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