© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 30 How Animals Move

MUSCLE CONTRACTION AND MOVEMENT © 2012 Parson Education, Inc.

Unit of muscle contraction Muscle fiber (cell) Nuclei Skeletal muscle Muscle fiber Nucleus Junction between two cells Cardiac muscle* Muscle fiber Smooth muscle* Nucleus *Under INVOLUNTARY control Intercalated discs

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)  Muscle fibers = single muscle cell –have many nuclei –Contains myofibrils

Plasma membrane Nuclei Myofibril Light band Dark band Light band Z line Sarcomere Single muscle fiber (cell)  Myofibrils = protein cables of overlapping –thick filaments –composed of the protein myosin and –thin filaments –composed of the protein actin.

Sarcomere Z line Thick filaments (myosin) Thin filaments (actin) Light band Dark band Light band Z line Sarcomere  Sarcomeres = contractile unit of muscle fiber –repeating groups of overlapping thick and thin filaments

Relaxed muscle Contracting muscle Fully contracted muscle Dark band Sarcomere Contracted sarcomere ZZ Sarcomere contracts (shortens) when its thin filaments slide across its thick filaments

Detailed structure of thin filaments Actin associated with two other proteins: -Tropomyosin - troponin

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

Motor neuron axon Synaptic terminal T tubule Action potential Mitochondrion Endoplasmic reticulum (ER) Myofibril Plasma membrane Sarcomere Ca 2  released from ER  A motor neuron –carries an action potential (nervous signal) to a muscle cell, –initiates a muscle contraction by triggering release of Ca 2+ from ER

Calcium ions bind to troponin, moving tropomyosin away from the myosin- binding sites on actin. 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 Role of Ca in muscle contraction

Relaxed muscle Contracting muscle Fully contracted muscle Dark band Sarcomere Contracted sarcomere ZZ Sliding Filament Model of Muscle Contraction: Sarcomere contracts (shortens) when its thin filaments slide across its thick filaments

A muscle contracts when thin filaments slide along thick filaments © 2012 Parson Education, Inc. 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

ATP required to power myosin movement and RELEASE from actin A muscle contracts when thin filaments slide along thick filaments

 Aerobic respiration –requires a constant supply of glucose and oxygen –provides most of the ATP used to power muscle movement during exercise.  Lactic acid fermentation –can provide ATP faster than aerobic respiration but –is less efficient. Aerobic respiration supplies most of the energy for exercise © 2012 Parson Education, Inc.

Figure 30.11

Supplying Fuel for High Performance

 Muscles can adapt to exercise by increasing the –levels of myoglobin, –number of mitochondria, and/or –number of capillaries going to muscles. © 2012 Parson Education, Inc.

Table 30.12

Figure Slow Intermediate Fast World- class sprinter Average couch potato Average active person Middle- distance runner World- class marathon runner Extreme endurance athlete Percentage of total muscle