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Chapter 10b
Sensory Physiology
Chemoreception: Smell and Taste
• Olfaction is one of the oldest senses
• Taste is a combination of five basic
sensations
• Taste transduction
Olfaction
• Link between smell, memory, and emotion
• Vomeronasal organ (VNO) in rodents
• Response to sex pheromones
• Olfactory cells
• Olfactory epithelium in nasal cavity
• Odorants bind to odorant receptors, Gprotein-cAMP-linked membrane receptors
Anatomy Summary: The Olfactory System
Olfactory
bulb
Olfactory
tract
Olfactory
epithelium
(a) The olfactory epithelium lies high within the nasal
cavity, and its olfactory cells project to the olfactory bulb.
Figure 10-14a
Anatomy Summary: The Olfactory System
Olfactory bulb
Bone
Secondary
sensory neurons
Primary sensory
neurons (olfactory
cells)
Olfactory
epithelium
(b) The olfactory cells synapse with secondary
sensory neurons in the olfactory bulb.
Figure 10-14b
Anatomy Summary: The Olfactory System
Olfactory receptor cell
axons (cranial nerve I)
carry information to
olfactory bulb.
Lamina propria
Basal cell layer includes
stem cells that replace
olfactory receptor cells.
Developing
olfactory cell
Olfactory cell
(sensory neuron)
Supporting cell
Olfactory cilia
(dendrites) contain
odorant receptors.
Mucus layer:
Odorant molecules must
dissolve in this layer.
(c) Olfactory cells in the olfactory epithelium live only about
two months. They are replaced by new cells whose axons
must find their way to the olfactory bulb.
Figure 10-14c
Olfactory Pathways
Figure 10-15
Taste Buds
Figure 10-16a–b
Taste Buds
Sweet Umami Bitter Salty or sour
Tight junction
Support cell
Presynaptic
cell
ATP
Serotonin
Receptor cells
Primary gustatory
neurons
(c) Taste ligands create Ca2+ signals that
release serotonin or ATP.
Figure 10-16c
Summary of Taste Transduction
1
Gustducin
Sweet, umami,
or bitter ligand
Salt
Sour
Na+
H+
1
GPCR
2
1 Ligands activate the taste cell.
1
Na+ 2
H+ 2
Signal
transduction
Cell
depolarizes
Ca2+
Ca2+
3
3
2 Various intracellular pathways
are activated.
? ?
Ca2+
Ca2+ 3
Ca2+
3 Ca2+ signal in the cytoplasm
triggers exocytosis or ATP
formation.
Ca2+
?
ATP
Serotonin
4
4
4
Primary gustatory
neurons
5
5
5
4 Neurotransmitter or ATP is
released.
5 Primary sensory neuron fires
and action potentials are
sent to the brain.
Figure 10-17
Summary of Taste Transduction
1
Gustducin
Sweet, umami,
or bitter ligand
Salt
Sour
Na+
H+
1
GPCR
2
1 Ligands activate the taste cell.
1
Na+ 2
H+ 2
Signal
transduction
Cell
depolarizes
Ca2+
Ca2+
3
3
2 Various intracellular pathways
are activated.
? ?
Ca2+
Ca2+ 3
Ca2+
3 Ca2+ signal in the cytoplasm
triggers exocytosis or ATP
formation.
Ca2+
?
ATP
Serotonin
4
4
4
Primary gustatory
neurons
5
5
5
4 Neurotransmitter or ATP is
released.
5 Primary sensory neuron fires
and action potentials are
sent to the brain.
Figure 10-17, steps 1–5
Summary of Taste Transduction
• Humans and animals may develop specific
hunger such as salt appetite
Salt
Sweet, umami,
or bitter ligand
1
Gustducin
Sour
H+
Na+
1
GPCR
2
1 Ligands activate the taste cell.
1
Na+ 2
H+ 2
Signal
transduction
Cell
depolarizes
Ca2+
Ca2+
3
?
2 Various intracellular pathways
are activated.
?
Ca2+
3
Ca2+ 3
Ca2+
3 Ca2+ signal in the cytoplasm
triggers exocytosis or ATP
formation.
Ca2+
?
ATP
Serotonin
4
4
4
Primary gustatory
neurons
5
5
5
4 Neurotransmitter or ATP is
released.
5 Primary sensory neuron fires
and action potentials are
sent to the brain.
Figure 10-17
The Ear: Hearing
•
•
•
•
•
Perception of sound
Sound transduction
The cochlea
Auditory pathways
Hearing loss
Anatomy Summary: The Ear
EXTERNAL EAR
MIDDLE EAR
The pinna
directs sound
waves into
the ear
INNER EAR
The oval window and the round window separate
the fluid-filled inner ear from the air-filled middle ear.
