Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 49.5: Animal skeletons function in support, protection, and movement The various types of animal movements – All result from muscles working against some type of skeleton

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Skeletons The three main functions of a skeleton are – Support, protection, and movement The three main types of skeletons are – Hydrostatic skeletons, exoskeletons, and endoskeletons

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hydrostatic Skeletons A hydrostatic skeleton – Consists of fluid held under pressure in a closed body compartment This is the main type of skeleton – In most cnidarians, flatworms, nematodes, and annelids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Annelids use their hydrostatic skeleton for peristalsis – A type of movement on land produced by rhythmic waves of muscle contractions Figure 49.25a–c (a) Body segments at the head and just in front of the rear are short and thick (longitudinal muscles contracted; circular muscles relaxed) and anchored to the ground by bristles. The other segments are thin and elongated (circular muscles contracted; longitudinal muscles relaxed.) (b) The head has moved forward because circular muscles in the head segments have contracted. Segments behind the head and at the rear are now thick and anchored, thus preventing the worm from slipping backward. (c) The head segments are thick again and anchored in their new positions. The rear segments have released their hold on the ground and have been pulled forward. Longitudinal muscle relaxed (extended) Circular muscle contracted Circular muscle relaxed Longitudinal muscle contracted Head Bristles

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exoskeletons An exoskeleton is a hard encasement – Deposited on the surface of an animal Exoskeletons – Are found in most molluscs and arthropods

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endoskeletons An endoskeleton consists of hard supporting elements – Such as bones, buried within the soft tissue of an animal Endoskeletons – Are found in sponges, echinoderms, and chordates

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The mammalian skeleton is built from more than 200 bones – Some fused together and others connected at joints by ligaments that allow freedom of movement

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The human skeleton Figure Ball-and-socket joints, where the humerus contacts the shoulder girdle and where the femur contacts the pelvic girdle, enable us to rotate our arms and legs and move them in several planes. 2 Hinge joints, such as between the humerus and the head of the ulna, restrict movement to a single plane. 3 Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side. key Axial skeleton Appendicular skeleton Skull Shoulder girdle Clavicle Scapula Sternum Rib Humerus Vertebra Radius Ulna Pelvic girdle Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges 1 Examples of joints 2 3 Head of humerus Scapula Humerus Ulna Radius

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Physical Support on Land In addition to the skeleton – Muscles and tendons help support large land vertebrates

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 49.6: Muscles move skeletal parts by contracting The action of a muscle – Is always to contract

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Skeletal muscles are attached to the skeleton in antagonistic pairs – With each member of the pair working against each other Figure Human Grasshopper Biceps contracts Triceps relaxes Forearm flexes Biceps relaxes Triceps contracts Forearm extends Extensor muscle relaxes Flexor muscle contracts Tibia flexes Extensor muscle contracts Flexor muscle relaxes Tibia extends

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vertebrate Skeletal Muscle Vertebrate skeletal muscle – Is characterized by a hierarchy of smaller and smaller units Figure Muscle Bundle of muscle fibers Single muscle fiber (cell) Plasma membrane Myofibril Light band Dark band Z line Sarcomere TEM 0.5  m I band A band I band M line Thick filaments (myosin) Thin filaments (actin) H zone Sarcomere Z line Nuclei animation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A skeletal muscle consists of a bundle of long fibers – Running parallel to the length of the muscle A muscle fiber (muscle cell) – Is itself a bundle of smaller myofibrils arranged longitudinally

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The myofibrils are composed to two kinds of myofilaments – Thin filaments, consisting of two strands of actin and one strand of regulatory protein – Thick filaments, staggered arrays of myosin molecules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Skeletal muscle is also called striated muscle – Because the regular arrangement of the myofilaments creates a pattern of light and dark bands

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Each repeating unit is a sarcomere – Bordered by Z lines The areas that contain the myofilments – Are the I band, A band, and H zone

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Sliding-Filament Model of Muscle Contraction According to the sliding-filament model of muscle contraction – The filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings As a result of this sliding – The I band and the H zone shrink Figure 49.29a–c (a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bands and H zone are relatively wide. (b) Contracting muscle fiber. During contraction, the thick and thin filaments slide past each other, reducing the width of the I bands and H zone and shortening the sarcomere. (c) Fully contracted muscle fiber. In a fully contracted muscle fiber, the sarcomere is shorter still. The thin filaments overlap, eliminating the H zone. The I bands disappear as the ends of the thick filaments contact the Z lines. 0.5  m Z H A Sarcomere

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The sliding of filaments is based on – The interaction between the actin and myosin molecules of the thick and thin filaments The “head” of a myosin molecule binds to an actin filament – Forming a cross-bridge and pulling the thin filament toward the center of the sarcomere

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Myosin-actin interactions underlying muscle fiber contraction Figure Thick filament Thin filaments Thin filament ATP ADP P i Cross-bridge Myosin head (low- energy configuration) Myosin head (high- energy configuration) + Myosin head (low- energy configuration) Thin filament moves toward center of sarcomere. Thick filament Actin Cross-bridge binding site 1Starting here, the myosin head is bound to ATP and is in its low- energy confinguration. 2 The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( I ) and is in its high-energy configuration. P 1The myosin head binds to actin, forming a cross- bridge. 3 4 Releasing ADP and ( i ), myosin relaxes to its low-energy configuration, sliding the thin filament. P 5 Binding of a new mole- cule of ATP releases the myosin head from actin, and a new cycle begins.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Role of Calcium and Regulatory Proteins A skeletal muscle fiber contracts – Only when stimulated by a motor neuron

