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Tuesday, Dec. 6th: HOW YOU BE?! • Lab Due—any problems? Saved file w/proper name? My file is your first two pages? • Today: Ch 47, Muscles • Article—Immunizations 47 Effectors: How Animals Get Things Done 47 Effectors: How Animals Get Things Done • 47.1 How Do Muscles Contract? • 47.2 What Determines Muscle Strength and Endurance? • 47.3 What Roles Do Skeletal Systems Play in Movement? • 47.4 What Are Some Other Kinds of Effectors? 47.1 How Do Muscles Contract? Muscles and skeletons: the musculoskeletal system. Muscles and skeletons are the effectors that produce movement. 47.1 How Do Muscles Contract? Three types of vertebrate muscle: • Skeletal: voluntary movement, breathing • Cardiac: beating of heart • Smooth: involuntary, movement of internal organs 47.1 How Do Muscles Contract? Skeletal muscle (striated): • Cells are called muscle fibers: multinucleate • Form from fusion of embryonic myoblasts • One muscle consists of many muscle fibers bundled together by connective tissue Figure 47.1 The Structure of Skeletal Muscle Figure 47.1 The Structure of Skeletal Muscle 47.1 How Do Muscles Contract? Contractile proteins: Actin: thin filaments Myosin: thick filaments Each muscle fiber has several myofibrils: bundles of actin and myosin filament. 47.1 How Do Muscles Contract? Each myofibril consists of repeating units: sarcomeres. Sarcomere: overlapping actin and myosin filaments. Bundles of myosin filaments are held in place by the protein titin, the largest protein in the body. Figure 47.1 The Structure of Skeletal Muscle (Part 2) Figure 47.1 The Structure of Skeletal Muscle (Part 3) 47.1 How Do Muscles Contract? The sliding filament theory of muscle contraction: • Depends on structure of actin and myosin molecules. • Myosin heads can bind specific sites on actin molecules to form cross bridges. Myosin changes conformation, causes actin filament to slide 5–10 nm. Figure 47.2 Sliding Filaments 47.1 How Do Muscles Contract? Muscle contraction is initiated by action potentials from a motor neuron at the neuromuscular junction. A motor unit: all the muscle fibers activated by one motor neuron. Figure 47.3 Actin and Myosin Filaments Overlap to Form Myofibrils 47.1 How Do Muscles Contract? One muscle may have many motor units. To increase strength of muscle contraction: increase rate of firing of motor neuron or recruit more motor neurons to fire (more motor units activated). 47.1 How Do Muscles Contract? Muscle cells are excitable: the plasma membrane can conduct action potentials. Acetylcholine is released by the motor neuron at the neuromuscular junction and opens ion channels in the motor end plate. Figure 47.4 The Neuromuscular Junction Photo 47.6 Leg muscles of the dogflea (Ctenocephalides canis), photographed in polarized light. 47.1 How Do Muscles Contract? Action potentials also travel deep within muscle fiber via T tubules. T tubules (transverse tubules) descend into the sarcoplasm (muscle fiber cytoplasm). T tubules run close to the sarcoplasmic reticulum (ER): a closed compartment that surrounds every myofibril. Figure 47.5 T Tubules in Action 47.1 How Do Muscles Contract? Sarcoplasmic reticulum has Ca2+ pumps. At rest there is high concentration of Ca2+ in the sarcoplasmic reticulum. Action potential reaches receptor proteins and opens the Ca2+ channels, Ca2+ flows out of sarcoplasmic reticulum and triggers interaction of actin and myosin. 47.1 How Do Muscles Contract? Actin filaments also include tropomyosin and troponin. Troponin has three subunits: one binds actin, one binds myosin, and one binds Ca2+. At rest, tropomyosin blocks the binding sites on actin. 