11.2.Muscles and movement
• State the roles of bones, ligaments, muscles, tendons
and nerves in human movement.
• Label a diagram of the human elbow joint, including
cartilage, synovial fluid, joint capsule, named bones
and antagonistic muscles (biceps and triceps).
• Outline the functions of the structures in the human
elbow joint named above.
• Compare the movements of the hip joint and the
knee joint.
• Describe the structure of striated muscle fibres, including the
myofibrils with light and dark bands, mitochondria, the
sarcoplasmic reticulum, nuclei and the sarcolemma
• Draw and label a diagram to show the structure of a sarcomere,
including Z lines, actin filaments, myosin filaments with heads, and
the resultant light and dark bands.
• Explain how skeletal muscle contracts, including the release of
calcium ions from the sarcoplasmic reticulum, the formation of
cross-bridges, the sliding of actin and myosin filaments, and the use
of ATP to break cross-bridges and re-set myosin heads.
• Analyse electron micrographs to find the state of contraction of
muscle fibres.
Components of our locomotory system
Components of our locomotory system
Bones: support and partially protect the body parts.
Ligaments: hold bones together and form protective
capsules around the moveable joints. They are made of
strong lightly elastic tissue.
Muscles: cause movements by contraction.
a. skeletal
b. smooth
c. cardiac
Tendons: attach muscles to bones at their points of
anchorage. They are made of dense connective tissue.
Nerves: connect central nervous system to other parts of
the body. They are bundles of many nerve fibers. They
stimulate muscles for movement.
The human elbow joint
The components of human elbow joint
Humerus, radius, ulna:
Biceps muscle:
Triceps muscles:
Ligaments:
Capsule:
Synovial membrane:
Synovial fluid:
Cartilage:
Types of joints:
• Movable joints: provide controlled movement
also known as synovial joints.
a. Ball and socket joints: are found in hip
joints that permit movements in all three planes
(circular movement: circumduction)
b. Hinge joint: restricts the movement to one
plane (flexion and extension. Example: Knee
joint
The human knee joint
MUSCLE CONTRACTION
AND MOVEMENT
© 2012 Parson Education, Inc.
The skeleton and muscles interact in movement
• Muscles and bones interact to produce
movement.
• Muscles
– are connected to bones by tendons and
– can only contract, requiring an antagonistic
muscle to
• reverse the action and
• relengthen muscles.
© 2012 Parson Education, Inc.
Figure 30.7A
Triceps
contracted,
biceps
relaxed
Biceps contracted,
triceps relaxed
(extended)
Biceps
Biceps
Triceps
Tendons
Triceps
Each muscle cell has its own contractile apparatus
• Muscle fibers are cells that consist of
bundles of myofibrils. Skeletal muscle cells
– are cylindrical,
– have many nuclei, and
– are oriented parallel to each other.
• Myofibrils contain overlapping
– thick filaments composed primarily of the
protein myosin and
– thin filaments composed primarily of the
protein actin.
© 2012 Parson Education, Inc.
Each muscle cell has its own contractile apparatus
• Sarcomeres are
– repeating groups of overlapping thick and thin
filaments and
– the contractile unit—the fundamental unit of
muscle action.
© 2012 Parson Education, Inc.
Figure 30.8_1
Muscle
Several muscle fibers
Single muscle fiber
(cell)
Figure 30.8
Ultra structure of muscle fiber
Muscle
Several muscle fibers
Single muscle fiber
(cell)
Nuclei
Plasma membrane
Myofibril
Light
band
Dark
band
Light
band
Z line
Sarcomere
Thick
filaments
(myosin)
Thin
filaments
(actin)
Z line
Sarcomere
Z line
Figure 30.8_2
Single muscle fiber
(cell)
Nuclei
Plasma membrane
Myofibril
Light
band
Dark
band
Sarcomere
Light
band
Z line
Figure 30.8_3
Light
band
Dark
band
Light
band
Z line
Sarcomere
Thick
filaments
(myosin)
Thin
filaments
(actin)
Z line
Sarcomere
Z line
Figure 30.8_4
A muscle contracts when thin filaments slide along
thick filaments
• According to the sliding-filament model of
muscle contraction, a sarcomere contracts
(shortens) when its thin filaments slide
across its thick filaments.