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When a muscle is at rest – The myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin Figure 49.31a Actin Tropomyosin Ca 2+ -binding sites Troponin complex (a) Myosin-binding sites blocked

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings For a muscle fiber to contract – The myosin-binding sites must be uncovered This occurs when calcium ions (Ca 2+ )calcium ions – Bind to another set of regulatory proteins, the troponin complex Figure 49.31b Ca 2+ Myosin- binding site (b) Myosin-binding sites exposed

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The stimulus leading to the contraction of a skeletal muscle fiber – Is an action potential in a motor neuron that makes a synapse with the muscle fiber Figure Motor neuron axon Mitochondrion Synaptic terminal T tubule Sarcoplasmic reticulum Myofibril Plasma membrane of muscle fiber Sarcomere Ca 2+ released from sarcoplasmic reticulum

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The synaptic terminal of the motor neuron – Releases the neurotransmitter acetylcholine, depolarizing the muscle and causing it to produce an action potential

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Action potentials travel to the interior of the muscle fiber – Along infoldings of the plasma membrane called transverse (T) tubules The action potential along the T tubules – Causes the sarcoplasmic reticulum to release Ca 2+ The Ca 2+ binds to the troponin-tropomyosin complex on the thin filamentsCa 2+ binds to the troponin-tropomyosin – Exposing the myosin-binding sites and allowing the cross-bridge cycle to proceed

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ACh Synaptic terminal of motor neuron Synaptic cleft T TUBULE PLASMA MEMBRANE SR ADP CYTOSOL Ca 2  P2P2 Cytosolic Ca 2+ is removed by active transport into SR after action potential ends. 6 Review of contraction in a skeletal muscle fiber Figure Acetylcholine (ACh) released by synaptic terminal diffuses across synaptic cleft and binds to receptor proteins on muscle fiber’s plasma membrane, triggering an action potential in muscle fiber. 1 Action potential is propa- gated along plasma membrane and down T tubules. 2 Action potential triggers Ca 2+ release from sarco- plasmic reticulum (SR). 3 Myosin cross-bridges alternately attach to actin and detach, pulling actin filaments toward center of sarcomere; ATP powers sliding of filaments. 5 Calcium ions bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin-binding sites exposed. 4 Tropomyosin blockage of myosin- binding sites is restored; contraction ends, and muscle fiber relaxes. 7

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neural Control of Muscle Tension Contraction of a whole muscle is graded – Which means that we can voluntarily alter the extent and strength of its contraction

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings There are two basic mechanisms by which the nervous system produces graded contractions of whole muscles – By varying the number of fibers that contract – By varying the rate at which muscle fibers are stimulated

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a vertebrate skeletal muscle – Each branched muscle fiber is innervated by only one motor neuron Each motor neuron – May synapse with multiple muscle fibers Figure Spinal cord Nerve Motor neuron cell body Motor unit 1 Motor unit 2 Motor neuron axon Muscle Tendon Synaptic terminals Muscle fibers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A motor unit – Consists of a single motor neuron and all the muscle fibers it controls Recruitment of multiple motor neurons – Results in stronger contractions

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A twitch – Results from a single action potential in a motor neuron More rapidly delivered action potentials – Produce a graded contraction by summation Figure Action potential Pair of action potentials Series of action potentials at high frequency Time Tension Single twitch Summation of two twitches Tetanus

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tetanus is a state of smooth and sustained contraction – Produced when motor neurons deliver a volley of action potentials

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Muscle Fibers Skeletal muscle fibers are classified as slow oxidative, fast oxidative, and fast glycolytic – Based on their contraction speed and major pathway for producing ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of skeletal muscles

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other Types of Muscle Cardiac muscle, found only in the heart – Consists of striated cells that are electrically connected by intercalated discs – Can generate action potentials without neural input

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In smooth muscle, found mainly in the walls of hollow organs – The contractions are relatively slow and may be initiated by the muscles themselves In addition, contractions may be caused by – Stimulation from neurons in the autonomic nervous system

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 49.7: Locomotion requires energy to overcome friction and gravity Movement is a hallmark of all animals – And usually necessary for finding food or evading predators Locomotion – Is active travel from place to place

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Swimming Overcoming friction – Is a major problem for swimmers Overcoming gravity is less of a problem for swimmers – Than for animals that move on land or fly

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Locomotion on Land Walking, running, hopping, or crawling on land – Requires an animal to support itself and move against gravity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diverse adaptations for traveling on land – Have evolved in various vertebrates Figure 49.36

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Flying Flight requires that wings develop enough lift – To overcome the downward force of gravity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONCLUSION For animals of a given body mass, swimming is the most energy- efficient and running the least energy- efficient mode of locomotion. In any mode, a small animal expends more energy per kilogram of body mass than a large animal. Flying Running Swimming 10 – – Body mass(g) Energy cost (J/Kg/m) CONCLUSION This graph compares the energy cost, in joules per kilogram of body mass per meter traveled, for animals specialized for running, flying, and swimming (1 J = 0.24 cal). Notice that both axes are plotted on logarithmic scales. RESULTS Physiologists typically determine an animal’s rate of energy use during locomotion by measuring its oxygen consumption or carbon dioxide production while it swims in a water flume, runs on a treadmill, or flies in a wind tunnel. For example, the trained parakeet shown below is wearing a plastic face mask connected to a tube that collects the air the bird exhales as it flies. EXPERIMENT The energy cost of locomotion – Depends on the mode of locomotion and the environment Figure Comparing Costs of Locomotion