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. skeletalb. smoothc. 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 jointHumerus, 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

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• 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.

The skeleton and muscles interact in movement

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Figure 30.7A

Biceps contracted,triceps relaxed(extended)

Biceps

Triceps

TendonsTriceps

Biceps

Tricepscontracted,bicepsrelaxed

• 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.

Each muscle cell has its own contractile apparatus

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• Sarcomeres are– repeating groups of overlapping thick and thin

filaments and– the contractile unit—the fundamental unit of

muscle action.

Each muscle cell has its own contractile apparatus

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Figure 30.8_1

Muscle

Several muscle fibers

Single muscle fiber(cell)

Figure 30.8Muscle

Several muscle fibers

Single muscle fiber(cell)

Plasma membrane

Nuclei

Myofibril

Lightband

Darkband

Lightband

Z line

Sarcomere

SarcomereZ lineZ line

Thickfilaments(myosin)

Thinfilaments(actin)U

ltra

stru

ctur

e of

mus

cle

fiber

Figure 30.8_2

Plasma membrane

Nuclei

Myofibril

Lightband

Darkband

Lightband

Z line

Sarcomere

Single muscle fiber(cell)

Figure 30.8_3

SarcomereZ lineZ line

Thickfilaments(myosin)

Thinfilaments(actin)

Lightband

Darkband

Lightband

Z line

Sarcomere

Figure 30.8_4

• 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.

A muscle contracts when thin filaments slide along thick filaments

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Figure 30.9A

Relaxed muscle

Contractingmuscle

Fully contractedmuscle

Dark band

Sarcomere

Contracted sarcomere

Z Z

• 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.

A muscle contracts when thin filaments slide along thick filaments

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Figure 30.9BThinfilaments

Thinfilament

Thickfilament

Thick filament

Z lineActin

Myosin head (low-energy configuration)

Myosin head (high-energy configuration)

Cross-bridge

Newpositionof Z lineThin filament moves

toward center of sarcomere.

1

2

3

ATP

ADPP

ADPP

4

ADP P

5

Myosin head (pivoting tolow-energy configuration)

ATP Myosin head (low-energy configuration)

Figure 30.9B_s1

Thinfilaments

Thick filament

Z line

Figure 30.9B_s2

Thinfilaments

Thick filament

Z line

Myosin head (low-energy configuration)

Actin

Thinfilament

Thickfilament

1

ATP

Figure 30.9B_s3

Thinfilaments

Thick filament

Z line

Myosin head (low-energy configuration)

Myosin head (high-energy configuration)

Actin

Thinfilament

Thickfilament

1

2

ATP

ADPP

Figure 30.9B_s4

Cross-bridge

3

ADPP

Figure 30.9B_s5

Myosin head(pivoting)

4

Newpositionof Z lineThin filament

moves toward center.

ADP P

Cross-bridge

3

ADPP

Figure 30.9B_s6

Myosin head(low-energy)

Myosin head(pivoting)

ATP

5

4

Newpositionof Z lineThin filament

moves toward center.

ADP P

Cross-bridge

3

ADPP

• A motor neuron– carries an action potential to a muscle cell,– releases the neurotransmitter acetylcholine

from its synaptic terminal, and– initiates a muscle contraction.

Motor neurons stimulate muscle contraction

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Figure 30.10A

Motor neuronaxon

Synapticterminal

T tubule

Action potentialMitochondrion

Endoplasmicreticulum (ER)

Myofibril

Plasma membraneSarcomere

Ca2

releasedfrom ER

• 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.

Motor neurons stimulate muscle contraction

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Figure 30.10B

Myosin-binding sites blocked

Myosin-binding sites exposed

Myosin-binding site

Ca2 floods thecytoplasmicfluid

ActinTropomyosin Ca2-binding sites

Troponin complex

• 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.

Motor neurons stimulate muscle contraction

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Figure 30.10C Spinal cord

Motor neuroncell body

Nerve

Motor neuronaxon

Synapticterminals

Muscle

Tendon

Muscle fibers(cells)

Nuclei

Bone

Motorunit 1

Motorunit 2