Chapter 35
Structural Support
and Movement
Albia Dugger • Miami Dade College
35.1 Muscles and Myostatin
• Skeletal muscle gets bulkier by enlarging existing cells
• Hormones such as testosterone and human growth hormone
increase muscle mass
• People who do not respond normally to the protein myostatin
have large muscles and unusual strength
• Bully whippets homozygous for a mutation that prevents them
from making myostatin are also heavily muscled
Disrupted Myostatin Function
Disrupted and Normal Myostatin Function
36.1 Invertebrate Skeletons
• Hydrostatic skeleton
• An enclosed fluid that contracting muscles act upon
• Found in sea anemones, earthworms)
• Exoskeleton
• A hardened external skeleton
• Found in some mollusks and all arthropods
• Endoskeleton
• An internal skeleton
• Found in echinoderms and vertebrates
Hydrostatic Skeleton: Sea Anemone
mouth
gastrovascular
cavity; the mouth
can close and
trap fluid inside
this cavity
Hydrostatic Skeleton: Earthworm
Exoskeleton: Fly
thorax
Exoskeleton: Spider
Endoskeleton: Echinoderm
Take-Home Message: What
kinds of skeletons do
invertebrates have?
• Soft-bodied animals such as sea anemones and earthworms
have a hydrostatic skeleton—an enclosed fluid that contractile
cells exert force upon.
• Some mollusks and all arthropods have a hardened external
skeleton, or exoskeleton.
• Echinoderms have an endoskeleton, an internal skeleton.
36.2 The Vertebrate Endoskeleton
• All vertebrates have an endoskeleton
• Usually consists primarily of bones
• Supports the body, site of muscle attachment
• Protects the spinal cord
• The vertebral column (backbone) is made up of individual
vertebrae separated by intervertebral disks made of
cartilage
Axial and Appendicular Skeleton
• Axial skeleton
• Skull
• Vertebral column
• Ribs
• Appendicular skeleton
• Pectoral girdle
• Pelvic girdle
• Limbs
Skeletal Elements of Early Reptile
rib cage vertebral column skull bones
pelvic girdle
pectoral
girdle
The Human Skeleton
• Some features of the human skeleton are adaptations to
upright posture and walking
• The brain and spinal cord connect through an opening in the
base of the skull called the foramen magnum
• Maintaining an upright posture requires that vertebrae and
intervertebral disks stack one on top of the other in an S
shape, rather than being parallel to the ground
A Skull
Cranial bones
Facial bones
D Pectoral Girdle
Clavicle (collarbone)
B Rib Cage
Sternum (breastbone)
Ribs (12 pairs)
C Vertebral Column
Vertebrae (26 bones)
Scapula (shoulder blade)
E Bones of the Arm
Humerus (upper arm bone
Radius (forearm bone)
Ulna (forearm bone)
Carpals (wrist bones)
1
Intervertebral disks
5
2
3
4
Metacarpals
(palm bones) Phalanges
(finger bones)
F Pelvic Girdle
G Bones of the Legs
Femur (thighbone)
Patella (kneecap)
Tibia (lower leg bone)
Fibula (lower leg bone)
Tarsals (ankle bones)
metatarsals (sole bones)
phalanges (toe bones)
Figure 35-8a p611
cervical
vertebrae
thoraic
vertebrae
lumbar
vertebrae
sacrum
coccyx
(tailbone)
Figure 35-8b p611
ANIMATED FIGURE: Human skeletal
system
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Take-Home Message: What type of skeleton do
humans and other vertebrates have?
• The endoskeleton of vertebrates usually consists mainly of
bone. Its axial portion includes the skull, vertebral column,
and ribs. Its appendicular part includes a pectoral girdle, a
pelvic girdle, and the limbs.
• Some features of the human skeleton such as an S-shaped
backbone are adaptations to upright posture and walking.
