11.2 Movement
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2009-2010
11.2.1 Human movement.
 Human movement is produced by the skeletal
acting as simple lever machines. The physics
of a lever system can be directly compared to
that of a limb.
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 In general terms the muscles and
bones of the spine (red) are force
magnifiers. This force is used to
stabilize the skeleton and provide
a stable platform (red) for the
movement of the limbs. Such lever
produce very little range of
movement but a great deal of
force.
 The muscles and bones of the
limbs are generally arranged into
3rd class levers and in such a way
to become distance magnifiers.
The reason for this is to provide
range of movement for the limb
rather than strength.
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 The image illustrates the
concept of 'range of
movement'.
Red = strength
 Blue = range of motion

 These simple ideas of
machines can be applied
to the skeletal system and
human movement.
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11.2.2 Joint structure
 A. Humerus (upper arm) bone.
 B. Synovial membrane that encloses the joint
capsule and produces synovial fluid.
 C. Synovial fluid (reduces friction and
absorbs pressure).
 D. Ulna (radius) the levers in the flexion and
extension of the arm.
 E. Cartilage (red) living tissue that reduces
the friction at joints.
 F. Ligaments that connect bone to bone and
produce stability at the joint.
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Antagonistic Pairs:
 To produce movement at a
joint muscles work in pairs.
 Muscles can only actively
contract and shorten. They
cannot actively lengthen.
 One muscles bends the limb
at the joint (flexor) which in
the elbow is the biceps.
 One muscles straightens the
limb at the joint (extensor)
which in the elbow is the
triceps.
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11.2.3 Elbow joint structure.
1. Humerus forms the shoulder joint also
2.
3.
4.
5.
6.
the origin for each of the two biceps
tendons
Biceps (flexor) muscle provides force for
an arm flexion (bending). As the main
muscle it is known as the agonist.
Biceps insertion on the radius of the
forearm
Elbow joint which is the fulcrum or pivot
for arm movement
5. Ulna one of two levers of the forearm
Technically in a flexion like this the
Biceps performs a concentric
contraction.
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Elbow Joint
 6. Triceps muscle is the
extensor whose contraction
straightens the arm.
 7. Elbow joint which is also
the pivot (fulcrum)for this
movement.
 It should be noted that the
description of movement is
fairly complex. A true
Triceps extension takes
place against gravity.
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Exercise:
 Bend your arm in a flexion. Point your elbow
upwards vertically. Raise your hand vertically
above your head. This is a true concentric
contraction of the Triceps
 Pick up a heavy object in concentric Biceps
flexion. Now lower and straighten your arm.
You should feel your Biceps contracted but
Triceps relaxed. That an eccentric contraction
of the Biceps This just shows how complex
movement can be!
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11.2.4 Movement at the hip and knee joint.
Comparison of movement at the hip and
knee joint:
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Knee Joint:
 The knee joint is an





example of a hinge joint.
The pivot is the knee joint.
The lever is the tibia and
fibula of the lower leg.
A knee extension is
powered by the quadriceps
muscles.
A knee flexion is powered
by the hamstring muscles.
Movement is one plane
only.
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The Hip Joint:
 Rotation is in all planes
and axis of movement.
 The lever is the femur and
the fulcrum is the hip
joint.
 The effort is provided by
the muscles of
quadriceps, hamstring
and gluteus
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The Shoulder
 A ball and socket joint.
 The humerus is the lever.
 The shoulder (scapula and


clavicle) form the pivot
joint.
Force is provided by the
deltoids, trapezius and
pectorals.
Movement is in all planes.
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11.2.5 Striated muscle structure.
1. Tendon connecting muscle to
bone. These are non-elastic
structures which transmit the
contractile force to the bond.
2. The muscle is surrounded by a
membrane which forms the
tendons at its ends.
3. Muscle bundle which contains
a number of muscle cells(4)
(Fibres) bound together. These
are the strands we see in
cooked meat. The plasma
membrane of a muscle cell is
called the sarcolemma and the
membrane reticulum is called
the sarcoplasmic reticulum.
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Striated Muscle Structure
4. The muscle fibre (Cell) is
multinucleated
 There are many parallel protein
structures inside called myofibrils.
 Myofibrils are combinations of two
filaments of protein called actin and
myosin.
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Actin and Myosin
The filaments overlap to give a distinct
banding pattern when seen with an
electron microscope.
 This shows the arrangement of actin
and myosin filaments in a myofibril
 The thick myosin filaments overlap with
the thinner actin filaments.
 Myofibril cross section:
 a) Actin only
 b) Myosin only
 c) Myosin attachment region adds
stability
 d) Actin and myosin overlap in cross
sections
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11.2.6 Structure of a sarcomere
 A sarcomere is a repeating unit of the
muscle myofibrils.
 defined by the distance between two Z
lines
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 Note:
 large number of mitochondria
 Diagonal myofibrils
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11.2.7 Mechanism of muscle
contraction.
1. Action potential arrives at the end of a
2.
3.
4.
5.
6.
motor neuron, at neuromuscular
junction.
Motor neuron releases the
neurotransmitter acetylcholine(Ach)
Ach binds to receptor protein opening
Na+ channels
Na+ enters the muscle cell (initiation of
action potential.
Aaction potential spreads rapidly
through the large muscle cell by
invaginations in the sarcolemma called
T-tubules.
This causes the sarcoplasmic
reticulum to release its store of Ca2+
into the myofibrils.
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6. Myosin filaments have cross bridge
lateral extensions.
7. Cross bridges include an ATPase
which can oxidise ATP and release
energy.
8.The cross bridges can link across to
the parallel actin filaments.
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9. Actin polymer is associated with
tropomyosin that occupies the binding
sites to which myosin binds in a
contraction.
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10. When relaxed the tropomyosin sits on
the outside of the actin blocking the
binding sites.
11. Myosin cannot cross bridges with
actin until the tropomyosin moves into
the groove.
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12. The calcium binds to troponin on the
thin filament, which changes shape,
moving tropomyosin into the groove in
the process.
13. Myosin cross bridges can now attach
and the cross bridge cycle can take
place.
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Cross Bridge Cycle:
The energy for the cycle is produced by the ATPase section of the cross
bridge structure. This energy temporarily changes the shape of the cross
bridge which is now attached to the actin. The two slide relative to each
other giving an overall shortening
1. The cross bridge swings out from the myosin and attaches to the thin
filament.
2. The cross bridge changes shape and rotates through 45°, causing the
filaments to slide. The energy from ATP splitting is used for this step, and
the products (ADP + Pi) are released.
3. A new ATP molecule binds to myosin and the cross bridge detaches from
the thin filament.
4. The cross bridge changes back to its original shape, while detached (so as
not to push the filaments back again). It is now ready to start a new cycle,
but further along the thin filament.
5. This model is for one myosin molecule cross bridging to one actin.
Looking at some of the diagrams we can see that there must be many
cross bridges formed.
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Cross Bridge Cycle
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11.2.8 Electron micrographs of muscle
fibre contraction.
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 These show that each sarcomere gets shorter (Z-Z) when
the muscle contracts, so the whole muscle gets shorter.
 But the dark band, which represents the thick filament,
does not change in length.
 This shows that the filaments don’t contract themselves,
but instead they slide past each other.
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