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IB-202-16-06
Chapter 49
Sensory and Motor Mechanisms
(pp 1045-1062)
Sensory input, motor output and
behavior!
The detection and processing of sensory
information and the generation of motor output is
the physiological basis for all animal behavior.
Behavior is not a linear sequence of sensing,
brain analysis and action, but rather a continuing
process. As animals move they are probing the
environment through that movement, sensing
changes and using the information to generate
the next action. It is a continuous cycle.
An example of sensing and acting
• Bats use sonar to detect their prey
• Moths, a common prey for bats can detect the
bat’s sonar with sensory hairs in the abdomen
and attempt to escape by diving in a spiral
pattern towards the ground.
• Both of these organisms have complex sensory
systems that facilitate their survival.
Figure 49.1
• The sensory and effector structures that
make up these systems have been
transformed by evolution into diverse
mechanisms that sense various stimuli and
generate the appropriate physical
movement
• The first step is converting the stimulus into
another form. Sensory receptors transduce
stimulus energy to electrical signals. The electrical
signals are transformed into action potentials and
travel to the the brain via sensory neurons
And the brain interprets them as a perception of the
stimuli and generates an appropriate response.
(Cross talk—some people see colors when they
hear music!—What is going on?) Action potentials
going from ear to visual center????
• Sensations begin with the detection of stimuli by sensory
receptors
• There are many kinds of receptors: heat, cold, pain,
pressure, light, hearing, osmotic, oxygen etc. Some are
located in the surface tissues of the body and others within
the brain, circulatory system and visceral organs.
• Locations:
• Exteroreceptors
–
Detect stimuli coming from the outside of the body such as
pressure waves, light and heat/cold.
• Interoreceptors
–
Detect internal stimuli chemoreceptors, osmoreceptors, pressure
etc.
Functions Performed by
Sensory Receptors
• All stimuli represent forms of energy
• Sensation involves converting this energy
into a change in the membrane potential of
sensory receptors
• Sensory receptors perform four functions
in this process
– Sensory transduction, amplification,
transmission, and integration
– The stretch receptor and hair receptor
represent these processes.
• Two types of sensory receptors exhibit
these functions
– A stretch receptor in a crayfish
Weak
muscle stretch
Muscle
Strong
muscle stretch
Stretch
receptor
Axon
Membrane
potential (mV)
Dendrites
–50 Receptor potential
–50
–70
–70
Action potentials
0
0
–70
–70
0 1 2 3 4 5 6 7
Time (sec)
(a) Crayfish stretch receptors have dendrites
embedded in abdominal muscles. When the
abdomen bends, muscles and dendrites
Figure 49.2a
stretch, producing a receptor potential in the
stretch receptor. The receptor potential triggers
action potentials in the axon of the stretch
Action potential has much more
energy than a decrease in receptor
potential! An example of an
amplification!
01 2 3 4 5 67
Time (sec)
receptor. A stronger stretch produces
a larger receptor potential and higher
requency of action potentials.
– A hair cell found in vertebrates
Depolarization of
hair cell!
“Hairs” of
hair cell
Fluid moving in
one direction
No fluid
movement
Neurotransmitter at
synapse
More
neurotransmitter
Action potentials
0
Membrane
potential (mV)
–70
Membrane
potential (mV)
Membrane
potential (mV)
–50
–50 Receptor potential
–70
–70
0
(b) Vertebrate hair cells have specialized cilia
or microvilli (“hairs”) that bend when surrounding fluid moves. Each hair cell releases
an excitatory neurotransmitter at a synapse
–70
0
–70
–70
01 2 3 4 5 6 7
Time (sec)
Figure 49.2b
Fluid moving in
other direction
Less
neurotransmitter
–50
Axon
Hyperpolarization
of hair cell. Less
likely to generate
an action potential!
0 1 2 3 4 5 6 7
Time (sec)
with a sensory neuron, which conducts action
potentials to the CNS. Bending in one direction
depolarizes the hair cell, causing it to release
more neurotransmitter and increasing frequency
Use of a neurotransmitter step and
amplification step!