47.1 How Do Muscles Contract? When Ca2+ is released, it binds to troponin, which changes conformation. Troponin is bound to tropomyosin— twisting of tropomyosin exposes binding sites on actin. When Ca2+ pumps remove Ca2+ from sarcoplasm, contraction stops. Figure 47.6 The Release of Ca2+ from the Sarcoplasmic Reticulum Triggers Muscle Contraction CONTRACTION OF SKELETAL MUSCLE CONTRACTION FLAGELLATED GREEN ALGA FLAGELLATED EUGLENID ROTIFERS FEEDING VIA FLAGELLA 47.1 How Do Muscles Contract? Cardiac muscle is also striated; cells are smaller than skeletal and have one nucleus. Cardiac muscle cells also branch and interdigitate: can withstand high pressures. Intercalated discs provide mechanical adhesions between cells. Figure 47.7 There are Three Kinds of Muscle Photo 47.8 Skeletal muscle in frog; cross striations and peripheral nuclei. LM, H&E stain. Photo 47.9 Human skeletal muscle; narrow dark line = Z line, broad dark line = A band. LM. CARDIAC MUSCLE CELL BEATING Photo 47.10 Myofibrils; bands of actin and myosin together appear darkest. Photo 47.11 Sarcomere from fish muscle. 47.1 How Do Muscles Contract? Pacemaker and conducting cells initiate and coordinate heart contractions. Heartbeat is myogenic—generated by the heart muscle itself. Autonomic nervous system modifies the rate of pacemaker cells, but is not necessary for their function. Photo 47.13 Human cardiac muscle; cross striations and central nuclei. LM, H&E stain. 47.1 How Do Muscles Contract? Contraction of cardiac muscle: • DHP proteins in T tubules are Ca channels; ryanodine receptors are iongated Ca2+ channels, sensitive to Ca2+. • Action potential causes Ca2+ to flow into sarcoplasm from T tubules; increase in Ca2+ opens the Ca2+ channels in sarcoplasmic reticulum—large increase in Ca2+ in sarcoplasm—initiates contraction. Ca2+-induced Ca2+ release 47.1 How Do Muscles Contract? Smooth muscle: in most internal organs; under autonomic nervous system control. Smooth muscle cells are arranged in sheets; have electrical contact via gap junctions. Action potential in one cell can spread to all others in the sheet. 47.1 How Do Muscles Contract? Plasma membrane of smooth muscle cells sensitive to stretch. Stretched cells depolarize and fire action potentials which starts contraction. 47.1 How Do Muscles Contract? Smooth muscle contraction: • Ca2+ influx to sarcoplasm stimulated by stretching, action potentials, or hormones. • Ca2+ binds with calmodulin: activates myosin kinase which phosphorylates myosin heads—can then bind and release actin. Figure 47.8 Mechanisms of Smooth Muscle Activation (Part 1) Figure 47.8 Mechanisms of Smooth Muscle Activation (Part 2) 47.1 How Do Muscles Contract? Skeletal muscle: minimum unit of contraction = a twitch. Twitch measured in terms of tension, or force it generates. A single action potential generates a single twitch. Force generated depends on how many fibers are in the motor unit. 47.1 How Do Muscles Contract? Tension generated by entire muscle depends on: • Number of motor units activated • Frequency at which motor units are firing 47.1 How Do Muscles Contract? Single twitch: if action potentials are close together in time, the twitches are summed, tension increases. Twitches sum because Ca2+ pumps can not clear Ca2+ from sarcoplasm before the next action potential arrives. Tetanus: when action potentials are so frequent there is always Ca2+ in the sarcoplasm. Figure 47.9 Twitches and Tetanus 47.1 How Do Muscles Contract? How long muscle fiber can sustain tetanic contraction depends on ATP supply. ATP is needed to break the myosin-actin bonds, and “re-cock” the myosin heads. To maintain contraction, actin–myosin bonds have to keep cycling. 47.1 How Do Muscles Contract? Muscle tone: a small but changing number of motor units are contracting. Muscle tone is constantly being adjusted by the nervous system. 47.2 What Determines Muscle Strength and Endurance? Slow-twitch muscle fibers: oxidative or red muscle. Contain myoglobin: oxygen binding protein; many mitochondria, wellsupplied with blood vessels. Maximum tension develops slowly, but is highly resistant to fatigue. 