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• Today: Ch 47, Muscles
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47
Effectors: How Animals Get
Things Done
47 Effectors: How Animals Get Things Done
• 47.1 How Do Muscles Contract?
• 47.2 What Determines Muscle
Strength and Endurance?
• 47.3 What Roles Do Skeletal Systems
Play in Movement?
• 47.4 What Are Some Other Kinds of
Effectors?
47.1 How Do Muscles Contract?
Muscles and skeletons: the
musculoskeletal system.
Muscles and skeletons are the effectors
that produce movement.
47.1 How Do Muscles Contract?
Three types of vertebrate muscle:
• Skeletal: voluntary movement,
breathing
• Cardiac: beating of heart
• Smooth: involuntary, movement of
internal organs
47.1 How Do Muscles Contract?
Skeletal muscle (striated):
• Cells are called muscle fibers:
multinucleate
• Form from fusion of embryonic
myoblasts
• One muscle consists of many muscle
fibers bundled together by connective
tissue
Figure 47.1 The Structure of Skeletal Muscle
Figure 47.1 The Structure of Skeletal Muscle
47.1 How Do Muscles Contract?
Contractile proteins:
Actin: thin filaments
Myosin: thick filaments
Each muscle fiber has several
myofibrils: bundles of actin and
myosin filament.
47.1 How Do Muscles Contract?
Each myofibril consists of repeating
units: sarcomeres.
Sarcomere: overlapping actin and
myosin filaments.
Bundles of myosin filaments are held in
place by the protein titin, the largest
protein in the body.
Figure 47.1 The Structure of Skeletal Muscle (Part 2)
Figure 47.1 The Structure of Skeletal Muscle (Part 3)
47.1 How Do Muscles Contract?
The sliding filament theory of muscle
contraction:
• Depends on structure of actin and
myosin molecules.
• Myosin heads can bind specific sites
on actin molecules to form cross
bridges. Myosin changes conformation,
causes actin filament to slide 5–10 nm.
Figure 47.2 Sliding Filaments
47.1 How Do Muscles Contract?
Muscle contraction is initiated by action
potentials from a motor neuron at the
neuromuscular junction.
A motor unit: all the muscle fibers
activated by one motor neuron.
Figure 47.3 Actin and Myosin Filaments Overlap to Form Myofibrils
47.1 How Do Muscles Contract?
One muscle may have many motor
units.
To increase strength of muscle
contraction: increase rate of firing of
motor neuron or recruit more motor
neurons to fire (more motor units
activated).
47.1 How Do Muscles Contract?
Muscle cells are excitable: the plasma
membrane can conduct action
potentials.
Acetylcholine is released by the motor
neuron at the neuromuscular junction
and opens ion channels in the motor
end plate.
Figure 47.4 The Neuromuscular Junction
Photo 47.6 Leg muscles of the dogflea (Ctenocephalides canis), photographed in polarized light.
47.1 How Do Muscles Contract?
Action potentials also travel deep within
muscle fiber via T tubules.
T tubules (transverse tubules) descend
into the sarcoplasm (muscle fiber
cytoplasm).
T tubules run close to the sarcoplasmic
reticulum (ER): a closed compartment
that surrounds every myofibril.
Figure 47.5 T Tubules in Action
47.1 How Do Muscles Contract?
Sarcoplasmic reticulum has Ca2+
pumps. At rest there is high
concentration of Ca2+ in the
sarcoplasmic reticulum.
Action potential reaches receptor
proteins and opens the Ca2+ channels,
Ca2+ flows out of sarcoplasmic
reticulum and triggers interaction of
actin and myosin.
47.1 How Do Muscles Contract?
Actin filaments also include tropomyosin
and troponin.
Troponin has three subunits: one binds
actin, one binds myosin, and one binds
Ca2+.
At rest, tropomyosin blocks the binding
sites on actin.
47.1 How Do Muscles Contract?
When Ca2+ is released, it binds to
troponin, which changes conformation.
Troponin is bound to tropomyosin—
twisting of tropomyosin exposes
binding sites on actin.
When Ca2+ pumps remove Ca2+ from
sarcoplasm, contraction stops.