01 2 3 4 5 6 7
Time (sec)
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.s
Sensory Transduction
• Sensory transduction is the conversion of
stimulus energy into a change in the
membrane potential of a sensory receptor
• This change in the membrane potential is
known as a receptor potential (resting
potential changes from -70 to -60)
• Many sensory receptors are extremely
sensitive
– With the ability to detect the smallest
physical unit of stimulus possible
Transmission
• After energy in a stimulus has been
transduced into a receptor potential
– Some sensory cells generate action
potentials, which are transmitted to the CNS
• Sensory cells without axons
– Release neurotransmitters at synapses with
sensory neurons
Integration
• The integration of sensory information
– Begins as soon as the information is
received
– Occurs at all levels of the nervous system
• The integration of sensory information
begins as soon as the information is
received. It occurs at all levels of the
nervous system
• Some receptor potentials are amplified
through summation
• Some receptor potentials are decreased
(attenuated) with repeated stimulation. This
is called sensory adaptation.
• Both of these responses can be viewed as
integration at the receptor level.
Types of Sensory Receptors
• Based on the energy they transduce,
sensory receptors fall into five categories
–
–
–
–
–
–
Mechanoreceptors
Chemoreceptors
Photoreceptors
Thermoreceptors
Pain receptors
Electromagnetic receptors includes (photo,
electrical and magnetism)
Mechanoreceptors
• Mechanoreceptors sense physical
deformation
– Caused by stimuli such as pressure, stretch,
motion, and sound
• The mammalian sense of touch relies on
mechanoreceptors that are the dendrites of
sensory neurons. These are naked nerves and
depolarization of the endings leads to an action
potential.
Cold
Light touch
Pain
Hair
Heat
Epidermis
Dermis
Figure 49.3
Nerve
Connective tissue
Hair movement
Strong pressure
Pain Receptors
• In humans, pain receptors, also called
nociceptors
– Are a class of naked dendrites in the
epidermis
– Respond to excess heat, pressure, or
specific classes of chemicals released from
damaged or inflamed tissues
Chemoreceptors
• Chemoreceptors include
– General receptors that transmit information about
the total solute concentration of a solution
– Specific receptors that respond to individual kinds of
molecules. Best example is that of a male moth’s
antennae sensing pheromone (bombykol) put out
by female moth a mile upwind. Male responds
when only 40 receptors bind compound / sec out of
20,000 receptors.
Figure 49.4
0.1 mm
• The most sensitive and specific
chemoreceptors known is present in the
antennae of the male silkworm moth
Electromagnetic Receptors
• Electromagnetic receptors detect various
forms of electromagnetic energy
– Such as visible light, electricity, and
magnetism
• Many mammals appear to use the Earth’s
magnetic field lines to orient themselves
as they migrate. There is also good
evidence that birds use magnetic field
lines during long migrations.
Figure 49.5b
(b) Some migrating animals, such as these beluga whales, apparently
sense Earth’s magnetic field and use the information, along with
other cues, for orientation.
Thermoreceptors
• Thermoreceptors, which respond to heat
or cold
– Help regulate body temperature by signaling
both surface and body core temperature.
– Infrared reception in pit vipers (rattlesnakes).
Pit Vipers (rattlesnakes) have
infrared receptors.
• Some snakes have very sensitive infrared receptors
–
That detect body heat of prey against a colder background
Snake can detect
.002C temp change
within the pit. Can
sense a rat 40 cm
away if its body
temp 10C above
the environmental.
Receptor just
branched ending of
the sensory axon.
Figure 49.5a
(a) This rattlesnake and other pit vipers have a pair of infrared receptors,
one between each eye and nostril. The organs are sensitive enough
to detect the infrared radiation emitted by a warm mouse a meter away.
The snake moves its head from side to side until the radiation is detected
equally by the two receptors, indicating that the mouse is straight ahead.
Pits below eyes.
Can also sense
direction
because of
depth of pit!
