IB Standards /
Review
Annie Lee, Sarah Bartley, Lauren Thames
Skeletons
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The three main functions of a skeleton:
support, protection, and movement
(11.2.1)
 A hard skeleton provides protection for soft
tissues and provides a framework for our
bodies.
– Name some examples?
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Three types of skeletons
– Hydrostatic skeletons, Exoskeletons, and
Endoskeletons
Hydrostatic Skeletons

Consists of fluid held
under pressure in a
closed body
compartment
– Cnidarians, flatworms,
nematods, and annelids

These animals are able
to change shape
because of the fluidfilled compartments
– Flexibility
– Ex. Worms.
Exoskeletons
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This type of skeleton is
a hard encasement
deposited on the
surface of the animal.
 Ex. Molluscs
 Arthropods have
cuticle exoskeletons, a
non-living coat. The
cuticle contains chitin
(polysaccharide similar
to cellulose).
Endoskeleton
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Consists of hard
supporting elements,
like bones.
– Buried within the soft
tissues of an animal.
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Echinoderms have
endoskeletons of hard
plates called ossicles
beneath their skin.
– Sea urchins vs. Sea
Stars
Joints

IB specifically wants
you to know the
human elbow joint.
(11.2.2)
 Specifically the
cartilage, synovial
fluid, joint capsule,
named bones, and
antagonistic muscles.
– Make sure you can label
these things !!
Elbow Joint Continued

IB also wants you to know the functions of the structures in
the human elbow joint (11.2.3)
 Cartilage
– A type of connective tissue with an abundance of collagenous
fibers embedded in chondroitin sulfate.
– Cartilage is retained in certain locations
• Disks that acts of cushions between vertebrae and the
caps on the ends of some bones
• Absorbs physical impact
 Synovial Fluid
– Thick stringy fluid found in the cavities of Synovial joints.
– Reduces friction between the cartilage and other tissues in
joints
 Joint Capsule (Articular Capsule)
– Envelope surrounding the Synovial joint
– Covers the end surfaces of bones
Joints Continued

Three types of joints:
 Ball-and-socket joint
– Where the Humerus contacts the shoulder girdle,
and our femur contacts the pelvic girdle

Hinge Joint
– Between the Humerus and the head of the Ulna

Pivot Joint
– Same place above
The Hip Joint and Knee Joint

IB wants you to know the comparison
between the knee joint and the hip joint
(11.2.4)
 Knee Joint
– Hinge joint, and is the biggest joint in our body

Hip Joint
– Ball-and-socket type of joint, specifically called a
synovial joint.
Muscles

The purpose of muscles is to provide
movement to the body by the providing ability
to move bones. (11.2.1. IB wants you to know
the purpose of muscles)
 The action of a muscle is to contract
– Muscles only extend passively

Antagonistic pairs, each member of the pair
working against each other.
– Ex. Flexing an arm
Vertebrate Skeletal Muscle


The skeletal muscle
Structure (11.2.5 IB
wants you to know the
skeletal muscle
structure and its
components)
– Hierarchy of smaller and
smaller units
– A muscle fiber = bundle
of smaller myofibrils
– Myofibrils = two types of
myofilaments (thin
filaments and thick
filaments)
Structure Continued
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Thin filaments
– Two strands of actin and one
strand of regulatory protein
Thick filaments
– Staggered arrays of myosin
molecules
The arrangement of myofilaments
make a pattern of light and dark
bands. Each repeating unit is called a
sarcomere.
There are two bands
– I Band: area near the edge of
sarcomere where there are only
thin filaments
– A Band: broad region that
corresponds to the length of the
thick filaments
• There is an H zone, which is
in the center of the
sarcomere
The Structure of the Sarcomere

Things to note
(11.2.6)
–
–
–
–
Z lines
Light band
Dark band
H zone
Sliding-Filament Model

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When the muscle
contracts, thin and thick
filaments do not change
in length when the
sarcomere shortens
There is an overlap
between both filaments
instead.
– Results in the I band and
the H zone shrinking
Sliding-Filament Model
Continued
The sliding/overlap of the filaments
result from Myosin-Actin interactions
 Take a look at the diagram

Myosin-Act Interaction
how this works…so pay attention)
(11.2.7. IB wants you to know
Role of Calcium and Regulatory
Proteins
Skeletal fiber only contracts when
activated by a motor neuron.
 This is where the Calcium and
Regulatory Proteins come into work

Role of Calcium and Regulatory
Proteins (11.2.7)
The Stimulus

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The stimulation provided by the motor neuron is an action
potential that makes a synapse with the muscle fiber.
The synaptic terminal releases neurotransmitters, called
acetylcholine
– Depolarization, causes it to produce action potential
The action potential spreads into …
– A plasma membrane called transverse (T) tubules
– And then the sarcoplasmic reticulum (SR) which the tubes
make close contact with
• The action potential opens Calcium ion channels in
the SR
• (look at diagram on pg. 1070)
A quick look at the standards..
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11.2.1: State the roles of bones, muscles, etc in human
movement
11.2.2: Label a diagram of the human elbow joint, including
cartilage, synovial fluid, joint capsule…etc.
11.2.3: Outline the functions of the structures in the human
elbow joint named in 11.2.2
11.2.4: Compare the movements of the hip joint and knee
joint
11.2.5: Describe the structure of striated muscle fibers,
including myofibrils with light and dark bands… etc
11.2.6: Draw and label a diagram to show the sarcomere,
including Z lines, actin filaments, myosin..etc
11.2.7: Explain how skeletal muscle contracts, including the
release of calcium ions from the SR, formation of cross
bridges…etc.