Figure 47.6 The Release of Ca2+ from the Sarcoplasmic Reticulum Triggers Muscle Contraction
CONTRACTION OF SKELETAL MUSCLE CONTRACTION
FLAGELLATED GREEN ALGA
FLAGELLATED EUGLENID
ROTIFERS FEEDING VIA FLAGELLA
47.1 How Do Muscles Contract?
Cardiac muscle is also striated; cells
are smaller than skeletal and have one
nucleus.
Cardiac muscle cells also branch and
interdigitate: can withstand high
pressures.
Intercalated discs provide mechanical
adhesions between cells.
Figure 47.7 There are Three Kinds of Muscle
Photo 47.8 Skeletal muscle in frog; cross striations and peripheral nuclei. LM, H&E stain.
Photo 47.9 Human skeletal muscle; narrow dark line = Z line, broad dark line = A band. LM.
CARDIAC MUSCLE CELL BEATING
Photo 47.10 Myofibrils; bands of actin and myosin together appear darkest.
Photo 47.11 Sarcomere from fish muscle.
47.1 How Do Muscles Contract?
Pacemaker and conducting cells initiate
and coordinate heart contractions.
Heartbeat is myogenic—generated by
the heart muscle itself.
Autonomic nervous system modifies the
rate of pacemaker cells, but is not
necessary for their function.
Photo 47.13 Human cardiac muscle; cross striations and central nuclei. LM, H&E stain.
47.1 How Do Muscles Contract?
Contraction of cardiac muscle:
• DHP proteins in T tubules are Ca
channels; ryanodine receptors are iongated Ca2+ channels, sensitive to Ca2+.
• Action potential causes Ca2+ to flow into
sarcoplasm from T tubules; increase in
Ca2+ opens the Ca2+ channels in
sarcoplasmic reticulum—large increase in
Ca2+ in sarcoplasm—initiates contraction.
Ca2+-induced Ca2+ release
47.1 How Do Muscles Contract?
Smooth muscle: in most internal organs;
under autonomic nervous system
control.
Smooth muscle cells are arranged in
sheets; have electrical contact via gap
junctions. Action potential in one cell
can spread to all others in the sheet.
47.1 How Do Muscles Contract?
Plasma membrane of smooth muscle
cells sensitive to stretch.
Stretched cells depolarize and fire action
potentials which starts contraction.
47.1 How Do Muscles Contract?
Smooth muscle contraction:
• Ca2+ influx to sarcoplasm stimulated by
stretching, action potentials, or hormones.
• Ca2+ binds with calmodulin: activates
myosin kinase which phosphorylates
myosin heads—can then bind and release
actin.
Figure 47.8 Mechanisms of Smooth Muscle Activation (Part 1)
Figure 47.8 Mechanisms of Smooth Muscle Activation (Part 2)
47.1 How Do Muscles Contract?
Skeletal muscle: minimum unit of
contraction = a twitch.
Twitch measured in terms of tension, or
force it generates.
A single action potential generates a
single twitch. Force generated depends
on how many fibers are in the motor
unit.
47.1 How Do Muscles Contract?
Tension generated by entire muscle
depends on:
• Number of motor units activated
• Frequency at which motor units are
firing
47.1 How Do Muscles Contract?
Single twitch: if action potentials are
close together in time, the twitches are
summed, tension increases.
Twitches sum because Ca2+ pumps can
not clear Ca2+ from sarcoplasm before
the next action potential arrives.
Tetanus: when action potentials are so
frequent there is always Ca2+ in the
sarcoplasm.
Figure 47.9 Twitches and Tetanus
47.1 How Do Muscles Contract?
How long muscle fiber can sustain tetanic
contraction depends on ATP supply.
ATP is needed to break the myosin-actin
bonds, and “re-cock” the myosin heads.
To maintain contraction, actin–myosin
bonds have to keep cycling.
47.1 How Do Muscles Contract?
Muscle tone: a small but changing
number of motor units are contracting.
Muscle tone is constantly being adjusted
by the nervous system.
47.2 What Determines Muscle Strength and Endurance?
Slow-twitch muscle fibers: oxidative or
red muscle.
Contain myoglobin: oxygen binding
protein; many mitochondria, wellsupplied with blood vessels.
Maximum tension develops slowly, but
is highly resistant to fatigue.
47.2 What Determines Muscle Strength and Endurance?
Slow-twitch fibers have reserves of
glycogen and fat; can produce ATP as
long as oxygen is available.
