yguhihuh

1. Psychology 355
The Auditory &
Vestibular Systems
Physiology of Auditory &
Vestibular Systems

2. Psychology 355 2
Introduction
Sensory Systems
A. Sense of hearing, audition
1. Detect sound
2. Perceive and interpret nuances
B. Sense of balance, vestibular system
1. Head and body location
2. Head and body movements

3. Psychology 355 3
The Nature of Sound
Sound
A. Audible variations in air pressure
B. Sound frequency: Number of cycles per
second expressed in units called Hertz (Hz)
C. Cycle: Distance between successive
compressed patches
D. Range: 20 Hz to 20,000 Hz
E. Pitch: High and Low
F. Intensity: Difference in pressure between
compressed and rarefied patches of air

4. Psychology 355 4
The Nature of Sound

5. Psychology 355 5
The Nature of Sound

6. Psychology 355 6
The Structure
of the Auditory System

7. Psychology 355 7
The Structure
of the Auditory System
I. Auditory pathway stages
A. Sound waves
B. Tympanic membrane
C. Ossicles
D. Oval window
E. Cochlea fluid
F. Sensory neuron response
II. Brain stem nuclei output
A. Thalamus to MGN to A1

8. Psychology 355 8
Components of the Middle Ear
The Middle Ear

9. Psychology 355 9
I. Sound Force Amplification by the Ossicles
A. Pressure: Force by surface area
B. Greater pressure at oval window than
tympanic membrane, moves fluids
II. The Attenuation Reflex
A. Response where onset of loud sound
causes tensor tympani and stapedius
muscle contraction
B. Function: Adapt ear to loud sounds,
understand speech better
The Middle Ear

10. Psychology 355 10
The Inner Ear
Anatomy of the Cochlea

11. Psychology 355 11
The Inner Ear
Anatomy of the Cochlea

12. Psychology 355 12
Physiology of the Cochlea
Pressure at oval window,
pushes perilymph into scala
vestibuli, round window
membrane bulges out
The Inner Ear

13. Psychology 355 13
The Organ of Corti
The Inner Ear

14. Psychology 355 14
Cilia
The Inner Ear

15. Psychology 355 15
Cilia
The Inner Ear

16. Psychology 355 16
The Inner Ear

17. Psychology 355 17
Transduction by Hair
Cells
Sound:
Basilar membrane
upward
reticular lamina up
stereocilia bends
outward
The Inner Ear

18. Psychology 355 18
The Inner Ear

19. Psychology 355 19
I. The Innervation of Hair Cells
A. One spiral ganglion fiber: One inner hair
cell, numerous outer hair cells
II. Amplification by Outer Hair Cells
A. Function: Sound transduction
B. Motor proteins: Change length of outer
hair cells
C. Prestin: Required for outer hair cell
movements
The Inner Ear

20. Psychology 355 20
The Inner Ear
The Basilar Membrane
Structural
properties: Wider
at apex, stiffness
decreases from
base to apex

21. Psychology 355 21
The Inner
Ear

22. Psychology 355 22
Central Auditory Processes
Auditory Pathway
A. More synapses at nuclei than visual
pathway, more alternative pathways
B. Anatomy
1. Dorsal cochlear nucleus, ventral
cochlear nucleus, superior olive,
inferior colliculus, MGN, lateral
lemniscus, auditory nerve fiber
2. Primary pathway: Ventral cochlear
nucleus to superior olive to inferior
colliculus to MGN to auditory
cortex

23. Psychology 355 23
Auditory
Pathway

24. Psychology 355 24
Auditory
Pathway

25. Psychology 355 25
Response Properties of Neurons in
Auditory Pathway
A. Characteristic frequency
Frequency at which neuron is most
responsive
B. Response
More complex and diverse on
ascending auditory pathway in
brain stem
Central Auditory Processes

26. Psychology 355 26
Encoding Sound
Intensity and Frequency
I. Encoding Information About Sound Intensity
A. Firing rates of neurons
B. Number of active neurons
II. Stimulus Frequency, Tonotopy, Phase Locking
A. Frequency sensitivity: Basilar membrane
B. Frequency: Highest at base, lowest at
cochlea apex
C. Tonotopy: Systematic organization of
characteristic frequency within auditory
structure

27. Psychology 355 27
Phase Locking
Consistent
firing of cell at
same sound
wave phase
Encoding Sound
Intensity and Frequency