• Concept 49.2: The mechanoreceptors
involved with hearing and equilibrium
detect settling particles or moving fluid
• Hearing and the perception of body
equilibrium
– Are related in most animals
Sensing Gravity and Sound in
Invertebrates
• Most invertebrates have sensory organs called
statocysts
–
That contain mechanoreceptors and function in their sense of
equilibrium
Statolith is a
secretion of
protein and
calcium
carbonate! In
fish they
Statolith
increase in size
as the fish grows
and can be used
to age fish by
counting the
Figure 49.6
annual rings
!
Ciliated
receptor cells
Cilia
Sensory nerve fibers
• Many arthropods sense sounds with body
hairs that vibrate or with localized “ears”
consisting of a tympanic membrane and
receptor cells. Cockroach escape
response!
Tympanic
membrane
Figure 49.7
1 mm
Sensory Perception in Aquatic Vertebrates
• The lateral line system of fishes and
tadpoles contains mechanoreceptors
– With hair cells that respond to water
movement
Lateral
line
Lateral line canal
Scale
Epidermis Neuromast
Neuromast
includes the
gelatinous cupula,
sensory hairs and
hair cells!
Segmental muscles of body wall
Opening of lateral
line canal
Lateral nerve
Cupula
Sensory
hairs
Supporting cell
Figure 49.12
Nerve fiber
Hair cell
Water flows through the
channel and deforms
the cupula. Also
pressure waves in the
water deform it!
Hearing and Equilibrium in
Vertebrates.
• In most terrestrial vertebrates
– The sensory organs for hearing and
equilibrium are closely associated in the ear
Deformation of hair cells basis for hearing in
mammals.
1
2 The middle ear and inner ear
Overview of ear structure
Incus
Middle
ear
Inner ear
Outer ear
Skull
bones
Semicircular
canals
Stapes
Malleus
Auditory nerve,
to brain
Pinna
Tympanic
membrane
Auditory
canal
Hair cells
Cochlea
Eustachian
tube
Tectorial
membrane
Tympanic
membrane
Oval
window
Eustachian
tube
Round
window
Cochlear duct
Bone
Vestibular canal
Auditory nerve
Basilar
membrane
Figure 49.8
Axons of
sensory neurons
4 The organ of Corti
To auditory
nerve
Tympanic canal
3 The cochlea
Organ of Corti
3 chambers!
Hearing
• Vibrating objects create percussion waves
in the air
– That cause the tympanic membrane (ear
drum) to vibrate
• The three bones of the middle ear
– Transmit the vibrations to the oval window on
the cochlea to the fluid of the inner ear.
• These vibrations create pressure waves in the
fluid in the cochlea
– That travel through the vestibular canal and into the
tympanic canal. They ultimately strike the round
window where they are dissipated.
Cochlea
Stapes
Axons of
sensory
neurons
Oval
window
Vestibular
canal
Perilymph
Base
Figure 49.9
Round
window
Tympanic
Basilar
canal
membrane
Apex
• The pressure waves in the vestibular canal
– Cause the basilar membrane to vibrate up and
down causing its hair cells to bend
• The bending of the hair cells depolarizes
their membranes
– Sending action potentials that travel via the
auditory nerve to the brain
• The cochlea can distinguish pitch
– Because the basilar membrane is not uniform along
its length (thinner at one end), it vibrates more
vigorously at a certain frequency! Louder greater
amplitude deforms hair more.
Cochlea
(uncoiled)
Apex
(wide and flexible)
Basilar
membrane
Receptor
potential
causes influx of
Ca+ which in
turn causes
release of
transmitter and Figure 49.10
action potential!
1 kHz
500 Hz
(low pitch)
2 kHz
4 kHz
8 kHz
16 kHz
(high pitch)
Base
(narrow and stiff)
Frequency producing maximum
vibration
Equilibrium
• Several of the organs of the inner ear
– Detect body position and balance
Equilibrium
• The utricle, saccule, and semicircular canals in
the inner ear function in balance and equilibrium
The semicircular canals, arranged in three
spatial planes, detect angular movements
of the head.