Muscles with high proportion of slowtwitch fibers are good for aerobic work
(e.g., long distance running, cycling,
swimming, etc.)
47.2 What Determines Muscle Strength and Endurance?
Fast-twitch fibers: glycolytic or white
muscle.
Fewer mitochondria, fewer blood
vessels, little or no myoglobin.
Develop greater maximum tension
faster, but fatigue more quickly.
Can’t replenish ATP for prolonged
contraction.
Figure 47.10 Slow-and Fast-Twitch Muscle Fibers (Part 1)
Figure 47.10 Slow-and Fast-Twitch Muscle Fibers (Part 2)
47.2 What Determines Muscle Strength and Endurance?
Proportion of fast- and slow-twitch fibers
in skeletal muscles is determined
mostly by genetic heritage.
Training can alter muscle properties to a
certain extent.
47.2 What Determines Muscle Strength and Endurance?
The resting length of the sarcomeres
determines how much force can be
generated.
If stretched, less overlap between actin
and myosin fibers mean fewer crossbridges and less force.
If contracted, there is no more space for
shortening.
Figure 47.11 Strength and Length
47.2 What Determines Muscle Strength and Endurance?
Exercise:
• Anaerobic activities increase muscle
strength: new actin and myosin
filaments form, muscle gets larger.
• Aerobic activities increase endurance:
oxidative capacity is enhanced by
increasing number of mitochondria,
blood vessels, myoglobin, and
enzymes.
47.2 What Determines Muscle Strength and Endurance?
Muscles have three systems for obtaining
ATP:
• Immediate system uses preformed ATP
• Glycolytic system metabolizes
carbohydrates to lactic acid and pyruvate
• Oxidative system metabolizes
carbohydrates and fats to H2O and CO2
Figure 47.12 Supplying Fuel for High Performance
47.2 What Determines Muscle Strength and Endurance?
Muscles contain creatine phosphate (CP)
which stores energy in a phosphate
bond that can transfer to ADP
Immediate system = ATP + CP. This
system is exhausted within seconds.
47.2 What Determines Muscle Strength and Endurance?
The glycolytic system enzymes are in
the sarcoplasm; ATP generated is then
available to myosin.
Not very efficient; lactic acid
accumulates.
Immediate and glycolytic systems
provide energy for less than one
minute.
47.2 What Determines Muscle Strength and Endurance?
Oxidative system produces large
amounts of ATP, but ATP must diffuse
from the mitochondria to the myosin:
rate is slower than other two systems.
47.2 What Determines Muscle Strength and Endurance?
At high levels of aerobic exercise, fuel
for ATP production comes mostly from
glycogen.
Depletion of muscle glycogen causes
fatigue.
Glycogen can be replaced more
rapidly on a high-carbohydrate diet;
“carbo-loading” by athletes.
47.3 What Roles Do Skeletal Systems Play in Movement?
Skeletal systems provide rigid supports
against which muscles can pull.
Three types of skeletal systems in
animals: hydrostatic, exoskeletons, and
endoskeletons.
47.3 What Roles Do Skeletal Systems Play in Movement?
Hydrostatic skeleton: a volume of fluid
enclosed in a body cavity surrounded
by muscle.
Examples: cnidarians, annelids, and
other invertebrates.
Figure 47.13 A Hydrostatic Skeleton
47.3 What Roles Do Skeletal Systems Play in Movement?
Exoskeleton: hardened outer surface to
which muscles attach.
Examples: mollusks, arthropods
Figure 47.14 The Clam Shell Is an Exoskeleton
47.3 What Roles Do Skeletal Systems Play in Movement?
Arthropod exoskeleton (or cuticle)
covers all outer surfaces and
appendages.
Cuticle containing stiffening materials
except at joints.
For growth to occur, the exoskeleton
must be shed, called molting.
47.3 What Roles Do Skeletal Systems Play in Movement?
Endoskeleton advantage: growth can
occur without shedding the skeleton.
Human skeleton: 206 bones, two
connective tissue types: cartilage and
bone.
Figure 47.15 The Human Endoskeleton
47.3 What Roles Do Skeletal Systems Play in Movement?
Cartilage:
• Cartilage cells produce a tough,
rubbery extracellular matrix of
polysaccharides and protein, mostly
collagen.
