Transcript EAR`OLES
“If a tree falls…”
If a tree falls in the
forest and there is nobody
around to hear it…
Does it make a noise?
NO…Sound (like colour) is all in your head!
Hearing
What is Sound?
Compression & Rarefaction
of air molecules.
Sound Waves
Amplitude (Loudness)
Strength or height of the
wave
Frequency (Pitch)
Distance twixt consecutive
peaks
Mix (Timbre)
Interaction of different
waves
1 Hertz = 1 Cycle/Sec
Human Hearing
20 - 20k Hz
Perceiving Pitch
Place Theory - pitch determined by
point of maximal vibration on
basilar membrane
Traveling Wave Theory 1957
Georg von Békésy
1899-1972
Frequency Theory - pitch determined by the rate
at which the hair cells fire (i.e., 1KHz tone cause
hair cells to fire 1k times/sec)
Volley Principle
The Ear
Houses two senses
Hearing
Equilibrium (balance)
Receptors are mechanoreceptors
Anatomy of the Ear
The ear is divided into three areas
Outer
(external)
ear
Middle
ear
Inner
ear
Figure 8.12
Slide 8.21
The External Ear
Involved in
hearing only
Structures of
the external
ear
Pinna
(auricle)
External
auditory canal
Figure 8.12
Slide 8.22
The External Auditory Canal
Narrow chamber in the temporal bone
Lined with skin
Ceruminous (wax) glands are present
Ends at the tympanic membrane
Slide 8.23
Outer Ear
auditory/8th nerve
pinna
auditory canal
tympanic membrane
malleus
cochlea
incus
Pinna - collect and direct “sound” into auditory canal
Auditory Canal - amplify & funnel “sound” to
tympanic membrane
Tympanic Membrane - collect “sound” &
vibrate ossicles
The Middle Ear or Tympanic Cavity
Air-filled cavity within the temporal bone
Only involved in the sense of hearing
Slide
Middle Ear
malleus
incus
handle
of malleus
long process
of incus
stapes
Malleus - vibrate & move the Incus
Incus - vibrate & move the Stapes
Stapes - vibrate against Oval Window of Cochlea
The Middle Ear or Tympanic Cavity
Two tubes are associated with the inner
ear
The opening from the auditory canal is
covered by the tympanic membrane
The auditory tube connecting the middle ear
with the throat
Allows for equalizing pressure during yawning
or swallowing
This tube is otherwise collapsed
Slide
Bones of the Tympanic Cavity
Three bones
span the cavity
Malleus
(hammer)
Incus (anvil)
Stapes (stirrip)
Figure 8.12
Slide
Bones of the Tympanic Cavity
Vibrations from
eardrum move
the malleus
These bones
transfer sound
to the inner ear
Figure 8.12
Slide
Inner Ear or Bony Labyrinth
Includes sense organs for hearing and
balance
Filled with
perilymph
Figure 8.12
Slide
Inner Ear or Bony Labrynth
A maze of bony chambers within the
temporal bone
Cochlea
Vestibule
Semicircular
canals
Slide
Inner Ear
lateral
semicircular
canal
posterior
semicircular
canal
anterior
semicircuar
canal
cochlea
vestibule
Cochlea - filled with fluid & contains receptors
for hearing (Hair Cells)
Basilar Membrane - divides length of cochlea & holds
the hair cells
Auditory Pathway
Organs of Hearing
Organ of Corti
Located within the cochlea
Receptors = hair cells on the basilar
membrane
Gel-like tectorial membrane is capable of
bending hair cells
Cochlear nerve attached to hair cells
transmits nerve impulses to auditory cortex
on temporal lobe
Organs of Hearing
Slide
Mechanisms of Hearing
Vibrations from sound waves move
tectorial membrane
Hair cells are bent by the membrane
An action potential starts in the cochlear
nerve
Continued stimulation can lead to
adaptation
Slide 8.28
Mechanisms of Hearing
Figure 8.14
Slide 8.29
Organs of Equilibrium
Receptor cells are in two structures
Vestibule
Semicircular canals
Figure 8.16a, b
Slide
Organs of Equilibrium
Equilibrium has two functional parts
Static equilibrium – sense of gravity at rest
Dynamic equilibrium – angular and rotary
head movements
Figure 8.16a, b
Slide
Static Equilibrium
Maculae – receptors in the vestibule
Report on the position of the head
Send information via the vestibular nerve
Anatomy of the maculae
Hair cells are embedded in the otolithic
membrane
Otoliths (tiny stones) float in a gel around
the hair cells
Movements cause otoliths to bend the hair
cells
Slide 8.31
Function of Maculae
Figure 8.15
Slide 8.32
Dynamic Equilibrium
Crista ampullaris –
receptors in the
semicircular canals
Tuft of hair cells
Cupula (gelatinous cap)
covers the hair cells
Figure 8.16c
Slide
Dynamic Equilibrium
Action of angular head
movements
The cupula stimulates the
hair cells
An impulse is sent via the
vestibular nerve to the
cerebellum
Figure 8.16c
Slide
Chemical Senses – Taste and
Smell
Both senses use chemoreceptors
Stimulated by chemicals in solution
Taste has four types of receptors
Smell can differentiate a large range of
chemicals
Both senses complement each other
and respond to many of the same
stimuli
Slide 8.34
Olfaction – The Sense of Smell
Olfactory receptors are in the roof of the
nasal cavity
Neurons with long cilia
Chemicals must be dissolved in mucus for
detection
Impulses are transmitted via the
olfactory nerve
Interpretation of smells is made in the
cortex
Slide 8.35
Olfactory Epithelium
Figure 8.17
Slide 8.36
The Sense of Taste
Taste buds
house the
receptor
organs
Location of
taste buds
Most are on
the tongue
Soft palate
Cheeks
Figure 8.18a, b
Slide 8.37
Structure of Taste Buds
Gustatory cells are the receptors
Have gustatory hairs (long microvilli)
Hairs are stimulated by chemicals
dissolved in saliva
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Structure of Taste Buds
Impulses are carried to the gustatory
complex by several cranial nerves
because taste buds are found in
different areas
Facial nerve
Glossopharyngeal nerve
Vagus nerve
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Anatomy of Taste Buds
Figure 8.18
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 8.40
Taste Sensations
Sweet receptors
Sugars
Saccharine
Some amino acids
Sour receptors
Acids
Bitter receptors
Alkaloids
Salty receptors
Metal ions
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 8.41
Developmental Aspects of the
Special Senses
Formed early in embryonic development
Eyes are outgrowths of the brain
All special senses are functional at birth
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 8.42