Each canal has at its base a
swelling called an ampulla,
containing a cluster of hair cells.
When the head changes its rate
of rotation, inertia prevents
endolymph in the semicircular
canals from moving with the head,
so the endolymph presses against
the cupula, bending the hairs.
Flow
of endolymph
Flow
of endolymph
Vestibular nerve
Cupula
Hairs
Hair
cell
Nerve
fibers
Vestibule
Utricle
Body movement
Saccule
Figure 49.11
The utricle and saccule tell the brain which
way is up and inform it of the body’s
position or linear acceleration.
The hairs of the hair cells
project into a gelatinous cap
called the cupula.
Bending of the hairs increases the
frequency of action potentials in
sensory neurons in direct
proportion to the amount of
rotational acceleration.
Hearing and Equilibrium in
Other Vertebrates
• Like other vertebrates, fishes and
amphibians
– Also have inner ears located near the brain
• Concept 49.3: The senses of taste and
smell are closely related in most animals
• The perceptions of gustation (taste) and
olfaction (smell)
– Are both dependent on chemoreceptors that
detect specific chemicals in the environment
• The taste receptors of insects are located
within sensory hairs called sensilla
– Which are located on the feet and in
mouthparts
EXPERIMENT Insects taste using gustatory sensilla (hairs) on their feet and
mouthparts. Each sensillum contains four chemoreceptors with dendrites that
extend to a pore at the tip of the sensillum. To study the sensitivity of each
chemoreceptor, researchers immobilized a blowfly (Phormia regina) by attaching
it to a rod with wax. They then inserted the tip of a microelectrode into one
sensillum to record action potentials in the chemoreceptors, while they used a
pipette to touch the pore with various test substances.
To brain
Chemoreceptors
Sensillum
Microelectrode
To voltage
recorder
CONCLUSION Any natural food probably stimulates multiple chemoreceptors. By
integrating sensations, the insect’s brain can apparently distinguish a very large
number of tastes.
Figure 49.13
Pore at tip
Pipette containing
test substance
Number of action potentials
in first second of response
RESULTS
Each chemoreceptor is especially sensitive to a particular
class of substance, but this specificity is relative; each cell can respond to some
extent to a broad range of different chemical stimuli.
Chemoreceptors
50
30
10
0
0.5 M
NaCl
0.5 M
Sucrose
Stimulus
Meat
Honey
• The receptor cells for taste in humans are
modified epithelial cells organized into taste buds
• Five taste perceptions involve several signal
transduction mechanisms
– Sweet, sour, salty, bitter, and umami (elicited
by glutamate)
• Transduction in taste receptors
– Occurs by several mechanisms
– Na and H+ (sour) diffuse through channels on
the taste receptor depolarizing it. Glutmate
binds to Na channel opening it. Quinine (bitter)
binds to K channels and closes them
(depolarizing). All generate action potential.
Sweetness next slide!
• Sensing sweetness
Taste pore
Sugar molecule
Taste bud
Sensory
receptor
cells
Sensory
neuron
Tongue
1
Sugar
A sugar molecule binds
to a receptor protein on
the sensory receptor cell.
G protein
Sugar
receptor
Cell depolarizes
because K builds
up in the cell from
the Na/K ATPase
pump.
Adenylyl cyclase
2 Binding initiates a signal transduction pathway
involving cyclic AMP and protein kinase A.
ATP
cAMP
Protein
kinase A
3 Activated protein kinase A closes K+ channels in
the membrane.
SENSORY
K+
RECEPTOR
CELL
Synaptic
4 The decrease in the membrane’s permeability to
K+ depolarizes the membrane.
vesicle
—Ca2+
5 Depolarization opens voltage-gated calcium ion
(Ca2+) channels, and Ca2+ diffuses into the receptor
cell.
Neurotransmitter
6 The increased Ca2+ concentration causes
synaptic vesicles to release neurotransmitter.