– Contraction shortens the sarcomere without
changing the lengths of the thick and thin
filaments.
– When the muscle is fully contracted, the thin
filaments overlap in the middle of the
sarcomere.
© 2012 Parson Education, Inc.
Figure 30.9A
Sarcomere
Dark band
Z
Z
Relaxed muscle
Contracting
muscle
Fully contracted
muscle
Contracted sarcomere
A muscle contracts when thin filaments slide along
thick filaments
• Myosin heads of the thick filaments
– bind ATP and
– extend to high-energy states.
• Myosin heads then
– attach to binding sites on the actin molecules
and
– pull the thin filaments toward the center of the
sarcomere.
© 2012 Parson Education, Inc.
Figure 30.9B
Thick filament
Thin
filaments
Z line
Actin
1
Thin
filament
ATP
Myosin head (lowenergy configuration)
Thick
filament
2
ADP
P
Myosin head (highenergy configuration)
3
ADP
Cross-bridge
P
ADP  P
Thin filament moves
toward center of sarcomere.
4
Myosin head (pivoting to
low-energy configuration)
5
ATP
Myosin head (lowenergy configuration)
New
position
of Z line
Figure 30.9B_s1
Thick filament
Thin
filaments
Z line
Figure 30.9B_s2
Thick filament
Thin
filaments
Z line
Actin
1 Thin
filament
Thick
filament
ATP
Myosin head (lowenergy configuration)
Figure 30.9B_s3
Thick filament
Thin
filaments
Z line
Actin
1 Thin
filament
ATP
Myosin head (lowenergy configuration)
ADP
P
Myosin head (highenergy configuration)
Thick
filament
2
Figure 30.9B_s4
3
ADP
P
Cross-bridge
Figure 30.9B_s5
3
ADP
Cross-bridge
P
ADP  P
Thin filament
moves toward center.
4
Myosin head
(pivoting)
New
position
of Z line
Figure 30.9B_s6
3
ADP
Cross-bridge
P
ADP  P
Thin filament
moves toward center.
4
Myosin head
(pivoting)
5
ATP
Myosin head
(low-energy)
New
position
of Z line
Motor neurons stimulate muscle contraction
• A motor neuron
– carries an action potential to a muscle cell,
– releases the neurotransmitter acetylcholine
from its synaptic terminal, and
– initiates a muscle contraction.
© 2012 Parson Education, Inc.
Figure 30.10A
Motor neuron
axon
Mitochondrion
Action potential
Synaptic
terminal
T tubule
Endoplasmic
reticulum (ER)
Myofibril
Plasma membrane
Sarcomere
Ca2
released
from ER
Motor neurons stimulate muscle contraction
• An action potential in a muscle cell
– passes along T tubules and
– into the center of the muscle fiber.
• Calcium ions
– are released from the endoplasmic reticulum
and
– initiate muscle contraction by moving the
regulatory protein tropomyosin away from the
myosin-binding sites on actin.
© 2012 Parson Education, Inc.
Figure 30.10B
Myosin-binding sites blocked
Tropomyosin
Actin
Ca2-binding sites
Troponin complex
Ca2 floods the
cytoplasmic
fluid
Myosin-binding sites exposed
Myosin-binding site
Motor neurons stimulate muscle contraction
• A motor unit consists of
– a neuron and
– the set of muscle fibers it controls.
• More forceful muscle contractions result
when additional motor units are activated.
© 2012 Parson Education, Inc.
Figure 30.10C
Motor Motor
unit 1 unit 2
Spinal cord
Nerve
Motor neuron
cell body
Motor neuron
axon
Synaptic
terminals
Nuclei
Muscle fibers
(cells)
Muscle
Tendon
Bone