47.2 What Determines Muscle Strength and Endurance? Slow-twitch fibers have reserves of glycogen and fat; can produce ATP as long as oxygen is available. Muscles with high proportion of slowtwitch fibers are good for aerobic work (e.g., long distance running, cycling, swimming, etc.) 47.2 What Determines Muscle Strength and Endurance? Fast-twitch fibers: glycolytic or white muscle. Fewer mitochondria, fewer blood vessels, little or no myoglobin. Develop greater maximum tension faster, but fatigue more quickly. Can’t replenish ATP for prolonged contraction. Figure 47.10 Slow-and Fast-Twitch Muscle Fibers (Part 1) Figure 47.10 Slow-and Fast-Twitch Muscle Fibers (Part 2) 47.2 What Determines Muscle Strength and Endurance? Proportion of fast- and slow-twitch fibers in skeletal muscles is determined mostly by genetic heritage. Training can alter muscle properties to a certain extent. 47.2 What Determines Muscle Strength and Endurance? The resting length of the sarcomeres determines how much force can be generated. If stretched, less overlap between actin and myosin fibers mean fewer crossbridges and less force. If contracted, there is no more space for shortening. Figure 47.11 Strength and Length 47.2 What Determines Muscle Strength and Endurance? Exercise: • Anaerobic activities increase muscle strength: new actin and myosin filaments form, muscle gets larger. • Aerobic activities increase endurance: oxidative capacity is enhanced by increasing number of mitochondria, blood vessels, myoglobin, and enzymes. 47.2 What Determines Muscle Strength and Endurance? Muscles have three systems for obtaining ATP: • Immediate system uses preformed ATP • Glycolytic system metabolizes carbohydrates to lactic acid and pyruvate • Oxidative system metabolizes carbohydrates and fats to H2O and CO2 Figure 47.12 Supplying Fuel for High Performance 47.2 What Determines Muscle Strength and Endurance? Muscles contain creatine phosphate (CP) which stores energy in a phosphate bond that can transfer to ADP Immediate system = ATP + CP. This system is exhausted within seconds. 47.2 What Determines Muscle Strength and Endurance? The glycolytic system enzymes are in the sarcoplasm; ATP generated is then available to myosin. Not very efficient; lactic acid accumulates. Immediate and glycolytic systems provide energy for less than one minute. 47.2 What Determines Muscle Strength and Endurance? Oxidative system produces large amounts of ATP, but ATP must diffuse from the mitochondria to the myosin: rate is slower than other two systems. 47.2 What Determines Muscle Strength and Endurance? At high levels of aerobic exercise, fuel for ATP production comes mostly from glycogen. Depletion of muscle glycogen causes fatigue. Glycogen can be replaced more rapidly on a high-carbohydrate diet; “carbo-loading” by athletes. 47.3 What Roles Do Skeletal Systems Play in Movement? Skeletal systems provide rigid supports against which muscles can pull. Three types of skeletal systems in animals: hydrostatic, exoskeletons, and endoskeletons. 47.3 What Roles Do Skeletal Systems Play in Movement? Hydrostatic skeleton: a volume of fluid enclosed in a body cavity surrounded by muscle. Examples: cnidarians, annelids, and other invertebrates. Figure 47.13 A Hydrostatic Skeleton 47.3 What Roles Do Skeletal Systems Play in Movement? Exoskeleton: hardened outer surface to which muscles attach. Examples: mollusks, arthropods Figure 47.14 The Clam Shell Is an Exoskeleton 47.3 What Roles Do Skeletal Systems Play in Movement? Arthropod exoskeleton (or cuticle) covers all outer surfaces and appendages. Cuticle containing stiffening materials except at joints. For growth to occur, the exoskeleton must be shed, called molting. 47.3 What Roles Do Skeletal Systems Play in Movement? Endoskeleton advantage: growth can occur without shedding the skeleton. Human skeleton: 206 bones, two connective tissue types: cartilage and bone. Figure 47.15 The Human Endoskeleton 47.3 What Roles Do Skeletal Systems Play in Movement? Cartilage: • Cartilage cells produce a tough, rubbery extracellular matrix of polysaccharides and protein, mostly collagen. • Cartilage is found on bone surfaces in joints, also ears, nose, larynx. 