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Chapter 49
• Sensory and Motor Mechanisms
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• Sensing and Acting
• e.g. Bats use sonar to detect their prey
• Moths, a common prey for bats
– Can detect the bat’s sonar and attempt to flee
Figure 49.1
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• Sensory receptors transduce stimulus energy
and transmit signals to CNS
• Sensations are action potentials
• The brain interprets  perception of stimuli
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• Exteroreceptors
– Stimuli f/ outside of the body
• Interoreceptors
– Detect internal stimuli
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– vertebrate hair cell
“Hairs” of
hair cell
Fluid moving in
one direction
No fluid
movement
Neurotransmitter at
synapse
More
neurotransmitter
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
(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
0
–70
–70
01 2 3 4 5 6 7
Time (sec)
–70
0 1 2 3 4 5 6 7
Time (sec)
01 2 3 4 5 6 7
Time (sec)
with a sensory neuron, which conducts action
potentials to the CNS. Bending in one direction of action potentials in the sensory neuron.
depolarizes the hair cell, causing it to release
Bending in the other direction has the opposite
more neurotransmitter and increasing frequency effects. Thus, hair cells respond to the direction
of motion as well as to its strength and speed.s
Figure 49.2b
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Sensory Transduction
• Conversion of stimulus energychange in
membrane potential of a sensory receptor
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Integration
• Begins as soon as the information is received
• Occurs at all levels of the nervous system
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Types of Sensory Receptors
• Mechanoreceptors
• Chemoreceptors
• Electromagnetic receptors
• Thermoreceptors
• Pain receptors
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Mechanoreceptors
• sense physical deformation
– e.g. pressure, stretch, motion, and sound
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• mammalian sense of touch
Cold
Light touch
Pain
Hair
Heat
Epidermis
Dermis
Figure 49.3
Nerve
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Connective tissue
Hair movement
Strong pressure
Chemoreceptors
• Transmit information about solute
concentration
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Figure 49.4
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0.1 mm
• e.g. antennae of the male silkworm moth
Electromagnetic Receptors
• Detect visible light, electricity, and magnetism
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• E.g. snake infrared receptors detect body heat
of prey
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.
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• Many mammals use the Earth’s magnetic field
lines to orient themselves as they migrate
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.
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Thermoreceptors
• Help regulate body temperature by signaling
both surface and body core temperature
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Pain Receptors (nociceptors)
• Respond to excess heat, pressure, etc.
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• The mechanoreceptors involved with hearing
and equilibrium detect moving fluid
• Hearing and the perception of body equilibrium
– Are related in most animals
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Sensing Gravity and Sound in Invertebrates
• Statocysts
Ciliated
receptor cells
Statolith
Figure 49.6
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Cilia
Sensory nerve fibers
• Arthropods sense sounds with body hairs that
vibrate or with localized “ears” consisting of a
tympanic membrane and receptor cells
Tympanic
membrane
Figure 49.7
1 mm
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Hearing and Equilibrium in Mammals
• e.g. human ear
1
2 The middle ear and inner ear
Overview of ear structure
Incus
Middle
ear
Inner ear
Outer ear
Stapes
Malleus
Skull
bones
Semicircular
canals
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
To auditory
nerve
4 The organ of Corti
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Tympanic canal
3 The cochlea
Organ of Corti
Hearing
• Vibrating objects create percussion waves in
the air tympanic membrane vibrates3
bones of the middle ear  vibrations to oval
window on the cochlea
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• vibrations create pressure waves in the fluid in
the cochlea vestibular canal ultimately
strike the round window
Cochlea
Stapes
Axons of
sensory
neurons
Oval
window
Vestibular
canal
Base
Figure 49.9
Round
window
Tympanic
canal
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Basilar
membrane
Perilymph
Apex
 hair cells bend depolarizes membranes
action potentials  auditory nerve  brain
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• The cochlea can distinguish pitch
Cochlea
(uncoiled)
Apex
(wide and flexible)
Basilar
membrane
1 kHz
500 Hz
(low pitch)
2 kHz
4 kHz
8 kHz
16 kHz
(high pitch)
Figure 49.10
Base
(narrow and stiff)
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Frequency producing maximum
vibration
Equilibrium
• semicircular canals in the inner ear
semicircular canals
The
, 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.