Malleus
Incus
Semicircular Oval
canals
window
Nerves
Stapes
Vestibular
appartus
Ear
canal
Tympanic
membrane
Cochlea
Round
window
To
pharynx
Internal jugular
vein
Eustachian
tube
Figure 10-18
Sound Waves
• Hearing is our perception of energy carried
by sound waves
Figure 10-19a
Sound Waves
Figure 10-19b
Sound Transmission Through the Ear
1 Sound waves strike
the tympanic
membrane and
become vibrations.
2 The sound wave
3 The stapes is attached to
energy is transferred
the membrane of the oval
to the three bones
window. Vibrations of the
of the middle ear,
oval window create fluid
which vibrate.
waves within the cochlea.
Cochlear nerve
Incus
Ear canal
Malleus
Oval
Stapes window
5
Vestibular duct
(perilymph)
3
2
1
Tympanic
membrane
6
Cochlear duct
(endolymph)
4
Tympanic duct
(perilymph)
Round
window
4 The fluid waves push on the
5 Neurotransmitter release
onto sensory neurons
flexible membranes of the
creates action potentials
cochlear duct. Hair cells bend
that travel through the
and ion channels open,
cochlear nerve to
creating an electrical signal that
the brain.
alters neurotransmitter release.
6 Energy from the waves
transfers across the
cochlear duct into the
tympanic duct and is
dissipated back into
the middle ear at the
round window.
Figure 10-20, steps 1–6
Anatomy Summary: The Cochlea
Oval
window
Saccule
Vestibular
duct
Cochlear
duct
Organ of
Corti
Cochlea
Uncoiled
Helicotrema
Round
window
Tympanic
duct
Basilar
membrane
Bony cochlear wall
Vestibular duct
Cochlear duct
Tectorial membrane
Organ of Corti
The movement of the tectorial
membrane moves the cilia on
the hair cells.
Basilar
Tympanic
membrane
duct
Cochlear nerve transmits
action potentials from
the hair cells to the
auditory cortex.
Fluid wave
Cochlear
duct
Tectorial
membrane
Hair
cell
Tympanic
duct
Basilar membrane
Nerve fibers of
cochlear nerve
Figure 10-21
Anatomy Summary: The Cochlea
Oval
window
Saccule
Vestibular
duct
Cochlear Organ of
duct
Corti
Cochlea
Uncoiled
Helicotrema
Round
window
Tympanic
Basilar
duct
membrane
Figure 10-21 (1 of 3)
Anatomy Summary: The Cochlea
• Perilymph in vestibular and tympanic duct
• Similar to plasma
• Endolymph in cochlear duct
• Secreted by epithelial cells
• Similar to intracellular fluid
Anatomy Summary: The Cochlea
Bony cochlear wall
Vestibular duct
Cochlear duct
Tectorial membrane
Organ of Corti
Basilar
membrane
Tympanic
duct
Cochlear nerve transmits
action potentials from
the hair cells to the
auditory cortex.
Figure 10-21 (2 of 3)
Anatomy Summary: The Cochlea
The movement of the tectorial
membrane moves the cilia on
the hair cells.
Fluid wave
Cochlear
duct
Tectorial
membrane
Hair
cell
Tympanic
duct
Basilar membrane
Nerve fibers of
cochlear nerve
Figure 10-21 (3 of 3)
Signal Transduction in Hair Cells
(a) At rest
(b) Excitation
(c) Inhibition
Tip link
Some
channels
open
Stereocilium
Channels closed.
Less cation entry
hyperpolarizes cell.
More channels
open.
Cation entry
depolarizes
cell.
Hair cell
Primary
sensory
neuron
Action potentials
Action potentials increase
No action potentials
mV
Action potentials in
primary sensory neuron
Time
0
mV
–30
Release
Membrane potential
of hair cell
Excitation opens
ion channels
Release
Inhibition closes
ion channels
Figure 10-22
Sensory Coding for Pitch
Figure 10-23a
Sensory Coding for Pitch
Figure 10-23b
Auditory Pathways
• Waves
• Electrical signals in cochlea
• Primary sensory neurons to brain in medulla
oblongata
• Sound projected to nuclei
• Main pathway synapses in nuclei in midbrain
and thalamus
• Auditory cortex
Anatomy Summary: The Cochlea
Right auditory cortex
Left auditory cortex
Right
thalamus
Left
thalamus
Midbrain
Pons
Right cochlea
Cochlear branch of right
vestibulocochlear nerve (VIII)
Left cochlea
Medulla
Cochlear branch of left
vestibulocochlear nerve (VIII)
Figure 10-24
Hearing Loss
• Conductive
• No transmission through either external or
middle ear
• Central
• Damage to neural pathway between ear and
cerebral cortex or to cortex itself
• Sensorineural
• Damage to structures of inner ear