CHAPTER 37
STRUCTURAL SUPPORT AND MOVEMENT:
A SUMMARY
AP Biology
Spring 2011
EVOLUTIONARY HERITAGE
• Skeleton: structural framework that functions in
maintaining body shape, supporting and protecting
cells, and accepting the force of contraction that
can bring about movements
EVOLUTIONARY HERITAGE
• Three types:
• Hydrostatic Skeleton: muscle cells apply the force of
contraction against a body fluid and thereby redistribute it
within a confined space
• Exoskeleton: rigid or flexible structures at the body surface
accept applied force of contraction
• Insect cuticle
• Endoskeleton: internal body parts, such as bones, receive
the applied force of muscle contraction
INVERTEBRATE SKELETONS
• Hydrostatic Skeletons:
• Soft bodied animals
• Many contractile cells oriented side by side, longitudinally,
in body wall
• Others oriented like rings around body cavity
• Stiff fibers form a mesh in body wall, help prevent
uncontrollable bulges when contraction makes fluid move
inside gut cavity
INVERTEBRATE SKELETONS
• Exoskeletons:
• Arthropods
• Hinged exoskeleton with attachment sites for sets of muscles
that move hard parts like levers
• Move by combination of muscles and hydraulic pressure
• Hydraulic: fluid pressure within a tube
INVERTEBRATE SKELETONS
• Invertebrates and Endoskeletons:
• Echinoderms: endoskeleton within dermis
• Ossicles: arrays of structural elements, made of tiny calcite
crystals
• Epidermis covers ossicles
• Echinoderm = spiny-skinned
• Move by combination of muscles and hydraulic pressure
VERTEBRATE SKELETON
• Human skeleton has 206
bones
• Pectoral girdle and pelvic
girdle- transfer weight to
limbs
• Appendicular portionpaired arms, hands, legs,
feet
• Axial portion- jaws, skull
bones, ribs, breast bone,
vertebra
VERTEBRATE SKELETON
• Vertebral column: bony parts
offer attachment sites for
paired muscles and protective
canal for spinal cord
• Column transmits torso’s weight to
lower limbs
• Backbone is curved into “S” shape
to keep body’s main axis in vertical
alignment
• Intervertebral disks: separates
bones of vertebra
• Cartilaginous shock absorbers and
flex points
BONE STRUCTURE AND FUNCTION
• Bone Tissue: bone cells and collagen fibers in a
calcium-hardened organic matrix
BONE STRUCTURE AND FUNCTION
• 3 types of bone cells:
• Osteoblasts: bone-forming cells; secrete the components of
the matrix; present on outer surface and internal cavities of
bones of adults
• Osteocytes: osteoblasts that become imprisoned in small
chambers after secreting matrix material around
themselves; most common cone cells in bony tissue of
adults
• Osteoclasts: bone cells that
break down bone tissue by
secreting acids and enzymes
into hardened matrix
BONE STRUCTURE AND FUNCTION
• 2 types of bone tissue:
• Compact: resists mechanical shock, laid down as dense
concentric rings around tiny canals for nerves and blood
vessels
• Osteocytes reside in narrow clefts between rings
• Spongy: present in femur’s shaft
and knobby ends, strong but
doesn’t weigh much, hardened
matrix is pocketed with open
spaces
BONE STRUCTURE AND FUNCTION
• Red marrow: major
site of blood cell
formation, fills the
spaces in spongy
bone
• Yellow marrow:
central cavity of
femur and most
mature bones of
adults, mostly fat, can
be converted to
blood cell-producing
red marrow with
severe blood loss
BONE FORMATION AND REMODELING
• First skeleton in embryos is made of cartilage
• Cartilage is model
• Osteoblasts infiltrate, transform cartilage to bone,
narrow cavity opens
BONE FORMATION AND REMODELING
• Bone Remodeling: osteoblasts help form new bone
tissue, which makes up for bone tissue that
osteoclasts are breaking down
• Bone is broken down to help maintain required blood levels
of calcium and phosphorous
BONE FORMATION AND REMODELING
• Until humans are 24 years old, osteoblasts secreting
more matrix than osteoclasts can break down, so