Figure 49.14
Sensory neuron
Smell in Humans
• Olfactory receptor cells
– Are neurons that line the upper portion of the
nasal cavity
Olfaction
• When odorant molecules bind to specific
receptors
– A signal transduction pathway is triggered,
sending action potentials to the brain
Brain
1000 ordorant
receptors in
humans.
Represents
3% of human
genes!
Probably don’t
use them all
anymore.
Action potentials
Odorant
Figure 49.15
Olfactory bulb
Nasal cavity
Bone
Epithelial cell
Odorant
receptors
Chemoreceptor
Plasma
membrane
Odorant
Cilia
Mucus
• Concept 49.4: Similar mechanisms
underlie vision throughout the animal
kingdom
• Many types of light detectors
– Have evolved in the animal kingdom and
may be homologous
Vision in Invertebrates
• Most invertebrates
– Have some sort of light-detecting organ.
Flatworms, some jelly fish, scallops
(molluscs), crustaceans and insects.
• One of the simplest is the eye cup of planarians
– Which provides information about light intensity and
direction but does not form images
Light
Eyes positioned
so that light
coming from
one side does
not illuminate
eye on opposite
side.
Light shining from
the front is detected
Photoreceptor
Visual pigment
Ocellus
Figure 49.16
Nerve to
brain
Screening
pigment
Light shining from
behind is blocked
by the screening pigment
• Two major types of image-forming eyes
have evolved in invertebrates
– The compound eye and the single-lens eye
Compound Eyes
• Compound eyes are found in insects and
crustaceans and consist of up to several
thousand light detectors called ommatidia
2 mm
(a) The faceted eyes on the
head of a fly,
photographed with
a stereomicroscope.
(b) The cornea and crystalline cone of
each ommatidium function as
a lens that focuses light on the
rhabdom, a stack of pigmented
plates inside a circle of
photoreceptors. The rhabdom
traps light and guides it to
photoreceptors. The image
formed by a compound eye is a
mosaic of dots produced by different
intensities of light entering the
many ommatidia from different angles.
Cornea
Crystalline
cone
Rhabdom
Axons
Figure 49.17a–b
Photoreceptor
Ommatidium
Lens
• Single-lens eyes
– Are found in some jellies, polychaetes,
spiders, and many molluscs
– Work on a camera-like principle
The Vertebrate Visual System
• The eyes of vertebrates are camera-like
– But they evolved independently and differ
from the single-lens eyes of invertebrates
Structure of the Eye
• The main parts of the vertebrate eye are
– The sclera, which includes the cornea
– The choroid, a pigmented layer
– The conjunctiva, that covers the outer
surface of the sclera
– The iris, which regulates the pupil
– The retina, which contains photoreceptors
– The lens, which focuses light on the retina
• The structure of the vertebrate eye
Sclera
Choroid
Retina
Ciliary body
Fovea (center
of visual field)
Suspensory
ligament
Cornea
Iris
Optic
nerve
Pupil
Aqueous
humor
Lens
Vitreous humor
Central artery and
vein of the retina
Figure 49.18
Optic disk
(blind spot)
• Humans and other mammals
– Focus light by changing the shape of the lens
Front view of lens
and ciliary muscle
Lens (rounder)
Ciliary muscles contract, pulling
border of choroid toward lens
Choroid
Suspensory ligaments relax
Retina
Ciliary
muscle
Lens becomes thicker and rounder,
focusing on near objects
Suspensory
ligaments
(a) Near vision (accommodation)
Ciliary muscles relax, and border of
choroid moves away from lens
Suspensory ligaments
pull against lens
Lens becomes flatter, focusing on
distant objects
Figure 49.19a–b
(b) Distance vision
Lens (flatter)
• The human retina contains two types of
photoreceptors
– Rods are sensitive to light but do not
distinguish colors
– Cones distinguish colors but are not as
sensitive
Sensory Transduction in the Eye
• Each rod or cone in the vertebrate retina
– Contains visual pigments that consist of a
light-absorbing molecule called retinal
bonded to a protein called opsin
• Rods contain the pigment rhodopsin
– Which changes shape when it absorbs light
Rod
Outer
segment
H
H2 C
H
CH3
C
CH3
C
H
H2 C
Disks
C
C
C
C
CH3 H
H3 C
H
C
C
C
C
H
O
C
H
C
C
H
H
CH3
cis isomer
Inside
of disk
Cell body
Enzymes
Light
Synaptic
terminal
H
H
H2 C
CH3
CH3
C
H
H
H
H2 C
C
C
C
C
Cytosol
Rhodopsin
Retinal
C
C
C
CH3 H
C
CH3
C
CH3
H
C
C
CH3
C
O
H
trans isomer
Opsin
Figure 49.20a, b
(a) Rods contain the visual pigment rhodopsin, which is embedded
in a stack of membranous disks in the rod’s outer segment.