35.4 Bone Structure and Function
• Bones have a variety of shapes and sizes
• Long bones (arms and legs)
• Flat bones (skull, ribs)
• Short bones (carpals)
• The human skeleton has 206 bones ranging from tiny ear
bones to the massive femur
Bone Anatomy
• Bones consist of three types of living cells in a secreted
extracellular matrix
• Osteoblasts build bones
• Osteocytes are mature osteoblasts
• Osteoclasts break down bone matrix
• Bone cavities contain bone marrow
• Red marrow in spongy bone forms blood cells
• Yellow marrow in long bones is mostly fat
Bone Anatomy: Long Bone
nutrient canal
location of
yellow marrow
compact
bone tissue
spongy
bone
tissue
Cross-section through a Femur
space occupied
by living bone cell
blood
vessel
one osteon
Table 35-1 p612
Bone Formation and Remodeling
• The embryonic skeleton consists of cartilage which is
modeled into bone, grows until early adulthood, and is
constantly remodeled
• Bones and teeth store the body’s calcium
• Calcitonin slows release of calcium from bones
• Parathyroid hormone releases bone calcium
• Sex hormones encourage bone building
• Cortisol slows bone building
Embryo:
cartilage model
of bone forms
Fetus:
blood vessel invades
model; osteoblasts
start producing bone
tissue; marrow
cavity forms
Newborn:
remodeling and
growth continue;
secondary boneforming centers
appear at knobby
ends of bone
Adult: mature bone
Figure 35-10 p613
Osteoporosis
• Osteoporosis (“porous bones”)
• When more calcium is removed from bone than is
deposited, bone become brittle and break easily
• Proper diet and exercise help keep bones healthy
Osteoporosis
A Normal bone
B Bone weakened by osteoporosis
Take-Home Message: What are the structural
and functional features of bones?
• Bones have a variety of shapes and sizes.
• A sheath of connective tissues encloses the bone, and the
bone’s inner cavity contains marrow. Red marrow produces
blood cells.
• All bones consist of bone cells in a secreted extracellular
matrix. A bone is continually remodeled; osteoclasts break
down the matrix of old bone and osteoblasts lay down new
bone. Hormones regulate this process.
35.5 Skeletal Joints—Where Bones Meet
• Joint
• Area of contact or near contact between bones
• Three types of joints
• Fibrous joints (teeth sockets): no movement
• Cartilaginous joints (vertebrae): little movement
• Synovial joints (knee): much movement
Synovial Joints
• In synovial joints, bones are separated by a fluid-filled cavity,
padded with cartilage, and held together by dense connective
tissue (ligaments)
• Different synovial joints have different movements
• Ball-and-socket joints (shoulder)
• Gliding joints (wrist and ankles)
• Hinged joints (elbows and knees)
fibrous joint
attaches
tooth to
jawbone
synovial joint (ball
and socket) between
humerus and scapula
cartilaginous joint
between rib and
sternum
artilaginous joint
between adjacent
vertebrae
synovial joint (hinge
type) between
humerus and radius
synovial joint (ball
and socket) between
pelvic girdle and
femur
Figure 35-12a p614
femur
patella
cartilage
cruciate
ligaments
menisci
tibia
fibula
Figure 35-12 p614
Joint Health
• Common joint injuries
• Sprained ankle; torn cruciate ligaments in knee; torn
meniscus in knee; dislocations
• Arthritis (chronic inflammation)
• Osteoarthritis; rheumatoid arthritis; gout
• Bursitis (inflammation of a bursa)
Increased Risk of Knee Osteoarthritis
Take-Home Message: What
are joints?
• Joints are areas where bones meet and interact.
• In the most common type, synovial joints, the bones are
separated by a small fluid-filled space and are held together
by ligaments of fibrous connective tissue.
35.6 Skeletal–Muscular Systems
• Tendons attach skeletal muscle to bone
• Muscle contraction transmits force to bone and makes it move
• Muscles and bones interact as a lever system
• Many skeletal muscles work in opposing pairs
• Skeletal muscle activity also generates body heat
tendons
biceps
radius
tendon
triceps
ulna
Figure 35-14 p616
Biceps brachii
bends forearm
at elbow
Triceps brachii
straightens forearm
Deltoid
raises arm at shoulder
Pectoralis major
draws arm forward
and in toward the body
Trapezius
elevates and rotates
shoulder blade (scapula)
Rectus abdominus
compresses the abdomen,
bends the back
Lattisimus dorsi
draws arm inward, extends
arm behind back, rotates
arm at shoulder
Sartorius
raises and rotates thigh;
flexes leg at knee; longest
muscle in the body
Quadriceps femoris
(set of four muscles)
flex the thigh at the hip,
extend the leg at the
knee
Gluteus maximus
(one of three buttock muscles)
extends and laterally rotates
thigh at the hip
Biceps femoris
(one of three hamstring
muscles) extends leg
straight back; bends knee
Gastrocnemius
bends leg at knee;
turns foot downward
Achilles tendon
attaches gastrocnemius
to the heel bone
Figure 35-15 p617
Take-Home Message: How do muscles and
tendons interact with bones?
