Transcript Life: The Science of Biology, Ninth Edition

SENSORY RECEPTION
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Ch. 46 Opener 1 Sensing Infrared Radiation
Ch. 46 Opener 2 Echolocating around an Obstacle Course
Fig. 27.2
Sensory Receptors
 Sensory receptors = specialized cells or neurons
that detect
– conditions of the external and internal world
 Sensory receptors convert stimulus to action
potential
– This is called sensory transduction
 Message of stimulus carried to CNS
– Interpretation of stimulus depends on area of CNS
stimulated
© 2012 Pearson Education, Inc.
• Sensory transduction begins with a receptor
protein that opens or closes ion channels in
response to stimulus
• Changes in ion flow change membrane
potential of sensory cell
• Receptor potential = membrane potential of
sensory cell
Sensory Receptor May be Found on Plasma
Membrane of a Separate Sensory Cell or on a
Sensory Neuron
© 2012 Pearson Education, Inc.
Figure 46.6 The Skin Feels Many Sensations
 Sensory receptor on
Separate Sensory Cell
– Vision
– Taste
– Hearing
– balance
 Sensory receptor on
specialized sensory nerve
ending
– Pain
– Heat
– Touch
– smell
Changes in receptor
potential lead to
formation of
action potentials
in sensory
neurons
 If receptor found on
sensory neuron stimulus triggers
action potentials in
receptor cell itself
© 2012 Pearson Education, Inc.
Sweet
receptor
2. sugar molecules bind
to sweet receptors
2
Sugar molecule
(stimulus)
Membrane
of a sensory
receptor cell
Signal
transduction 3
pathway
Ion
channels
Sensory
receptor
cell
4
Ion
3. the binding triggers
some ion channels in
the membrane to close
and others to open
4. Change in ion
flow change in
membrane
potential
(receptor
potential) of
sensory cell
LE 49-14
Taste pore
Sugar
molecule
Sensory
receptor
cells
Taste
bud
Tongue
Sensory
neuron
G protein
Adenylyl cyclase
Sugar
Sugar receptor
ATP
cAMP
Protein
kinase A
SENSORY
RECEPTOR
K+
CELL
Synaptic
vesicle
Ca2+
Neurotransmitter
Sensory neuron
How is stimulus interpreted?
 Different stimuli trigger different receptors and sensory cells;
which trigger different sensory neurons and travel to different
parts of brain
“Sugar” interneuron
“Salt” interneuron
Sugar
receptor
cell
Salt
receptor
cell
Brain
Taste
bud
Sensory
neurons
No sugar
Increasing sweetness
Taste
bud
No salt
Increasing saltiness
How is INTENSITY of stimulus detected?
 The stronger the stimulus,
– the more neurotransmitter released by the receptor cell
and
– the more frequently the sensory neuron transmits action
potentials to the brain.
 Repeated stimuli may lead to sensory adaptation,
the tendency of some sensory receptors to become
less sensitive when they are stimulated repeatedly.
© 2012 Pearson Education, Inc.
 The stronger the stimulus,
– the more neurotransmitter released by the receptor cell and
– the more frequently the sensory neuron transmits action potentials to
the brain.
“Hairs” of a
receptor cell
Neurotransmitter
at a synapse
Sensory
neuron
Fluid
movement
Fluid
movement
More
neurotransmitter
molecules
Fewer
neurotransmitter
molecules
Action
potentials
Action
potentials
1 Receptor cell at rest
2 Fluid moving in one direction
3 Fluid moving in the other direction
 Repeated stimuli may lead to sensory adaptation, the
tendency of some sensory receptors to become less sensitive
when they are stimulated repeatedly.
Figure 29.3B_3
Fluid
movement
Fewer
neurotransmitter
molecules
3
Fluid moving in the other direction
LE 49-2a
Weak
muscle stretch
Muscle
Stretch
receptor
Membrane
potential (mV)
Dendrites
Strong
muscle stretch
–50 Receptor potential
–50
–70
–70
Action potentials
0
0
–70
–70
Axon
0 1 2 3 4 5 6 7
Time (sec)
Crayfish stretch receptors have
dendrites embedded in abdominal
muscles. When the abdomen bends,
muscles and dendrites stretch, producing a
receptor potential in the stretch receptor. The
receptor potential triggers action potentials
0 1 2 3 4 5 6 7
Time (sec)
in the axon of the stretch receptor. A stronger
stretch produces a larger receptor potential
and higher frequency of action potentials.
