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

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.

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 © 2012 Parson Education, Inc.

Figure 30.7A Biceps contracted, triceps relaxed (extended) Biceps Triceps Tendons Triceps Biceps Triceps contracted, biceps relaxed

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 © 2012 Parson Education, Inc.

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 © 2012 Parson Education, Inc.

Figure 30.8_1 Muscle Several muscle fibers Single muscle fiber (cell)

Figure 30.8 Muscle Several muscle fibers Single muscle fiber (cell) Plasma membrane Nuclei Myofibril Light band Dark band Light band Z line Sarcomere Z line Thick filaments (myosin) Thin filaments (actin) Ultra structure of muscle fiber

Figure 30.8_2 Plasma membrane Nuclei Myofibril Light band Dark band Light band Z line Sarcomere Single muscle fiber (cell)

Figure 30.8_3 Sarcomere Z line Thick filaments (myosin) Thin filaments (actin) Light band Dark band Light band 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 © 2012 Parson Education, Inc.

Figure 30.9A Relaxed muscle Contracting muscle Fully contracted muscle Dark band Sarcomere Contracted sarcomere ZZ

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 © 2012 Parson Education, Inc.

Figure 30.9B Thin filaments Thin filament Thick filament Thick filament Z line Actin Myosin head (low- energy configuration) Myosin head (high- energy configuration) Cross-bridge New position of Z line Thin filament moves toward center of sarcomere ATP ADP P P 4 P  5 Myosin head (pivoting to low-energy configuration) ATP Myosin head (low- energy configuration)

Figure 30.9B_s1 Thin filaments Thick filament Z line

Figure 30.9B_s2 Thin filaments Thick filament Z line Myosin head (low- energy configuration) Actin Thin filament Thick filament 1 ATP

Figure 30.9B_s3 Thin filaments Thick filament Z line Myosin head (low- energy configuration) Myosin head (high- energy configuration) Actin Thin filament Thick filament 1 2 ATP ADP P

Figure 30.9B_s4 Cross-bridge 3 ADP P

Figure 30.9B_s5 Myosin head (pivoting) 4 New position of Z line Thin filament moves toward center. ADPP  Cross-bridge 3 ADP P

Figure 30.9B_s6 Myosin head (low-energy) Myosin head (pivoting) ATP 5 4 New position of Z line Thin filament moves toward center. ADPP  Cross-bridge 3 ADP P

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 © 2012 Parson Education, Inc.

Figure 30.10A Motor neuron axon Synaptic terminal T tubule Action potential Mitochondrion Endoplasmic reticulum (ER) Myofibril Plasma membrane Sarcomere Ca 2  released from 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 © 2012 Parson Education, Inc.

Figure 30.10B Myosin-binding sites blocked Myosin-binding sites exposed Myosin-binding site Ca 2  floods the cytoplasmic fluid Actin Tropomyosin Ca 2  -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 © 2012 Parson Education, Inc.

Figure 30.10C Spinal cord Motor neuron cell body Nerve Motor neuron axon Synaptic terminals Muscle Tendon Muscle fibers (cells) Nuclei Bone Motor unit 1 Motor unit 2