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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.
• Lateral line system (mechanoreceptors)
– hair cells that respond to water movement
Lateral
line
Lateral line canal
Scale
Epidermis Neuromast
Segmental muscles of body wall
Opening of lateral
line canal
Lateral nerve
Cupula
Sensory
hairs
Supporting cell
Figure 49.12
Nerve fiber
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Hair cell
• Taste and smell are closely related
• Gustation (taste) and olfaction (smell)
dependent on chemoreceptors that detect
specific chemicals
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• The taste receptors of insects are located on
the feet and in mouthparts
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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
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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
Taste in Humans
• Modified epithelial cells organized into taste
buds
• Five taste perceptions; sweet, sour, salty, bitter,
and umami (elicited by glutamate)
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Smell in Humans
• Olfactory receptor cells line the upper portion of
the nasal cavity
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• When odorant molecules bind to specific
receptors a signal transduction pathway is
triggered, sending action potentials to the brain
Brain
Action potentials
Odorant
Olfactory bulb
Nasal cavity
Bone
Epithelial cell
Odorant
receptors
Chemoreceptor
Plasma
membrane
Figure 49.15
Odorant
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Cilia
Mucus
Vision
• Most invertebrates
– Have some sort of light-detecting organ
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• e.g. eye cup of planarians
Light
Light shining from
the front is detected
Photoreceptor
Nerve to
brain
Visual pigment
Ocellus
Figure 49.16
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Screening
pigment
Light shining from
behind is blocked
by the screening pigment
• 2 types of image-forming eyes have evolved in
invertebrates
– compound eye and the single-lens eye
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• Compound eyes are found in insects and
crustaceans
2 mm
(a) The faceted eyes on the
head of a fly,
photographed with
a stereomicroscope.
Cornea
(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.
Crystalline
cone
Rhabdom
Axons
Figure 49.17a–b
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Photoreceptor
Ommatidium
Lens
• Single-lens eyes
– found in some jellies, polychaetes, spiders,
and many molluscs
– camera-like principle
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The Vertebrate Visual System
• Camera-like eye
– But they evolved independently and differ from
the single-lens eyes of invertebrates
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Structure of the Eye
• Main parts:
– sclera, which includes the cornea
– choroid, a pigmented layer
– conjunctiva, that covers the outer surface of
the sclera
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– iris, regulates the pupil
– retina, contains photoreceptors
– lens, focuses light on the retina
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• 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
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Optic disk
(blind spot)
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
Suspensory
ligaments
objects
(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
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Lens (flatter)
• Retina contains two types of photoreceptors
– Rods,sensitive to light but do not distinguish
colors
– Cones, distinguish colors but are not as
sensitive
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• 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.
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(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.
• Signals from rods and conesbipolar cells
ganglion cells optic nerve brain
Left
visual
field
Right
visual
field
Left
eye
Right
eye
Optic nerve
Optic chiasm
Lateral
geniculate
nucleus
Primary
visual cortex
Figure 49.24
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• Integrating centers in the cerebral cortex create
visual perceptions
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Animal skeletons
• Support, protection, and movement
• Movement results from muscles working
against some type of skeleton
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Hydrostatic Skeletons
• Fluid held under pressure in a closed body
compartment
• Cnidarians, flatworms, nematodes, and
annelids
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• Annelids use their hydrostatic skeleton for
peristalsis (rhythmic waves of muscle
contractions)
(a) Body segments at the head and just in front of the rear
are short and thick (longitudinal muscles contracted;
circular muscles relaxed) and anchored to the ground by
bristles. The other segments are thin and elongated
(circular muscles contracted; longitudinal muscles
relaxed.)
Longitudinal
muscle relaxed
(extended)
Bristles
(b) The head has moved forward because circular muscles
in the head segments have contracted. Segments
behind the head and at the rear are now thick and
anchored, thus preventing the worm from slipping
backward.
(c) The head segments are thick again and anchored in
their new positions. The rear segments have released
their hold on the
ground and have been pulled forward.
