Movement
Topic 11.2
Assessment Statements
11.2 U1
Bones and exoskeletons provide anchorage
for muscles and act as levers.
11.2 U2
Synovial joints allow certain movements but
not others.
11.2 S2
Annotation of a diagram of the human
elbow.
11.2 U3
Movement of the body requires muscles to
work in antagonistic pairs.
11.2 A1
Antagonistic pairs of muscles in an insect leg.
Role of bones and
Exoskeleton
Leverage
Bones act as levers
A lever is a rigid rod that rotates around a fixed
point (fulcrum)
effort
Force applied
to the lever is
called effort
Force that resists
motion is called
the load.
fulcrum
lever
Levers in our body
Joints act as fulcrums
L
E
Synovial joints
Movements of joints
Rotation
AnTagonistic Pairs
Assessment Statements
11.2 U4
11.2 U5
11.2 U6
11.2 U7
11.2 U8
11.2 U9
11.2 S3
11.2 S4
Skeletal muscle fibers are multinucleate and contain
specialized endoplasmic reticulum.
Muscle fibers contain many myofibrils.
Each myofibril is made up of contractile sarcomeres.
The contraction of the skeletal muscle is achieved by
the sliding of actin and myosin filaments.
ATP hydrolysis and cross bridge formation are
necessary for the filaments to slide.
Calcium ions and the proteins tropomyosin and
troponin control muscle contractions.
Drawing labeled diagrams of the structure of a
sarcomere.
Analysis of electron micrographs to find the state of
Skeletal Muscle
Skeletal Muscle
• Muscle tissue is made of muscle fibers
• A muscle fiber is a large cell that contains many nuclei
• Inside each muscle fiber are numerous myofibrils
• Each myofibril is surrounded by a special endoplasmic
reticulum called a sarcoplasmic reticulum.
• Between myofibrils many mitochondria are found
• Each myofibril is composed of repeating units called
sarcomeres.
• Each sarcomere is composed of actin and myosin filaments.
Skeletal Muscle
Sarcolema =
plasma
membrane
Sarcoplasmic
Reticulum =
Endoplasmic
Reticulum
• goes around
every myofibril
• Stores calcium
Muscle fibers
contain myofibrils
Actin ( thin filaments)
Myosin (thick filaments)
tutorial on sarcomere components
sarcomere
How does skeletal
muscle contract?
Sliding Filament Hypothesis:
(1950 – H. Huxley & J. Hanson – London)
• If muscle fibers slide then band pattern
should change during contraction.
• Light bands would become shorter
• Sarcomere would become shorter
• Dark bands would stay the same length
Relaxed and
Contracted muscle
The size of the light area indicates
contracting or relaxing
Sliding filament
theory:
Myosin has side branches with heads that
create a bridge to the actin filament
• ATP binds to the myosin head breaking the
bridge and changing the head position releasing
it from the actin
• The ATP hydrolyzes into ADP & Phosphate.
This causes the head to attach to the actin at a
specific binding site
• As the ADP and phosphate are released the
head bends & the actin filament is pulled
toward the center
•
Sliding filament
theory:
Role of Calcium
• Calcium is very important in the contraction
process.
• The influx of Ca+ is stimulated by the nerve
impulse
• The sarcoplasmic reticulum releases Ca+
• An influx of Ca+ causes opening of myosin
binding sites on the actin filament.
• This allows contraction to occur.
• When Ca+ concentration decreases the binding
sites close and the muscle relaxes
How movement
Occurs
animation of the actin myosin mechanism to create movement
How Movement
Occurs:
Watch the animation from the Campbell CD
on Muscle Contraction
How movement
Occurs
Click the link below to
watch this simulation of
how a muscle works.
Muscle Contraction simulation