1. IB Biology Neurology Unit Option E
The Ear and Hearing
IB Biology
Neurology Unit
Option E

2. The Ear Functions: Utilizes mechanoreceptors Hearing
Equilibrium (balance)
Utilizes mechanoreceptors

3. Anatomy of the Ear Three areas Outer (external) Ear Middle Ear
Inner Ear

4. The External Ear Function: Hearing only Structures: Pinna (auricle)
External auditory canal
Figure 8.12
Slide 8.22
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

5. Pinna
Collects soundwaves

6. The External Auditory Canal
Narrow chamber in the temporal bone
Lined with skin
Contains ceruminous glands
Ends at the tympanic membrane
Slide 8.23
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

7. Mastoid Process Bony ridge behind the pinna
Provides support to the external ear and posterior wall of the middle ear cavity

8. The Middle Ear Air-filled cavity within the temporal bone
Function: Hearing only
Separated from outer ear by
tympanic membrane
Slide 8.24a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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

10. Bones of the Middle Ear Ossicles: Malleus (hammer) Incus (anvil)
Stapes (stirrip)
Figure 8.12
Slide 8.25a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

11. Ossicles Act as a lever system
Action initiated from vibration of tympanic membrane
A = malleus
B = incus
C = stapes

12. External and Middle Ear Functioning: An Overview
Soundwaves (collected by pinna) travel through external auditory canal
Soundwaves lead to tympanic membrane vibrations.
Tympanic membrane vibrations move malleus
Malleus contacts incus
Incus contacts stapes
Stapes movement initiates inner ear response!!

14. Eustachian Tube
Lined with mucus membrane; connects middle ear to back of the throat (nasopharynx)
Equalizes air pressure
Normally closed except during yawning or swallowing
Not a part of the hearing process

15. INNER EAR FUNCTIONS: Hearing! Balance! Fluid-filled (perilymph)
Figure 8.12
Slide 8.26a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

16. Structures of the Inner Ear
Cochlea
Vestibule
Semicircular Canals

18. Cochlea snail-shaped organ with a series of fluid-filled tunnels
converts mechanical energy into electrical energy

19. Structures of the Inner Ear (Cont.)
Oval Window – located at the base
of the stapes; when the stapes vibrates,
the cochlear fluid (perilymph) is set into motion
Round Window – functions as the pressure relief port for the fluid set into motion initially by the movement of the stapes in the oval window

20. Organ of Corti
The end organ of hearing; contains stereocilia and hair cells.

21. Central Auditory System
8th Cranial Nerve or “Auditory Nerve” carries signals from cochlea to brain
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

22. 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 strike the tympanic membrane, causing it to vibrate like a drum, and changing it into mechanical energy. The malleus, which is attached to the tympanic membrane, starts the ossicles into motion. (The middle ear components mechanically amplify sound). The stapes moves in and out of the oval window of the cochlea creating a fluid motion. The fluid movement within the cochlea causes membranes in the Organ of Corti to shear against the hair cells. This creates an electrical signal which is sent via the Auditory Nerve to the brain, where sound is interpreted!

23. Vestibular System Consists of three semi-circular canals
Shares fluid with the cochlea
Controls balance
No part in hearing process