1. Topic 12 The Auditory and Vestibular Systems Lange
Biology Neurobiology
Topic 12
The Auditory and Vestibular Systems
Lange

2. Introduction
Sensory Systems
Sense of hearing, audition
Detect sound
Perceive and interpret nuances
Sense of balance, vestibular system
Head and body location
Head and body movements

3. The Nature of Sound
Sound
Audible variations in air pressure
Sound frequency: Number of cycles per second expressed in units called hertz (Hz)
Cycle: Distance between successive compressed patches

4. The Nature of Sound
Sound
Range: 20 Hz to 20,000 Hz
Pitch: High pitch = high frequency; low frequency = low pitch
Intensity: High intensity louder than low intensity

5. The Structure of the Auditory System

6. The Middle Ear
Components of the Middle Ear

7. 5 – Stapedius muscle
9 – Tensor Tympani muscle

8. The Middle Ear
Sound Force Amplification by the Ossicles
Pressure: Force by surface area
Greater pressure at oval window than tympanic membrane, moves fluids
The Attenuation Reflex
Response where onset of loud sound causes tensor tympani and stapedius muscle contraction
Function: Adapt ear to loud sounds, understand speech better

9. The Inner Ear
Anatomy of the Cochlea
Perilymph: Fluid in scala vestibuli and scala tympani
Endolymph: Fluid in scala media
Endocochlear potential: Endolymph electric potential 80 mV more positive than perilymph

10. The Inner Ear
Physiology of the Cochlea
Pressure at oval window, pushes perilymph into scala vestibuli, round window membrane bulges out
The Response of Basilar Membrane to Sound
Structural properties: Wider at apex, stiffness decreases from base to apex
Research: Georg von Békésy
Endolymph movement bends basilar membrane near base, wave moves towards apex

11. Georg von Békésy - Hungarian biophysicist born in Budapest.
In 1961, he was awarded the Nobel Prize in Physiology or Medicine for his research on the function of the cochlea in the mammalian hearing .

12. The Inner Ear
Travelling wave in the Basilar Membrane

13. The Inner Ear
The Organ of Corti and Associated Structures

14. The Inner Ear
Transduction by Hair Cells
Research: A.J. Hudspeth.
Sound: Basilar membrane upward, reticular lamina up and stereocilia bends outward

15. External ear
Middle ear
Internal ear
Air
External
acoustic
meatus
Malleus, incus,
stapes
(ossicles)
Tympanic
membrane
Oval
window
Fluids in cochlear canals
Pinna
Upper and middle
Lower
Pressure
Time
Spiral organ
(of Corti)
stimulated
One
vibration
Amplitude
Amplification
in middle ear

16. Central Auditory Processes
Auditory Pathway

17. Mechanisms of Sound Localization
Techniques for Sound Localization
Horizontal: Left-right, Vertical: Up-down
Localization of Sound in Horizontal Plane
Interaural time delay: Time taken for sound to reach from ear to ear
Interaural intensity difference: Sound at high frequency from one side of ear

18. Mechanisms of Sound Localization
Interaural time delay and interaural intensity difference

19. Mechanisms of Sound Localization
The Sensitivity of Binaural Neurons to Sound Location

20. Mechanisms of Sound Localization
Localization of Sound in Vertical Plane
Vertical sound localization based on reflections from the pinna

21. Auditory Cortex
Primary Auditory Cortex
Axons leaving MGN project to auditory cortex via internal capsule in an array
Structure of A1 and secondary auditory areas: Similar to corresponding visual cortex areas

22. The Vestibular System Importance of Vestibular System
Balance, equilibrium, posture, head, body, eye movement
Vestibular Labyrinth
Otolith organs - gravity and tilt
Semicircular canals - head rotation
Use hair cells, like auditory system, to detect changes

23. Figure 15.35: Structure of a macula, p. 594.
Macula of
saccule
Macula of
utricle
Kinocilium
Stereocilia
Otoliths
Otolithic
membrane
Hair bundle
Hair cells
Supporting
cells
Vestibular
nerve fibers

24. Figure 15.36: The effect of gravitational pull on a macula receptor cell in the utricle, p. 595.
Otolithic
membrane
Kinocilium
Ster
eocilia
Depolarization
Hyperpolarization
Receptor
potential
(Hairs bent towar
kinocilium) d
(Hairs bent away
from kinocilium)
Nerve
impulses
generated in
vestibular fiber
Increased
impulse frequency
Decreased
impulse frequency
Excitation
Inhibition

25. Figure 15.37: Location and sturcture of a crista ampullaris, p. 596.
Flow of
endolymph
(a)
Crista
ampullaris
Fibers of
vestibular nerve
Cupula
(b)
Turning motion
Ampulla
of left ear
Ampulla of
right ear
Cupula
Cupula at rest
Position
of cupula
during turn
Position of cupula
during turn
Fluid motion in
ducts
Increased firing
Horizontal ducts
Decreased firing
(c)
(d)
Afferent fibers of vestibular nerve

26. The Vestibular System
The Semicircular Canal
Structure

27. The Vestibular System Push-Pull Activation of Semicircular Canals
Three semicircular canals on one side
Helps sense all possible head-rotation angles
Each paired with another on opposite side of head
Push-pull arrangement of vestibular axons:

28. The Vestibular System The Vestibulo-Ocular Reflex (VOR)
also known as the oculocephalic reflex
a reflex eye movement that stabilizes images on the retina during head movement
Stabilization occurs by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field

29. END.