Figure 49.25a–c
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Circular
muscle
contracted
Circular
muscle
relaxed
Longitudinal
muscle
contracted
Head
Exoskeletons
• Hard encasement deposited on the surface of
an animal
• Molluscs and arthropods
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Endoskeletons
• Hard supporting elements such as bones,
buried within the soft tissue of an animal
• Sponges, echinoderms, and chordates
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• Mammalian skeleton; 200 bones, some fused
together and others connected at joints by
ligaments that allow freedom of movement
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• The human skeleton
key
Axial skeleton
Appendicular
skeleton
Skull
Examples
of joints
Head of
humerus
Scapula
1
Shoulder
girdle
Clavicle
Scapula
Sternum
Rib
Humerus
2
Vertebra
3
Radius
Ulna
Pelvic
girdle
1 Ball-and-socket joints, where the humerus contacts
the shoulder girdle and where the femur contacts the
pelvic girdle, enable us to rotate our arms and
legs and move them in several planes.
Humerus
Carpals
Phalanges
Ulna
Metacarpals
Femur
Patella
2 Hinge joints, such as between the humerus and
the head of the ulna, restrict movement to a single
plane.
Tibia
Fibula
Ulna
Figure 49.26
Tarsals
Metatarsals
Phalanges
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Radius
3 Pivot joints allow us to rotate our forearm at the
elbow and to move our head from side to side.
Physical Support on Land
• Skeleton, muscles, and tendons help support
large land vertebrates
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• Muscles move skeletal parts by contracting
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• muscles are attached to the skeleton in
antagonistic pairs, working against each other
Human
Grasshopper
Extensor
muscle
relaxes
Biceps
contracts
Triceps
relaxes
Tibia
flexes
Forearm
flexes
Extensor
muscle
contracts
Biceps
relaxes
Forearm
extends
Figure 49.27
Flexor
muscle
contracts
Triceps
contracts
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Tibia
extends
Flexor
muscle
relaxes
Vertebrate Skeletal Muscle
• hierarchy of smaller and smaller units
Muscle
Bundle of
muscle fibers
Nuclei
Single muscle fiber
(cell)
Plasma membrane
Myofibril
Z line
Light
band
Dark band
Sarcomere
0.5 m
TEM
I band
A band
I band
M line
Thick
filaments
(myosin)
Thin
filaments
(actin)
Figure 49.28
Z line
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H zone
Sarcomere
Z line
• Skeletal muscle muscle fiber myofibrils
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• Myofibrils are composed to 2 kinds of
myofilaments
– Thin filaments, consisting of actin
– Thick filaments, arrays of myosin molecules
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• Skeletal muscle is striated
– Because the regular arrangement of the
myofilaments creates a pattern of light and
dark bands
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The Sliding-Filament Model of Muscle Contraction
• The filaments slide past each other
longitudinally, producing more overlap between
the thin and thick filaments
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0.5 m
(a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bands
and H zone are relatively wide.
Z
H
A
Sarcomere
(b) Contracting muscle fiber. During contraction, the thick and
thin filaments slide past each other, reducing the width of the
I bands and H zone and shortening the sarcomere.
(c) Fully contracted muscle fiber. In a fully contracted muscle
fiber, the sarcomere is shorter still. The thin filaments overlap,
eliminating the H zone. The I bands disappear as the ends of
the thick filaments contact the Z lines.
Figure 49.29a–c
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• Based on the interaction between the actin and
myosin molecules of the thick and thin
filaments
• The “head” of a myosin molecule binds to an
actin filament
– Forming a cross-bridge and pulling the thin
filament toward the center of the sarcomere
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• Myosin-actin interactions underlying muscle
fiber contraction
Thick filament
1 Starting here, the myosin head is
bound to ATP and is in its lowenergy confinguration.
Thin filaments
5 Binding of a new molecule of ATP releases the
myosin head from actin,
and a new cycle begins.
Thin filament
Myosin head (low-
ATP
Thick
filament
Thin filament moves
toward center of sarcomere.
Figure 49.30
+
Cross-bridge
binding site
Actin
ADP
Myosin head (lowenergy configuration)
ADP
2 The myosin head hydrolyzes
ATP to ADP and inorganic
phosphate ( P I ) and is in its
high-energy configuration.
energy configuration)
ATP
Pi
ADP
Pi
4 Releasing ADP and ( P i), myosin
relaxes to its low-energy configuration,
sliding the thin filament.
