Daniel Batista
Pr.2 03/21/2012
A structure which
muscles interact with
to facilitate motion.
A skeleton can
consist of fluid or
external hard parts.
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Fluid-filled closed chamber(s) that muscles
act against.
Cnidarians (Jellyfish) & annelids (ringworms)
Sea Anemone
In sea anemones, water fills and is trapped in a
gastrovascular cavity, contractions by its muscles
redistribute water and alter body shape.
Earthworm
Possess a coelom divided into fluid-filled segments,
muscles both longitudinal and circular contract around
them to lengthen or shorten the segments.
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Stiff body covering to which muscles attach.
Bivalve mollusks like clams have a hinged
two-part shell.
Arthropods have hinged exoskeleton with
attached muscles. Some also use the
movement of body fluid as well(spiders).
“Bones over Muscle”
Same concept as our own skeleton, however the “bones”
are on the inside and muscles contract from within.
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Internal framework of hardened elements to
which muscles attached.
Echinoderms and vertebrates have an
endoskeleton.
Starfish Endoskeleton
All vertebrates have an
endoskeleton.
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Vertebrates refers to vertebral column.
This along with the bones of the head and rib
cage = axial skeleton.
Pectoral(shoulder) girdle, pelvic(hip) girdle,
and limbs(or bony fins) attached to the axial
skeleton are the appendicular skeleton.
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In humans:
Brain and spinal chord connect through an
opening called the foramen magnum
As upright walkers, vertebrae are parallel to
ground instead of perpendicular. Because of
this we experience back pain as we age due
to excess pressure on our intervertebral
discs.
Human Skeletal System
Living cells in a secreted
extracellular matrix.
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Movement by interacting with skeletal muscle
system
Support and anchor muscles
Protection
Mineral Storage
Blood cell formation
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There are Long bones such as femurs and flat
bones such as the bones of the skull.
Bones are wrapped in dense connective tissue
sheath with nerves and blood vessels.
The Extracellular matrix of bones is made up
of collagen(protein) w/ calcium and
phosphorus salts.
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3 types of Bone cells:
◦ Osteoblasts: bone builders/ secrete matrix
◦ Osteoclasts: secrete enzymes and acids to break
down bone
◦ Osteocytes: former osteoblasts now surrounded by
the matrix they secreted.
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Long Bones have two types of tissues:
◦ Compact Bone: form the shaft and outer layer,
contain many functional units called osteons which
have concentric rings of bone tissue w/ bone cells
b/w rings. Nerves and blood vessels run through
the center of osteons.
◦ Spongy Bone: Fills the shaft and ends of a long
bone, strong and lightweight, matrix riddled with
open spaces.
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The cavities inside a bone contain bone
marrow
◦ Red marrow fills the spaces in spongy bone, major
site of blood cell formation.
◦ Yellow marrow fills the central cavity of mature long
bones, mainly fat.
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The first skeleton that forms in vertebrates
consists of cartilage. In cartilaginous fishes it
remains that way, and in other vertebrates it
serves as a model for an adult skeleton of
bone. Osteoblasts move in and replace
cartilage.
Even once a bone stops growing in an adult,
it is constantly changing: repairing
microscopic cracks from normal movement
and breaking down to release mineral ions.
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Bones store most of the body’s calcium,
regulated by hormones(calcitonin).
Formation and remodeling influenced by
hormones
◦ Testosterone & estrogen encoarage bone
deposition.
◦ Cortisol(stress) slows it.
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After about 24 years of age, osteoblasts
secrete less matrix that osteoclasts
breakdown, gradually reducing bone mass.
Osteoporosis is when this reaches a point
where the bones become weaker and more
likely to break.
Most common in postmenopausal women b/c
they no longer produce sex hormones that
encourage deposition.
Allow no, little, or much range
of motion
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Joint: area of contact or near contact b/w
bones
3 types:
◦ Fibrous: Bones held securely in place by dense
connective tissue (teeth)
◦ Cartilaginous: pads of cartilage allow a bit of
movement (vertebrae)
◦ Synovial joints: Bones separated by a small cavity
and smooth cartilage covers ends. Ligaments hold
bones in place, some forming a capsule enclosing
the joint that secretes lubricating synovial fluid.
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Ball-and-socket joints: wide range of
rotational motion(shoulders).
In the joints of the wrist and ankles, bones
glide past one another.
Joints of the knee and elbows allow
movement on one plane only.
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Sprained ankle: a tearing of the ligaments in
your ankle.
A tear of cruciate(cross, in this case they
cross one another in the knee joint) ligaments
in the knee can require surgery.
A torn meniscus, a c-shaped wedge of
cartilage that cushions between the bones
and reduces friction.
Dislocation of the bones of a joint.
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Arthritis is chronic inflammation of a joint
◦ Osteoarthritis: occurs at worn down cartilage of an
often used joint at old age.
◦ Rheumatoid arthritis: autoimmune disorder,
immune system attacks the fluid secreting lining of
synovial joints.
◦ Gout: crystals of uric acid form at a joint, normally a
byproduct of protein breakdown, increased levels
can occur due to obesity and too much alcohol
intake.
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When a bursa (fluid filled sack acting as a
cushion in many joints)becomes inflamed.
Caused by repeating a movement which puts
pressure on a bursa.
