Transcript Receptor potential

Chapter 29
The Senses
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
SENSORY RECEPTION
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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
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• 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
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Figure 29.3A
Heat Light touch Pain
Cold
Hair
Epidermis
Dermis
Nerve
to brain
Connective
tissue
Hair
movement
Strong
pressure
 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
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Changes in receptor potential lead to formation of
action potentials in sensory neurons
 If receptor found on separate cell - stimulus triggers
release of neurotransmitters from sensory cell
“Hairs” of a
receptor cell
Neurotransmitter
at a synapse
Sensory
neuron
Action
potentials
Action
potentials
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Figure 29.2A
Sugar
molecule
Taste
pore
1
Taste
bud
Sensory
receptor
cells
Sensory
neuron
Sweet
receptor
2
Sugar molecule
(stimulus)
Membrane
of a sensory
receptor cell
Signal
transduction
pathway
3
Ion
channels
4
Sensory
receptor
cell
Ion
Receptor
potential
5
Neurotransmitter
Sensory neuron
mV
Action potential
to the brain
6
No sugar
Sugar present
Rates of action potentials
Figure 29.2A_1
Sugar
molecule
Taste
pore
Taste
bud
1
Sensory
receptor
cells
1. sugar
molecules
enter the
taste bud
Sensory
neuron
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
(usually Na channels)
in the membrane to
close and others to
open
4. Change in ion
flow changes
membrane
potential
(receptor
potential) of
sensory cell
5. Change receptor
potential triggers
release of
neurotransmitter
Ion channels
Sensory
receptor
cell
4
Ion
Receptor
potential
5
6. AP
triggered in
sensory
neuron
Neurotransmitter
Sensory neuron
mV
Action potential
to the brain
6
No sugar
Sugar present
Rates of action potentials
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
Note:
Release of
neurotransmitter
from taste bud
due to opening of
Ca2+ channels!!
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.
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 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.
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.
HEARING AND BALANCE
Both hearing and balance use hair cells as
sensory cells
Hair cells = type of mechanoreceptor
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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
You do not need to all the
parts of the ear
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
Outer ear
Middle ear
Eardrum
Bones
Inner ear
Organ of
Corti (inside
the cochlea)
 Pressure waves transmitted to the fluid of the cochlea
– bend hair cells in the organ of Corti against the basilar membrane
and
– trigger nerve signals to the brain.
 Louder sounds generate more action potentials.
 Various pitches stimulate different regions of the organ of
Corti.
LE 49-9
Cochlea
Stapes
Vestibular
canal
Oval
window
Perilymph
Apex
Base
Round
window
Tympanic
canal
Axons of
sensory
neurons
Basilar
membrane
LE 49-10
Cochlea
(uncoiled)
Basilar
membrane
Apex
(wide and
flexible)
500 Hz (low pitch)
1 kHz
2 kHz
4 kHz
8 kHz
16 kHz
(high pitch)
Base
(narrow and stiff)
Frequency
producing
maximum vibration
Fig. 27.13a
Fig. 27.13b
29.5 The inner ear houses our organs of balance
 The three semicircular canals detect changes in
the head’s rotation or angular movement.
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Figure 29.5
Semicircular
canals
Nerve
Cochlea
Utricle
Saccule
Flow of fluid
Flow
of fluid
Cupula
Hairs
Hair
cell
Nerve fibers
Cupula
Direction of body movement
Fig. 27.14a
Fig. 27.14b
VISION
 All animal light detectors are based on cells called
photoreceptors that contain pigment molecules
that absorb light.
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Figure 29.7A
Figure 29.7B
29.10 The human retina contains two types of
photoreceptors: rods and cones
 The human retina contains two types of
photoreceptors.
1. Rods
– contain the visual pigment rhodopsin, which can absorb dim
light, and
– can detect shades of gray in dim light.
2. Cones
– contain the visual pigment photopsin, which absorbs bright
colored light, and
– allow us to see color in bright light.
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29.10 The human retina contains two types of
photoreceptors: rods and cones
 When rhodopsin and photopsin absorb light,
– they change chemically, and
– the change alters the permeability of the cell’s
membrane to ions
– The resulting receptor potential triggers a change in the
release of neurotransmitter
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Figure 29.7C
Sclera
Choroid
Ciliary body
Retina
Ligament
Cornea
Fovea
(center of
visual field)
Iris
Pupil
Optic
nerve
Aqueous
humor
Lens
Vitreous
humor
Artery
and vein
Blind spot
Figure 29.10B
Retina
Optic
nerve
Retina
Neurons
Photoreceptors
Rod Cone
Optic
nerve
fibers
To the brain
Figure 29.10B_1
Retina
Neurons
Photoreceptors
Rod Cone
Optic
nerve
fibers
To the brain
Figure 29.10A
Rod
Synaptic
terminals
Cell
body
Membranous disks
containing visual
pigments
Cone
Fig. 27.10
LE 49-20
Rod
Outer
segment
Disks
Inside
of disk
Cell body
cis isomer
Light
Enzymes
Synaptic
terminal
Cytosol
Retinal
Rhodopsin
Opsin
trans isomer
Page 543
TASTE AND SMELL
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Figure 29.12
29.11 Taste and odor receptors detect chemicals
present in solution or air
 Taste and smell depend on chemoreceptors that
detect specific chemicals in the environment.
 Chemoreceptors
– in taste buds detect molecules in solution and
– lining the nasal cavity detect airborne molecules.
 Taste and smell interact. Much of what we taste is
really smell.
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29.11 Taste and odor receptors detect chemicals
present in solution or air
 Taste receptors
– are located in taste buds on the tongue and
– produce five taste sensations:
1. sweet,
2. salty,
3. sour,
4. bitter, and
5. umami (the savory flavor of meats and cheeses).
© 2012 Pearson Education, Inc.
Figure 29.11
Brain
Olfactory
bulb
Bone
Nasal cavity
Epithelial
cell
Sensory
neuron
(chemoreceptor)
Odorous
substance
Cilia
Mucus
Figure 29.UN04
Sensory
receptors
are grouped into several types
(a)
(b)
involved
in
touch, hearing,
balance
many are
(d)
pain and
thermoreceptors
involved
in
many types
found in
taste and
smell
human skin
electromagnetic
receptors
sensitive
to
(c)
most common are
(e)