28. Psychology 355 28
I. Techniques for Sound Localization
A. Horizontal: Left-right, Vertical: Up-down
II. Localization of Sound in Horizontal Plane
A. Interaural time delay: Time taken for
sound to reach from ear to ear
B. Interaural intensity difference: Sound at
high frequency from one side of ear
C. Duplex theory of sound localization:
1. Interaural time delay: 20-2000 Hz
2. Interaural intensity difference: 2000-
20000 Hz
Mechanisms of Sound Localization

29. Psychology 355 29
The Sensitivity of Binaural Neurons to
Sound Location
Monaural: Sound in one ear
Binaural: Sound at both ears
Superior olive: Cochlear nuclei input to
superior olive, greatest response to
specific interaural delay
Mechanisms of Sound Localization

30. Psychology 355 30
Mechanisms of Sound Localization
I. Delay Lines and Neuronal Sensitivity to Interaural
Delay
A. Sound from left side, activity in left cochlear
nucleus, sent to superior olive
B. Sound reaches right ear, activity in right
cochlear nucleus, first impulse far
C. Impulses reach olivary neuron at the same
time summation action potential
II. Localization of Sound in Vertical Plane
A. Sweeping curves of outer ear

31. Psychology 355 31
Mechanisms of
Sound Localization
A given binaural
neuron indicates the
amount of phase
disparity between
inputs from the left
and right ear.

32. Psychology 355 32
I. Acoustic Radiation
A. Axons leaving MGN project to auditory
cortex via internal capsule in an array
B. Structure of A1 and secondary auditory
areas: Similar to corresponding visual
cortex areas
II. Neuronal Response Properties
A. Frequency tuning: Similar characteristic
frequency
B. Isofrequency bands: Similar
characteristic frequency, diversity
among cells
Auditory Cortex

33. Psychology 355 33
Principles in Study of Auditory Cortex
Tonotopy, columnar organization of cells with similar
binaural interaction
Auditory Cortex

34. Psychology 355 34
I. Importance of Vestibular System
A. Balance, equilibrium, posture, head, body,
eye movement
II. The Vestibular Labyrinth
Lateral line Organs
Small pits or tubes
Function
Sense vibration
or pressure
changes
The Vestibular System

35. Psychology 355 35
The Vestibular System
Head Angle
Linear Acceleration
Head Rotation

36. Psychology 355 36
The Vestibular System
The Otolith Organs

37. Psychology 355 37
The Vestibular System
The Otolith Organs

38. Psychology 355 38
The Vestibular System
I. The Semicircular Canals
A. Function: Detect head movements
II. Structure
A. Crista: Sheet of cells where hair
cells of semicircular canals clustered
B. Ampulla: Bulge along canal,
contains crista
C. Cilia: Project into gelatinous cupula
D. Kinocili oriented in same direction
so all excited or inhibited together
E. Semicircular canals: Filled with
endolymph

39. Psychology 355 39
The Vestibular
System

40. Psychology 355 40
I. Push-Pull Activation of Semicircular Canals
A. Three semicircular canals on one side
1. Helps sense all possible head-rotation
angles
B. Canal: Each paired with another on
opposite side of head
C. Push-pull arrangement of vestibular
axons: Rotation causes excitation on
one side, inhibition on the other
The Vestibular System

41. Psychology 355 41
I. The Vestibulo-Ocular Reflex (VOR)
A. Function: Line of sight fixed on visual
target
B. Mechanism: Senses rotations of head,
commands compensatory movement of
eyes in opposite direction
C. Connections from semicircular canals, to
vestibular nucleus, to cranial nerve
nuclei  excite extraocular muscles
The Vestibular System

42. Psychology 355 42
The Vestibular System
Vestibular Pathology
A. Drugs (e.g., antibiotics) can damage
vestibular system
B. Effects:
1. Trouble fixating on visual targets
2. Walking and standing difficult

43. Psychology 355 43
Concluding Remarks
Hearing and Balance
A. Nearly identical sensory receptors (hair
cells)
B. Movement detectors: Periodic waves,
rotational, and linear force
C. Auditory system: Senses external
environment
D. Vestibular system: Senses movements
of itself

44. Psychology 355 44
Concluding Remarks
Hearing and Balance
A. Auditory Parallels Visual System
1. Tonotopy (auditory) and Retinotopy
(visual) preserved from sensory cells
to cortex code
B. Convergence of inputs from lower levels
 Neurons at higher levels have more
complex responses

45. Psychology 355
End of Presentation