bone mass increases
• Bones become denser and stronger, later in life
osteoblast activity declines, bones weaken
• Osteoporosis: significant loss of bone density
WHERE BONES MEET- SKELETAL JOINTS
• Joints: areas of contact or near-contact between
bones
• Ligaments: straps of dense connective tissue at
many joints, attach bone to bone
• Tendons: attach bone to muscle
WHERE BONES MEET- SKELETAL JOINTS
• Arthritis: joint inflammation
and degenerative disorders
• Osteoarthritis: cartilage at
freely moving joints wears
away
• Rheumatoid arthritis: joint
membranes become inflamed,
thicken, cartilage degenerates,
bone deposits accumulate as
a result of autoimmune
response
SKELETAL-MUSCULAR SYSTEM
• Muscle fiber: groups fused together into one
multinucleated muscle fiber
• Bundles sheathed in dense connective tissue, extends past
them
SKELETAL-MUSCULAR SYSTEM
• Attachment sites of muscles:
• Act as lever system, is which a rigid rod is attached to a
fixed point and moves about it
• Muscles connect to bones (rigid rods) near a joint (fixed
position)
• When contract, transmit force that makes bones move
SKELETAL-MUSCULAR SYSTEM
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Skeletal muscles also interact with one another
Some work in pairs or groups, some work in opposition
Only skeletal muscles are the functional partner of bones
Human body has close to 700 skeletal muscles
SKELETAL MUSCLE CONTRACTION
• Long, slender muscle
fibers run parallel with
muscle’s long axis
• Myofibrils: bundle of
contractile filaments
that run from one end
of fiber to the other
• Bands give muscle
striated appearance
SKELETAL MUSCLE CONTRACTION
• Sarcomeres: repeated one after another along
length of myofibril
• Each end is anchored to its neighbor at a Z band, a dense
mesh of cytoskeletal elements
SKELETAL MUSCLE CONTRACTION
• Actin: thin filaments, extend from Z bands toward
sarcomere center
• Myosin: thick filaments, starts at center of
sarcomere, runs parallel with thin filaments but not
all the way to the Z band
SKELETAL MUSCLE CONTRACTION
• Muscle fibers, myofibrils, think filaments, and thick
filaments have the same orientation
• Run parallel with long axis
• Repetitive orientation focuses the force of
contraction, so all sarcomeres in all fibers of a
muscle work together to pull a bone in the same
direction
SLIDING FILAMENT MODEL
SLIDING FILAMENT MODEL
• Myosin heads move actin filaments toward
sarcomere’s center by short, repetitive ATP driven
strokes
• Myosin filaments stay in place, actin filaments slide
past them
• Both Z bands pulled inward wit them, shortens
sarcomere
• Myosin heads latch onto binding sites along actin
filaments
SLIDING FILAMENT MODEL
• Part of myosin head is enzymatic, catalyzes
phosphate-group transfer from ATP, which is the
energy that drives contraction
• Myosin forms cross-bridge to actin when local
concentration of calcium ions rises and a binding
site for myosin’s head is exposed
• Once head binds, tilts towards sarcomere’s center
and actin slides along with it
• When another ATP boost breaks grip on actin,
myosin head reverts to resting position
SLIDING FILAMENT THEORY
• http://www.youtube.com/watch?v=EdHzKYDxrKc
• http://www.youtube.com/watch?v=pWP1u7rRJS8
CONTRACTION
• Action Potential: voltage
difference of interstitial
fluid and cytoplasm of a
cell membrane can
reverse in response to a
stimulus
CONTRACTION
• Signals from nervous system
strongly spread rapidly from
stimulation site, then along
T tubules (transverse tubule)
• Small tubes are extensions
of plasma membrane
• Actin filaments in
sarcomeres are attached
to them
• Sarcoplasmic reticulum: takes
up, stores, and releases
calcium ions in a controlled
way
CONTRACTION
• Arrival of action potentials causes calcium ions to
flow out of chambers
• Released ions diffuse into myofibrilis and reach actin
filaments