• Cartilage is found on bone surfaces in
joints, also ears, nose, larynx.
47.3 What Roles Do Skeletal Systems Play in Movement?
Bone: extracellular matrix of calcium
phosphate.
Bone cells: osteoblasts make new bone
matrix. When they become enclosed in bone
they are called osteocytes.
Osteoclasts: reabsorb bone.
Bone is constantly being replaced and
remodeled.
Figure 47.16 Renovating Bone
47.3 What Roles Do Skeletal Systems Play in Movement?
How bone cell activities are coordinated
is not well known.
Stress on bones provides information to
cells.
Astronauts in zero gravity: bones
decalcify.
Weight-bearing exercise builds up bone,
effective in preventing osteoporosis.
47.3 What Roles Do Skeletal Systems Play in Movement?
Membranous bone: forms on a scaffold
of connective tissue; (e.g., outer bones
of skull).
Cartilage bone is first cartilaginous,
then ossifies or hardens; (e.g.,) bones
of limbs. Growth can occur throughout
the ossification process.
Figure 47.17 The Growth of Long Bones
47.3 What Roles Do Skeletal Systems Play in Movement?
Bone structure:
• Compact: solid and hard
• Cancellous: with numerous cavities,
appears spongy; lightweight but strong
Most bones have both types.
47.3 What Roles Do Skeletal Systems Play in Movement?
Compact bone in mammals is called
Haversian bone; structural units are
Haversian systems.
Each system: concentric bony cylinders
with osteocytes in between.
Center canal has blood vessels and
nerves.
Figure 47.18 Most Compact Bone Is Composed of Haversian Systems
Photo 47.23 Several Haversian systems in human compact bone. LM, polarized light.
47.3 What Roles Do Skeletal Systems Play in Movement?
Joints are where two or more bones
come together.
Different types of joints allow different
kinds of movement.
Figure 47.19 Types of Joints
47.3 What Roles Do Skeletal Systems Play in Movement?
Muscles can exert force in only one
direction; muscles create movement by
working in antagonistic pairs:
• Flexor: the muscle that bends or flexes
the joint.
• Extensor: the muscle the straightens
or extends the joint.
47.3 What Roles Do Skeletal Systems Play in Movement?
• Ligaments: bands of connective tissue
that hold bones together at joints.
• Tendons: connective tissue straps that
join muscle to bone.
Figure 47.20 Joints, Ligaments, and Tendons
47.3 What Roles Do Skeletal Systems Play in Movement?
Bones are a system of levers moved by
muscles.
Levers have a power arm and a load
arm that work around a fulcrum (pivot
point).
Figure 47.21 Bones and Joints Work Like Systems of Levers
47.4 What Are Some Other Kinds of Effectors?
Chromatophores: pigment-containing
cells in the skin that can change the
color or pattern of the animal.
Some animals can change color in
minutes or even seconds to blend in
with their background or send signals.
47.4 What Are Some Other Kinds of Effectors?
Three types of chromatophores:
• Fixed cell boundaries: pigment
granules are moved by microfilaments.
• Amoeboid movement: when flattened,
more pigment shows.
• Changes shape because of muscle
fibers radiating out from cell.
Figure 47.22 Chromatophores Help Animals Camouflage Themselves or Communicate
Photo 47.26 Sanddab; chromatophores create camouflage pattern.
Photo 47.27 Chamaeleo jacksoni, a chameleon lizard; Kenya.
Photo 47.28 Octopus rubescens, chromatophores adapted to mimic coral.
CHROMATOPHORES AND MELANOPHORES IN FISH SCALES
VISUAL COMMUNICATION IN SQUID
47.4 What Are Some Other Kinds of Effectors?
Glands: effector organs that produce
and release chemicals.
Endocrine and exocrine glands.
Some reptiles, amphibians, mollusks,
and fish have poison glands.
47.4 What Are Some Other Kinds of Effectors?
Electric organs generate electricity in
certain fishes.
Electric organs evolved from muscles;
they produce electric potentials in the
same way as nerves and muscles.
Large disk-shaped cells in stacks: all
discharge simultaneously.
47.4 What Are Some Other Kinds of Effectors?
Some organisms emit light, this is called
bioluminescence
Depends on the enzyme luciferase and
the substrate luciferin.
Used in mate attraction and prey
attraction.