Rhodopsin consists of the light-absorbing molecule retinal
bonded to opsin, a protein. Opsin has seven  helices that span
the disk membrane.
(b) Retinal exists as two isomers. Absorption of light converts
the cis isomer to the trans isomer, which
causes opsin to change its conformation (shape).
After a few minutes, retinal detaches from opsin.
In the dark, enzymes convert retinal back to its cis
form, which recombines with opsin to form rhodopsin.
Processing Visual Information
• The processing of visual information
begins in the retina itself. This is
accomplished by the interconnections with
three types of cells before an action
potential is transmitted to the brain via the
optic nerve. Some of these connections
are inhibitory while others are stimulatory.
• Absorption of light by retinal
– Triggers a signal transduction pathway
Light
EXTRACELLULAR
FLUID
INSIDE OF DISK
Active rhodopsin
PDE
CYTOSOL
Plasma
membrane
Membrane
potential (mV)
0
Dark Light
Inactive rhodopsin
Transducin
cGMP
Disk membrane
– 40
GMP
Na+
1 Light
isomerizes
retinal, which
activates
rhodopsin.
Figure 49.21
2 Active
rhodopsin
in turn
activates a G
protein called
transducin.
3 Transducin
activates the
enzyme
phosphodiesterae
(PDE).
4 Activated PDE
detaches cyclic
guanosine
monophosphate
(cGMP) from
Na+ channels in
the plasma
membrane by
hydrolyzing
cGMP to GMP.
– 70
– Hyperpolarization
Time
Na+
5 The Na+ channels
close when cGMP
detaches. The
membrane’s
permeability to
Na+ decreases,
and the rod
hyperpolarizes.
• In the dark, both rods and cones
– Release the neurotransmitter glutamate into
the synapses with neurons called bipolar
cells, which are either hyperpolarized or
depolarized
• In the light, rods and cones hyperpolarize
– Shutting off their release of glutamate
• The bipolar cells
– Are then either depolarized or hyperpolarized
Dark Responses
Rhodopsin inactive
Rhodopsin active
Na+ channels open
Na+ channels closed
Rod depolarized
Rod hyperpolarized
Glutamate
released
Figure 49.22
Light Responses
Bipolar cell either
depolarized or
hyperpolarized,
depending on
glutamate receptors
No glutamate
released
Bipolar cell either
hyperpolarized or
depolarized,
depending on
glutamate receptors
• Three other types of neurons contribute to
information processing in the retina
– Ganglion cells, horizontal cells, and amacrine cells
Retina
Optic nerve
To
brain
Retina
Photoreceptors
Neurons
Cone Rod
Amacrine
cell
Figure 49.23
Optic
nerve
fibers
Ganglion
cell
Horizontal
cell
Bipolar
cell
Pigmented
epithelium
• Signals from rods and cones
– Travel from bipolar cells to ganglion cells
• The axons of ganglion cells are part of the optic
nerve
– That transmit information to the brain
Optic nerve
Optic chiasm
Lateral
geniculate
nucleus
Figure 49.24
Primary
visual cortex
Left
visual
field
Right
visual
field
Left
eye
Right
eye
• Most ganglion cell axons lead to the lateral
geniculate nuclei of the thalamus
– Which relays information to the primary visual
cortex
• Several integrating centers in the cerebral
cortex
– Are active in creating visual perceptions