• Actin binding sites for myosin heads are blocked in
resting muscle fibers, calcium clears them
CONTRACTION
• Figure 37.17: cross-bridge binding site blocked
• Proteins, tropomyosin and troponin, positioned in or
near grooves at actin filament surface
http://www.youtube.com/watch?v=mWPmUqRZYls
CONTRACTION
• Calcium levels low  proteins joined so tightly that
tropomyosin is forced out of groove
• Moves slightly which blocks cross-bridge binding site
• Calcium levels high  calcium ions bind with
troponin to cause shape change
• Troponin now has different molecular grip on tropomyosin
filament, which is free to slip back into groove
• Binding site now exposed
ENERGY FOR CONTRACTION
• Muscle fiber has small amounts of ATP when starts
contracting
• Produce more by transferring one phosphate group
from creatine phosphate to ADP
ENERGY FOR CONTRACTION
• 6x as much creatine phosphate as ATP
• Supply only fuels ~15sec of contraction
• After contraction, supply of creatine phosphate
restored, ATP donates phosphate to creatine
ENERGY FOR CONTRACTION
• Prolonged moderate exercise
• Aerobic respiration provides energy
• First 10-15 min: Muscle fiber converts stored glycogen to
glucose (starting substrate)
• Next 30 min
• Glucose and fatty acids
sustain activity
• Fatty acids become main
energy source for further
contraction
• Lactose transposable form
of energy (anaerobic
pathway)
TYPES OF CONTRACTIONS
• Motor Unit: a motor neuron and all of the muscle
fibers that are functionally connected to it
• When motor neuron is stimulated, all fibers in motor unit
contract
• Muscle Twitch: contractile force that is generated;
contraction
TYPES OF CONTRACTIONS
• Tetanus:
• Applying a new stimulus before a response ends makes
muscles twitch again
• Repeatedly stimulating motor unit during short interval
makes all of twitches run together
• Resulting sustained contraction
• Generates 3-4 times force of single twitch
TYPES OF CONTRACTIONS
• Muscle Tension: mechanical force exerted by a
muscle on an object
• Load: opposing force of muscle tension
• Weight or object or gravity’s pull on muscle
• Muscle tension exceeds opposing forces 
stimulated muscle shorten
TYPES OF CONTRACTIONS
• Isotonically contracting muscles: shorten and move
load
• Isometrically contracting muscles: develop tension
as attempt to lift something that is too heavy, but
they cannot shorten
MUSCLE FATIGUE
• When ongoing, strong stimulation keeps a muscle in
a state of tetanic contraction
• Muscle fatigue: decrease in muscle’s capacity to
generate force, decline in tension
• Needs rest to contract again
• Glycogen depletion is one factor in muscle fatigue
MUSCLE FATIGUE
• Brief intense exercise  fatigue and recover fast
• Prolonged, moderate exercise  fatigue slow and
recover slow
• Muscle cramp: abrupt involuntary, often painful
contraction that resists release
• Message and heat can relieve
• To avoid: stretch, avoid overexertion, dehydration
MUSCLE DYSTROPHIES
• Muscular Dystrophies: class of genetic disorders in
which muscles progressively weaken and
degenerate
• Duchenne muscular dystrophy  children
• Mutant gene on X chromosome
• Myotonic muscular dystrophy  adults
MUSCLES, EXERCISING, AGING
• Cannot make more muscle fibers
• Existing ones get bigger, more active, and more
resistant to fatigue
• Aerobic exercise: long in duration, increase number
of mitochondria in muscles and number of blood
capillaries
• Strength training: brief
intense exercise, causes
muscle fibers to thicken,
stimulates enzymes
necessary for glycolysis
MUSCLES, EXERCISING, AGING
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Aging: number and size of muscle fibers decline
Tendons (muscle to bone) stiffen, more likely to tear
Muscle mass does not increase much
Aerobic exercise improves blood circulation
Modest strength training can slow loss of muscle
tissue