDLE EAR
A closed air filled cavity in the petrous part of the temporal bone
6 sided box
Lateral wall
Medial wall
Anterior wall
Posterior wall
Roof
Floor

8. The temporal bone

9. Tympanic Membrane Thin membrane
Forms boundary between outer and middle ear
Vibrates in response to sound waves
Changes acoustical energy into mechanical energy

11. The Ossicles Ossicular chain = malleus, incus & stapes Malleus Incus
TM attaches at Umbo
Incus
Connector function
Stapes
Smallest bone in the body
Footplate inserts in oval window on medial wall
The ossicles focus/amplify vibration of TM to smaller area, enables vibration of cochlear fluids

14. Eustachian Tube (“The Equalizer”)
Mucous-lined, connects middle ear cavity to nasopharynx
“Equalizes” air pressure in middle ear
Normally closed, opens under certain conditions
May allow a pathway for infection

16. Stapedius Muscle Attaches to stapes
Contracts in response to loud sounds; (the Acoustic Reflex)
Changes stapes mode of vibration makes it less efficient and reduce loudness perceived
Absent acoustic reflex could signal conductive loss or marked sensorineural loss

17. Middle ear – applied anatomy
Otitis media

18. Inner Ear

19. Semicircular canals:
Superior
Posterior
Lateral
Utricle
Saccule
Vestibulocochlear nerve
Cochlea
Stapes

21. Vestibulocochlear nerve (CNVIII)
The vestibulocochlear nerve (auditory vestibular nerve), transmits sound and equilibrium (balance) information from the inner ear to the brain.
It consists of the cochlear nerve (auditory n.), carrying information about hearing, and the vestibular nerve, carrying information about balance.
Fibers of the auditory nerve are present in the hair cells of the inner ear.
Auditory Cortex: Temporal lobe of the brain where sound is perceived and analyzed.

23. How Sound Travels Through The Ear
Acoustic energy, in the form of sound waves, is channeled into the ear canal by the pinna. Sound waves hit the tympanic membrane and cause it to vibrate, like a drum, changing it into mechanical energy. The malleus, which is attached to the tympanic membrane, starts the ossicles into motion. The stapes moves in and out of the oval window of the cochlea creating a fluid motion, or hydraulic energy. The fluid movement causes membranes in the Organ of Corti to shear against the hair cells. This creates an electrical signal which is sent up the Auditory Nerve to the brain. The brain interprets it as sound!

24. THANK YOU