Skeletal-Muscular Systems
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Bundles of muscle fibers sheathed in dense
connective tissue
Muscle fiber: cylindrical cell, multiple
nuclei(desdended from a group of cells that
fused together in the developing embryo),
contractile filaments.
Most muscle/bone interaction is like a lever.
The bone is a rigid rod near a fixed
point(joint). Muscle contraction transmits
force to move the bone.
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Muscles can only pull on bone, not push
Most muscles work in opposition
Tendons connect muscle to bone.
Have a role in respiration and circulation.
ATP fueled movements of
protein filaments inside
muscle fibers result in
contraction.
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Muscle fibers are packed with myofibrils,
each a bundle of contractile filaments that
run the length of the fiber.
Light-to-dark bands show up along the
myofibrils stained for microscopy, giving it a
striated appearance.
These bands are units of muscle contraction,
sarcomeres.
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The contractile units of muscles
Mesh of cytoskeletal elements called z bands
anchor adjacent sarcomeres.
The sarcomere has parallel arrays of thin and
thick filaments.
Thin filaments of two chains of actin(globular
protein) attached to z-bands extend inward.
Thick filaments of myosin(motor protein) are
positioned in the center, ends a few
nanometers from the thin filaments.
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Filaments do not change length, the myosin
bring actin filaments towards center,
contracting the sarcomere.
Myosin has hundreds of “heads” that can
attach to the actin.
When the muscle receives a signal from the
nervous system, calcium levels around
filaments rise.
Calcium allows myosin heads to bind to actin.
ATP binds to myosin heads.
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The ATP is used and converted to ADP +
Phosphate, causing the heads to tilt towards
the center, moving the actin.
ADP+P is released and more ATP binding to
the head releases the head.
This process continues as long as calcium
and ATP is available.
Muscle cells are excitable, like
neurons.
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Neuromuscular junction: synapse b/w muscle
and motor neuron.
For a muscle contract, an Action Potential
must travel to the junction to release
acetylcholine(ACh)
Binding ACh to the receptors on muscle fibers
excites them (like neurons) causing an A.P.
that travels along the muscle fiber
membrane, through T-tubules, to the
sarcoplasmic membrane( a special Smooth
E.R. around myofibrils and contain Calcium.
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Arrival of the A.P. opens voltage-gated
channels allowing Calcium to flow down its
concentration gradient.
When contraction ends, calcium pumps return
it to the sarcoplasmic reticulum.
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Calcium affects these two proteins that
regulate binding of myosin & actin filaments.
At rest, tropomyosin wraps around actin
covering the binding sites. Troponin is bound
to the tropomyosin and can reversibly bind
calcium ions.
When calcium binds to the troponin, it
changes shape and pulls the tropomyosin
away from the binding sites.
ATP and creatine phosphate
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The muscle first uses ATP, but little is stored
within cells.
After ATP, muscles turn to creatine
phosphate, which transfers a phosphate to
ADP to make more ATP. This keeps the
muscle going until ATP production from othe
pathways catch up.
During prolonged moderate activity, most
ATP is produced via cellular respiration.
Fibers respond as a unit.
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Motor Unit: One motor neuron and all of the
muscle fibers it synapses with.
Muscle twitch: When you briefly stimulate a
motor neuron and its fibers contract for a few
milliseconds.
If a new stimuli occurs before a response
ends, the fibers twitch again.
Repeatedly stimulating a motor unit cause a
sustained contraction, tetanus.
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Muscle Fatigue: when unrelenting stimulation
keeps a muscle in tetanus and decreases the
muscle’s capacity to generate force; muscle
relaxes despite continued stimulation.
In humans, we are born with all of our muscle
fibers, we do not grow new ones.
Aerobic exercise promotes muscle endurance
by increasing blood flow and mitocondria.
Brief, intense exercise promote synthesis of
myosin and actin to exert more tension.
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As we age, we lose muscle fibers.
Tendons stiffen and are more likely to tear.
Older people can exercise for long periods
but their muscles will no longer increase in
mass as much.
They can perform moderate weight training
to slow the loss however.
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A class of genetic disorders in which skeletal
muscles progressively weaken.
Duchenne: occurs in children, mutation of a
gene in the X chromosome. The gene codes
for dystrophin, a protein found in plasma
membrane of muscle fibers.
The mutant protein allows foreign material to
enter fiber which breaks it down.
Myotonic: occurs in Adults.
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When neurons cannot escite muscle fibers,
they wither away.
An example is poliovirus which infects and
kills motor neurons.
Amyotrophic lateral sclerosis (ALS) als okills
motor neurons. (Stephen Hawking)
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Bacteria of the genus Clostridium produce toxins
that disrupt the signal from nerves to muscles. C.
botulinum can be found in canned foods and its
spores release the toxin botulinum that keeps
motor neurons from releasing ACh.
Bacteria C. tetani live in the gut of grazing
animals, whose spores can live in the soil for
years. If they get into a deep wound, they grow a
toxin that is delivered to the brain and spinal
cord. This toxin restricts the release of GABA
neurotransmitter which control inhibition of
motor neurons.
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W/o GABA, symptomes of tetanus begin.
Over stimulated muscles stiffen and cannot
relax. The backbone is locked in an extreme
curve and the jaw is locked.
Death occurs when the respiratory and heart
muscles get locked in contraction.