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Pi
Cross-bridge
Myosin head (highenergy configuration)
13 The myosin head binds to
actin, forming a crossbridge.
The Role of Calcium and Regulatory Proteins
• When a muscle is at rest
– The myosin-binding sites on the thin filament
are blocked by the regulatory protein
tropomyosin
Tropomyosin
Actin
Figure 49.31a
Ca2+-binding sites
(a) Myosin-binding sites blocked
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Troponin complex
• For a muscle fiber to contract
– The myosin-binding sites must be uncovered
• This occurs when calcium ions (Ca2+)
– Bind to another set of regulatory proteins, the
troponin complex
Ca2+
Myosinbinding site
Figure 49.31b
(b) Myosin-binding sites exposed
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• Stimulus leading to the contraction of muscle
fiber is an action potential in a motor neuron
Motor
neuron axon
Mitochondrion
Synaptic
terminal
T tubule
Sarcoplasmic
reticulum
Myofibril
Figure 49.32
Plasma membrane
of muscle fiber
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Ca2+ released
from sarcoplasmic
reticulum
Sarcomere
• The synaptic terminal of the motor neuron
– Releases the neurotransmitter acetylcholine,
depolarizing the muscle and causing it to
produce an action potential
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• Action potentials  transverse (T) tubules
 Causes the sarcoplasmic reticulum to release
Ca2+ Ca2+ binds to the troponin-tropomyosin
complex exposing the myosin-binding sites
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Review
Synaptic
terminal
of motor
neuron
Acetylcholine
PLASMA MEMBRANE
T TUBULE
Synaptic cleft
1
(
ACh
SR
2
Action potential
Ca2

3
Action potential
triggers Ca2+
release from sarcoplasmic reticulum
(SR).
7
Tropomyosin blockage
4
Ca2
CYTOSOL
6
ADP
P2
Calcium ions bind
Cytosolic Ca2+ is
removed by active
transport into
SR after action
potential ends.
5
Myosin cross-bridges
Figure 49.33
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Neural Control of Muscle Tension
• 2 mechanisms by which the nervous system
produces graded contractions
– varying the number of fibers that contract
– varying the rate at which muscle fibers are
stimulated
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• A twitch
– from a single action potential
• More rapidly delivered action potentials
– produce a graded contraction by summation
Tension
Tetanus
Summation of
two twitches
Single
twitch
Action
potential
Time
Pair of
action
potentials
Figure 49.35
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Series of action
potentials at
high frequency
• Tetanus is a state of smooth and sustained
contraction
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• Types of skeletal muscles
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Other Types of Muscle
• Cardiac muscle, striated cells electrically
connected by intercalated discs
– Can generate action potentials without neural
input
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• Smooth muscle, contractions slow and may be
caused by stimulation from autonomic nervous
system
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• Movement (locomotion) is a hallmark of all
animals
– finding food or evading predators
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Swimming
• Overcoming friction major problem
• Overcoming gravity less of a problem than for
animals that move on land or fly
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Locomotion on Land
• Walking, running, hopping, or crawling on land
– Requires an animal to support itself and move
against gravity
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Flying
• Lift to overcome the downward force of gravity
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Comparing Costs of Locomotion
EXPERIMENT
Physiologists typically determine an animal’s rate of energy use during locomotion by measuring
its oxygen consumption or carbon dioxide production while it swims in a water flume, runs on a treadmill, or flies in a
wind tunnel. For example, the trained parakeet shown below is wearing a plastic face mask connected to a tube that
collects the air the bird exhales as it flies.
RESULTS
This graph compares the energy cost, in joules per kilogram of
body mass per meter traveled, for animals specialized for running, flying, and
swimming (1 J = 0.24 cal). Notice that both axes are plotted on logarithmic scales.
Flying
CONCLUSION
Running
102
Energy cost (J/Kg/m)
For animals of a given
body mass, swimming is the most energyefficient and running the least energyefficient mode of locomotion. In any mode,
a small
animal expends more energy per
CONCLUSION
kilogram of body mass than a large animal.
10
1
Swimming
10–1
10–3
Figure 49.37
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1
103
Body mass(g)
106
• Swimming expends less energy per meter
traveled than for flying or running
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