• Tendons of dense connective tissue attach skeletal muscles
to bones.
• Small muscle movements can bring about large movements
of bones.
• Muscles can only pull on a bone; they cannot push. At many
joints, movement is controlled by a pair of muscles that act in
opposition.
35.7 How Does Skeletal Muscle Contract?
• A muscle fiber is a cylindrical contractile cell that runs the
length of the muscle
• A skeletal muscle fiber has many nuclei, and is filled with
threadlike myofibrils
• Myofibrils are bundles of contractile filaments run the length
of the muscle fiber
Structure of Skeletal Muscle
• Myofibrils are divided into bands (striations) that define units
of contraction (sarcomeres)
• Z-bands attach sarcomeres to each other
• Sarcomeres contain two types of filaments
• Thin, globular protein filaments (actin)
• Thick, motor protein filaments (myosin)
A Muscle
in a sheath
of connective
tissue
B Bundle of muscle
fibers wrapped in
connective tissue
C Cross section of a muscle
fiber, a multinucleated cell
whose interior is crammed
full of threadlike protein
structures called
myofibrils. (Colorized
scanning electron
micrograph)
Figure 35-16a-c p618
D Portion of
one myfibril.
sarcomere
sarcomere
Z band
Z band
H zone
Z band
E Each myofibril consists of
many contractile units called
sarcomeres arranged end to
end.
sarcomere
Figure 35-16de p618
sarcomere
F Each sarcomere has a dark Z
band at either end, and alternating
rows of thick and thin protein
filaments in between them.
G Thick filaments are composed
of parallel bundles of the motor
protein myosin. A myosin molecule
has a head that can bind to actin
and a long tail.
myosin head
H Thin filaments consist mostly of
the globular protein actin, with lesser
amounts of two other proteins (troponin
and tropomyosin).
tropomyosin
actin
troponin
Figure 35-16f-h p618
The Sliding Filament Model
• Sliding filament model
• Interactions among protein filaments within a muscle
fiber’s individual contractile units (sarcomeres) bring
about muscle contraction
• A sarcomere shortens when actin filaments are pulled
toward the center of the sarcomere by ATP-fueled
interactions with myosin filaments
relaxed sarcomere
muscle
contraction
contracted sarcomere
Figure 35-17 p619
ATP
myosin head
ATP
1
2
ADP, Pi
3
ADP
ADP, Pi
ADP
4
5
ATP
ATP
Figure 35-17 p619
Take-Home Message: How does a muscle’s
structure affect its function?
• Sarcomeres are the basic units of contraction in skeletal
muscle. Sarcomeres are lined up end to end in myofibrils that
run parallel with muscle fibers. These fibers, in turn, run
parallel with the whole muscle.
• The parallel orientation of skeletal muscle components
focuses a muscle’s contractile force in a particular direction.
Take-Home Message: (cont.)
• Energy-driven interactions between myosin and actin
filaments cause the sarcomeres of a muscle cell to shorten
and bring about muscle contraction.
• During muscle contraction, the length of actin and myosin
filaments does not change, and the myosin filaments do not
change position. Sarcomeres shorten because myosin
filaments pull neighboring actin filaments inward toward the
center of the sarcomere.
Video: How Muscles Hold Tension
ANIMATION: Muscle Contractions
35.8 Nervous Control of Muscle Contraction
• Like neurons, muscle cells are excitable
• Skeletal muscle contracts in response to a signal from a
motor neuron
• Release of ACh at a neuromuscular junction causes an action
potential in the muscle cell
Nervous Control of Contraction
• Action potentials travel along muscle plasma membrane,
down T tubules, to the sarcoplasmic reticulum (a smooth
endoplasmic reticulum)
• Action potentials open voltage-gated channels in
sarcoplasmic reticulum, triggering calcium release that allows
contraction in myofibrils
1 A signal travels
motor neuron
along the axon of a
motor neuron, from
the spinal cord to a
skeletal muscle.
section from spinal cord
2 The signal is
transferred from the motor
neuron to the muscle at
neuromuscular junctions.
