Transcript Slide 1

Biology 463 - Neurobiology
Topic 12
The Auditory and
Vestibular Systems
Lange
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
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
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
The Structure of the Auditory System
The Middle Ear
Components of the Middle Ear
5 – Stapedius muscle
9 – Tensor Tympani muscle
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
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
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
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 .
The Inner Ear
Travelling wave in the Basilar Membrane
The Inner Ear
The Organ of Corti and Associated Structures
The Inner Ear
Transduction by Hair
Cells
– Research: A.J.
Hudspeth.
– Sound: Basilar
membrane
upward, reticular
lamina up and
stereocilia bends
outward
External ear
Tympanic
membrane
Malleus, incus,
stapes
(ossicles)
Internal ear
Oval
window
Fluids in cochlear canals
Upper and middle
Lower
Pressure
Pinna
Air
External
acoustic
meatus
Middle ear
One
vibration
Amplitude
Amplification
in middle ear
Spiral organ
(of Corti)
stimulated
Time
Central Auditory Processes
Auditory Pathway
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
Mechanisms of Sound Localization
Interaural time delay and interaural intensity difference
Mechanisms of Sound Localization
The Sensitivity of Binaural Neurons to Sound Location
Mechanisms of Sound Localization
Localization of Sound in Vertical Plane
– Vertical sound localization based on reflections from the
pinna
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
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
Figure 15.35: Structure of a macula, p. 594.
Macula of
saccule
Macula of
utricle
Kinocilium
Stereocilia
Otoliths Otolithic
membrane
Hair bundle
Hair cells
Vestibular
nerve fibers
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Supporting
cells
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
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 d
kinocilium)
Nerve
impulses
generated in
vestibular fiber
Increased
impulse frequency
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Excitation
(Hairs bent away
from kinocilium)
Decreased
impulse frequency
Inhibition
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Figure 15.37: Location and sturcture of a crista ampullaris, p. 596.
Flow of
endolymph
Crista
ampullaris
(a)
Fibers of
vestibular nerve
Cupula
(b)
Turning motion
Cupula
Position
of cupula
during turn
(c)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Increased firing
(d)
Ampulla
of left ear
Ampulla of
right ear
Cupula at rest
Position of cupula
during turn
Fluid motion in
ducts
Horizontal ducts
Decreased firing
Afferent fibers of vestibular nerve
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
The Vestibular System
The Semicircular Canal
Structure
The Vestibular System
Push-Pull Activation of
Semicircular Canals
– Three semicircular
canals on one side
• Helps sense all
possible headrotation angles
– Each paired with
another on opposite
side of head
– Push-pull
arrangement of
vestibular axons:
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
END.