47.3 What Roles Do Skeletal Systems Play in Movement? Bone: extracellular matrix of calcium phosphate. Bone cells: osteoblasts make new bone matrix. When they become enclosed in bone they are called osteocytes. Osteoclasts: reabsorb bone. Bone is constantly being replaced and remodeled. Figure 47.16 Renovating Bone 47.3 What Roles Do Skeletal Systems Play in Movement? How bone cell activities are coordinated is not well known. Stress on bones provides information to cells. Astronauts in zero gravity: bones decalcify. Weight-bearing exercise builds up bone, effective in preventing osteoporosis. 47.3 What Roles Do Skeletal Systems Play in Movement? Membranous bone: forms on a scaffold of connective tissue; (e.g., outer bones of skull). Cartilage bone is first cartilaginous, then ossifies or hardens; (e.g.,) bones of limbs. Growth can occur throughout the ossification process. Figure 47.17 The Growth of Long Bones 47.3 What Roles Do Skeletal Systems Play in Movement? Bone structure: • Compact: solid and hard • Cancellous: with numerous cavities, appears spongy; lightweight but strong Most bones have both types. 47.3 What Roles Do Skeletal Systems Play in Movement? Compact bone in mammals is called Haversian bone; structural units are Haversian systems. Each system: concentric bony cylinders with osteocytes in between. Center canal has blood vessels and nerves. Figure 47.18 Most Compact Bone Is Composed of Haversian Systems Photo 47.23 Several Haversian systems in human compact bone. LM, polarized light. 47.3 What Roles Do Skeletal Systems Play in Movement? Joints are where two or more bones come together. Different types of joints allow different kinds of movement. Figure 47.19 Types of Joints 47.3 What Roles Do Skeletal Systems Play in Movement? Muscles can exert force in only one direction; muscles create movement by working in antagonistic pairs: • Flexor: the muscle that bends or flexes the joint. • Extensor: the muscle the straightens or extends the joint. 47.3 What Roles Do Skeletal Systems Play in Movement? • Ligaments: bands of connective tissue that hold bones together at joints. • Tendons: connective tissue straps that join muscle to bone. Figure 47.20 Joints, Ligaments, and Tendons 47.3 What Roles Do Skeletal Systems Play in Movement? Bones are a system of levers moved by muscles. Levers have a power arm and a load arm that work around a fulcrum (pivot point). Figure 47.21 Bones and Joints Work Like Systems of Levers 47.4 What Are Some Other Kinds of Effectors? Chromatophores: pigment-containing cells in the skin that can change the color or pattern of the animal. Some animals can change color in minutes or even seconds to blend in with their background or send signals. 47.4 What Are Some Other Kinds of Effectors? Three types of chromatophores: • Fixed cell boundaries: pigment granules are moved by microfilaments. • Amoeboid movement: when flattened, more pigment shows. • Changes shape because of muscle fibers radiating out from cell. Figure 47.22 Chromatophores Help Animals Camouflage Themselves or Communicate Photo 47.26 Sanddab; chromatophores create camouflage pattern. Photo 47.27 Chamaeleo jacksoni, a chameleon lizard; Kenya. Photo 47.28 Octopus rubescens, chromatophores adapted to mimic coral. CHROMATOPHORES AND MELANOPHORES IN FISH SCALES VISUAL COMMUNICATION IN SQUID 47.4 What Are Some Other Kinds of Effectors? Glands: effector organs that produce and release chemicals. Endocrine and exocrine glands. Some reptiles, amphibians, mollusks, and fish have poison glands. 47.4 What Are Some Other Kinds of Effectors? Electric organs generate electricity in certain fishes. Electric organs evolved from muscles; they produce electric potentials in the same way as nerves and muscles. Large disk-shaped cells in stacks: all discharge simultaneously. 47.4 What Are Some Other Kinds of Effectors? Some organisms emit light, this is called bioluminescence Depends on the enzyme luciferase and the substrate luciferin. Used in mate attraction and prey attraction.