Here, ACh released by the
neuron’s axon terminals
diffuses into the muscle
fiber and causes action
potentials.
neuromuscular junction
section from skeletal muscle
T
sarcoplasmic
tubule reticulum
3 Action potentials
propagate along a muscle
fiber’s plasma membrane
down toT tubules, then to
the sarcoplasmic
reticulum, which releases
calciumions. The ions
promote interactions of
myosin and actin that
result in contraction.
one
myofibril
in muscle
fiber
muscle
fiber’s
plasma
membrane
Stepped Art
Figure 35-18 p620
ANIMATED FIGURE: Nervous system and
muscle contraction
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Troponin and Tropomyosin
• Two proteins regulate bonding of actin to myosin
• Tropomyosin prevents actin from binding to myosin
• Troponin has calcium binding sites
• Calcium binds to troponin, which pulls tropomyosin away from
myosin-binding sites on actin
• Cross-bridges form, sarcomeres shorten, and muscle
contracts
Role of Calcium in Muscle Contraction
actin
troponin
tropomyosin
A Resting muscle. Calcium ion (Ca++) concentration is low and
tropomyosin covers the myosin-binding sites on actin.
Ca++
exposed myosin-binding sites
B Excited muscle. Ca++ binds to troponin, which shifts and
moves tropomyosin, exposing myosin-binding sites on actin.
Motor Units and Muscle Tension
• Motor unit
• One motor neuron and all of the muscle fibers its axons
synapse with
• Muscle tension
• The mechanical force exerted by a muscle
• The more motor units stimulated, the greater the muscle
tension
Disrupted Control of Skeletal Muscle
• Some genetic disorders, diseases, or toxins can cause
muscles to contract too little or too much
• Botulism (Clostridium botulinum toxin) prevents motor
neurons from releasing ACh
• Tetanus (C. tetani toxin) prevent inhibition of motor
neurons
• Polio virus impairs motor neuron function
• Amyotrophic lateral sclerosis (ALS) also kills motor
neurons
Tetanus
Polio
ALS
Take-Home Message: How do nervous signals
cause muscle contraction?
• A skeletal muscle contracts in response to a signal from a
motor neuron. Release of ACh at a neuromuscular junction
causes an action potential in the muscle cell.
• An action potential results in release of calcium ions, which
affect proteins attached to actin. Resulting changes in the
shape and location of these proteins open the myosin-binding
sites on actin, allowing cross-bridge formation.
ANIMATION: Calcium and Cross Bridge
Cycles
35.9 Muscle Metabolism
• Multiple metabolic pathways can supply the ATP required for
muscle contraction
• Muscles use any stored ATP, then transfer phosphate from
creatine phosphate to ADP to form ATP
• With ongoing exercise, aerobic respiration and lactic acid
fermentation supply ATP
Three Energy-Releasing Pathways
1
dephosphorylation
of creatine
phosphate
ADP + Pi
creatine
2
aerobic
respiration
oxygen
3
lactate
fermentation
glucose from bloodstream and
from glycogen breakdown in cells
Types of Muscle Fibers
• Red fibers (high in myoglobin)
• Have an abundance of mitochondria
• Produce ATP mainly by aerobic respiration
• Myoglobin allows aerobic respiration to continue even if
blood flow is insufficient to meet oxygen need
• White fibers (no myoglobin)
• Have few mitochondria
• Make ATP mainly by lactate fermentation
Fast and Slow Fibers
• Muscle fibers are subdivided into fast fibers or slow fibers
based on the ATPase activity of their myosin
• All white fibers are fast fibers; red fibers can be fast or slow
• The mix of fiber types in each skeletal muscle varies between
individuals and has a genetic basis
Effects of Exercise
• Muscle fatigue is a decrease in capacity to generate force;
muscle tension declines despite repeated stimulation
• Aerobic exercise makes muscles more resistant to fatigue by
increasing blood supply and number of mitochondria
• Intense exercise increases actin and myosin
• Exercise increases production of lipoprotein lipase (LPL),
which allows muscle to take up fatty acids and triglycerides
Low Activity, Low LPL
Take-Home Message:
What factors affect muscle metabolism?
• Muscle contraction requires ATP. When excited, muscle first
uses stored ATP, then transfers phosphate from creatine
phosphate to ADP to form ATP. With prolonged exercise,
aerobic respiration and lactate fermentation provide ATP.
• Exercise increases blood flow to muscles, the number of
mitochondria, production of actin and myosin, and the
muscle’s ability to take up lipids from the blood for use as an
energy source.