Chemoreceptors
 Olfaction (smell)
– Pheromones and VNO
 Gustation (taste)
© 2012 Pearson Education, Inc.
Fig. 27.4-1
Fig. 27.4-2
Figure 46.5 Taste Buds Are Clusters of Sensory Cells
Figure 46.4 Olfactory Receptors Communicate Directly with the Brain
Mechanoreceptors
 Hearing and Balance
– Hair cells
 Lateral line in fish
 Pain, touch, muscle movements
– Stretch receptors
© 2012 Pearson Education, Inc.
LE 49-8
Middle
ear
Inner ear
Outer ear
Semicircular canals
Stapes
Middle
ear
Incus
Skull bones
Auditory nerve,
to brain
Malleus
Pinna
Tympanic
Auditory membrane
canal
Eustachian
tube
Tympanic
membrane
Oval
window
Cochlea
Round
window
Eustachian tube
Tectorial
membrane
Hair cells
Bone
Cochlea duct
Vestibular
canal
Basilar
membrane
Axons of
To auditory
sensory neurons nerve
Auditory
nerve
Tympanic
canal
Organ of Corti
Figure 46.10 Hair Cells Have Mechanosensors on Their Stereocilia
LE 49-2b
No fluid
movement
“Hairs” of
hair cell
Fluid moving in
one direction
More
neurotransmitter
Neurotransmitter at
synapse
Less
neurotransmitter
–50
–50
–70
Action potentials
0
–70
Membrane
potential (mV)
–50 Receptor potential
Membrane
potential (mV)
Membrane
potential (mV)
Axon
Fluid moving in
other direction
–70
0
Vertebrate hair cells have specialized cilia
or microvilli (“hairs”) that bend when
surrounding fluid moves. Each hair cell
releases an excitatory neurotransmitter
0
–70
–70
0 1 2 3 4 5 6 7
Time (sec)
–70
0 1 2 3 4 5 6 7
Time (sec)
at a synapse with a sensory neuron, which
conducts action potentials to the CNS.
Bending in one direction depolarizes the
hair cell, causing it to release more
0 1 2 3 4 5 6 7
Time (sec)
neurotransmitter and increasing frequency of
action potentials in the sensory neuron. Bending
in the other direction has the opposite effects.
Thus, hair cells respond to the direction of motion
as well as to its strength and speed.
Figure 46.9 Sensing Pressure Waves in the Inner Ear
Figure 46.9 Sensing Pressure Waves in the Inner Ear (Part 1)
Figure 46.11 Organs of Equilibrium
Figure 46.12 The Lateral Line Acoustic System Contains Mechanosensors
Photoreceptors
 Detect various regions of electromagentic
spectrum
– Visible light
– Infra-red
– UV
© 2012 Pearson Education, Inc.
Figure 46.17 Convergent Evolution of Eyes
Figure 46.21 The Human Retina
Figure 46.19 Rods and Cones
Figure 46.13 Light Changes the Conformation of Rhodopsin
LE 49-20
Rod
Outer
segment
Disks
Inside
of disk
Cell body
cis isomer
Light
Enzymes
Synaptic
terminal
Cytosol
Retinal
Rhodopsin
Opsin
trans isomer
Figure 46.20 Absorption Spectra of Cone Cells
Figure 46.14 A Rod Cell Responds to Light (Part 2)
Figure 46.15 Light Absorption Closes Sodium Channels
LE 49-21
Light
Active
rhodopsin
INSIDE OF DISK
EXTRACELLULAR
FLUID
PDE
Plasma
membrane
Inactive
rhodopsin
Transducin
Disk
membrane
Membrane
potential (mV)
0
Dark Light
cGMP
–40
GMP
Na+
Hyperpolarization
–70
Time
CYTOSOL
Na+
LE 49-22
Dark Responses
Light Responses
Rhodopsin inactive
Rhodopsin active
Na+ channels open
Na+ channels closed
Rod depolarized
Rod hyperpolarized
Glutamate
released
No glutamate
released
Bipolar cell either
depolarized or
hyperpolarized,
depending on
glutamate receptors
Bipolar cell either
hyperpolarized or
depolarized,
depending on
glutamate receptors
LE 49-23
Retina
Optic nerve
To
brain
Retina
Photoreceptors
Neurons
Cone Rod
Amacrine
cell
Optic
nerve Ganglion
fibers cell
Horizontal
cell
Bipolar
cell
Pigmented
epithelium